Still, the fact that more research is needed is true for all geoengineering techniques. So even though the scientists within our group focus most closely on stratospheric aerosol injection, we believe that MCB research is valuable.

Other analyses are broadly consistent:

The International Energy Agency finds that stated national policies will result in oil and gas production in 2050 as high as 2020; with coal halved.

The OECD finds that a world economy four times larger than today is projected to need 80% more energy in 2050; and without new policy action and the global energy mix in 2050 will not differ significantly from today.

The intentions of the world’s five largest fossil fuel producers are clear — and civilisation-threatening — as reported by the UN:

In China, oil production is projected to be flat to 2050, but gas will increase more than 60 percent from 2020 to 2050, while coal use will remain high till 2030 then decline sharply.

In the United States, oil production will grow and then remain at record levels to 2050, and gas is projected to continuously and significantly increase to 2050; whilst coal will drop by half.

Projections for Russia are available only to 2035, with coal and gas production projected to increase significantly, while oil remains flat.

In Saudi Arabia, oil production is projected to grow by 26 to 47 percent by 2050, with gas up 40 percent between 2019 and 2050. Together they make up half of the Saudi economy.

And in Australia, one of the world’s top two liquified natural gas and coal exporters, gas production is projected to stay above the current level for the next 15 years, with coal remaining high over the same period, above 450 million metric tons annually.

We are heading towards 3–4°C.

This outlook suggests Earth is heading towards 3°C of warming and perhaps a good deal more, because current climate models which project warming of around 2.7°C do not adequately account for all the system-level reinforcing feedbacks.

In 2021, the pre-eminent UK international affairs think-tank Chatham House said a “plausible worst-case scenario” is 3.5°C or more, which could be an underestimate if tipping points are reached sooner than the orthodox science suggests. This now seems to be the reality.

A clear majority of scientists expected warming of more than 3°C, and 82% expected to see catastrophic impacts of climate change in their lifetime, according to a 2021 survey by the journal Nature.

Questions about the size of the aerosol forcing, and the related issue of how sensitive the climate is to changes in greenhouse gases, remain an issue of scientific contention.

New climate history research published in December 2023, based on a study of the last 66 million years, concluded that global temperature may be more sensitive to CO2 levels than current models estimate. It showed that the last time CO2 levels were as high as today was around 14 million year ago, which is longer than previous estimates, and that climate sensitivity — the amount of warming resulting from a doubling of atmospheric CO2 — may be between between 5°C and 8°C, compared to the IPCC orthodoxy of 1.5–4.5°C.

The level of greenhouse gases is currently around 560 parts per million, double the pre-industrial level. Some of those gases such as methane are short-lived so this level of forcing is not written in stone, but nevertheless if Hansen et al. are right that a doubling may lead to around 4–5°C of warming, then another 30 years of high emissions means humans will have created an increasingly unliveable planet.

Has the impact of aerosols been widely understood? In what the New York Times described as “an eye-opening Nature commentary”, Geeta Persad and her colleagues wrote in late 2022 that “overall, vast emissions of aerosols since the start of the industrial age have had a profound cooling effect” and that without them “the global warming we see today would be 30 to 50 percent greater”, warning that “the impacts of aerosols on climate risk are often ignored”.

In 2018, a group of eminent scientists explored the potential — once warming had exceeded the 1.5–2°C range — for self-reinforcing positive feedbacks in major elements of the climate system to push passed a planetary threshold that would prevent temperature stabilisation, and drive the system to a “Hothouse Earth”. They warned that “we are in a climate emergency… this is an existential threat to civilisation”.

The 2023 State of the Climate Report: Entering uncharted territory warned of: “potential collapse of natural and socioeconomic systems in such a world [of 2.6°C warming] where we will face unbearable heat, frequent extreme weather events, food and fresh water shortages, rising seas, more emerging diseases, and increased social unrest and geopolitical conflict.”

Whatever the words, the understanding is widely shared that contemporary nations and societies, and likely the global social system, are heading towards collapse. “If we carry on the way we are going now, I can’t see this civilisation lasting to the end of this century”, says Professor Tim Lenton. The US Defence Secretary Lloyd Austin III calls the risks “existential”.

Opening the Innovation Zero Congress in London in May 2023, Potsdam Institute Director Prof. Johan Rockstrom described the path we are on:

“2.5°C global mean surface temperature rise is a disaster. It’s something that humanity has absolutely no evidence that we can cope with… [There] would be a 10-metre sea-level rise. There would be a collapse of all the big biomes on planet Earth – the rainforest, many of the temperate forests – abrupt thawing of permafrost, we will have complete collapse of marine biology… Over one-third of the planet around the equatorial regions will be uninhabitable because you will pass the threshold of health, which is around 30°C. It’s only in some parts of the Sahara Desert today that has that kind of average temperature.”

Chatham House’s Climate Risk Assessment 2021 concludes that by 2050 global food demand would be 50% higher, but crop yields may drop by 30%. As desertification spreads across the dry sub-tropics, and one-third of the planet experiences unprecedented heat, it is not difficult to see why they concluded that cascading climate impacts will “drive political instability and greater national insecurity, and fuel regional and international conflict”.

What is worse is the setback to climate action posed by current conflicts and military posturing in Europe, the Middle East and east Asia, which are huge political distractions from dealing with the greatest threat to humanity, and all of which have the potential to spread more widely.

To maintain military flexibility, the US insisted in 1997 that direct military carbon emissions be excluded from international carbon accounting. Those emissions, around 5 percent of the total global, are far less than the indirect emissions from conflict, as recent estimates here and here indicate.

Projections show that by 2100 the expansion of the Sahara due to desertification will embrace Israel/Palestine, as well as spreading across the Mediterranean into Spain, Italy, Greece and Turkey (see map).

The Australian Prime Minister has finally spoken out about the escalating climate threat whilst inspecting damage from the recent Queensland floods: “All of this is a reminder that the science told us that climate change would mean there would be more extreme weather events and they would be more intense. And unfortunately, we are seeing that play out with the number of events that we’re having to deal with right around Australia”.

Just so, except that in common with leaders globally, the Australian government continues to have its head stuck in the sand about the real risks climate change now represents. It refuses to release an intelligence assessment of climate-security risks, and has fumbled a domestic climate risk assessment.

As a result, the community remains ill-informed and unprepared for what is coming.

Datasets of global temperatures vary a little depending on method, but two of the most significant are Berkeley Earth which put 2023 at 1.54°C above the pre-industrial (1850-1900) level, and Copernicus/ECMWF at 1.48°C.

Berkeley said that “a single year exceeding 1.5°C is a stark warning sign of how close the overall climate system has come to exceeding this Paris Agreement goal. With greenhouse gas emissions continuing to set record highs, it is likely that climate will regularly exceed 1.5°C in the next decade.”

2023 was notable for:

Global average warming hitting the 1.5°C mark, and new monthly records for global temperature every month from June to December. The October to December period was 1.74°C.

New national record high annual averages for an estimated 77 countries.

The first year that global average ocean surface temperatures exceeded 1°C, with once-in-a-century levels of warmth in the North Atlantic.

Two days in November when global average temperature, for the first time ever, reached 2°C above the pre-industrial levels.

Catastrophic flooding from Greece to Beijing to Vermont, and earlier in the year major flooding in New Zealand associated with a rain bomb and then cyclone Gabrielle.

Severe wildfires in Europe, Russia, Maui and North America; fires in Canada burned 18.5 million hectares of land.

The 2023 extremes were a shock. Prof. Katharine Hayhoe told the Guardian that: “We have strongly suspected for a while that our projections are underestimating extremes, a suspicion that recent extremes have proven likely to be true… We are truly in uncharted territory in terms of the history of human civilisation on this planet.”

Explanations for 2023 are incomplete, but warming is accelerating and 2024 is likely to be hotter

What happened in 2023 was not what scientists’ models anticipated at the beginning of the year and fell well outside the confidence intervals of any of the estimates. Carbon Brief says that “while there are a number of factors that researchers have proposed to explain 2023’s exceptional warmth, scientists still lack a clear explanation for why global temperatures were so unexpectedly high… researchers are just starting to disentangle the causes of the unexpected extreme global heat the world experienced in 2023”.

One person who has a clear view is the former NASA climate chief James Hansen who says that “the 1.5 degree limit is deader than a doornail” and warns that warming will accelerate to 1.7°C by 2030 and “2°C will be reached by the late 2030s”.

Children whose future has and is being compromised

Climate scientists, who recognise the shortcomings of the inadequacy of proposed responses

Campaigners looking for solutions rather than just screaming, “Do something!”

Politicians and leaders, who need positive plans and messages to encourage voters

Businesses concerned about their fiduciary responsibilities to their shareholders, employees, and customers

Bankers, insurers and hedge funds that need to take action to preserve the value of their portfolios

Hydrocarbon companies that grasp the need to transition

Most content is published under Creative Commons: Attribution-Noncommercial-No Derivative Works. Please visit our Use & Privacy Policy page for additional information.

Yale Climate Connections is grateful for the generous financial support of the Grantham Foundation for the Protection of the Environment and of individual Yale University alumni. We also thank the CO2 Foundation for its support of our Spanish-language articles. Yale Climate Connections is solely responsible for all content.

In the past 150 years, Earth's climate has been warming at a rate that is unprecedented in at least the last 2000 years¹. This human-caused warming has caused widespread adverse impacts and related losses and damages to nature and people, which will continue in the future as global climate continues to warm². Detecting changes in the rate of warming is crucial for informed decision-making in international climate negotiations, with the aim of limiting global warming to specific levels. However, it remains a significant challenge to detect such changes due to the substantial internal variability of the climate system on a decadal scale (e.g., ref. ³). In this paper, we address this challenge by examining the global heat accumulation rate across the entire climate system, including the ocean, atmosphere, cryosphere, and land. By focusing on this integrated view, rather than solely relying on changes in global mean surface temperature, we can mitigate the impact of variability and gain a more comprehensive understanding^4,5.

Global heat accumulation in the climate system, resulting from the current positive Earth's Energy Imbalance (EEI) at the top of the atmosphere, is primarily dominated by changes in Global Ocean Heat Content (GOHC)⁴. GOHC changes account for approximately 90% of the total heat increase in the past fifty years, while land heating, ice melting, and atmospheric warming contribute around 5%, 3%, and 1% respectively^6,7,8. Several studies have indicated an increase in the global heat accumulation rate in recent decades, with values rising from 0.50 [0.32 to 0.69] W/m² during the period 1971-2006 to 0.79 [0.52 to 1.06] W/m² (90% confidence interval) for the period 2006-2018 (ref.^{4,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22} and Fig. 1). Some studies have even suggested a potential doubling of EEI in the last decade compared to the previous one^6,17.

Other analyses are broadly consistent:

The International Energy Agency finds that stated national policies will result in oil and gas production in 2050 as high as 2020; with coal halved.

The OECD finds that a world economy four times larger than today is projected to need 80% more energy in 2050; and without new policy action and the global energy mix in 2050 will not differ significantly from today.

The intentions of the world’s five largest fossil fuel producers are clear — and civilisation-threatening — as reported by the UN:

In China, oil production is projected to be flat to 2050, but gas will increase more than 60 percent from 2020 to 2050, while coal use will remain high till 2030 then decline sharply.

In the United States, oil production will grow and then remain at record levels to 2050, and gas is projected to continuously and significantly increase to 2050; whilst coal will drop by half.

Projections for Russia are available only to 2035, with coal and gas production projected to increase significantly, while oil remains flat.

In Saudi Arabia, oil production is projected to grow by 26 to 47 percent by 2050, with gas up 40 percent between 2019 and 2050. Together they make up half of the Saudi economy.

And in Australia, one of the world’s top two liquified natural gas and coal exporters, gas production is projected to stay above the current level for the next 15 years, with coal remaining high over the same period, above 450 million metric tons annually.

We are heading towards 3–4°C.

This outlook suggests Earth is heading towards 3°C of warming and perhaps a good deal more, because current climate models which project warming of around 2.7°C do not adequately account for all the system-level reinforcing feedbacks.

In 2021, the pre-eminent UK international affairs think-tank Chatham House said a “plausible worst-case scenario” is 3.5°C or more, which could be an underestimate if tipping points are reached sooner than the orthodox science suggests. This now seems to be the reality.

A clear majority of scientists expected warming of more than 3°C, and 82% expected to see catastrophic impacts of climate change in their lifetime, according to a 2021 survey by the journal Nature.

Questions about the size of the aerosol forcing, and the related issue of how sensitive the climate is to changes in greenhouse gases, remain an issue of scientific contention.

New climate history research published in December 2023, based on a study of the last 66 million years, concluded that global temperature may be more sensitive to CO2 levels than current models estimate. It showed that the last time CO2 levels were as high as today was around 14 million year ago, which is longer than previous estimates, and that climate sensitivity — the amount of warming resulting from a doubling of atmospheric CO2 — may be between between 5°C and 8°C, compared to the IPCC orthodoxy of 1.5–4.5°C.

The level of greenhouse gases is currently around 560 parts per million, double the pre-industrial level. Some of those gases such as methane are short-lived so this level of forcing is not written in stone, but nevertheless if Hansen et al. are right that a doubling may lead to around 4–5°C of warming, then another 30 years of high emissions means humans will have created an increasingly unliveable planet.

Has the impact of aerosols been widely understood? In what the New York Times described as “an eye-opening Nature commentary”, Geeta Persad and her colleagues wrote in late 2022 that “overall, vast emissions of aerosols since the start of the industrial age have had a profound cooling effect” and that without them “the global warming we see today would be 30 to 50 percent greater”, warning that “the impacts of aerosols on climate risk are often ignored”.

In 2018, a group of eminent scientists explored the potential — once warming had exceeded the 1.5–2°C range — for self-reinforcing positive feedbacks in major elements of the climate system to push passed a planetary threshold that would prevent temperature stabilisation, and drive the system to a “Hothouse Earth”. They warned that “we are in a climate emergency… this is an existential threat to civilisation”.

The 2023 State of the Climate Report: Entering uncharted territory warned of: “potential collapse of natural and socioeconomic systems in such a world [of 2.6°C warming] where we will face unbearable heat, frequent extreme weather events, food and fresh water shortages, rising seas, more emerging diseases, and increased social unrest and geopolitical conflict.”

Whatever the words, the understanding is widely shared that contemporary nations and societies, and likely the global social system, are heading towards collapse. “If we carry on the way we are going now, I can’t see this civilisation lasting to the end of this century”, says Professor Tim Lenton. The US Defence Secretary Lloyd Austin III calls the risks “existential”.

Opening the Innovation Zero Congress in London in May 2023, Potsdam Institute Director Prof. Johan Rockstrom described the path we are on:

“2.5°C global mean surface temperature rise is a disaster. It’s something that humanity has absolutely no evidence that we can cope with… [There] would be a 10-metre sea-level rise. There would be a collapse of all the big biomes on planet Earth – the rainforest, many of the temperate forests – abrupt thawing of permafrost, we will have complete collapse of marine biology… Over one-third of the planet around the equatorial regions will be uninhabitable because you will pass the threshold of health, which is around 30°C. It’s only in some parts of the Sahara Desert today that has that kind of average temperature.”

Chatham House’s Climate Risk Assessment 2021 concludes that by 2050 global food demand would be 50% higher, but crop yields may drop by 30%. As desertification spreads across the dry sub-tropics, and one-third of the planet experiences unprecedented heat, it is not difficult to see why they concluded that cascading climate impacts will “drive political instability and greater national insecurity, and fuel regional and international conflict”.

What is worse is the setback to climate action posed by current conflicts and military posturing in Europe, the Middle East and east Asia, which are huge political distractions from dealing with the greatest threat to humanity, and all of which have the potential to spread more widely.

To maintain military flexibility, the US insisted in 1997 that direct military carbon emissions be excluded from international carbon accounting. Those emissions, around 5 percent of the total global, are far less than the indirect emissions from conflict, as recent estimates here and here indicate.

Projections show that by 2100 the expansion of the Sahara due to desertification will embrace Israel/Palestine, as well as spreading across the Mediterranean into Spain, Italy, Greece and Turkey (see map).

The Australian Prime Minister has finally spoken out about the escalating climate threat whilst inspecting damage from the recent Queensland floods: “All of this is a reminder that the science told us that climate change would mean there would be more extreme weather events and they would be more intense. And unfortunately, we are seeing that play out with the number of events that we’re having to deal with right around Australia”.

Just so, except that in common with leaders globally, the Australian government continues to have its head stuck in the sand about the real risks climate change now represents. It refuses to release an intelligence assessment of climate-security risks, and has fumbled a domestic climate risk assessment.

As a result, the community remains ill-informed and unprepared for what is coming.

In the past 150 years, Earth's climate has been warming at a rate that is unprecedented in at least the last 2000 years¹. This human-caused warming has caused widespread adverse impacts and related losses and damages to nature and people, which will continue in the future as global climate continues to warm². Detecting changes in the rate of warming is crucial for informed decision-making in international climate negotiations, with the aim of limiting global warming to specific levels. However, it remains a significant challenge to detect such changes due to the substantial internal variability of the climate system on a decadal scale (e.g., ref. ³). In this paper, we address this challenge by examining the global heat accumulation rate across the entire climate system, including the ocean, atmosphere, cryosphere, and land. By focusing on this integrated view, rather than solely relying on changes in global mean surface temperature, we can mitigate the impact of variability and gain a more comprehensive understanding^4,5.

Global heat accumulation in the climate system, resulting from the current positive Earth's Energy Imbalance (EEI) at the top of the atmosphere, is primarily dominated by changes in Global Ocean Heat Content (GOHC)⁴. GOHC changes account for approximately 90% of the total heat increase in the past fifty years, while land heating, ice melting, and atmospheric warming contribute around 5%, 3%, and 1% respectively^6,7,8. Several studies have indicated an increase in the global heat accumulation rate in recent decades, with values rising from 0.50 [0.32 to 0.69] W/m² during the period 1971-2006 to 0.79 [0.52 to 1.06] W/m² (90% confidence interval) for the period 2006-2018 (ref.^{4,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22} and Fig. 1). Some studies have even suggested a potential doubling of EEI in the last decade compared to the previous one^6,17.

On the first day, experts spoke and answered questions about the particular risks in which they specialized. The second day was for breakout groups to discuss these threats. These groups generated the overall Platform for Survival, which was adopted in a plenary session.

As a follow-up, we created a new website, tosavetheworld.ca, and gradually adopted an organizational title: Project Save the World. We acquired a YouTube channel and began holding forums by Zoom — hour-long discussions by experts about these global threats, live on YouTube, and which we edited and posted permanently both on YouTube and our website. We advertise these conversations on social media and by mailed posters to a growing list of frequent viewers.

Although initially Project Save the World was produced and managed as the project of Peace Magazine,

a small publication for peace activists, over time the strength of the two organizations reversed. Peace Magazine’s circulation was declining markedly, whereas the work and expense involved in producing the website and forum series mushroomed. Also, the magazine’s 40-year archive, which is available as text-only on the Internet, attracts a large audience of people searching for particular topics with browsers.

During Covid, the magazine’s printing house went out of business so we began to publish the magazine exclusively in a digital form, available through a magazine aggregating company, PressReader, although the paid subscriptions remain insufficient to predict a bright future as a profit-seeking publication.

However, the digital format made it possible to distribute the magazine free-of-charge to thousands of like-minded organizations worldwide. Just as the prospects of the print magazine vanished, the actual distribution of the digital publication multiplied by the thousands. We were mainly producing articles based on the discussions of researchers in the forum series. In effect, the magazine had morphed into an exceptionally fine house organ, the newsletter of Project Save the World.

Now in 2023, that de facto reversal will be recognized with legal and official changes. CANDIS, the not-for-profit corporation that had owned and controlled Peace Magazine, will turn over the magazine to a newly incorporated not-for-profit, Project Save the World, and then dissolve, having no further purpose. The magazine will fulfill part of Project Save the World’s official purpose, namely “the advancement of education by providing an open forum for qualified researchers to discuss their research with other experts and to make those results available to the public.”

The second half of this purpose — making the results available to the public — is now fulfilled by all three of our platforms; our two websites, the forum of videos and audio podcasts, and our digital newsletter/“Peace Magazine.” These services are all widely available withut charge as our offering toward the survival of humankind. But we thank those subscribers to the magazine who remain with us loyally and still pay, now mainly throughPressReader, CAN $20 per year.

We. the members of Project Save the World, are all people who have supported some of these activities, either by volunteering to work on the publication, a website, or the “broadcasts” or by donating money – usually about CAN $100 — at least once within the past three years. If newcomers wish to participate in these projects, please contact us, for we have a list of chores that sometimes requires volunteer assistance. Email us, stating your interests and aptitudes, at project@tosavetheworld.ca.

It’s time to act in order to keep the planet cool. Humans can help Earth turn down its thermostat, enhancing its own natural processes to reduce global temperatures. We have grouped these processes together into what we call The Planet Earth Coolkit.

We need you to help us get the message out that global cooling is possible!

Global warming is the biggest threat to mankind. It is time now to Cool Planet Earth.

In the past 150 years, Earth's climate has been warming at a rate that is unprecedented in at least the last 2000 years¹. This human-caused warming has caused widespread adverse impacts and related losses and damages to nature and people, which will continue in the future as global climate continues to warm². Detecting changes in the rate of warming is crucial for informed decision-making in international climate negotiations, with the aim of limiting global warming to specific levels. However, it remains a significant challenge to detect such changes due to the substantial internal variability of the climate system on a decadal scale (e.g., ref. ³). In this paper, we address this challenge by examining the global heat accumulation rate across the entire climate system, including the ocean, atmosphere, cryosphere, and land. By focusing on this integrated view, rather than solely relying on changes in global mean surface temperature, we can mitigate the impact of variability and gain a more comprehensive understanding^4,5.

Global heat accumulation in the climate system, resulting from the current positive Earth's Energy Imbalance (EEI) at the top of the atmosphere, is primarily dominated by changes in Global Ocean Heat Content (GOHC)⁴. GOHC changes account for approximately 90% of the total heat increase in the past fifty years, while land heating, ice melting, and atmospheric warming contribute around 5%, 3%, and 1% respectively^6,7,8. Several studies have indicated an increase in the global heat accumulation rate in recent decades, with values rising from 0.50 [0.32 to 0.69] W/m² during the period 1971-2006 to 0.79 [0.52 to 1.06] W/m² (90% confidence interval) for the period 2006-2018 (ref.^{4,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22} and Fig. 1). Some studies have even suggested a potential doubling of EEI in the last decade compared to the previous one^6,17.

years1

. Tis human-caused warming has caused widespread adverse impacts and related losses and damages to

nature and people, which will continue in the future as global climate continues to warm2

. Detecting changes in

the rate of warming is crucial for informed decision-making in international climate negotiations, with the aim

of limiting global warming to specifc levels. However, it remains a signifcant challenge to detect such changes

due to the substantial internal variability of the climate system on a decadal scale (e.g., ref. 3

). In this paper, we

address this challenge by examining the global heat accumulation rate across the entire climate system, including

the ocean, atmosphere, cryosphere, and land. By focusing on this integrated view, rather than solely relying on

changes in global mean surface temperature, we can mitigate the impact of variability and gain a more comprehensive understanding4,5

.

Global heat accumulation in the climate system, resulting from the current positive Earth’s Energy Imbalance

(EEI) at the top of the atmosphere, is primarily dominated by changes in Global Ocean Heat Content (GOHC)4

.

GOHC changes account for approximately 90% of the total heat increase in the past ffy years, while land heating, ice melting, and atmospheric warming contribute around 5%, 3%, and 1% respectively6–8

. Several studies

have indicated an increase in the global heat accumulation rate in recent decades, with values rising from 0.50

[0.32 to 0.69] W/m2

during the period 1971–2006 to 0.79 [0.52 to 1.06] W/m2

(90% confdence interval) for the

period 2006–2018 (ref.4,6–22 and Fig. 1). Some studies have even suggested a potential doubling of EEI in the last

decade compared to the previous one6,17.

Despite this suggestive body of evidence, no study has conducted an analysis of heat accumulation acceleration since 1960 to date. While the results presented in Fig. 1 provide insights, they represent accumulation rates

computed over varying time spans, with higher rates calculated over decadal periods and lower rates calculated

over multi-decadal periods. Tis variation in time spans makes it challenging to make defnitive and quantifed

statements about acceleration. Additionally, the use of diverse datasets and methodologies can signifcantly

impact the calculated accumulation rates. Te only notable climate variable where acceleration has previously

been detected in past decades is Global Mean Sea Level (GMSL)23–31. Tis GMSL acceleration has been attributed

to factors such as increasing GOHC leading to thermal expansion of seawater, declining land water storage, or

increasing land ice melt25–27,31,32.

In this paper, we present the frst observation-based quantifcation of the acceleration of Earth’s system heating. Our study adopts a systematic approach, incorporating multiple datasets and employing various methods.

We estimate the rate of change and acceleration of Earth’s heat content using a collection of GOHC time series

Climate change and the severity of its impacts are increasing much faster than calculated by various models and analyses projecting future conditions. What’s more, the impacts are interacting to push critical ecological, hydrologic, and glacial systems over thresholds, known as tipping points, thus amplifying climate disasters. This truth is being told by current events, not speculative assumptions. The reports released to inform COP28 deliberations confirm 2023 as the worst year yet of climate change with the Global South and vulnerable populations around the world bearing the brunt.

Still, the fact that more research is needed is true for all geoengineering techniques. So even though the scientists within our group focus most closely on stratospheric aerosol injection, we believe that MCB research is valuable.

Increased greenhouse gas concentrations combined with reductions in aerosol pollution have led to rapid increases in human-induced effective radiative forcing, which has in turn led to atmosphere, land, cryosphere and ocean warming (Gulev et al., 2021). This in turn has led to an intensification of many weather and climate extremes, particularly more frequent and more intense hot extremes, and heavy precipitation across most regions of the world (Seneviratne et al., 2021). Given the speed of recent change, and the need for evidence-based decision-making, this Indicators of Global Climate Change (IGCC) update assembles the latest scientific understanding on the current state and evolution of the climate system and of human influence to support policymakers whilst the next Intergovernmental Panel on Climate Change (IPCC) assessment is under preparation. This first annual update is focused on indicators related to heating of the climate system, building from greenhouse gas emissions towards estimates of human-induced warming and the remaining carbon budget. In future years, this effort could be expanded to encompass other indicators, including global precipitation changes and related extremes.

We adopt the Global Carbon Budget ethos of a community-wide inclusive effort that synthesises work from across a large and diverse global scientific community in a timely fashion (Friedlingstein et al., 2022a). Like the Global Carbon Budget, this initiative arises from the international science community to establish a knowledge base to support policy debate and action to meet the Paris Agreement temperature goal.

This update complements other international efforts under the auspices of the Global Climate Observing System (GCOS) and the World Meteorological Organization (WMO). Annual state-of-the-climate reports are released by the WMO which use much of the same data analysed here for surface temperature and energy budget trends. The Bulletin of American Meteorological Society (BAMS) releases annual state-of-the-climate reports covering many essential variables including temperature and greenhouse gas concentrations. However, these reports focus on statistics from the previous year and make slightly different choices over datasets and analysis compared to the IPCC (see Sect. 5). The Global Carbon Project publishes updated carbon dioxide datasets which are used directly in this report. There is no similarly structured activity that provides all the necessary datasets to update the assessment of human influence on global surface temperature annually.

The update is based on methodologies for key climate indicators assessed by the IPCC Sixth Assessment Report (AR6) of the physical science basis of climate change (Working Group One (WGI) report; IPCC, 2021a) as well as Chap. 2 of the WGIII report (Dhakal et al., 2022) and is aligned with the efforts initiated in AR6 to implement FAIR (Findable, Accessible, Interoperable, Reusable) principles for reproducibility and reusability (Pirani et al., 2022; Iturbide et al., 2022). IPCC reports make a much wider assessment of the science and methodologies - we do not attempt to reproduce the comprehensive nature of these IPCC assessments here.

The IPCC Special Report on Global Warming of 1.5?^°C (SR1.5), published in 2018, provided an assessment of the level of human-induced warming and cumulative emissions to date (Allen et al., 2018) and the remaining carbon budget (Rogelj et al., 2018) to support the evidence base on how the world is progressing in terms of meeting aspects of the Paris Agreement. The AR6 WGI Report, published in 2021, assessed past, current and future changes of these and other key global climate indicators, as well as undertaking an assessment of the Earth's energy budget. It also updated its approach for estimating human-induced warming and global warming level. In AR6 WGI and here, reaching a level of global warming is defined as the global surface temperature change, averaged over a 20-year period, exceeding a particular level of global warming, for example, 1.5?^°C global warming. Given the current rates of change and the likelihood of reaching 1.5?^°C of global warming in the first half of the 2030s (Lee et al., 2021, 2023; Riahi et al., 2022), it is important to have robust, trusted and also timely climate indicators in the public domain to form an evidence base for effective science-based decision-making.

When making their assessments, authors of IPCC reports assess published literature but also apply established published analysis methods to assessed datasets, such as the dataset produced by the latest climate model intercomparison projects (Lee et al., 2021). The authors combine and analyse both model and observational data as part of their expert assessment, making assessments of the trustworthiness and error characteristics of different datasets. It is this synthetic analysis by IPCC authors that derives the estimates of key climate indicators. Wherever possible, these same assessed methodological approaches are implemented here to provide the updates with variations clearly flagged and documented. The same approach, using the same datasets (updated by 2 years) and methods as employed in WGI, was used in the AR6 Synthesis Report (2023) (AR6 SYR; Lee et al., 2023) to provide an updated assessment of the latest atmospheric well-mixed greenhouse gas concentrations (up to 2021) and decadal average change in global surface temperature (+1.15?^°C [1.00-1.25?^°C] in 2013-2022 for global surface temperature). However, the assessment of human-induced warming was not updated (and therefore only covers warming up to the decade 2010-2019), nor was the remaining carbon budget updated, so the related information in the AR6 SYR report remained based on data up to the end of 2019.

The indicators in this first annual update give important insights into the magnitude and the pace of global warming. This paper provides the basis for a dashboard of climate indicators grounded in IPCC methodologies and directly traceable to reports published as part of the AR6 cycle. We employ datasets that can be updated on a regular basis between the publication of IPCC reports. Note that there are other similar initiatives underway to update other AR6 cycle products; for example, the evolution of the WGI Interactive Atlas (Gutiérrez et al., 2021) is being developed under the Copernicus Climate Change Service (C3S) and has potential connections and synergies with this initiative that will be explored in the future.

Our longer-term ambition is to rigorously track both climate system change and methodological improvements between IPCC report cycles, thereby building consistency and awareness. An example of why tracking methodological change is important was the updated estimate for historic warming (the increase in global surface temperature from 1850-1900 to 1986-2005). This was 0.08 [-0.01 to 0.12]?^°C higher in the AR6 than in the fifth assessment report (AR5) and SR1.5. Datasets and methods of evaluating global temperature changes altered between the AR5 and AR6, leading to a small shift in the historical temperature. This was reflected in changes between AR5 and AR6, whereas SR1.5 mostly relied on methodologies from AR5 (see AR6 WGI Cross Chap. Box 2.3, Gulev et al., 2021). Annual updates provide indications of possible future methodological shifts that subsequent IPCC reports may make as science advances and can detail their impact on perceived trends.

The update is organised as follows: emissions (Sect. 2) and greenhouse gas (GHG) concentrations (Sect. 3) are used to develop updated estimates of effective radiative forcing (Sect. 4). Observations of global surface temperature change (Sect. 5) and Earth's energy imbalance (Sect. 6) are key global indicators of a warming world. The global surface temperature change is formally attributed to human activity in Sect. 7, which tracks human-induced warming. Section 8 updates the remaining carbon budget to policy-relevant temperature thresholds. Section 9 gives an example of global-scale indicators associated with climate extremes of maximum land surface temperatures.

An important purpose of the exercise is to make these indicators widely available and understood. Plans for a web dashboard are discussed in Sect. 10 and code and data availability in Sect. 11, and conclusions are presented in Sect. 12. Data are available at https://doi.org/10.5281/zenodo.8000192 (Smith et al., 2023a).

Increased greenhouse gas concentrations combined with reductions in aerosol pollution have led to rapid increases in human-induced effective radiative forcing, which has in turn led to atmosphere, land, cryosphere and ocean warming (Gulev et al., 2021). This in turn has led to an intensification of many weather and climate extremes, particularly more frequent and more intense hot extremes, and heavy precipitation across most regions of the world (Seneviratne et al., 2021). Given the speed of recent change, and the need for evidence-based decision-making, this Indicators of Global Climate Change (IGCC) update assembles the latest scientific understanding on the current state and evolution of the climate system and of human influence to support policymakers whilst the next Intergovernmental Panel on Climate Change (IPCC) assessment is under preparation. This first annual update is focused on indicators related to heating of the climate system, building from greenhouse gas emissions towards estimates of human-induced warming and the remaining carbon budget. In future years, this effort could be expanded to encompass other indicators, including global precipitation changes and related extremes.

We adopt the Global Carbon Budget ethos of a community-wide inclusive effort that synthesises work from across a large and diverse global scientific community in a timely fashion (Friedlingstein et al., 2022a). Like the Global Carbon Budget, this initiative arises from the international science community to establish a knowledge base to support policy debate and action to meet the Paris Agreement temperature goal.

This update complements other international efforts under the auspices of the Global Climate Observing System (GCOS) and the World Meteorological Organization (WMO). Annual state-of-the-climate reports are released by the WMO which use much of the same data analysed here for surface temperature and energy budget trends. The Bulletin of American Meteorological Society (BAMS) releases annual state-of-the-climate reports covering many essential variables including temperature and greenhouse gas concentrations. However, these reports focus on statistics from the previous year and make slightly different choices over datasets and analysis compared to the IPCC (see Sect. 5). The Global Carbon Project publishes updated carbon dioxide datasets which are used directly in this report. There is no similarly structured activity that provides all the necessary datasets to update the assessment of human influence on global surface temperature annually.

The update is based on methodologies for key climate indicators assessed by the IPCC Sixth Assessment Report (AR6) of the physical science basis of climate change (Working Group One (WGI) report; IPCC, 2021a) as well as Chap. 2 of the WGIII report (Dhakal et al., 2022) and is aligned with the efforts initiated in AR6 to implement FAIR (Findable, Accessible, Interoperable, Reusable) principles for reproducibility and reusability (Pirani et al., 2022; Iturbide et al., 2022). IPCC reports make a much wider assessment of the science and methodologies - we do not attempt to reproduce the comprehensive nature of these IPCC assessments here.

The IPCC Special Report on Global Warming of 1.5?^°C (SR1.5), published in 2018, provided an assessment of the level of human-induced warming and cumulative emissions to date (Allen et al., 2018) and the remaining carbon budget (Rogelj et al., 2018) to support the evidence base on how the world is progressing in terms of meeting aspects of the Paris Agreement. The AR6 WGI Report, published in 2021, assessed past, current and future changes of these and other key global climate indicators, as well as undertaking an assessment of the Earth's energy budget. It also updated its approach for estimating human-induced warming and global warming level. In AR6 WGI and here, reaching a level of global warming is defined as the global surface temperature change, averaged over a 20-year period, exceeding a particular level of global warming, for example, 1.5?^°C global warming. Given the current rates of change and the likelihood of reaching 1.5?^°C of global warming in the first half of the 2030s (Lee et al., 2021, 2023; Riahi et al., 2022), it is important to have robust, trusted and also timely climate indicators in the public domain to form an evidence base for effective science-based decision-making.

When making their assessments, authors of IPCC reports assess published literature but also apply established published analysis methods to assessed datasets, such as the dataset produced by the latest climate model intercomparison projects (Lee et al., 2021). The authors combine and analyse both model and observational data as part of their expert assessment, making assessments of the trustworthiness and error characteristics of different datasets. It is this synthetic analysis by IPCC authors that derives the estimates of key climate indicators. Wherever possible, these same assessed methodological approaches are implemented here to provide the updates with variations clearly flagged and documented. The same approach, using the same datasets (updated by 2 years) and methods as employed in WGI, was used in the AR6 Synthesis Report (2023) (AR6 SYR; Lee et al., 2023) to provide an updated assessment of the latest atmospheric well-mixed greenhouse gas concentrations (up to 2021) and decadal average change in global surface temperature (+1.15?^°C [1.00-1.25?^°C] in 2013-2022 for global surface temperature). However, the assessment of human-induced warming was not updated (and therefore only covers warming up to the decade 2010-2019), nor was the remaining carbon budget updated, so the related information in the AR6 SYR report remained based on data up to the end of 2019.

The indicators in this first annual update give important insights into the magnitude and the pace of global warming. This paper provides the basis for a dashboard of climate indicators grounded in IPCC methodologies and directly traceable to reports published as part of the AR6 cycle. We employ datasets that can be updated on a regular basis between the publication of IPCC reports. Note that there are other similar initiatives underway to update other AR6 cycle products; for example, the evolution of the WGI Interactive Atlas (Gutiérrez et al., 2021) is being developed under the Copernicus Climate Change Service (C3S) and has potential connections and synergies with this initiative that will be explored in the future.

Our longer-term ambition is to rigorously track both climate system change and methodological improvements between IPCC report cycles, thereby building consistency and awareness. An example of why tracking methodological change is important was the updated estimate for historic warming (the increase in global surface temperature from 1850-1900 to 1986-2005). This was 0.08 [-0.01 to 0.12]?^°C higher in the AR6 than in the fifth assessment report (AR5) and SR1.5. Datasets and methods of evaluating global temperature changes altered between the AR5 and AR6, leading to a small shift in the historical temperature. This was reflected in changes between AR5 and AR6, whereas SR1.5 mostly relied on methodologies from AR5 (see AR6 WGI Cross Chap. Box 2.3, Gulev et al., 2021). Annual updates provide indications of possible future methodological shifts that subsequent IPCC reports may make as science advances and can detail their impact on perceived trends.

The update is organised as follows: emissions (Sect. 2) and greenhouse gas (GHG) concentrations (Sect. 3) are used to develop updated estimates of effective radiative forcing (Sect. 4). Observations of global surface temperature change (Sect. 5) and Earth's energy imbalance (Sect. 6) are key global indicators of a warming world. The global surface temperature change is formally attributed to human activity in Sect. 7, which tracks human-induced warming. Section 8 updates the remaining carbon budget to policy-relevant temperature thresholds. Section 9 gives an example of global-scale indicators associated with climate extremes of maximum land surface temperatures.

An important purpose of the exercise is to make these indicators widely available and understood. Plans for a web dashboard are discussed in Sect. 10 and code and data availability in Sect. 11, and conclusions are presented in Sect. 12. Data are available at https://doi.org/10.5281/zenodo.8000192 (Smith et al., 2023a).

Marine Cloud Brightening (MCB) is potentially the first feasible way to start cooling the planet by reflecting more sunlight back to space.

Deployment would help slow global temperature rise, refreeze the poles and mitigate extreme weather such as storms, fires, droughts, heatwaves and floods.

Sea salt sprayed into the lower atmosphere in targeted areas is expected to prove a harmless way to reverse warming.

MCB has potential to reverse sea level rise with benefit to cost ratio estimated at 50,000 to 1.

MCB has been recognised for 50 years as a simple way to cool the oceans. It relies on the ‘Twomey Effect’, from its discoverer Dr Sean Twomey, who showed that clouds with smaller drops reflect more sunlight and are brighter than clouds with larger drops. Dr John Latham then showed that the optimal cloud drop size for MCB can be produced with sea salt particles smaller than one micron.

The Opportunity

Around 23% of the sun’s energy is reflected away from the Earth by clouds. Typically, only around 40% of the tropical and subtropical oceans are covered by cloud at any time. Increasing cloud cover in these regions by 3-4% could provide sufficient cooling to halt today’s warming trend.

Where do marine clouds come from? Phytoplankton, seaweed, and corals produce the ‘smell of the sea’ (dimethyl sulphide, or DMS). This substance reacts and combines with airborne sea salt and mineral dust to produce microscopic particles known as cloud condensation nuclei (CCN). These CCN particles float naturally in the air, and water vapour naturally condenses onto them up high where the air is cold, forming clouds in the sky. The more DMS there is in the air over the oceans, the brighter the clouds, the longer they last before ‘burning off’ in the sun, and the greater their total cooling effect.

Other analyses are broadly consistent:

The International Energy Agency finds that stated national policies will result in oil and gas production in 2050 as high as 2020; with coal halved.

The OECD finds that a world economy four times larger than today is projected to need 80% more energy in 2050; and without new policy action and the global energy mix in 2050 will not differ significantly from today.

The intentions of the world’s five largest fossil fuel producers are clear — and civilisation-threatening — as reported by the UN:

In China, oil production is projected to be flat to 2050, but gas will increase more than 60 percent from 2020 to 2050, while coal use will remain high till 2030 then decline sharply.

In the United States, oil production will grow and then remain at record levels to 2050, and gas is projected to continuously and significantly increase to 2050; whilst coal will drop by half.

Projections for Russia are available only to 2035, with coal and gas production projected to increase significantly, while oil remains flat.

In Saudi Arabia, oil production is projected to grow by 26 to 47 percent by 2050, with gas up 40 percent between 2019 and 2050. Together they make up half of the Saudi economy.

And in Australia, one of the world’s top two liquified natural gas and coal exporters, gas production is projected to stay above the current level for the next 15 years, with coal remaining high over the same period, above 450 million metric tons annually.

We are heading towards 3–4°C.

This outlook suggests Earth is heading towards 3°C of warming and perhaps a good deal more, because current climate models which project warming of around 2.7°C do not adequately account for all the system-level reinforcing feedbacks.

In 2021, the pre-eminent UK international affairs think-tank Chatham House said a “plausible worst-case scenario” is 3.5°C or more, which could be an underestimate if tipping points are reached sooner than the orthodox science suggests. This now seems to be the reality.

A clear majority of scientists expected warming of more than 3°C, and 82% expected to see catastrophic impacts of climate change in their lifetime, according to a 2021 survey by the journal Nature.

Questions about the size of the aerosol forcing, and the related issue of how sensitive the climate is to changes in greenhouse gases, remain an issue of scientific contention.

New climate history research published in December 2023, based on a study of the last 66 million years, concluded that global temperature may be more sensitive to CO2 levels than current models estimate. It showed that the last time CO2 levels were as high as today was around 14 million year ago, which is longer than previous estimates, and that climate sensitivity — the amount of warming resulting from a doubling of atmospheric CO2 — may be between between 5°C and 8°C, compared to the IPCC orthodoxy of 1.5–4.5°C.

The level of greenhouse gases is currently around 560 parts per million, double the pre-industrial level. Some of those gases such as methane are short-lived so this level of forcing is not written in stone, but nevertheless if Hansen et al. are right that a doubling may lead to around 4–5°C of warming, then another 30 years of high emissions means humans will have created an increasingly unliveable planet.

Has the impact of aerosols been widely understood? In what the New York Times described as “an eye-opening Nature commentary”, Geeta Persad and her colleagues wrote in late 2022 that “overall, vast emissions of aerosols since the start of the industrial age have had a profound cooling effect” and that without them “the global warming we see today would be 30 to 50 percent greater”, warning that “the impacts of aerosols on climate risk are often ignored”.

In 2018, a group of eminent scientists explored the potential — once warming had exceeded the 1.5–2°C range — for self-reinforcing positive feedbacks in major elements of the climate system to push passed a planetary threshold that would prevent temperature stabilisation, and drive the system to a “Hothouse Earth”. They warned that “we are in a climate emergency… this is an existential threat to civilisation”.

The 2023 State of the Climate Report: Entering uncharted territory warned of: “potential collapse of natural and socioeconomic systems in such a world [of 2.6°C warming] where we will face unbearable heat, frequent extreme weather events, food and fresh water shortages, rising seas, more emerging diseases, and increased social unrest and geopolitical conflict.”

Whatever the words, the understanding is widely shared that contemporary nations and societies, and likely the global social system, are heading towards collapse. “If we carry on the way we are going now, I can’t see this civilisation lasting to the end of this century”, says Professor Tim Lenton. The US Defence Secretary Lloyd Austin III calls the risks “existential”.

Opening the Innovation Zero Congress in London in May 2023, Potsdam Institute Director Prof. Johan Rockstrom described the path we are on:

“2.5°C global mean surface temperature rise is a disaster. It’s something that humanity has absolutely no evidence that we can cope with… [There] would be a 10-metre sea-level rise. There would be a collapse of all the big biomes on planet Earth – the rainforest, many of the temperate forests – abrupt thawing of permafrost, we will have complete collapse of marine biology… Over one-third of the planet around the equatorial regions will be uninhabitable because you will pass the threshold of health, which is around 30°C. It’s only in some parts of the Sahara Desert today that has that kind of average temperature.”

Chatham House’s Climate Risk Assessment 2021 concludes that by 2050 global food demand would be 50% higher, but crop yields may drop by 30%. As desertification spreads across the dry sub-tropics, and one-third of the planet experiences unprecedented heat, it is not difficult to see why they concluded that cascading climate impacts will “drive political instability and greater national insecurity, and fuel regional and international conflict”.

What is worse is the setback to climate action posed by current conflicts and military posturing in Europe, the Middle East and east Asia, which are huge political distractions from dealing with the greatest threat to humanity, and all of which have the potential to spread more widely.

To maintain military flexibility, the US insisted in 1997 that direct military carbon emissions be excluded from international carbon accounting. Those emissions, around 5 percent of the total global, are far less than the indirect emissions from conflict, as recent estimates here and here indicate.

Projections show that by 2100 the expansion of the Sahara due to desertification will embrace Israel/Palestine, as well as spreading across the Mediterranean into Spain, Italy, Greece and Turkey (see map).

The Australian Prime Minister has finally spoken out about the escalating climate threat whilst inspecting damage from the recent Queensland floods: “All of this is a reminder that the science told us that climate change would mean there would be more extreme weather events and they would be more intense. And unfortunately, we are seeing that play out with the number of events that we’re having to deal with right around Australia”.

Just so, except that in common with leaders globally, the Australian government continues to have its head stuck in the sand about the real risks climate change now represents. It refuses to release an intelligence assessment of climate-security risks, and has fumbled a domestic climate risk assessment.

As a result, the community remains ill-informed and unprepared for what is coming.

Datasets of global temperatures vary a little depending on method, but two of the most significant are Berkeley Earth which put 2023 at 1.54°C above the pre-industrial (1850-1900) level, and Copernicus/ECMWF at 1.48°C.

Berkeley said that “a single year exceeding 1.5°C is a stark warning sign of how close the overall climate system has come to exceeding this Paris Agreement goal. With greenhouse gas emissions continuing to set record highs, it is likely that climate will regularly exceed 1.5°C in the next decade.”

2023 was notable for:

Global average warming hitting the 1.5°C mark, and new monthly records for global temperature every month from June to December. The October to December period was 1.74°C.

New national record high annual averages for an estimated 77 countries.

The first year that global average ocean surface temperatures exceeded 1°C, with once-in-a-century levels of warmth in the North Atlantic.

Two days in November when global average temperature, for the first time ever, reached 2°C above the pre-industrial levels.

Catastrophic flooding from Greece to Beijing to Vermont, and earlier in the year major flooding in New Zealand associated with a rain bomb and then cyclone Gabrielle.

Severe wildfires in Europe, Russia, Maui and North America; fires in Canada burned 18.5 million hectares of land.

The 2023 extremes were a shock. Prof. Katharine Hayhoe told the Guardian that: “We have strongly suspected for a while that our projections are underestimating extremes, a suspicion that recent extremes have proven likely to be true… We are truly in uncharted territory in terms of the history of human civilisation on this planet.”

Explanations for 2023 are incomplete, but warming is accelerating and 2024 is likely to be hotter

What happened in 2023 was not what scientists’ models anticipated at the beginning of the year and fell well outside the confidence intervals of any of the estimates. Carbon Brief says that “while there are a number of factors that researchers have proposed to explain 2023’s exceptional warmth, scientists still lack a clear explanation for why global temperatures were so unexpectedly high… researchers are just starting to disentangle the causes of the unexpected extreme global heat the world experienced in 2023”.

One person who has a clear view is the former NASA climate chief James Hansen who says that “the 1.5 degree limit is deader than a doornail” and warns that warming will accelerate to 1.7°C by 2030 and “2°C will be reached by the late 2030s”.

It’s time to act in order to keep the planet cool. Humans can help Earth turn down its thermostat, enhancing its own natural processes to reduce global temperatures. We have grouped these processes together into what we call The Planet Earth Coolkit.

We need you to help us get the message out that global cooling is possible!

Global warming is the biggest threat to mankind. It is time now to Cool Planet Earth.

In the past 150 years, Earth's climate has been warming at a rate that is unprecedented in at least the last 2000 years¹. This human-caused warming has caused widespread adverse impacts and related losses and damages to nature and people, which will continue in the future as global climate continues to warm². Detecting changes in the rate of warming is crucial for informed decision-making in international climate negotiations, with the aim of limiting global warming to specific levels. However, it remains a significant challenge to detect such changes due to the substantial internal variability of the climate system on a decadal scale (e.g., ref. ³). In this paper, we address this challenge by examining the global heat accumulation rate across the entire climate system, including the ocean, atmosphere, cryosphere, and land. By focusing on this integrated view, rather than solely relying on changes in global mean surface temperature, we can mitigate the impact of variability and gain a more comprehensive understanding^4,5.

Global heat accumulation in the climate system, resulting from the current positive Earth's Energy Imbalance (EEI) at the top of the atmosphere, is primarily dominated by changes in Global Ocean Heat Content (GOHC)⁴. GOHC changes account for approximately 90% of the total heat increase in the past fifty years, while land heating, ice melting, and atmospheric warming contribute around 5%, 3%, and 1% respectively^6,7,8. Several studies have indicated an increase in the global heat accumulation rate in recent decades, with values rising from 0.50 [0.32 to 0.69] W/m² during the period 1971-2006 to 0.79 [0.52 to 1.06] W/m² (90% confidence interval) for the period 2006-2018 (ref.^{4,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22} and Fig. 1). Some studies have even suggested a potential doubling of EEI in the last decade compared to the previous one^6,17.

Other analyses are broadly consistent:

The International Energy Agency finds that stated national policies will result in oil and gas production in 2050 as high as 2020; with coal halved.

The OECD finds that a world economy four times larger than today is projected to need 80% more energy in 2050; and without new policy action and the global energy mix in 2050 will not differ significantly from today.

The intentions of the world’s five largest fossil fuel producers are clear — and civilisation-threatening — as reported by the UN:

In China, oil production is projected to be flat to 2050, but gas will increase more than 60 percent from 2020 to 2050, while coal use will remain high till 2030 then decline sharply.

In the United States, oil production will grow and then remain at record levels to 2050, and gas is projected to continuously and significantly increase to 2050; whilst coal will drop by half.

Projections for Russia are available only to 2035, with coal and gas production projected to increase significantly, while oil remains flat.

In Saudi Arabia, oil production is projected to grow by 26 to 47 percent by 2050, with gas up 40 percent between 2019 and 2050. Together they make up half of the Saudi economy.

And in Australia, one of the world’s top two liquified natural gas and coal exporters, gas production is projected to stay above the current level for the next 15 years, with coal remaining high over the same period, above 450 million metric tons annually.

We are heading towards 3–4°C.

This outlook suggests Earth is heading towards 3°C of warming and perhaps a good deal more, because current climate models which project warming of around 2.7°C do not adequately account for all the system-level reinforcing feedbacks.

In 2021, the pre-eminent UK international affairs think-tank Chatham House said a “plausible worst-case scenario” is 3.5°C or more, which could be an underestimate if tipping points are reached sooner than the orthodox science suggests. This now seems to be the reality.

A clear majority of scientists expected warming of more than 3°C, and 82% expected to see catastrophic impacts of climate change in their lifetime, according to a 2021 survey by the journal Nature.

Questions about the size of the aerosol forcing, and the related issue of how sensitive the climate is to changes in greenhouse gases, remain an issue of scientific contention.

New climate history research published in December 2023, based on a study of the last 66 million years, concluded that global temperature may be more sensitive to CO2 levels than current models estimate. It showed that the last time CO2 levels were as high as today was around 14 million year ago, which is longer than previous estimates, and that climate sensitivity — the amount of warming resulting from a doubling of atmospheric CO2 — may be between between 5°C and 8°C, compared to the IPCC orthodoxy of 1.5–4.5°C.

The level of greenhouse gases is currently around 560 parts per million, double the pre-industrial level. Some of those gases such as methane are short-lived so this level of forcing is not written in stone, but nevertheless if Hansen et al. are right that a doubling may lead to around 4–5°C of warming, then another 30 years of high emissions means humans will have created an increasingly unliveable planet.

Has the impact of aerosols been widely understood? In what the New York Times described as “an eye-opening Nature commentary”, Geeta Persad and her colleagues wrote in late 2022 that “overall, vast emissions of aerosols since the start of the industrial age have had a profound cooling effect” and that without them “the global warming we see today would be 30 to 50 percent greater”, warning that “the impacts of aerosols on climate risk are often ignored”.

In 2018, a group of eminent scientists explored the potential — once warming had exceeded the 1.5–2°C range — for self-reinforcing positive feedbacks in major elements of the climate system to push passed a planetary threshold that would prevent temperature stabilisation, and drive the system to a “Hothouse Earth”. They warned that “we are in a climate emergency… this is an existential threat to civilisation”.

The 2023 State of the Climate Report: Entering uncharted territory warned of: “potential collapse of natural and socioeconomic systems in such a world [of 2.6°C warming] where we will face unbearable heat, frequent extreme weather events, food and fresh water shortages, rising seas, more emerging diseases, and increased social unrest and geopolitical conflict.”

Whatever the words, the understanding is widely shared that contemporary nations and societies, and likely the global social system, are heading towards collapse. “If we carry on the way we are going now, I can’t see this civilisation lasting to the end of this century”, says Professor Tim Lenton. The US Defence Secretary Lloyd Austin III calls the risks “existential”.

Opening the Innovation Zero Congress in London in May 2023, Potsdam Institute Director Prof. Johan Rockstrom described the path we are on:

“2.5°C global mean surface temperature rise is a disaster. It’s something that humanity has absolutely no evidence that we can cope with… [There] would be a 10-metre sea-level rise. There would be a collapse of all the big biomes on planet Earth – the rainforest, many of the temperate forests – abrupt thawing of permafrost, we will have complete collapse of marine biology… Over one-third of the planet around the equatorial regions will be uninhabitable because you will pass the threshold of health, which is around 30°C. It’s only in some parts of the Sahara Desert today that has that kind of average temperature.”

Chatham House’s Climate Risk Assessment 2021 concludes that by 2050 global food demand would be 50% higher, but crop yields may drop by 30%. As desertification spreads across the dry sub-tropics, and one-third of the planet experiences unprecedented heat, it is not difficult to see why they concluded that cascading climate impacts will “drive political instability and greater national insecurity, and fuel regional and international conflict”.

What is worse is the setback to climate action posed by current conflicts and military posturing in Europe, the Middle East and east Asia, which are huge political distractions from dealing with the greatest threat to humanity, and all of which have the potential to spread more widely.

To maintain military flexibility, the US insisted in 1997 that direct military carbon emissions be excluded from international carbon accounting. Those emissions, around 5 percent of the total global, are far less than the indirect emissions from conflict, as recent estimates here and here indicate.

Projections show that by 2100 the expansion of the Sahara due to desertification will embrace Israel/Palestine, as well as spreading across the Mediterranean into Spain, Italy, Greece and Turkey (see map).

The Australian Prime Minister has finally spoken out about the escalating climate threat whilst inspecting damage from the recent Queensland floods: “All of this is a reminder that the science told us that climate change would mean there would be more extreme weather events and they would be more intense. And unfortunately, we are seeing that play out with the number of events that we’re having to deal with right around Australia”.

Just so, except that in common with leaders globally, the Australian government continues to have its head stuck in the sand about the real risks climate change now represents. It refuses to release an intelligence assessment of climate-security risks, and has fumbled a domestic climate risk assessment.

As a result, the community remains ill-informed and unprepared for what is coming.

Climate change and the severity of its impacts are increasing much faster than calculated by various models and analyses projecting future conditions. What’s more, the impacts are interacting to push critical ecological, hydrologic, and glacial systems over thresholds, known as tipping points, thus amplifying climate disasters. This truth is being told by current events, not speculative assumptions. The reports released to inform COP28 deliberations confirm 2023 as the worst year yet of climate change with the Global South and vulnerable populations around the world bearing the brunt.

outsized potential role to play in advancing CDR

to the level required to meet Paris Agreement

targets. Marine CDR (mCDR) has the potential,

when responsibly deployed and scaled, to

offer significant climate benefits, while also

contributing to sustainable economic development

for coastal communities, maritime nations, and

small island developing states (SIDS). Additionally,

certain mCDR approaches may yield co-benefits

such as improvements to ocean health, via local

mitigation of ocean acidification, to coastal

ecosystems and commercial aquaculture.

Examples of mCDR include:

Ocean alkalinity enhancement (OAE) via

electrochemical systems, or the physical

application of clean alkaline minerals to

coastlines, coastal watersheds, or the open ocean;

Electrochemical or photochemical systems that

directly remove CO2 from the ocean;

Dedicated cultivation or harvesting of aquatic

biomass, including macroalgae and microalgae (for

sinking to the deep ocean, long-duration terrestrial

storage, or potential incorporation into long-lived

products); and

Restoration, enhancement, and scaling of carbon

sinks associated with seagrass, mangroves, and

other coastal marine ecosystems (coastal “blue

carbon”).

The possibility of points-of-no-return in the climate system has been discussed for two decades^1,2,3. A point-of-no-return can be seen as a threshold which, once surpassed, fundamentally changes the dynamics of the climate system. For example, by triggering irreversible processes like thawing of the permafrost, drying of the rainforests, or acidification of surface waters. Recently, Lenton et al.⁴ summarized the global situation and warned that thresholds may be closer in time than commonly believed.

The purpose of this article is to report that we have identified a point-of-no-return in our climate model ESCIMO - and that it is already behind us. ESCIMO is a "reduced complexity earth system" climate model⁵ which we run from 1850 to 2500. In ESCIMO the global temperature keeps rising to 2500 and beyond, irrespective of how fast humanity cuts the emissions of man-made greenhouse gas (GHG) emissions. The reason is a cycle of self-sustained thawing of the permafrost (caused by methane release), lower surface albedo (caused by melting ice and snow) and higher atmospheric humidity (caused by higher temperatures). This cycle appears to be triggered by global warming of a mere?+?0.5 °C above the pre-industrial level.

Datasets of global temperatures vary a little depending on method, but two of the most significant are Berkeley Earth which put 2023 at 1.54°C above the pre-industrial (1850-1900) level, and Copernicus/ECMWF at 1.48°C.

Berkeley said that “a single year exceeding 1.5°C is a stark warning sign of how close the overall climate system has come to exceeding this Paris Agreement goal. With greenhouse gas emissions continuing to set record highs, it is likely that climate will regularly exceed 1.5°C in the next decade.”

2023 was notable for:

Global average warming hitting the 1.5°C mark, and new monthly records for global temperature every month from June to December. The October to December period was 1.74°C.

New national record high annual averages for an estimated 77 countries.

The first year that global average ocean surface temperatures exceeded 1°C, with once-in-a-century levels of warmth in the North Atlantic.

Two days in November when global average temperature, for the first time ever, reached 2°C above the pre-industrial levels.

Catastrophic flooding from Greece to Beijing to Vermont, and earlier in the year major flooding in New Zealand associated with a rain bomb and then cyclone Gabrielle.

Severe wildfires in Europe, Russia, Maui and North America; fires in Canada burned 18.5 million hectares of land.

The 2023 extremes were a shock. Prof. Katharine Hayhoe told the Guardian that: “We have strongly suspected for a while that our projections are underestimating extremes, a suspicion that recent extremes have proven likely to be true… We are truly in uncharted territory in terms of the history of human civilisation on this planet.”

Explanations for 2023 are incomplete, but warming is accelerating and 2024 is likely to be hotter

What happened in 2023 was not what scientists’ models anticipated at the beginning of the year and fell well outside the confidence intervals of any of the estimates. Carbon Brief says that “while there are a number of factors that researchers have proposed to explain 2023’s exceptional warmth, scientists still lack a clear explanation for why global temperatures were so unexpectedly high… researchers are just starting to disentangle the causes of the unexpected extreme global heat the world experienced in 2023”.

One person who has a clear view is the former NASA climate chief James Hansen who says that “the 1.5 degree limit is deader than a doornail” and warns that warming will accelerate to 1.7°C by 2030 and “2°C will be reached by the late 2030s”.

Marine Cloud Brightening (MCB) is potentially the first feasible way to start cooling the planet by reflecting more sunlight back to space.

Deployment would help slow global temperature rise, refreeze the poles and mitigate extreme weather such as storms, fires, droughts, heatwaves and floods.

Sea salt sprayed into the lower atmosphere in targeted areas is expected to prove a harmless way to reverse warming.

MCB has potential to reverse sea level rise with benefit to cost ratio estimated at 50,000 to 1.

MCB has been recognised for 50 years as a simple way to cool the oceans. It relies on the ‘Twomey Effect’, from its discoverer Dr Sean Twomey, who showed that clouds with smaller drops reflect more sunlight and are brighter than clouds with larger drops. Dr John Latham then showed that the optimal cloud drop size for MCB can be produced with sea salt particles smaller than one micron.

Datasets of global temperatures vary a little depending on method, but two of the most significant are Berkeley Earth which put 2023 at 1.54°C above the pre-industrial (1850-1900) level, and Copernicus/ECMWF at 1.48°C.

Berkeley said that “a single year exceeding 1.5°C is a stark warning sign of how close the overall climate system has come to exceeding this Paris Agreement goal. With greenhouse gas emissions continuing to set record highs, it is likely that climate will regularly exceed 1.5°C in the next decade.”

2023 was notable for:

Global average warming hitting the 1.5°C mark, and new monthly records for global temperature every month from June to December. The October to December period was 1.74°C.

New national record high annual averages for an estimated 77 countries.

The first year that global average ocean surface temperatures exceeded 1°C, with once-in-a-century levels of warmth in the North Atlantic.

Two days in November when global average temperature, for the first time ever, reached 2°C above the pre-industrial levels.

Catastrophic flooding from Greece to Beijing to Vermont, and earlier in the year major flooding in New Zealand associated with a rain bomb and then cyclone Gabrielle.

Severe wildfires in Europe, Russia, Maui and North America; fires in Canada burned 18.5 million hectares of land.

The 2023 extremes were a shock. Prof. Katharine Hayhoe told the Guardian that: “We have strongly suspected for a while that our projections are underestimating extremes, a suspicion that recent extremes have proven likely to be true… We are truly in uncharted territory in terms of the history of human civilisation on this planet.”

Explanations for 2023 are incomplete, but warming is accelerating and 2024 is likely to be hotter

What happened in 2023 was not what scientists’ models anticipated at the beginning of the year and fell well outside the confidence intervals of any of the estimates. Carbon Brief says that “while there are a number of factors that researchers have proposed to explain 2023’s exceptional warmth, scientists still lack a clear explanation for why global temperatures were so unexpectedly high… researchers are just starting to disentangle the causes of the unexpected extreme global heat the world experienced in 2023”.

One person who has a clear view is the former NASA climate chief James Hansen who says that “the 1.5 degree limit is deader than a doornail” and warns that warming will accelerate to 1.7°C by 2030 and “2°C will be reached by the late 2030s”.

Climate catalyst works in two main ways. Firstly, it speeds up the natural removal from the air of powerful greenhouse gases such as methane. Secondly, it increases the direct cooling influence of clouds, by brightening them and making them last longer in the sky. Clouds are brightened the same way as proposed for Marine Cloud brightening (MCB). The difference is that instead of using evaporated seawater droplets to increase cloud droplet number, microscopic particles of a non-toxic substance perform the same function. When the particles rainout they 'flocculate' (a process used in wastewater treatment, to purify water), removing any potential nanoparticle hazard. They then gradually transform to clay mineral, which is completely inert.

We suggest that an additional safe cooling technology such as climate catalyst should be made available, because it offers additional advantages over MCB. For example, in addition to cooling large areas of ocean and ice sheets, climate catalyst could keep areas at risk of wildfire moist before the fire season. When wildfires do occur, it could reduce the climate warming effect of the smoke by shortening its lifetime in the air. That is because climate catalyst speeds up the natural process by which the smoke particles rain out. It also lightens their colour, which reduces their warming influence in several ways. In addition, climate catalyst helps to protect the ozone layer by preventing smoke particles and other ozone destroyers from entering the stratosphere.

Methane and smoke (black carbon aerosol) are very powerful greenhouse warming agents. If Climate Catalyst proves able to remove them from the air safely and cost-effectively, they represent the 'low-hanging fruit' of climate action. The additional benefit of cloud cooling makes Climate Catalyst an even more compelling proposition.

Existing industry processes and low-cost substances can be used to produce climate catalyst particles. It could be dispersed in remote areas from ships, drones, and land-based dispersal facilities. The bulk of the climate cooling needed could be achieved by dispersing it from existing ships traversing the ocean. Climate catalyst utilizes some of the components of ships' emission gases for its enhanced methane removal chemistry.

Currently Climate Catalyst is a proposal looking for funding to be tested, first in laboratories to develop the safest, most effective formulation, then field trialled to optimize cooling operations. If the trials are successful, we would request regulatory support from governments to ensure it is used in well-coordinated, peaceful, environmentally beneficial ways. Only then should it be scaled up to cool the world's oceans and ice sheets. We accept that even that should be done incrementally, to ensure the effects are always beneficial. Fortunately, if Climate Catalyst needs to be stopped for any reason, it gets rained out of the air within a few days to weeks. At that point it no longer has any direct effect on the climate.

While active in the air Climate catalyst might alter weather patterns, therefore dispersal operations need careful planning. It should be dispersed when/where it is needed in a way that induces favourable weather across the globe on a long-term basis. Such a program would doubtless be controversial and would need to be managed transparently by a trusted intergovernmental body of experienced meteorologists and climate scientists.

Humanity needs to come to terms with the fact that we have profoundly altered the Earth's atmosphere and climate. Therefore, climate cooling interventions will be needed for the foreseeable future until the atmosphere's gas concentrations can be restored to their preindustrial levels.

outsized potential role to play in advancing CDR

to the level required to meet Paris Agreement

targets. Marine CDR (mCDR) has the potential,

when responsibly deployed and scaled, to

offer significant climate benefits, while also

contributing to sustainable economic development

for coastal communities, maritime nations, and

small island developing states (SIDS). Additionally,

certain mCDR approaches may yield co-benefits

such as improvements to ocean health, via local

mitigation of ocean acidification, to coastal

ecosystems and commercial aquaculture.

Examples of mCDR include:

Ocean alkalinity enhancement (OAE) via

electrochemical systems, or the physical

application of clean alkaline minerals to

coastlines, coastal watersheds, or the open ocean;

Electrochemical or photochemical systems that

directly remove CO2 from the ocean;

Dedicated cultivation or harvesting of aquatic

biomass, including macroalgae and microalgae (for

sinking to the deep ocean, long-duration terrestrial

storage, or potential incorporation into long-lived

products); and

Restoration, enhancement, and scaling of carbon

sinks associated with seagrass, mangroves, and

other coastal marine ecosystems (coastal “blue

carbon”).

Marine Cloud Brightening (MCB) is potentially the first feasible way to start cooling the planet by reflecting more sunlight back to space.

Deployment would help slow global temperature rise, refreeze the poles and mitigate extreme weather such as storms, fires, droughts, heatwaves and floods.

Sea salt sprayed into the lower atmosphere in targeted areas is expected to prove a harmless way to reverse warming.

MCB has potential to reverse sea level rise with benefit to cost ratio estimated at 50,000 to 1.

MCB has been recognised for 50 years as a simple way to cool the oceans. It relies on the ‘Twomey Effect’, from its discoverer Dr Sean Twomey, who showed that clouds with smaller drops reflect more sunlight and are brighter than clouds with larger drops. Dr John Latham then showed that the optimal cloud drop size for MCB can be produced with sea salt particles smaller than one micron.

The other is to restore the pre-industrial climate by 2050 by removing legacy CO2.

Carbon-dioxide removal (CDR)) tops the tech headlines with increasing frequency, leading to the impression that we are rapidly developing a multitude of mostly industrial options for creating a safe climate.

What many miss is that the vast majority of “carbontech” CDR approaches are designed to develop the carbon-offset market. By definition, offsets only compensate for continued emissions. They do not touch the 1,000 gigatons of legacy CO2 that is causing most of the climate havoc.

In fact, CDR today serves two distinct policy purposes. Each has merit, yet achieving the two goals requires quite different approaches and budgets and would create strikingly different results.

The two goals of CDR are:

Developing a CDR industry that underpins the carbon-offset market—thus adhering literally to the 1992 United Nations goal to “stabilize” greenhouse gas levels. Today this means stabilizing at dangerous levels never before experienced by our species. This is of course now called “net-zero emissions;” and

Following what appears to be the original intent of the United Nations Framework Convention on Climate Change: to restore GHG levels proven safe for humanity and nature as we know it. Restoring historically safe GHG levels is commonly called “climate restoration.”

of marine CDR (http://oceaniron.org). Owing to concerns surrounding the ethics of marine

CDR, ExOIS is organized around a responsible code of conduct that prioritizes activities

for the collective benefit of our planet with an emphasis on open and transparent

studies that include public engagement (2; see inset pg. 3).

Our goal is to establish open-source conventions for implementing OIF for marine

CDR that can be assessed with appropriate monitoring, reporting, and verification

(MRV) protocols, going beyond just carbon accounting, to assess ecological and other

non-carbon environmental effects (eMRV). As urgent as this is, it will still take 5 to 10

years of intensive work and considerable resources to accomplish this goal.

We present here a “Paths Forward’’ report that stems from a week-long workshop held

at the Moss Landing Marine Laboratories in May 2023 that was attended by international

experts spanning atmospheric, oceanographic, and social sciences as well as legal specialists

(see inside back cover). At the workshop, we reviewed prior OIF studies, distilled

the lessons learned, and proposed several paths forward over the next decade to lay the

foundation for evaluating OIF for marine CDR. Our discussion very quickly resulted in

a recommendation for the need to establish multiple “Ocean Iron Observatories’’ where,

through observations and modeling, we would be able to assess with a high degree of

certainty both the durable removal of atmospheric carbon dioxide—which we term the

“centennial tonne”—and the ecological response of the ocean.

3 PATHS FORWARD FOR EXPLORING OCEAN IRON FERTILIZATION

In a five-year phase I period, we prioritize five major research activities:

1. Next generation field studies

Studies of long-term (durable) carbon storage will need to be longer (year or more) and

larger (>10,000 km2) than past experiments, organized around existing tools and models, but

with greater reliance on autonomous platforms. While prior studies suggested that ocean

systems return to ambient conditions once iron infusion is stopped, this needs to be verified.

We suggest that these next field experiments take place in the NE Pacific to assess the

processes controlling carbon removal efficiencies, as well as the intended and unintended

ecological and geochemical consequences.

2. Regional, global and field study modeling

Incorporation of new observations and model intercomparisons are essential to accurately

represent how iron cycling processes regulate OIF effects on marine ecosystems and carbon

sequestration, to support experimental planning for large-scale MRV, and to guide decision

making on marine CDR choices.

3. New forms of iron and delivery mechanisms

Rigorous testing and comparison of new forms of iron and their potential delivery

mechanisms is needed to optimize phytoplankton growth while minimizing the financial

and carbon costs of OIF. Efficiency gains are expected to generate responses closer to those

of natural OIF events.

4. Monitoring, reporting, and verification

Advances in observational technologies and platforms are needed to support the development,

validation, and maintenance of models required for MRV of large-scale OIF deployment. In

addition to tracking carbon storage and efficiency, prioritizing eMRV will be key to developing

regulated carbon markets.

5. Governance and stakeholder engagement

Attention to social dimensions, governance, and stakeholder perceptions will be essential

from the start, with particular emphasis on expanding the diversity of groups engaged in

marine CDR across the globe. This feedback will be a critical component underlying future

decisions about whether to proceed, or not, with OIF for marine CDR.

Paramount in the plan is the need to move carefully. Our goal is to conduct these five activities in parallel

to inform decisions steering the establishment of ocean iron observatories at multiple locations in phase

II. When completed, this decadal plan will provide a rich knowledge base to guide decisions about if,

when, where, and under what conditions OIF might be responsibly implemented for marine CDR.

The consensus of our workshop and this report is that now is the time for actionable studies to begin.

Quite simply, we suggest that some form of marine CDR will be essential to slow down and reverse the

most severe consequences of our disrupted climate. OIF has the potential to be one of these climate

mitigation strategies. We have the opportunity and obligation to invest in the knowledge necessary to

ensure that we can make scientifically and ethically sound decisions for the future of our planet.

Still, the fact that more research is needed is true for all geoengineering techniques. So even though the scientists within our group focus most closely on stratospheric aerosol injection, we believe that MCB research is valuable.

The stratosphere (see NOAA image below) is a layer of the Earth’s atmosphere that ranges between 7 to 31 miles above the ground between the Troposphere and the Mesophere. The stratosphere is an ideal target for atmospheric geoengineering because it is relatively isolated from human populations, is accessible by planes (and other transport/delivery methods), and doesn’t have weather such as rain that would cause aerosol spray particles to fall quickly to the ground

In recent years, discussions of climate change have shown growing interest in “tipping elements” of the Earth system, also imprecisely referred to as “tipping points.” This refers to Earth system components like the tropical rainforests of Amazonia or the Greenland and Antarctic ice sheets which may exhibit large-scale, long-term changes upon reaching critical global warming, greenhouse gas, or other thresholds. Once such thresholds are passed, some tipping elements could in turn produce additional greenhouse gas emissions or change the Earth's energy balance in ways that moderately reinforce warming. In this review, we summarize the current state of scientific knowledge on 10 systems that some have referred to as potential tipping elements of the climate system. We describe the mechanisms important to each system, highlight the response of these systems to climate change so far, and explain the dynamics of potential future changes that these systems could undergo in response to further climate change. Overall, even considering remaining scientific uncertainties, tipping elements will influence future climate change and may involve major impacts on ecosystems, climate patterns, and the carbon cycle starting later this century. Aggressive efforts to stabilize climate change could significantly reduce such impacts.

Datasets of global temperatures vary a little depending on method, but two of the most significant are Berkeley Earth which put 2023 at 1.54°C above the pre-industrial (1850-1900) level, and Copernicus/ECMWF at 1.48°C.

Berkeley said that “a single year exceeding 1.5°C is a stark warning sign of how close the overall climate system has come to exceeding this Paris Agreement goal. With greenhouse gas emissions continuing to set record highs, it is likely that climate will regularly exceed 1.5°C in the next decade.”

2023 was notable for:

Global average warming hitting the 1.5°C mark, and new monthly records for global temperature every month from June to December. The October to December period was 1.74°C.

New national record high annual averages for an estimated 77 countries.

The first year that global average ocean surface temperatures exceeded 1°C, with once-in-a-century levels of warmth in the North Atlantic.

Two days in November when global average temperature, for the first time ever, reached 2°C above the pre-industrial levels.

Catastrophic flooding from Greece to Beijing to Vermont, and earlier in the year major flooding in New Zealand associated with a rain bomb and then cyclone Gabrielle.

Severe wildfires in Europe, Russia, Maui and North America; fires in Canada burned 18.5 million hectares of land.

The 2023 extremes were a shock. Prof. Katharine Hayhoe told the Guardian that: “We have strongly suspected for a while that our projections are underestimating extremes, a suspicion that recent extremes have proven likely to be true… We are truly in uncharted territory in terms of the history of human civilisation on this planet.”

Explanations for 2023 are incomplete, but warming is accelerating and 2024 is likely to be hotter

What happened in 2023 was not what scientists’ models anticipated at the beginning of the year and fell well outside the confidence intervals of any of the estimates. Carbon Brief says that “while there are a number of factors that researchers have proposed to explain 2023’s exceptional warmth, scientists still lack a clear explanation for why global temperatures were so unexpectedly high… researchers are just starting to disentangle the causes of the unexpected extreme global heat the world experienced in 2023”.

One person who has a clear view is the former NASA climate chief James Hansen who says that “the 1.5 degree limit is deader than a doornail” and warns that warming will accelerate to 1.7°C by 2030 and “2°C will be reached by the late 2030s”.