There have been several proposals for using waves to

pump sea water for energy generation. Some involve

water moving over the top of a wall [1] or ramp [2], [3]

into a lagoon above sea level with height optimized to

maximize the product of head and flow volume. For the

hurricane-suppressing project we need a head only just

large enough to overcome the density difference between

the upper and lower thermal layers.

For a salt concentration of 35,000 ppm and

temperature range from 25 C down to 10C this is only

2.76 kg/m3 so that the head of water needed is very small

compared with ocean wave heights. This means that we

can use a low freeboard enclosure with a wall of nonreturn

valves. Most of the water will enter horizontally

rather than by over topping. A sectional view of the

design is shown in figure 1. A vertical non-permeable

tube below the valve wall will carry the water down to the

thermocline. The lower part will be subject to a gentle,

steady hoop tension.

Methane is a powerful greenhouse gas and an important precursor of tropospheric ozone; both are key air pollutants and short-lived climate forcers (SLCFs). Several factors in addition to rising anthropogenic methane emissions have influenced the evolution of atmospheric methane from its pre-industrial level of ~700?ppb to its present-day value of over 1900?ppb. The Intergovernmental Panel on Climate Change's Sixth Assessment Report (Szopa et al., 2021) assessed how changes in emissions of nitrogen oxide (NO_x), carbon monoxide (CO), and non-methane volatile organic compounds (NMVOCs) have contributed to historical changes in methane via their impacts on OH, the main sink for methane. A range of modelling studies have explored these indirect impacts on methane (e.g. Shindell et al., 2005, 2009; Stevenson et al., 2013; Thornhill et al., 2021). For example, the Atmospheric Chemistry and Climate Model Intercomparison Project found that 1850-2000 increases in anthropogenic NO_x emissions had reduced year 2000 methane levels by 955?ppb, whilst growing emissions of CO and NMVOCs had increased methane by 150 and 59?ppb respectively (Table 7 of Stevenson et al., 2013). These results have quite large uncertainties (at least ±10?%, based on the model range in Stevenson et al., 2013) but indicate that non-methane (especially NO_x) emissions have had very significant impacts on methane. Better understanding of what controls methane and its evolution is vital for progress towards the Paris Climate Agreement target that seeks to limit warming to 1.5?^°C above pre-industrial levels.

Following the onset of the COVID-19 pandemic in early 2020, the trace gas composition of the global atmosphere changed substantially. Atmospheric NO_x levels decreased as surface and aviation NO_x emissions fell (Bauwens et al., 2020; Cooper et al., 2022), whilst the measured growth rate of methane (CH₄) rose sharply in 2020 (Laughner et al., 2021). The observed NO_x changes are clearly linked to falls in emissions resulting from lockdowns, but the driver of the methane increases is less clear, with some studies discussing causes related to decreases in OH (e.g. Weber et al., 2020; Laughner et al., 2021), whereas others suggest rises in sources (e.g. Feng et al., 2022). Methane, NO_x, CO, and NMVOCs are linked via the oxidising capacity of the atmosphere, specifically by the abundance of the hydroxyl (OH) radical. The response of global atmospheric chemistry to the large lockdown perturbation since early 2020 provides an opportunity to explore the sensitivity of the NO_x-CO-NMVOC-OH-CH₄ system and to compare models and observations. Here, we use model-derived sensitivities of global methane to NO_x, CO, and NMVOC emissions as well as the estimated changes in anthropogenic emissions of these species related to the COVID-19 lockdowns to calculate estimated impacts from lockdown emission changes on the growth rate of global methane, and we compare this to observations.

Nature has created the perfect carbon capture and removal mechanism, known as the carbon pump. Tiny photosynthetic phytoplankton convert carbon into biomass, fulfilling their role as the primary producers of the oceanic ecosystem.

As predators consume them, only 1% of the carbon captured reaches the sea bottom. We have developed a method to safely harness phytoplankton fixation, while improving the sequestration ratio by two orders of magnitude.

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.

Despite its high abundance in the Earth's crust, iron concentrations are very low in the ocean. This is due to the low solubility of iron in the oxic and slightly alkaline seawater of today's oceans, uptake by microorganisms and limited input from external sources. Consequently, the bioavailability of this element is very low in many oceanic regions [1]. Iron is essential for cell metabolism, especially for electron transport. Photosynthesis, respiration, and nitrogen fixation require high cellular concentrations of iron [2].

Microorganisms, particularly bacteria, have evolved several different iron uptake mechanisms [3], [4]. Inorganic iron can be acquired either in its reduced ferrous (Fe²⁺) [5], or oxidized ferric (Fe³⁺) state [6]. However, in well-oxygenated seawater, the free ion concentrations of both forms are low, and bacteria have developed alternative strategies to access the organically complexed pool. The synthesis and uptake of siderophores, strong chelators of ferric iron, is one example [7], but bacteria can also acquire iron from free heme (a prosthetic group of porphyrin containing an atom of iron) or heme-containing proteins using both direct uptake and hemophores [8]. Such strategies have been identified in diverse marine bacteria [9].

Many recent studies have highlighted the strategies used by diatoms and cyanobacteria to minimize their iron demand, such as reducing the expression of "expensive" iron genes in the photosystem I complex [10], [11] and nitrogenase [12], or else increasing flavodoxin production [13], [14]. Genomic analysis of Prochlorococcus clades isolated from iron-depleted oceanic regions showed that several genes encoding for iron-containing proteins were absent, thereby reducing the cellular iron quota [15].

The relation between genomic iron uptake strategies and oceanic environments has recently been investigated in cyanobacteria, the most abundant photosynthetic group of marine bacteria. Many Synechococcus genomes from strains isolated in the open ocean lack most known genes for iron stress, while genomes from strains isolated in coastal and upwelling areas contain many such genes, suggesting that maintaining multiple iron limitation compensation strategies is not a selective advantage in the open ocean [16]. Consistent with this, the light-harvesting gene isiA of Synechococcus has been proposed as a biomarker of HNLC regions [17]. However, heterotrophic bacteria also compete for iron at low concentrations, and can account for up to 50% of the total planktonic iron uptake [18]. Additionally, they may modify iron chemistry through the production of organic ligands and thereby regulating phytoplankton production [19]. Because metagenomes contain the gene content of the community of most abundant and therefore most successful microorganisms, they provide a complementary glimpse to organismal studies into the genetic basis of adaptation to the environment.

We set up a database of 2319 sequences, corresponding to 140 gene families and 10 different iron-related metabolic pathways, to explore the mechanisms involved in iron acquisition in the ocean. The caveats of using Blast Best Hits and evalue cutoffs have been discussed previously [20]. Here, we defined a stringent criterion to discard false positives: we only considered Reciprocal Best Hits with coverage and identity threshold empirically estimated from our database. We investigate the link between genomic iron metabolism strategies of microbial communities and iron concentrations among 54 worldwide distributed marine metagenomes (Figure 1). Iron concentrations at each location were taken from a biogeochemical model that incorporates information about the sources and cycling of iron in the ocean and were compared to independently acquired observed iron concentrations. We thus established the relationships between microbial communities' iron-related gene prevalence, taxonomic affiliation and iron concentrations in different marine habitats.

as a result (Hartmann and Short, 1980; Ramanathan et al.,

1989). The solar radiation reflected by marine low clouds

(albedo) increases with the amount of liquid water they contain and as the size of cloud droplets decreases (Stephens,

1978). Twomey (1974, 1977) showed that, for a fixed liquid

water path (LWP), cloud albedo increases with the concentration of cloud droplets (Nd). Thus anthropogenic aerosol pollution increases cloud albedo and cools climate. A total of 4

decades of subsequent research has established the “Twomey

effect” as being the largest contributor to the overall cooling

impact of aerosols on climate (Zelinka et al., 2014; Bellouin

et al., 2020).

In recent decades, evidence showing cloud macrophysical adjustments to aerosol increases has mounted. Albrecht (1989) suggested that reduced droplet sizes would

lead to suppressed collision–coalescence, greater retention of

water, and an augmentation of the Twomey effect. Modeling and observations both show precipitation suppression by

aerosol in warm clouds (Ackerman et al., 2004; Sorooshian

et al., 2010; Terai et al., 2015), and yet observations of ship

tracks (Coakley and Walsh, 2002; Toll et al., 2019), pollution

plumes (Toll et al., 2019; Trofimov et al., 2020), and largescale shipping lanes (Diamond et al., 2020) reveal LWP reductions in the mean. Modeling has shown that aerosols can

cause both positive and negative LWP adjustments (Ackerman et al., 2004; Wood, 2007), with the sign of the change

dependent on meteorological and aerosol conditions. Reduced LWP stems from increased cloud-top entrainment of

dry free-tropospheric air due to smaller cloud droplets and/or

turbulent invigoration of the boundary layer caused by suppressed precipitation (Wang et al., 2003; Ackerman et al.,

2004; Bretherton et al., 2007; Wood, 2007). A recent paper

by Glassmeier et al. (2021) illustrates that the sign of LWP

adjustments depends not only on the meteorological conditions but also on the number of aerosol particles, which cause

positive adjustments when the aerosol number is small, and

precipitation suppression increases the condensate retention.

Negative adjustments are found when the aerosol number is

large, due to the aforementioned entrainment drying. Studies using shipping and land-based pollution sources suggest

that mean LWP decreases may offset the Twomey response

to a degree that ranges from 3 % (Trofimov et al., 2020) to

perhaps 20 % (Toll et al., 2019; Diamond et al., 2020). LWP

adjustments in low clouds are poorly handled in large-scale

models (Malavelle et al., 2017), which almost universally

show LWP increases in simulations of anthropogenic aerosol

impacts (Lohmann and Feichter, 2005; Isaksen et al., 2009;

Bellouin et al., 2020). Global models also tend to show cloud

cover increases in response to aerosol, but these appear to be

small compared with the Twomey responses and LWP adjustments (Zelinka et al., 2014). Cloud cover adjustments are

difficult to constrain using observations (e.g., Gryspeerdt et

al., 2016; Possner et al., 2018)

These largely unsupported presumptions distort risk assessments and discount the urgent need to develop a viable mitigation strategy. Due to political pressures, many critical scientific concerns are ignored or preemptively dismissed in international negotiations. As a result, the present and growing crisis and the level of effort and time that will be required to control and rebalance the climate are severely underestimated.

In conclusion, the paper outlines the key elements of a realistic policy approach that would augment current efforts to constrain dangerous warming by supplementing current mitigation approaches with climate cooling interventions.

In the early 1970s in the United Kingdom (UK) and elsewhere research into ‘alternative’ energy sources was growing partly as a consequence of emergent theories of global warming and the oil crisis. The latter arose out of the Arab producers of the Organization of Petroleum Exporting Countries (OPEC) putting in place an embargo on oil exports to the United States in October 1973 and threatening to cut back overall production 25% (Udall 1973). Any research into a new, untested and unorthodox energy technology that could displace traditional and polluting energy supply methods required at least some realistic start-up funding. Given the size of funding needed the most likely source for such untested technologies would be governmental. The new technology discussed in this case study was one method for extracting energy from sea waves: the Edinburgh Wave Power Project led by Professor Stephen Salter who was head of the Department of Mechanical Engineering at Edinburgh University (ERA 2021).

Given that our concerns for this book relate to the ethical issues that can arise in such situations a series of questions immediately present themselves: What are the immediate consequences of giving funding to new technologies that could undermine previous (traditional) ways of producing energy? What range of ‘interests’ are involved? What broader policies influence the research and the views of funders and government? Does it matter who funds the research? Is there too much opportunity for misconduct depending on how funds are disbursed? And does it matter who analyses the results? These are the kind of questions addressed in the following case study.

At this point I must declare an interest of my own. I am a supporter of alternative energy technologies that could reduce all forms of environmental pollution and, thereby, help minimize human-induced global warming. More specifically the origins of such a view lie in my experience with the Wave Power Project itself from 1974 to 1977. My wife was then a Personal Assistant (P.A.) to Stephen Salter and told me of her frustration in getting the main source of funding to deliver the correct funding in good time. She constantly had to phone the funder and was regularly offered unreasonable excuses for delays—the consequence of which were that the salaries for the young engineering researchers were rarely paid in time and money for materials always delayed. Such a tactic seemed problematic to me at the time until she explained the funding was disbursed by the UK Atomic Energy Authority—one of the ‘old’ polluting technologies that alternative energy projects were directly challenging. Perhaps this was a rationale for the tactic that could only be described as ‘undermining’?

For my college teaching post at the time I was tasked with delivering a series of lectures of a ‘general’ nature and thought something on alternative energy technologies would be of interest to my experienced mature students—who were all ‘older adults’ entering further and higher education for the first time. I invited both the Wave Power Project and the Atomic Energy Authority to come and give a talk about the merits of their approach. The Wave Power Project sent one of their researchers who gave an informed and stimulating talk about the balance in terms of cost and effectiveness of different energy sources and showed some photographs to illustrate their ongoing work. The Atomic Energy Authority sent no-one but delivered (at their considerable expense) boxes of hundreds of reprinted articles to be distributed freely for the benefit of my students. All the articles were in support of nuclear energy without providing a balanced perspective on the controversies surrounding nuclear energy. I cannot say I suffered a ‘confirmation bias’ prior to those experiences, but it certainly grew subsequently as my suspicions of at least some lack of fairness in funding were aroused.

These details, in relation to a specific research activity, illustrates that ‘who funds and how?’ raises a series of ethical questions along with whether a balanced assessment of alternative options—in any field of research—is vital to honest, reliable and trustworthy research. Trust in the funding source becomes part of transparency of practice that can help the public and policymakers decide on the best ways of proceeding with an innovative, and potentially challenging, technology.

Go to:

8.2. More Background and Context

Research into marine wave power really began with Salter’s experiments using a dynamically shaped float (the ‘Duck’) that linked via a spine to a series of other floating ‘Ducks’ which bobbed up and down in the waves. The Duck was a 300-tonne floating canister designed to drive a generator from the motion of bobbing up and down on waves like a duck. It is still regarded as the most efficient of any wave power system produced, converting up to 80% of the wave energy to electricity which was to be then cabled ashore. All the experiments were successful until 1982 when the work suddenly stopped. Salter (2016) provides a full discussion of both the key technical issues and the emergent governance problems.

The funding problem arose from the control of all renewable energy research—not just wave power—during the 1970s and 1980s coming from an organisation that was part of the United Kingdom Atomic Energy Authority. The Department of Energy’s research and development advisory council (ACORD) operated at long range from all the projects and its staff was recruited largely from the nuclear and the depletable energy industries. In other words, wave power research was funded and controlled by the regulators of the nuclear, coal and gas industries.

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.

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.

It is far easier to modify Earth's albedo than to determine whether it should be done or what the consequences might be of such an action. One serious concern is that such an action could be unilaterally undertaken by a small nation or smaller entity for its own benefit without international sanction and regardless of international consequences. Transparency in discussing this subject is critical. In the spirit of that transparency, Climate Intervention: Reflecting Sunlight to Cool Earth was based on peer-reviewed literature and the judgments of the authoring committee; no new research was done as part of this study and all data and information used are from entirely open sources. By helping to bring light to this topic area, this book will help leaders to be far more knowledgeable about the consequences of albedo modification approaches before they face a decision whether or not to use them.

Contributor(s): National Research Council; Division on Earth and Life Studies; Board on Atmospheric Sciences and Climate; Ocean Studies Board; Committee on Geoengineering Climate: Technical Evaluation and Discussion of Impacts

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.

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.”

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

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.

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).

On 28 February 2022 the Intergovernmental Panel on Climate Change released their 6th Assessment Report, a nearly 4000-page document 8 years in the making. That same day United Nations (UN) Secretary General António Guterres spoke to press stating: “Today’s IPCC report is an atlas of human suffering and a damning indictment of failed climate leadership…The abdication of leadership is criminal.”1 That this would be his response should come as no surprise; 4 months prior the UN Environment Program published their emissions gap report illustrating that even if the participants of extant climate abatement agreements adhered to their promises, we would still be on track for a 2.7c rise in global temperature over pre-industrial levels2. What is most interesting about the UN Secretary General’s speech is not his assessment of the global response to climate change but the curious exclusion of UN responsibility. After all, the IPCC was created in 1988 and has since their first assessment report in 1990 been the world’s primary resource on the scope, velocity, and outcomes of anthropogenic climate change while providing policy recommendations disseminated to governments worldwide. Given that present climate agreements are predicated on the data and recommendations produced by the IPCC it is fair to interrogate the continued viability of the IPCC as a global resource for climate information. This paper will determine whether this organization can be relied upon as the world leader in climate research and if the IPCC has played an active role in minimizing the existential catastrophe which threatens to extinguish most life on this planet.

1

for young people. Governments will not make required changes to energy policies based on

theoretical threats – there must be sufficient empirical evidence of harm to force action. Thus,

delayed response makes it difficult to avoid near-term, growing, climate impacts, but it does

not prevent achievement of policies that will lead to a hospitable climate with a bright future

for young people. Time is running short, however, and effective actions at this point require a

good understanding of ongoing climate change and the responsible mechanisms.

The proximate cause of ongoing global warming is Earth’s energy imbalance (EEI). Earth is

now absorbing more energy incoming from the Sun than the planet is sending back to space

as reflected solar light and emitted thermal (heat) radiation. As long as that imbalance is

positive – more energy coming in than going out – Earth will continue to get hotter. Factors

that alter Earth’s energy balance are called climate forcings. There are two large human-made

climate forcings: changes of atmospheric greenhouse gases (GHGs) and changes of aerosols.

GHGs reduce heat radiation to space; thus, an increase of GHGs causes a positive energy

imbalance, more energy coming in than going out, which causes warming. Aerosols reflect

sunlight to space, which is a negative contribution to EEI that causes cooling.

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”.

Bellouin, N., O. Boucher, J. Haywood, C. Johnson, A. Jones, J. Rae, and S. Woodward, 2007: Improved representation of aerosols for HadGEM2. Hadley Centre Tech. Note 73, 42 pp. [Available online at http://www.metoffice.gov.uk/media/pdf/8/f/HCTN_73.pdf.]