Human-caused emissions of aerosols – tiny, light‑scattering particles produced mainly by burning fossil fuels – have long acted as an invisible brake on global warming.
This is largely because they absorb or reflect incoming sunlight and influence the formation and brightness of clouds.
These combined effects act to lower regional and global temperatures.
Aerosols also have a substantial impact on human health, with poor outdoor air quality from particulate matter contributing to millions of premature deaths per year.
Efforts to improve air quality around the world in recent decades have reduced aerosol emissions, bringing widespread benefits for health.
However, while cutting aerosols clears the air, it also unmasks the warming caused by carbon dioxide (CO2) and other greenhouse gases (GHGs).
In this explainer, Carbon Brief unpacks the climate effects of aerosols, how their emissions have changed over time and how they could impact the pace of future warming.
Key points include:
- Clean air rules are driving a rapid decline in sulphur emissions around the world. Global sulphur dioxide (SO2) emissions have fallen by around 40% since the mid‑2000s.
- There is around half a degree of warming today that is “hidden” by aerosols. Without the cooling from sulphate and other aerosols, today’s global temperature would already be close to 2C above pre‑industrial levels, rather than the approximately 1.4C the world is currently experiencing.
- Chinese SO2 emissions have fallen by more than 70% between 2006 and 2017 as the national government has brought in a series of air-pollution measures. These declines have added around 0.06C to global warming since 2006.
- Shipping’s low‑sulphur fuel rules have added to recent warming. The International Maritime Organization’s (IMO’s) 2020 cap on marine‑fuel sulphur has already warmed the planet by an estimated 0.04C, albeit with a wide range of estimates across published studies.
- Roughly one‑quarter of the increase in global temperature over the past two decades stems from this unmasking of human-caused heat. Altogether, recent aerosol cuts may have contributed ~0.14C of the ~0.5C of warming the world has experienced since 2007.
- By unmasking warming from CO2 and other GHGs, aerosols have flipped from reducing the rate of decadal warming (as emissions increased) to increasing the rate of warming (as emissions decreased) after 2005.
- Sulphate and other aerosols are a major component of PM2.5 air pollution, which has been linked to millions of premature deaths each year.
- Most future‑emissions pathways project continued aerosol declines. Unless methane and other short-lived GHGs fall at the same time, the rate of warming could accelerate in the coming decades even if CO2 emissions plateau.
Aerosol emissions
The term “aerosols” can be a source of confusion as it often evokes images of spray cans and concerns over depletion of the ozone layer. However, aerosols are a broad category that refer to solid or liquid particles that are fine enough to remain suspended in the atmosphere for extended periods of time.
The major climate-relevant aerosols include SO2, nitrate (NO3), ammonia (NH4), mineral dust, sea spray and carbonaceous aerosols, such as black carbon and organic aerosols.
They vary in size – from nanometres to tens of micrometres – and generally have a short residence time in the lower atmosphere, lasting days to weeks before drifting back to the surface or being washed out in rain.
This means that unlike long-lived GHGs, such as CO2 or nitrous oxide (N2O), aerosols only continue to impact the climate while they are being released. If emissions stop, their climate impacts quickly dissipate.
Aerosols affect the climate by absorbing or reflecting incoming sunlight, or by influencing the formation and brightness of clouds. Most aerosols have a cooling impact because they scatter sunlight away from the Earth and back to space. However, others, including black carbon, cause warming by absorbing incoming sunlight and heating the lower atmosphere.
The figure below shows climate model output looking at the global temperature impact of each different driver of climate change (referred to as “climate forcings” or “radiative forcings”) individually. It includes GHGs, aerosols and other human-caused drivers (such as land albedo changes or tropospheric ozone), as well as natural factors (such as volcanoes and variations in solar output).
Lines above zero show forcings that have an overall warming impact, while those below zero have a cooling effect.
Global average surface temperature changes between 1850 and 2024 caused by each category of climate forcing. Calculated based on the FaIR climate model by comparing all-forcing model simulations to those with an individual forcing removed, following an approach developed by Dr Chris Smith. Observed surface temperatures (using the WMO average of six groups) are shown by the dashed black line.
The warming associated with GHG emissions and cooling associated with aerosol emissions are the largest factors driving the global temperature changes, particularly over the past 70 years.
In the absence of aerosol emissions, the best estimate of current warming would be approximately 0.5C higher, with the world approaching 2C rather than the 1.4C that the world is experiencing today.
Cooling from aerosols has likely masked a substantial portion of the warming that the world would otherwise have experienced.
Different aerosols and their climate effects
There are a number of different types of aerosols, whose climate impacts vary based on both the properties of the particles and the magnitude of human emissions. Of these, SO2 – often referred to as just “sulphur” – has the largest climate impact and is responsible for the bulk of aerosol masking (around -0.5C) that is occurring today.
Black carbon has a modest warming effect on the climate globally (~0.1C), but a much larger impact on Arctic temperatures where it can darken snow and ice, increasing the sunlight they absorb from the sun.
Organic carbon emissions have a modest cooling effect (around -0.1C), while emissions of ammonia and nitrate have an even-smaller cooling effect (around -0.02C). Others, such as dust and sea salt, are primarily natural and changes have had negligible effects on global temperatures.
The table below, adapted from the IPCC AR6 climate science report, provides details on the major aerosols, including their primary sources, effective radiative forcing and temperature impacts over the 1750-2019 period.
| Aerosol type | Primary sources | Effective radiative forcing in watts per metre squared (w/m2), 1750-2019 | Temperature impact, 1750-2019 |
|---|---|---|---|
| Sulphur / Sulphate (SO4) | Fossil fuel and biomass SO2 | -0.9 (-1.6 to -0.3) | Strong cooling with -0.5C (-0.1C to -0.9C) of offset warming globally. Dominant aerosol cooling component. |
| Black carbon (BC) | Incomplete combustion (diesel, coal, biomass) | 0.1 (-0.2 to 0.4) | Warming of 0.1C globally (-0.1C to 0.3C). Offsets some cooling; major regional Arctic impact. |
| Organic carbon (OC) | Biomass burning, biofuel and volatile organic compounds (VOCs) | -0.2 (-0.4 to 0.0) | Cooling of -0.1C globally (-0.2C to 0C). |
| Nitrate (NO3) and ammonia (NH3) | Nitrous oxide (NOX) from vehicles and industry and ammonia (NH3) from agriculture | -0.03 (-0.07 to 0.00) | Small global cooling effect of -0.02C (-0.05C to 0.01C). Regionally important where ammonia is abundant. |
| Dust (mineral) | Natural (deserts); some land-use change | ~0 (uncertain, ±0.1) | Small globally with an uncertain sign, but potentially larger regional effects. Anthropogenic fraction of dust forcing is small. |
| Sea salt | Ocean spray (natural) | 0 (natural baseline) | No trend or forcing attributable to human activity. |
Aerosol cooling was relatively modest until around 1950, after which SO2 emissions substantially increased worldwide, driven by a rapid increase in coal combustion and industrial activity.
The cooling effect of aerosols peaked around the year 2000 and has been declining over the past two decades. The figure below highlights the impact of aerosols on global temperature change over time.
Global average surface temperature changes over 1850-2024 caused by aerosols, based on the FaIR climate model.
However, the cooling effects of aerosols remain uncertain due both to their regional nature and the complex nature of interactions between aerosols and clouds.
There is also a relationship between aerosol forcing and climate sensitivity, which is a measure of how much warming is expected from a doubling of atmospheric CO2. In general, climate models with a higher sensitivity tend to have higher aerosol cooling that counterbalances the larger GHG-driven warming. The reduction of uncertainty in aerosol cooling – particularly the effects of aerosols on cloud formation – is a major focus of scientists in their attempts to reduce the uncertainty in climate sensitivity estimates.
The climate impacts of aerosols are broadly divided into two groups, shown in the chart below. The first is a direct effect (blue line), where they scatter and absorb incoming radiation from the sun, preventing it reaching the Earth’s surface. The second is an indirect effect (dark blue line) on cloud formation, where aerosols serve as “condensation nuclei” around which clouds form.
For example, aerosols can enhance the coverage, reflectance and lifetime of low-level clouds, causing a strong cooling effect.
Global average surface temperature changes between 1850 and 2024 caused by direct and indirect aerosol effects, based on the FaIR climate model.
Of the two, direct aerosol effects generally have the smaller effect, with less uncertainty around their impact. They cool the planet by around -0.13C (-0.31C to 0C) today.
Indirect aerosol effects have a larger magnitude and uncertainty, with a -0.42C (-1C to -0.11) cooling impact globally today.
The recent sixth assessment report (AR6) report from the Intergovernmental Panel on Climate Change (IPCC) increased the estimated magnitude of indirect aerosol forcing, compared to the fifth assessment report (AR5). This increase was based on an improved understanding and modelling of aerosol-cloud adjustments.
While global average temperature is the focus here, it is important to note that – unlike CO2 and other GHGs – aerosols in the lower atmosphere are not “well mixed”. That is, they are not spread evenly through the atmosphere.
Rather, their short lifetime results in strong regional variation in aerosol concentrations and associated climate effects, which can have a large impact on local temperature and rainfall extremes. Regions such as east or south-east Asia, which have high sulphur emissions, have experienced larger aerosol cooling than regions with lower emissions.
The one exception is when aerosols are injected higher up in the atmosphere in the stratosphere. There, they tend to have a much longer lifetime – measured in years rather than days – and are much more well-mixed.
(Today, meaningful increases in stratospheric aerosols only occur as a result of particularly explosive eruptions of sulphur-rich volcanoes, which cool the Earth for a few years after a major eruption. However, intentionally introducing sulphate aerosols into the stratosphere has been proposed as a potential “geoengineering” strategy to temporarily mask the effects of warming. These ideas have been controversial in the scientific community.)
Aerosol emissions have a huge impact on public health. The substances are generally considered to be conventional air pollutants and are precursors of fine particulate matter air pollution (PM2.5).
Outdoor air pollution associated with sulphur and other aerosol emissions contributes to millions of premature deaths annually. As a result, much of the impetus to rapidly cut aerosols arises from public health concerns. Despite the contribution to more rapid warming, a reduction in aerosols represents a massive improvement in health and welfare for people worldwide.
Rapid declines in global sulphur emissions
Global emissions of the most climatically important aerosol – SO2 – have declined precipitously since peaking around 50 years ago.
SO2 cuts were initially driven by clean air regulations adopted by the US, UK and EU in the 1970s and 1980s in response to the growing effects of SO2 on both air pollution and acid rain.
As the figure below illustrates, SO2 emissions across the US, UK and EU have subsequently fallen from 68m tonnes per year in 1973 to just 3.3m tonnes per year today.
Annual SO2 emissions by country and by international shipping and aviation, 1850-2022. Data from the Community Earth atmospheric Data System (CEDS).
In the first decade of the 21st century, SO2 cuts in the UK, US and EU were counterbalanced by growing SO2 emissions in China, driven by a rapid expansion of coal use and industrial activity.
Between 2000 and 2007, global SO2 emissions saw a renewed increase, as China’s SO2 emissions reached 38m tonnes per year by 2006.
However, following an international and domestic focus on air pollution in the aftermath of the 2008 Beijing Olympics, China embarked on an ambitious programme to clean up air pollution. The nation has since cut its SO2 emissions by more than 70% to around 10m tonnes of SO2 today.
Meanwhile, SO2 emissions from global shipping recently dropped by around 65%, after the IMO instituted regulations requiring the use of low-sulphur marine fuels from 2020.
Many other countries have also broadly seen aerosol declines since 1990, although there are exceptions. For example, India’s expansion of coal generation has driven increasing SO2 emissions.
Annual SO2 emissions from China, international shipping and the rest of the world. Data from the Community Earth atmospheric Data System (CEDS).
While global SO2 emissions started decreasing in the 1980s, these declines were relatively modest until around 2008, after which they have dropped precipitously.
Global SO2 emissions today are 48% lower than they were in 1979 and 40% lower than in 2006.
It is this recent rapid decline in global SO2 emissions that has driven the reduction in overall global aerosol cooling – and a subsequent decline in the associated masking of GHG warming – discussed earlier.
Effects of low-sulphur shipping fuel
The climate effects of the IMO’s 2020 phase-out of most of the sulphur content in shipping fuel has received a lot of attention over the past two years (see Carbon Brief’s earlier coverage of the topic).
This has been explored by researchers as a potential explanation for the record levels of warming the world has experienced in recent years.
Determining the climate effects of low-sulphur shipping fuel is less straightforward than simply assessing the reduction in global SO2 emissions.
The impact of additional SO2 emissions on cloud formation diminishes as emissions increase, meaning that reductions in SO2 over areas with low background sulphate concentrations, such as the ocean, could result in a proportionately larger warming effect than in highly polluted areas, such as south Asia.
This is somewhat countered by the concentration of shipping in specific “lanes” and by natural emissions of dimethyl sulphide produced by algae that are not present on land. Assessing the radiative forcing impact of the IMO’s 2020 regulations in greater detail requires the use of sophisticated climate models that can simulate these regional effects.
Carbon Brief conducted a survey of the literature on the climate impacts of the 2020 low-sulphur marine fuel regulations. Of eight studies published in peer-reviewed journals over the past two years, shown in the chart below, most determined a radiative forcing change of around 0.11 to 0.14 watts per meter squared (w/m2).
One estimate from Skeie et al. (2024) was a bit lower at around 0.08 w/m2 and another from Hansen et al. (2025) was substantially higher than all the others at 0.5 w/m2.
Estimates of global average radiative forcing changes from the IMO 2020 regulations published in the last two years. See the Methodology section for links to individual studies.
To account for these differing studies, Carbon Brief used the FaIR climate model emulator to simulate the effects of the radiative forcing estimated in each study on global average surface temperatures between 2020 and 2030. This includes 841 different simulations for each study to account for uncertainties in the climate response to aerosol forcing. (See: Methodology for further details.)
These estimates were then all combined to provide a central estimate (50th percentile) that gives each study equal weight, as well as a 5th to 95th percentile range across all the simulations for each different forcing estimate, as shown in the figure below.
Range (5th to 95th percentile) and central estimate (50th percentile) of simulated global average surface temperature responses to the IMO 2020 regulations across the radiative forcing estimates in the literature. Analysis by Carbon Brief using the FaIR model.
Overall, this approach provides a best estimate of 0.04C (0.02C to 0.16C) additional warming from the IMO’s 2020 regulations as of 2025, increasing to 0.05C (0.03C to 0.2C) by 2030.
These large uncertainty ranges are due to the inclusion of the Hansen et al. (2025) estimate, which represents something of an outlier relative to other published studies. Note that the warming of the climate system associated with the IMO 2020 regulations increases over time in the plot due to the ocean’s slow rate of warming buffering the climate response to forcing changes.
Declines in Chinese SO2 are unmasking warming
China’s reduction of SO2 emissions by more than 70% since 2007 represents a remarkable public health success story. It is estimated to have prevented hundreds of thousands of premature deaths from air pollution annually.
These rapid emissions cuts by China represent more than half the reduction in global SO2 emissions since 2007. They have been a major contributor to global temperature increases over the past two decades.
To determine the impact of Chinese SO2 reductions on global average surface temperatures, Carbon Brief used Chinese SO2 emissions data from the Community Emissions Data System (CEDS) combined with the FaIR climate model emulator.
The figure below shows the central estimate and 5th to 95th percentile across 841 different FaIR model simulations to account for uncertainties in the climate response to SO2 emissions.
Range (5th to 95th percentile) and median (50th percentile) of simulated global mean surface temperature responses to declines in Chinese SO2 emissions. Analysis by Carbon Brief using the FaIR model.
The figure above shows that Chinese SO2 declines were likely responsible for a global temperature increase of around 0.06C (0.02C to 0.13C) between 2007 and 2025, increasing to 0.7C (0.02C to 0.14C) by 2030.
Much of this increase occurred between 2007 and 2020, with a more modest contribution of Chinese aerosol changes to warming in recent years.
These results are nearly identical to those found in a study currently undergoing peer review by Dr Bjørn Samset and colleagues at CICERO, which finds a best estimate of 0.07C (0.02C to 0.12C) using a large set of simulations from eight different Earth system models.
This suggests that Chinese SO2 reductions are responsible for approximately 12% of the around 0.5C warming the world experienced between 2007 and 2024.
What aerosol cuts mean for current and future warming
It is clear that rapid reductions in global SO2 emissions have had a major impact on the global climate.
The combination of declines in emissions since 2007 in China and the rest of the world, along with declines in SO2 from shipping after 2020, have collectively unmasked a substantial amount of warming driven by GHGs.
While the reduction in SO2 emissions in other countries has been proportionately smaller than that seen in China, collectively it adds up to 0.03C (0.01C to 0.07C) of warming in 2025.
The figure below provides a best-estimate of all three factors: declines in SO2 emissions in shipping, China and the rest of the world.
Combined central (50th percentile) estimates of modeled global average surface temperature changes from IMO 2020, Chinese SO2 and rest-of-world SO2 declines between 2005 and 2030. Analysis by Carbon Brief using the FaIR model.
Taken together, these declines in SO2 emissions may represent around 0.14C additional warming today, or more than a quarter of the approximately 0.5C warming the world has experienced between 2007 and 2024.
However, the uncertainty in the climate response to changes in aerosol emissions remains large, particularly for changes in shipping emissions, so it is hard to rule out either a much smaller or much larger effect.
These results are in line with other recent analyses showing that changes in aerosol emissions are contributing to an increase in the rate of human-caused global warming in recent years.
The figure below uses a similar FaIR-based climate modeling approach to assess how different factors contributing to human-caused warming have changed over time.
Drivers of decadal warming rates between 1970-1979 and 2015-2024, excluding natural factors like volcanoes and solar cycle variation. From an analysis using the FaIR model at The Climate Brink, adapted from earlier work by Dr Chris Smith.
This shows that the rate of human-caused warming remained relatively flat at around 0.18C per decade from 1980 to 2005, before accelerating to around 0.27C over the past decade.
The primary driver of this recent acceleration in warming has been declining aerosol emissions.
Aerosols have flipped from reducing the rate of decadal warming (as emissions increased) to increasing the rate of warming (as emissions decreased) after 2005 by unmasking warming from CO2 and other GHGs.
The rate of warming from CO2 has increased over time as emissions have increased, though it has plateaued over the past decade as increases in global emissions have slowed.
However, the rate of warming from all GHG emissions – CO2, methane and others – has been relatively consistent since 1970. This is primarily due to the declining contribution of other GHGs to additional warming, likely associated with the phaseout of halocarbons after the Montreal Protocol.
Future declines in aerosols are expected in most of the Shared Socioeconomic Pathways (SSPs) used to simulate potential levels of future warming for the IPCC AR6 report, as shown in the figure below.
Modelled future SO2 emissions are generally dependent on broader mitigation trends – worlds with less fossil-fuel use result in less sulphur emissions – but are also highly variable across different models.
Observed SO2 emissions (black line) are broadly at the same level as (though slightly below) the SSP2-4.5 scenario (yellow line), which is the pathway that most closely matches current climate policies.
Observed SO2 emissions are also similar to those in the very-high emissions SSP5-8.5 scenario (lower grey line), while being higher than emissions in the most ambitious mitigation scenario (SSP1-1.9, green line) and below those in the SSP1-2.6 scenario (navy blue line).
Given differences across modeling groups, it is hard to infer too much about which SSP scenario is most in line with real-world SO2 emissions. However, it is worth noting that the current SSPs do not include a scenario where SO2 emissions continue to rapidly decline while emissions of CO2 and other GHGs increase.
Interestingly, the best-estimate cooling effect from sulphur dioxide is more or less counterbalanced by the warming effect of methane emissions today. As a result, scenarios where all GHG emissions are brought to zero do not result in sustained additional warming due to unmasking from declining aerosols.
However, if CO2 emissions alone were reduced to zero, while non-CO2 emissions were held constant, cutting global aerosol emissions to zero would result in between 0.2C and 1.2C of additional warming.
This means that aerosol emissions represent something of a wildcard for future warming over the 21st century. Continued rapid reductions in SO2 emissions will contribute to an acceleration in the rate of global warming in the coming years.
Methodology
Carbon Brief used the FaIR climate model to determine the effects of aerosol emissions on the climate, building on the work of Dr Chris Smith. Runs were done using the constrained ensemble approach using “fair-calibrate v1.4.”1 to be consistent with the IPCC AR6 parameter range. More details on the constrained ensemble approach can be found in Smith et al. (2024).
Figures showing the global mean surface temperature impact of different climate forcings in isolation were performed by calculating the difference between all-forcing runs and runs where a single forcing (e.g. from GHG emissions) was removed, following the approach used to generate Figure 7.8 in the IPCC AR6 climate science report.
IMO 2020 forcing estimates were taken from the following studies published in the peer-reviewed literature over the past two years:
- Yuan et al. (2024)
- Yoshika et al. (2024)
- Quaglia and Visioni (2024)
- Skeie et al. (2024)
- Gettelman et al. (2024)
- Jordan and Henry (2024)
- Watson-Parris et al. (2024)
- Hansen et al. (2025)
IMO 2020 global average surface temperature changes were calculated by running 841 different FaIR simulations for each of the different forcing estimates identified in the literature, which is the default setting for the FaiR constrained ensemble to provide a range of results consistent with the IPCC AR6 parameter range.
This produced 6,728 total simulations, from which a central (50th percentile) estimate and uncertainty range (5th to 95th percentile) were calculated.
These results were further validated by comparing them to the Earth system model-based estimates in individual studies where near-term global average surface temperature change estimates were provided (Yoshika et al. (2024); Quaglia and Visioni (2024); Gettelman et al. (2024); Jordan and Henry (2024); Watson-Parris et al. (2024); and Hansen et al. (2025).
The results of each of these studies were within the range of FaIR based estimates for the respective study’s radiative forcing – and generally quite close to FaIR’s median estimate for that study, as shown in the table below.
| Study | Carbon Brief’s Estimate (2025) | Published Estimate |
|---|---|---|
| Yoshika et al., 2024 | 0.041C (0.032C to 0.053C) | 0.04C |
| Quaglia and Visioni, 2024 | 0.044C (0.034C to 0.057C) | 0.08C (0.05C to 0.11C) |
| Gettelman et al., 2024 | 0.038C (0.029C to 0.049C) | 0.04C |
| Jordan and Henry 2024 | 0.044C (0.034C to 0.057C) | 0.046C (0.036C to 0.056C) |
| Watson-Parris et al., 2024 | 0.035C (0.027C to 0.045C) | 0.03C (-0.09C, 0.19C) |
| Hansen et al., 2025 | 0.157C (0.123C to 0.205C) | 0.2C |
It is worth noting that the uncertainties associated with converting SO2 forcing estimates to warming outcomes are generally much smaller than converting SO2 emissions into warming outcomes.
The effect of Chinese SO2 reductions were based on a comparison of two scenarios. The first is where Chinese SO2 emissions remained constant at their peak (2007) levels and did not decline. The second is where Chinese emissions followed observational estimates from CEDS between 2005 and 2022 and then remained constant at 2022 levels thereafter (which represents a conservative assumption that likely underestimates future effects of SO2 emissions declines on global temperatures given the strong downward trend). Global average surface temperature changes were calculated by running 841 different FaIR simulations in emissions mode for two scenarios and analysing the difference between the two.
The resulting estimate of 0.06C (0.02C to 0.13C) warming by 2025 was validated by comparing it to the Samset et al. (2025) preprint, which finds a nearly identical best estimate of 0.07C (0.02C to 0.12C) using a large set of simulations from eight different Earth system models.
The effects of the rest of the world’s SO2 declines were estimated using the same approach used for Chinese SO2 emissions, using CEDS emissions data. International shipping and aviation aerosols were excluded from the rest of the world estimate as to not double count IMO 2020 effects.
The post Explainer: How human-caused aerosols are ‘masking’ global warming appeared first on Carbon Brief.
Explainer: How human-caused aerosols are ‘masking’ global warming
People around the world have donated almost $90 million to a government-led campaign to help Nepal recover from its recent devastating Himalayan flood, according to a Nepali climate negotiator, even as the UN chief slammed the tiny amount of money in a new fund to deal with such disasters.
Individuals and companies from Nepal and abroad have chipped in from $5 to “many millions” of dollars to the Prime Minister’s Disaster Relief Fund, Manjeet Dhakal, an advisor to the poorest countries at UN climate talks, told an event on Monday focused on early warning systems.
The prompt and substantial response from the public contrasts with the slower, more limited support that is potentially on offer from the UN’s new Fund for Responding to Loss and Damage (FRLD), set up by governments to compensate developing countries for climate disasters.
Comment: Human security relies on adapting to the world’s new climate reality
Over three weeks have passed since Nepal’s finance and environment ministers asked the FRLD board to take an urgent decision to allocate funding to help Nepal protect people and restore essential services in the wake of the disaster, which caused around 1,450 deaths and left more than 5,000 people missing.
“Time is of the essence,” the ministers wrote in an appeal to the FRLD on August 31, which was swiftly followed by a letter from a group of developing-country board members urging the FRLD board’s co-chairs to organise an extraordinary meeting to come up with a response.
Loss and damage fund hesitates
Yet, despite informal online meetings, the co-chairs have yet to convene a meeting with the power to allocate funds. The board’s next scheduled meeting begins on December 15.
Dhakal said on Monday that the request has “received some positive response, but still there is some discussion ongoing about how to respond to that”.
“If they can’t respond in a timely manner, then is [the fund] fit for purpose in terms of disasters that the world would be facing in the coming years? The scale and intensity of these disasters is increasing,” he said.
With just $820 million pledged to it by rich countries and not all of that yet delivered, the FRLD has earmarked just $350 million to spend in its initial phase and without further contributions could run out of money next year.
Because of these limited funds, and a huge number of requests for funding totalling nearly $3 billion, the FRLD has said it will only give out a maximum of $20 million to each project for now. It has yet to approve funding for any projects.
Dhakal recently told The Nation magazine that this amount was just a “symbolic gesture”. Nepal’s government has estimated the costs of recovery and reconstruction at $4.8 billion, with homes, roads, bridges, hospitals and hydropower stations in the affected area needing to be repaired and rebuilt.
“Ridiculously small” funding
In a speech to the UN General Assembly on Tuesday, the body’s outgoing Secretary-General António Guterres criticised the “ridiculously small” level of funds made available by wealthy governments to the FRLD. Developed countries should “make the loss and damage fund work at scale”, he said.
The Portuguese diplomat told world leaders that when he travelled to Nepal three years ago, he had “sounded the alarm on accelerating glacier melt, warning that the rooftops of the world are caving in”.
“Some dismissed it all as overstating dangers, but as tragic events have shown, impacts are arriving sooner, hitting harder, and spreading further than many anticipated,” he said.
A recent study by scientists with the World Weather Attribution group found that climate change contributed to the rock-ice avalanche which sparked a huge flash flood along a river valley on the Nepal-Tibet border.
Speaking at a separate event in New York on Monday, leading climate scientist Johan Rockström highlighted those findings on the role of global warming in the Himalayan disaster.
“This will be potentially the first poster-child case of a loss and damage invoice, because here we have a proven case of a catastrophe which would not have occurred if it hadn’t been for human-caused climate change,” he said.
The post As loss and damage fund stalls, Nepal crowdfunds flood relief appeared first on Climate Home News.
As loss and damage fund stalls, Nepal crowdfunds flood relief
Climate Change
Explainer: How sea level rise poses an ‘existential threat’ to humans, heritage and nature
For millions of people around the world, rising sea levels are already reshaping economies, livelihoods and cultures.
The world’s oceans are currently rising at a faster rate than at any time in at least the past three millennia, with human influence the “dominant cause” of sea level rise since at least 1970.
At the UN general assembly in New York this week, world leaders are set to adopt a high-level declaration on the “existential threats” posed by sea level rise.
The declaration notes: “Sea level rise is not a distant scenario, but a real and lived experience for many.”
On average, global sea levels rose by 20 centimetres (cm) between 1901 and 2018.
This is due to both the melting of glaciers and ice sheets and the expansion of seawater as it warms, as well as changes in land-water storage.
The rate of the rise has accelerated in recent years, with ocean levels rising 10.6cm since 1993.
Sea level rise can vary locally due to seismic and volcanic activity, groundwater extraction and changes to the Earth’s surface resulting from ice melt.
Under a moderate-emissions scenario, scientists predict that global average sea level will rise an additional 56cm by 2100, relative to a 1995-2014 baseline.
Here, Carbon Brief unpacks some of the key ways that sea level rise threatens both societies and ecosystems.
Cities and coastal communities
Around 770 million people – 10% of the world’s population – are at “acute risk” of negative impacts from sea level rise, according to a report from the UN secretary general released last month.
(The report defines locations at acute risk as those that are less than five metres above the high-tide line.)
The people at risk include the residents of several of the world’s largest cities, including Mumbai and Kolkata in India and Shenzhen and Guangzhou in China. It also encompasses the entire populations of many island nations. (See: Small island developing states.)
There are two ways to consider sea level rise.
Global-average sea level rise is the amount the ocean surface has moved upwards, on average, relative to a baseline.
Relative, or local, sea level rise, is how much the ocean has risen in a given place. This can vary from the global average due to a number of factors, including land motion and ocean circulation, as well as changes to the Earth’s surface, rotation and gravitational pull due to the melting of the ice sheets.
Higher sea levels bring with them myriad dangers for coastal communities: they can increase persistent flooding and inundation, strengthen dangerous storm surges and erode beaches and cliffs. Sea level rise also causes the water table of coastal land to rise, which exacerbates flood risk.
The frequency of 100-year “extreme sea level events” has already increased 12-fold since 1900. These are events where high tides, storm surges and relative sea level rise combine to produce exceptionally high sea levels. Under a moderate-emissions scenario, these events are likely to occur at least annually – and, potentially, even more frequently – in many places by the end of the century.
In addition to damage to homes and other buildings, critical infrastructure – such as water systems and wastewater management projects – is increasingly vulnerable to flooding as a result of sea level rise. Flooding can cut communities off from essential services, such as hospitals and markets, with low-income and other marginalised groups disproportionately affected.
Inland encroachment of seawater leads to the saltwater intrusion and threatens agriculture in low-lying coastal areas.
Vertical land motion can also amplify the risk of rising seas. This includes a shifting of the land in response to seismic or volcanic activity or to land sinking, known as subsidence. The changes in local sea level due to these types of vertical motion can equal or surpass the contributions of climate-driven sea level rise.
Many of the coastal cities experiencing the largest changes in their relative sea level are located in east and south-east Asia. One notable example is Jakarta, Indonesia, which has been sinking by up to 15cm per year over the past decade, due largely to the overextraction of groundwater, which leads to the collapse of underground aquifers.
But even as the risks from sea level rise increase, population growth in coastal areas continues to outstrip that of inland areas. Between 2000 and 2018, the global population grew by slightly more than 23%. The population living within 5km of a coast increased by 28% over that same time.
The associated development of coastal areas means that, even without future sea level rise, global losses from flooding in the world’s largest 136 coastal cities could reach up to $52bn per year by 2050 – up from $6bn in 2005.
In response to the growing threats posed by sea level rise, communities around the world have implemented a number of adaptive actions.
In 2003, the Italian city of Venice began a years-long project to construct three floodgates that could be raised during high tide events to protect the city’s lagoon from the encroachment of the Adriatic Sea. The system was engaged for the first time in October 2020 and then another 48 times in the following two years.
Other communities have opted for less technologically intensive adaptations, including constructing seawalls, restoring mangrove forests and marshes, disincentivising development in high-risk areas and relocating residents, buildings and infrastructure to higher ground or inland areas.
However, existing adaptations may not be sufficient to protect communities. Under a low-emissions scenario, these protections may be breached 10 times as frequently over the next 30 years as they currently are.
Biodiversity and coastal ecosystems
The world’s coastal ecosystems are rapidly being destroyed due to both development and sea level rise.
This combination of pressures is called “coastal squeeze”, where ecosystems that may have otherwise shifted inland in response to sea level rise find their paths blocked by human-made structures.
Coastal squeeze has contributed to the widespread loss of the world’s wetlands.
Globally, nearly 28m hectares of coastal wetlands – including estuaries, tidal flats, mangroves and seagrass – have disappeared since 1970, according to the 2025 “global wetland outlook” report. This is an area equivalent to roughly the size of Ecuador.
Although the report names conversion to agriculture as the largest driver of wetland loss, it notes:
“Climate change is increasingly exacerbating the impact of other drivers on wetlands and human wellbeing through changes in the frequency and intensity of extreme weather events, associated fires, floods and droughts and through sea level rise.”
In the continental US, just 16% of coastal wetlands are migrating inland at rates that exceed local sea level rise. Nearly three-quarters of sites are moving at rates that do not outpace sea level rise, while 11% are submerging.
Low-lying islands are particularly threatened by sea level rise, due to their large amounts of coastline relative to their land areas. At the same time, islands are often “hotspots” of biodiversity, with many home to species found nowhere else in the world. More than 20% of the Earth’s known plant species are found only on islands.
A 2013 study modelled the impact of different amounts of sea level rise on 10 island biodiversity hotspots, comprising nearly 4,450 individual islands. It found that in a future with one metre of sea level rise, around 6% of the island habitat area would be completely submerged, while more than 11% of the hotspot islands would see their land area reduced by at least half. This could put dozens of species at risk of extinction, the study said.
In 2024, researchers documented the first known extirpation, or local extinction, of a plant species in the US due to sea level rise. Hurricanes and storm surges – amplified by sea level rise – began to kill off the only US population of the Key Largo cactus in the 2010s.
The remaining cacti suffered from soil erosion and saltwater intrusion and the final remaining specimens were removed in 2021 in an effort to cultivate them in greenhouses. (Other Caribbean islands, including Cuba, do still have surviving populations of the cactus.)
As native flora and fauna are diminished or even eliminated by rising sea levels, coastal ecosystems may become vulnerable to colonisation by invasive alien species, further harming biodiversity.
And as coastal communities are forced to relocate due to sea level rise, there are knock-on effects for biodiversity as they develop on new lands. These secondary biodiversity impacts are likely to be particularly prevalent in south-east Asia, due to the large number of people living in low-lying areas who may be forced to migrate due to sea level rise.
Small island developing states
Sea level rise poses an “acute and disproportionate” threat to small island developing states, says the recent UN report. It adds:
“Even under moderate scenarios, rising seas will render many low-lying coastal zones and small island developing states increasingly uninhabitable without extraordinary adaptation.”
Climate change is already resulting in loss and damage to small island nations, which are particularly vulnerable to both climate change in general and sea level rise specifically.
This vulnerability is in large part due to the geography of these countries. Several small island Pacific states are made up of atolls – ring-shaped coral or sandy islands that encircle lagoons. These often have average elevations of 1-2 metres above sea level and maximum elevations of 3-5 metres above sea level.
Some modelling evidence has shown that reef islands can grow vertically in response to sea level rise, as waves washing over the islands transport sediment from the ocean onto the surface. However, the strength of such waves would likely make these islands unsuitable for building on.
Other research has shown that Pacific islands respond in many different ways to rising sea levels, with “complex” outcomes, both positive and negative.
In addition, most of the small-island nations in the Pacific Ocean are located in a region where relative sea level rise from the melting of the Antarctic ice sheet is projected to be 11-33% higher than the global average rise in 2100 – regardless of emissions scenario.
The effects of this higher-than-average sea level rise is already evident.
In 1999, Kiribati lost two small, uninhabited islands to the rising seas. Several uninhabited islands in the Solomon Islands had vanished by 2014, while a further six islands had been severely eroded by the ocean, necessitating the relocation of some communities.
In addition, most small island developing states are located in parts of the ocean that are often hit by tropical cyclones. Sea level rise can enhance storm surge, leading to greater destruction during such storms.
However, small island developing states are also vulnerable “because they lack the means to address the impacts on their own”, reads the UN report.
According to the UN, these countries will require up to $6bn annually by 2035 in order to adapt to climate change. However, they received just $1.2bn in public adaptation finance in 2022-23.
Currently, small island developing states experience “expected” annual climate damages of $1.64bn due to coastal flooding, equivalent to 0.13% of their cumulative GDP. But, even if warming were limited to 1.5C above pre-industrial temperatures, these annual damages are projected to grow to $24bn.
In the international policy arena, questions have arisen over what should happen to island nations’ maritime boundaries as their land is enveloped by the sea. This is because maritime holdings, such as exclusive economic zones, are determined based on a country’s land borders.
However, a 2025 report by the UN International Law Commission considered the legal implications of sea level rise. It concluded that international law allows for countries’ borders to stay the same, “notwithstanding changes to the coastline as a result of climate change-related sea level rise”. It also noted:
“There is a need to develop legal and practical solutions to better protect persons affected by sea level rise, including those who remain in situ and those who are internally or externally displaced by it.”
Other small islands also face similar issues in their exposure to threats posed by sea level rise.
Coral reefs
Coral reefs are among the ecosystems that are most vulnerable to climate change.
They are also being visibly affected already – almost entirely due to ocean warming. Even though these ecosystems are completely submerged to begin with, they are also impacted by sea level rise.
As the ocean rises, the water over shallow ecosystems deepens.
The effects of this are twofold. Deeper water reduces the temperatures experienced by reefs. This can act as a buffer against marine heatwaves and global ocean warming.
At the same time, the increased depth reduces the amount of light that can reach the coral communities, which can impact their survival.
In addition, sea level rise-assisted erosion will add more sediment to the near-shore waters. These particles can settle on corals, impeding their ability to feed and reproduce, as well as interfering with photosynthesis by the zooxanthellae algae that live symbiotically with corals. Together, this leads to slower coral growth and increased stress on reefs.
So far, reefs in some parts of the world have been able to “keep pace” with sea level rise, growing vertically at accelerated rates and therefore maintaining suitable levels of light availability.
However, modelling has shown that few reefs have the capacity to continue to maintain their distance from the surface under a moderate-emissions scenario.
As coral reefs degrade, the seafloor below them can wear away. This erosion is contributing to greater apparent levels of sea level rise on coral reefs in the Caribbean, as well as the US states of Florida and Hawaii.
Sea level rise may also have the ability to spur reef growth in shallow environments previously thought to be uninhabitable for corals. In Sanya Bay in the northern South China Sea, sea level rise since the mid-1980s has allowed for the recolonisation of a reef that had been dormant for more than five millennia.
But the opportunities for such recolonisation are far outstripped by the loss of coral elsewhere. Since 1980, the world has lost nearly 10% of its coral cover due to climate change-induced ocean warming. The UN declaration reads:
“Every fraction of a degree of global warming increases the risks to coral reefs.”
Heritage sites
Throughout human history, many societies developed along rivers and coastlines, due to the abundance of food and ease of transportation. However, their proximity to the sea means that many of these sites are now at risk of being damaged or destroyed by sea level rise.
Cultural heritage includes “physical sites, living heritage, traditional lands, burial grounds, underwater cultural heritage, archaeological and sacred sites and culturally significant coastal landscapes”, according to the UN sea level rise report.
Several studies have mapped the cultural and natural heritage sites that are most at risk from flooding and erosion due to sea level rise.
There are 49 Unesco world heritage sites located at low elevations along the coast of the Mediterranean Sea. Nearly every one of these is already at risk from erosion or severe flooding events – 42 face issues with erosion, while 37 are at risk from a 100-year flood event. Both of these risks will increase over the remainder of the century as sea levels continue to rise.
The locations at risk include the archaeological sites of the ancient cities of Carthage in present-day Tunisia and Ephesus in Turkey, the ruins of Pompeii and Herculaneum in Italy and the medieval Cathedral of St James in Šibenik, Croatia.
The sea level rise associated with warming of 3C above pre-industrial temperatures would impact nearly one-fifth of all Unesco cultural world heritage sites. The sites at risk include Japan’s Hiroshima Peace Memorial, South Africa’s Robben Island, Chile’s Rapa Nui and the Sydney Opera House. Many of these become vulnerable at lower levels of global warming.
In Africa, 56 out of 284 cultural and natural heritage sites already face threats from flooding or erosion due to sea level rise. This number is expected to nearly triple – to 191 threatened sites – by 2050 under a moderate-emissions scenario. However, mitigating emissions could reduce the number of very-highly exposed sites – those with at least 75% of their area vulnerable – by one-quarter.
Globally, there are 386 Unesco heritage sites along the coast that are, at most, 20 metres above sea level and are therefore potentially affected by coastal erosion and flood hazards.
These threatened sites include 289 cultural heritage sites and 91 natural heritage sites, as well as six “mixed” sites that are recognised for both their cultural and natural significance.
The UN declaration calls for action to mitigate damage to significant sites, saying:
“Protection, preservation and documentation of cultural heritage is a priority.”
The post Explainer: How sea level rise poses an ‘existential threat’ to humans, heritage and nature appeared first on Carbon Brief.
Explainer: How sea level rise poses an ‘existential threat’ to humans, heritage and nature
The Nepali government has requested $20m from the UN fund for “loss and damage”, following the devastating floods that hit the country in late August.
This amounts to just 0.7% of the $2.7bn it has estimated in “physical damage” to infrastructure and “economic losses” from the flooding, according to Carbon Brief analysis.
The $20m request would, nevertheless, make Nepal the fourth-largest claimant to the UN loss-and-damage fund, which is intended to help deal with climate-related disasters.
Developing countries have already made 176 applications to the UN fund for responding to loss and damage, requesting, in total, $2.8bn to help recover from a variety of damaging events, such as drought, floods and storms.
Yet, to date, predominantly developed nations have only pledged $0.8bn to support the fund.
This means requests to the fund are already three times larger than the total amount pledged, raising questions about its potential to respond to emergencies.
As yet, no funding has been paid out of the fund to developing countries grappling with intensifying and more frequent climate change-induced disasters since it was established in 2023.
Nepal’s needs
On 26 August, Nepal was hit by flash floods following a catastrophic rock-ice avalanche in the Himalayan border region. The flooding has killed more than 1,400 people, with thousands still missing.
Days later, the Nepali government sought an “urgent response” from the board of the UN fund for climate-driven loss and damage.
It subsequently requested $20m in “financial compensation” from the fund. This is the maximum amount that can currently be requested for a single project.
“Loss and damage” is a term used to describe how climate change is causing serious and, in many cases, irreversible impacts around the world. Nations established the UN fund in 2023, after decades of effort by climate-vulnerable nations.
Nepal’s national disaster management authority has now released an extensive rapid preliminary assessment of “damage and needs” from the floods.
As the chart below shows, Nepal’s $20m loss-and-damage claim would only cover 0.7% of what authorities describe as $2.7bn in “total damage and loss” from the floods.
When accounting for another $4.8bn in “recovery and reconstruction” costs – part of how loss and damage is internationally defined – then Nepal’s $20m claim would be just 0.3% of the needs it estimates.
Reacting to the analysis, Nepal’s climate negotiator Raju Pandit Chhetri tells Carbon Brief that the country’s $20m request was for “rapid response”, adding:
“That money is going to be a peanut if it was to be invested into reconstruction.”
Requests vs pledges
Vulnerable, developing countries have long argued that developed nations should be held responsible for loss and damage, while countries such as the US have blocked moves that could have led to them being liable for climate-related damages
From December 2025 until July 2026, developing countries made 176 applications to the loss-and-damage fund, requesting over $2.8bn in assistance.
So far, predominantly developed countries have pledged only $822m to the fund. (Some nations that are not categorised as “developed” under the UN, such as the UAE and South Korea, have also committed funds.)
Funding requests from developing countries to date are, therefore, more than triple what has been pledged.
Moreover, only around half of the money pledged so far has been paid into the fund by donor nations, with large sums from France, Italy and the UAE still outstanding.
The fund has made $342m available in its initial funding round in July 2026. However, as of September, no money from the fund has been distributed to any countries facing climate-related disasters.
According to Carbon Brief analysis, off the 176 loss-and-damage fund requests received from 118 countries, more than 60% are from least developed countries – such as Nepal – and small-island nations. So far, each individual funding request is capped at $20m.
The flood-related request is Nepal’s fourth appeal to the fund and, as the chart below shows, this makes it the fourth-largest claimant overall.
Nine other countries have made multiple requests to the fund. Madagascar – hit by back-to-back cyclones after a prolonged drought – has made six requests in total.
Drought-ravaged Suriname, Ecuador, Brazil and Barbados have specified that their funding requests are part of an “emergency response”.
‘Rapid response’
Nepal’s $20m claim has sparked a conversation on climate justice and the ability of the loss-and-damage fund to deliver, in the face of increasingly frequent extreme-weather events.
In a letter sent five days after the disaster, Nepal’s finance minister Dr Swarnim Wagle appealed to the fund’s board to mobilise an “urgent response” that would “signal” that the fund:
“[I]s capable of responding with humanity, speed, flexibility and solidarity when climate-vulnerable countries face losses and damages beyond their capacity to address alone.”
Board members from Asia-Pacific and African countries wrote a letter in support of the Himalayan country in crisis, urging the board to convene and “potentially agree to a provisional set-aside allocation of resources to support rapid response funding for Nepal”.
They pointed out that the board’s response to Nepal could offer “procedural lessons” in how to strengthen its “rapid-response” to sudden-onset extreme-weather events. Such support is explicitly part of the fund’s mandate.
On 14 September, developed-country members of the fund’s board wrote that they supported a “consultation” on Nepal, but made no commitments in terms of actual funding.
Harjeet Singh, loss-and-damage expert and global convenor of the Fill the Fund campaign, tells Carbon Brief that the fund’s board deals with most funding requests as regular projects, rather than emergencies. Singh continues:
“Developed countries gave a really cold response to Nepal’s request. They have not addressed it because they know that if this happens once, they are going to be under pressure all the time. This is unacceptable.”
Meanwhile, BBC News reported that Nepal plans to use climate attribution studies to strengthen its claim.
According to a rapid attribution study by World Weather Attribution and climate experts who spoke to Carbon Brief, factors such as glacial retreat and permafrost thaw that played a key role in the disaster have been linked to climate change. A full attribution study is pending.
Nepal’s prime minister Balendra Shah will address the UN general assembly on 24 September and is expected to raise issues around climate justice, loss and damage and the vulnerability of mountain countries.
The next board meeting of the loss and damage fund is on 15 December, two months from now, and a fortnight after the conclusion of COP31 in Turkey.
Pandit Chhetri tells Carbon Brief:
“It’s a shame that, until now, the fund has not been able to even give a penny to developing countries. And, starkly, the event in Nepal only demonstrates why this kind of fund is so important for highly vulnerable, poor, developing countries.”
Pandit Chhetri adds that, after nearly three weeks since the disaster, there is yet to be a decision on the request and that the country has “only received messages of solidarity”, with no assurance of rapid response funds. He says that it is “quite an interesting scene for [us] to observe”, adding:
“If the fund cannot respond in a crisis like this for a country like Nepal – when you have this massive destruction and devastation – then what is the use of the fund itself? That’s why it is a test for the fund, though the resources are limited.”
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The post Analysis: Nepal’s $20m ‘loss-and-damage’ claim only covers 0.7% of flood costs appeared first on Carbon Brief.
Analysis: Nepal’s $20m ‘loss-and-damage’ claim only covers 0.7% of flood costs
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