Estimating Earth’s climate sensitivity, the global average warming from doubling CO2 above pre-industrial levels, is an urgent task as it governs how much the world will warm from fossil-fuel emissions.
Recent work has essentially ruled out low values of climate sensitivity below about 2C, but how much do we know about high values of climate sensitivity?
There is an active debate about the likely upper bound of climate sensitivity, which informs the worst-case projections of warming over the coming decades.
One way to narrow this down is to study the major climate changes of Earth’s past seen in palaeoclimate “proxy data”. These records are scattered across the planet, found in everything from ice cores and ocean sediments to tree rings and coral reefs.
Combining proxy data with climate models helps scientists understand what past changes were caused by natural fluctuations in CO2 and what changes we can expect from human-caused CO2 increases in the future.
In our new study, published in Science Advances, we find that the Last Glacial Maximum – a period of extensive ice cover about 21,000 years ago – provides even stronger evidence for modern-day climate sensitivity than previously thought.
Our estimates suggest a central estimate of “equilibrium” climate sensitivity of 2.9C, with a very likely range of 2.1-4.1C.
This is around a 30% narrowing of the 2.0-5.0C range in the latest assessment from the Intergovernmental Panel on Climate Change (IPCC).
Our findings give us more confidence that very high climate sensitivity is unlikely. They also support the IPCC’s central estimate for climate sensitivity of around 3.0C and lower estimate of 2.0C, confirming that warming would still be severe if we do not reduce fossil-fuel emissions.
Progress in climate sensitivity
For many years, the estimated range for equilibrium climate sensitivity (ECS) remained stubbornly wide.
After the landmark Charney report established a “consensus” position from a study group convened by the US National Research Council back in 1979, many IPCC assessments over several decades were unable to narrow it further.
This is illustrated in the chart below, which shows the Charney report estimated range for ECS (grey bar) on the left, followed by each IPCC report in sequence, from the first in 1990 (“FAR”, light blue) through to the most recent AR6 range on the right (red). Central estimates are shown with a dot, where available. The coloured bars indicate the estimated likely range for ECS and very likely ranges are marked with whiskers.
Estimates of ECS published in successive IPCC assessments since the Charney report in 1979. Dots show central estimates. The coloured bars show the likely range and the very likely range is given by whiskers. Chart by Carbon Brief
Ahead of the IPCC’s sixth assessment report (AR6), a four-year project from an international team of scientists made a significant advance.
The resulting paper by Prof Steven Sherwood, Dr Mark Webb and colleagues, published in the Review of Geophysics in 2020, formally combined multiple lines of evidence from observed data to improve understanding of the climate “feedbacks” that can amplify or dampen surface warming. The paper played a key role in the narrower ECS range in AR6 (red bar in chart above) – particularly in raising the lower bound to 2.0C and setting the upper bound at 5.0C.
However, observed data from recent warming are not as useful for constraining the upper end of ECS estimates. This is because climate feedbacks – especially how warming affects cloud properties that either enhance or reduce their overall cooling effect – depend on spatial patterns of temperature change. Climate scientists have dubbed this phenomenon the “pattern effect”.
Pattern effects
Temperature patterns over recent decades differ substantially from what we expect in the long-term. This means that climate feedbacks are likely to change in the future too, making observed warming a relatively poor predictor of how high climate sensitivity could be.
This is where palaeoclimate data comes in. The Last Glacial Maximum (LGM) has been touted as the best evidence for or against high values of climate sensitivity. By estimating how much colder the Earth was when CO2 levels were so much lower during the LGM, scientists can predict how much warmer the Earth would be with higher CO2 levels decades from now.
However, doing so requires isolating how much of the LGM cooling came from lower CO2 and correcting for how the climate’s sensitivity to CO2 differs between the cold LGM and the warm modern-day climate. Prior to our study, no one had quantified the impact of temperature patterns on climate sensitivity in the palaeoclimate record.
Traditionally, the additional cooling effect of the vast LGM ice sheets, which covered much of Canada and northern Eurasia, has been estimated from the amount of sunlight they directly reflect. But the ice sheets also caused the nearby northern Pacific and Atlantic oceans to cool and produce more low clouds, amplifying global cooling by reflecting even more sunlight. This ocean cooling is illustrated by the dark blue shading in the left-hand map below.
By linking these adjacent cloud changes to the ice sheets, we found that relatively more of the LGM cooling was caused by the ice sheets and relatively less came from the lowered CO2.
Importantly, these amplifying cloud feedbacks are unique to the climate during the ice age and, therefore, do not apply to modern CO2-driven warming that will not have similarly large ice-sheet changes.
As a result, the amount of cooling from lower CO2 at the LGM is not consistent with very high values of modern-day climate sensitivity above around 4C.
Accounting for differences between the LGM and modern climates allows us to lower the upper end of climate sensitivity estimates, representing a major shift in how palaeoclimate data is used to inform our future.
Combining palaeoclimate data with climate models
Quantifying the climate differences mentioned above for the LGM requires estimating temperature patterns and climate feedbacks from 21,000 years ago.
An obvious challenge is that our instrumental temperature records span only centuries and our satellite observations of clouds span only decades. Fortunately, there have been two major advances in recent years that allowed us to quantify the pattern effects from the distant past.
First, palaeoclimate data assimilation is a recently developed method that combines climate model simulations with proxy data, producing globally complete reconstructions of surface temperatures during the LGM. However, there are still major uncertainties in this method. Various groups have recently reconstructed the ice age, finding somewhat different temperature patterns. To assess this uncertainty, we use four available reconstructions.
Second, we use these reconstructed surface temperatures in global atmosphere models to estimate climate feedbacks during the LGM and compare them to feedbacks expected from CO2 doubling. Because different models produce different climate feedbacks – even when given the same reconstructed surface temperatures – we assess this feedback uncertainty using five different atmosphere models.
Despite the uncertainties, a consistent story emerged. Climate feedbacks strongly amplified LGM temperature changes, much more so than climate feedbacks under modern-day warming from CO2 alone. We traced these differences primarily to cloud feedbacks in the North Pacific and North Atlantic Oceans where the patterns of temperature change strongly differ between the LGM – due to the presence of large ice sheets – and future warming from CO2.
At first glance, the extra amplifying feedbacks of the LGM could appear to suggest that climate sensitivity is higher than we thought. A recent study led by Dr James Hansen, former director of the NASA Goddard Institute for Space Studies, reported that some of the same reconstructions used here are consistent with a modern-day climate sensitivity of around 4.8C.
However, that interpretation is reversed when we recognise that those amplifying feedbacks are unique to the ice age climate and do not apply to the modern-day climate.
The result is that modern-day climate sensitivity, as estimated from the LGM, is actually lower than has been reported by studies such as Hansen’s that have not accounted for the unique effect of ice sheets on climate feedbacks.
Our findings also challenge a common assumption that warmer climates are more sensitive than colder climates. While that assumption appears likely to be true for climates warmer than today, it appears to be false for climates colder than today when the effect of ice sheets on temperature patterns and feedbacks is included.
Implications for future warming
The LGM, after accounting for how temperature patterns impact climate feedbacks, ends up being an even stronger constraint on modern-day climate sensitivity – especially the upper bound.
To the best of our knowledge, this is the first time that considering pattern effects has helped constrain climate sensitivity instead of adding to its uncertainty for modern-day climate.
Given the importance of combining multiple lines of evidence, we use the community framework from the Sherwood, Webb et al (2020) study, updated to include our estimate of how climate feedbacks differ between the LGM and modern-day warming.
As the chart below shows, our revised best estimate of climate sensitivity (blue) becomes 2.9C with a very likely range of 2.1-4.1C, a substantial narrowing of uncertainty by reducing the upper bound.
In contrast, the IPCC AR6 very likely range was 2.0-5.0C with a best estimate of 3C (red), while the Sherwood, Webb et al (2020) study reported 2.3-4.7C and central estimate of 3.1C (yellow).
Modern-day ECS estimates from recent assessments, including the Sherwood, Webb et al (2020 study (yellow), IPCC AR6 (red) and this study (blue). Dots show central estimates. The coloured bars show the likely range and the very likely range is given by whiskers. Chart by Carbon Brief based on data provided by V Cooper and K Armour
While the lower bound and central estimates are mostly unchanged, our findings reduce the upper bound by approximately 1C.
Based on the modelled relationship between climate sensitivity and future warming, lowering the upper bound on climate sensitivity from 5C to 4.1C translates to a reduction of 0.4-0.8C in the upper end of global warming estimates by 2100 (the range reflects uncertainty in future emissions). In other words, this is a substantial reduction in the likelihood of extremely high warming.
Our results for the LGM show that temperature patterns and their effects on climate feedbacks must be accounted for when using past climates to estimate modern-day climate sensitivity.
Spatial reconstructions of past climates are a necessity and there are opportunities for further progress in constraining climate sensitivity by analysing temperature patterns and feedbacks in other past climates.
The post Guest post: Ice-age analysis suggests worst-case global warming is less likely appeared first on Carbon Brief.
Guest post: Ice-age analysis suggests worst-case global warming is less likely
New Zealand’s parliament has adopted a controversial new law blocking a whole avenue of climate litigation and shutting down its most advanced corporate lawsuit, which has been blamed by the government for shaking business confidence and investment.
The Climate Change Response (Tort Liability) Amendment Bill, expected to take effect in the coming days after it is formally signed by the Governor-General, prevents all current and future civil claims for climate loss or harm under tort law.
Justice minister Paul Goldsmith said last week that the aim was to give businesses “certainty around their climate change obligations”, noting it would not alter the government’s responsibilities under the Climate Change Response Act 2002 nor business obligations under the Emissions Trading Scheme.
“Our response to climate change is best managed by the Government at a national level and not through piece-meal litigation in the courts,” he added in a statement.
Such litigation, he said, “risks developing a new regime that contradicts the framework Parliament has already enacted” to tackle climate change.
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Experts say that despite dismissing the lawsuit, the ruling sets a precedent by confirming that climate science can establish legal liability for the damage caused by emissions
Goldsmith singled out a key domestic climate lawsuit brought by Northland iwi leader and activist Mike Smith against six big companies: dairy firms Fonterra and Dairy Holdings, energy firms Genesis Energy and Z Energy, New Zealand Steel and coal mining firm BT Mining. A seventh original defendant, Channel Infrastructure, was dropped after it permanently decommissioned its Marsden Point oil refinery.
Smith argued that these companies had caused him harm under public nuisance and negligence law, as well as a third breach of a duty to cease contributing to climate change that has yet to be tested domestically. He did not seek financial compensation, instead asking for the companies to immediately stop emitting or contributing to net greenhouse gas emissions.
In one of the most advanced corporate climate accountability lawsuits in the world, a trial had been scheduled for April 2027 after the Supreme Court unanimously allowed the case to continue.
Corporate lobbying in the shadows
Smith described the passing of the bill as “deeply concerning”, particularly as it coincided with the Supreme Court hearing another of his climate lawsuits. In that case, Smith v Attorney-General, he argues that the government’s response to climate change and its impacts on Māori communities in particular breaches rights to life and culture.
“That timing raises profound questions about the separation of powers and the rule of law,” said Smith. “Whatever one’s view of the merits of these cases, it is deeply troubling when parliament intervenes to remove a legal pathway while the courts are actively considering fundamental questions about climate responsibility, rights and the crown’s obligations.”
The bill – which says that no person (including the government) can be found liable in tort for emissions-related climate change effects – followed major lobbying efforts by the companies defending themselves in Smith’s lawsuit. They outlined a proposed legal amendment in a briefing note to the government in 2024.
The centre-right government has been fiercely criticised over its lack of transparency in relation to this lobbying activity. The national ombudsman recently found that the Prime Minister’s Office effectively withheld information requested by the Environmental Law Initiative about meetings, discussions and conversations regarding Smith’s case.
Green groups fail to stop bill
The bill sparked huge concern among environmental campaigners in New Zealand and elsewhere. Greenpeace Aotearoa called it a “shocking abuse of executive power” and the vast majority of submissions to a parliamentary inquiry said it should be rejected.
But in the end, it was adopted with little resistance, moving relatively smoothly through parliament, passing its third reading by 67 votes to 53. Sam Bookman, climate law lecturer at Melbourne Law School, told Climate Home News he was not surprised by this, given that the coalition government has a secure majority.
A complaint has been made to the UN special rapporteur on climate change and human rights by Smith, the National Iwi Chairs Forum Pou Tikanga and youth coalition Climate Clinic Aotearoa over what they see as the government’s heavy-handed approach. Smith is also challenging the new law in yet another lawsuit.
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Bookman thinks it “very unlikely” that such a challenge will succeed, noting that New Zealand’s constitution is firmly anchored in parliamentary sovereignty.
But the expert in climate law does not see the bill as the end of legal action in the country, noting that New Zealand has a “sophisticated climate litigation landscape with a growing number of specialist and experienced lawyers and NGOs”.
The country is also approaching its next general election in November, and some opposition parties have pledged to restore access to the courts if elected.
Amanda Larsson, global project lead on agriculture for Greenpeace International, said: “This law deserves to be tested, and I strongly encourage the international climate litigation community to unite and help defend New Zealanders’ fundamental right to hold polluters accountable before this becomes a global blueprint.”
Copycat legislation on the rise
New Zealand’s move is part of a small but growing legislative effort to shut down climate litigation around the world.
In the US, Republican politicians introduced legislation in the House and Senate in April that would shield fossil fuel firms from climate liability lawsuits. Similar laws have already been passed at state level in Tennessee, Utah, Iowa and Louisiana.
The German state of Bavaria has put forward a similar proposal to the Federal Council, aiming to block private climate claims as well as the recognition and enforcement of foreign judgments imposing such liability. There are also proposals to limit available remedies and actions in the Netherlands and Belgium.
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Bookman said he expects more efforts to counter climate damages litigation and advised plaintiffs to think about how to respond, including drawing on broader support in opposing them.
“Even though it’s very hard for plaintiffs to win these types of cases, companies are very eager to avoid the expense, embarrassment and political accountability that come even with unsuccessful lawsuits,” he said.
The post New Zealand moves to protect business with law curtailing climate litigation appeared first on Climate Home News.
New Zealand moves to protect business with law curtailing climate litigation
Bhima Yudhistira Adhinegara is the Executive Director of the Center of Economic and Law Studies (CELIOS), an Indonesia-based economic think tank. Muhammad Zulfikar Rakhmat is the Director of the China-Indonesia desk at CELIOS.
Indonesia produces around 60% of the world’s nickel, a metal used to manufacture batteries for electric vehicles (EVs) – more than any other country in the world. But in 2026, the government sharply reduced how much of its nickel can be extracted from the ground.
Production quotas were reduced by around 40% this year compared to 2025. Weda Bay, the largest nickel mine on Earth, had its allowance cut by more than 70% and exhausted its full-year quota by the end of May, halting mining entirely; it cannot resume large-scale extraction until next year unless regulators grant an extension.
The policy has sparked a vivid debate in Indonesian policy circles: how can the country shift its strategy from a decade of mining vast quantities of cheap nickel to producing a high-value and low-carbon material that the rest of the world wants for EV batteries.
The cuts aren’t a silver bullet to clean up Indonesia’s nickel industry, whose smelters are powered by coal – the most polluting fossil fuels. But alongside stricter enforcement of environmental rules, it is one side of efforts to produce more sustainable nickel for a premium.
Restricting Indonesia’s nickel output
Production quotas were introduced to stop the collapse of nickel prices because of oversupply in the market. Prices had fallen more than 40% in 2023 alone and kept sliding as Indonesian supply kept growing, hitting a four-year low of around $13,900 a ton in late 2025.
Critics called the recent tightening of production quotas proof that Indonesia’s nickel strategy has failed, arguing that the industry shouldn’t need to throttle its own output to survive. But when assessed against what the policy was supposed to do – push up nickel prices – it has worked. Prices jumped to $20,000 a ton in May, the highest since 2024.
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Chinese industry groups representing companies that have invested billions to mine and refine the country’s nickel were furious, warning Indonesia’s president Prabowo Subianto that the cuts put $50 billion worth of investment at risk. But much of that Chinese capital is sunk into smelters and processing plants built specifically to run on Indonesian ore, and cannot simply be moved elsewhere. That gives Jakarta more room to hold its ground than the warning suggests.
Stronger environmental enforcement
Since the start of the year, Indonesia’s forestry task force has seized more than four million hectares of land from mines and plantations operating illegally in protected forests, collecting over two trillion rupiah ($113 million) in fines.
This included 148 hectares seized from Weda Bay for lacking a forestry permit. The share of nickel produced from illegal small-scale mining also fell from about a quarter in 2022 to roughly 10% by 2024.
The crackdown responds to serious environmental damages in the nickel industry. On Obi Island, a waste pond collapsed after heavy rain in June 2025, flooding three villages and killing a resident. Internal company tests found chromium-6 – a carcinogen – in the water, in quantities far above the legal limit. The footprint of another mine near Raja Ampat, which is home to some of the world’s richest coral reefs, grew 60-fold in just eight years.
The market is responding to early cleanup efforts. Low-carbon nickel now sells for a real premium, roughly $18,800 to $19,300 a ton compared with $17,900 to $18,300 otherwise, as carmakers seek to source cleaner materials to comply with the European Union’s new emissions rules for imports.
In turn, this is incentivising the industry to do more to green its operations. Vale Indonesia’s smelter in South Sulawesi now runs almost entirely on hydropower, for example.
None of this addresses coal use, however. Major Indonesian nickel producers still emitted an estimated 15 million metric tons of greenhouse gases in 2023. Indonesia may be cracking down on illegal mining and rewarding cleaner producers but it is still running its mines on the dirtiest fuel available.
Unequal benefits
For Indonesia to truly benefit from producing cleaner and high-value nickel, it needs to reap the economic benefits too. Although the industry has boosted the country’s economic growth, the reality on the ground tells a different story.
Konawe in Southeast Sulawesi is home to a major smelting complex. Growth in the district jumped from 6% to 22% between 2015 and 2023, driven almost entirely by the nickel industry, according to a study by the Lowy Institute study. At the same time, poverty levels increased slightly and unemployment remained unchanged.
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In Halmahera, another epicentre of the nickel industry, spending by the poorest fifth grew just 5% between 2019 and 2022, compared with 28% for the wealthiest fifth, according to a separate study.
Part of the reason for this inequality is the system for transferring mining royalties to district authorities where the mines are located. In theory, they are entitled to the largest share. But in practice, payments are delayed, companies routinely dispute what they owe and royalties are pooled and distributed across a larger area.
The Natural Resource Governance Institute has found that decentralisation handed local governments power to approve new mines faster than they could build their capacity to manage them. Higher output raises national income on paper, but local governments remain constrained by fiscal rules and infrastructure costs that scale with mining.
None of this makes the 2026 quota cuts a mistake. Indonesia has every right to defend its pricing power over a resource it controls. But limiting extraction isn’t going to fix underlying issues around environmental enforcement and revenue-sharing. That requires rules that are consistently enforced, royalties that reach communities living by the mines, and a plan to wean smelters off coal.
The post Indonesia’s nickel production cuts are not enough to create a sustainable industry appeared first on Climate Home News.
Indonesia’s nickel production cuts are not enough to create a sustainable industry
Climate Change
Risk of “catastrophic” oil spill reaching Kimberley coast found in Woodside’s Scott Reef gas drilling plans
SYDNEY, Monday 24 August 2026 – New analysis of Woodside modelling released by Greenpeace Australia Pacific and Environs Kimberley has revealed the oil and gas corporation’s plans to drill at Scott Reef could cause an oil spill up to 30 times bigger than the 2009 Montara disaster, impacting the Kimberley coastline and reaching as far as Indonesia.
The new analysis details the “catastrophic” oil spill risk put to environmental regulators for approval by Woodside in its Browse to North West Shelf Project (Browse) plans, the worst-case scenario being a blowout directly below Scott Reef, polluting whale migratory pathways and covering isolated turtle nesting ground with oil condensate.
An FOI application (F348) revealed the federal environment department (DCCEEW) asked offshore oil and gas regulator NOPSEMA to look into the oil spill risk in 2025. NOPSEMA’s response to the application refused access to its report, and one document shows DCCEEW sought further advice this year.
Greenpeace and Environs Kimberley are calling on the Federal Government to publicly release the NOPSEMA report given the risk of an uncontrolled release of oil condensate from directly below Scott Reef.
Hannah Schuch, Senior Campaigner at Greenpeace Australia Pacific, said: “Woodside is aware that drilling at Scott Reef risks a massive oil spill that would have severe, far-reaching consequences. It appears environmental regulators are aware too.
“The state and federal governments need to take this risk from Woodside’s drilling plans seriously, as they could end up allowing the worst oil spill in Australian history.
“The pygmy blue whales that migrate up and down the WA coast with their newborns each year could be swimming and feeding in toxic, oil-slicked water. Woodside’s proposal to drill at Scott Reef is an environmental disaster waiting to happen, and the WA and federal governments have one surefire way to prevent catastrophe — reject Browse.”
Martin Prichard, Executive Director at Environs Kimberley, said: “A catastrophic oil spill by Woodside would be disastrous not just for marine life in the area but also for the Kimberley’s $500 million tourism industry.
“The state and federal governments will see five marine parks on the Kimberley coast included in the risk area of a catastrophic Woodside oil spill.
“The Montara oil spill was disastrous for West Timor with the toxic oil destroying seaweed farmers’ livelihoods. The Kimberley dodged a bullet with Montara, we were lucky the spill didn’t head our way. Myself and a crew flew over the Montara oil spill and followed it as far as we could. It was like a scene from a disaster movie.”
After the WA Environmental Protection Authority deemed Browse “unacceptable” due, in part, to oil spill risk, Woodside submitted a mitigation plan based on technology that has never been used “in anger”, a weakness stated in an independent expert review of the plan.
Professor Richard Steiner, independent oil spill expert, said: “A large offshore spill is impossible to effectively contain or recover. Historically, only 2-6% of total spill volume is recovered and the ecological injury from the release of toxic hydrocarbons in the sea can be severe, extensive, and long-term.
“Here in Alaska, government research concludes that several marine populations injured by the 1989 Exxon Valdez oil spill, including whales, fish, and seabirds, are still not recovering today, 37 years later. We should expect similar long-term ecological impacts in Western Australia if there were to be a major oil spill. The only sure way to avoid the risk of a catastrophic marine oil spill is to not develop oil and gas projects in marine environments.”
-ENDS-
Media contact
Emma Sangalli on emma.sangalli@greenpeace.org or 0431 513 465
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