The UK’s Climate Change Act is a landmark piece of legislation that guides the nation’s response to global warming and has proved highly influential around the world.

Increasingly, the law has come under attack from right-wing politicians, who want to scrap the UK’s net-zero target and the policies supporting it.

Conservative leader Kemi Badenoch has announced that her party would “repeal” the Climate Change Act entirely, if her party is able to form the next government.

The opposition leader said she still believed that “climate change is real”, but offered no replacement for the legislation that the Conservatives have backed since its inception.

Her proposal drew intense criticism from scientists, business leaders and even senior Conservatives, who argued that abandoning the act would harm the UK economy and drive more climate extremes.

Meanwhile, the hard-right populist Reform UK party – which is currently leading in the polls – has also rejected climate action and promised to “ditch net-zero”.

Below, Carbon Brief explains what the Climate Change Act does – and does not – mean for the UK, correcting inaccurate comments as the UK’s political right veers further away from the previous consensus on climate action.

• Why does the UK have the Climate Change Act?
• What does the Climate Change Act require?
• The costs and benefits of the Climate Change Act
• How nearly 70 countries followed the UK’s Climate Change Act
• What comes next under the Climate Change Act?
• What would happen if the Climate Change Act was repealed?

Why does the UK have the Climate Change Act?

It is well-known that the Climate Change Act was voted through the UK parliament with near-unanimous cross-party support. In October 2008, some 465 MPs voted in favour, including 263 Labour members, 131 Conservatives, 52 Liberal Democrats. Just five Conservatives voted against.

Less widely appreciated is the fact that the Labour government only agreed to legislate in the face of huge public and political pressure, including from then-Conservative leader David Cameron.

Jill Rutter, senior fellow at thinktank the Institute for Government (IfG), tells Carbon Brief that the Conservatives “can also claim significant credit for the Climate Change Act”.

This is at odds with comments made by Badenoch, who described it as “Labour’s law”, when pledging to repeal it if she were ever elected as prime minister.

In early 2005, two Friends of the Earth campaigners – Bryony Worthington and Martyn Williams – had drafted a Climate Change Bill, inspired by the “worsening problem of climate change and the inadequacy of the government’s policy response”, according to a 2018 academic paper.

Worthington tells Carbon Brief they had “decided [the government’s plan] was rubbish and we needed a different approach”, based on five-yearly carbon budgets rather than single-year goals.

Their draft was introduced into parliament that July, as a private members’ bill, by high-profile backbench MPs from the three main political parties: Labour’s Michael Meacher; the Conservatives’ John Gummer (now Lord Deben); and Norman Baker for the Liberal Democrats.

This was the centrepiece of Friends of the Earth’s “Big Ask” campaign, gaining huge public support and backing from more than 100 other NGOs, 412 MPs and celebrities such as Radiohead frontman Thom Yorke.

Then, in December 2005, Cameron was elected Conservative leader, using support for climate action as part of his efforts to “‘decontaminate’ the Tory brand”, according to an IfG retrospective.

With the Labour government still resisting the idea of new climate change legislation, Cameron made what the IfG called a “really significant political intervention” on 1 September 2006, throwing his weight behind the “Big Ask” and publishing his own draft bill, on green recycled paper.

As the Guardian reported at the time, a letter from Cameron and others “call[ed] on the government to enshrine annual targets for carbon dioxide (CO2) emissions into a bill, to be introduced in the next Queen’s speech…the government believes a bill is unnecessary”.

At prime minister’s questions on 25 October 2006, Cameron continued to press Labour prime minister Tony Blair, who was still not committed to legislation.

Cameron went beyond the “Big Ask” draft by calling for an independent commission with executive powers, able to adjust the UK’s climate goals. Cameron asked Blair:

“Are we getting a bill: yes or no?…Will it include the two things that really matter: annual targets and an independent body that can measure and adjust them in the light of circumstances?”

The IfG says a former aide to David Miliband, who was then environment secretary, “remembers him commenting that Labour could not get into the position of being the only major party not in favour of the proposed bill”.

Finally, in November 2006, the Labour government confirmed in the Queen’s speech that it would introduce a new climate change bill.

Emphasising the cross-party consensus, Lord Deben tells Carbon Brief: “It was the Tories who wrote it and it was the Labour Party who accepted it – and all parties supported it.” He adds:

“It’s not just that every Tory leader since [then] has supported climate change, the Climate Change Act [and the] Climate Change Committee, but it’s simply that, actually, they ought to, because they invented it.”

The Labour government published its own draft climate change bill in March 2007 and this, after lengthy negotiation, went on to become the 2008 act.

Cameron continued to campaign for “independent experts, not partisan…ministers” to set the UK’s statutory climate targets, but this responsibility was, ultimately, left to the government.

Rutter tells Carbon Brief that, in pledging to repeal the 2008 act, Badenoch is “rejecting” a Conservative “inheritance” on climate change that runs back to Margaret Thatcher. She says:

“One of the defining features of climate policy to date in the UK has been the political consensus that has underpinned it. That may have been because Margaret Thatcher was the first leading world politician to draw attention to climate change in 1989 [via a speech at the UN in New York].”

Rutter adds that David Miliband had only been able to convince then-chancellor Gordon Brown to accept legally binding targets as a result of Cameron’s enthusiasm for the cause. She says:

“Although it was Labour legislation, brought forward by David Miliband (though implemented by brother Ed), the reason Miliband was…able to convince a sceptical Gordon Brown at the Treasury that the UK should set legally binding targets, was the enthusiasm with which new Conservative leader David Cameron embraced the Friends of the Earth ‘Big Ask’ campaign as part of his moves to detoxify the Conservative party after its 2005 defeat. Theresa May then increased the target [in 2019] from 80% to net-zero as part of her legacy. It is that long Conservative inheritance on climate action that Badenoch is now rejecting.”

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What does the Climate Change Act require?

The Climate Change Act sets out an overall “framework” for both cutting the UK’s emissions and preparing the country for the impacts of climate change.

At its heart is a legally binding goal for reducing greenhouse gas emissions by 2050. Originally envisaged as a 60% reduction on 1990 levels, this was quickly increased to 80%.

In 2019, amid a surge in concern about climate change, the then-Conservative government strengthened the target again to a reduction to “at least 100%” below 1990 levels, more commonly referred to as net-zero.

On the pathway to this long-term goal, the act also requires the government to set legally binding interim targets known as ”carbon budgets”. These must be set 12 years in advance, to allow time for the government and the rest of the economy to plan ahead.

The carbon budgets set limits on emissions over five-year periods, providing greater flexibility than annual goals, while tackling the cumulative emissions that determine global warming.

Section 13 of the act specifies that the government has a “duty to prepare proposals and policies for meeting carbon budgets”. There is also a requirement for the government to explain how its actions will achieve its climate goals.

(In addition, the act requires the government to set out a programme of measures for climate adaptation and how it intends to meet them.)

The final key pillar of the act is the creation of the Climate Change Committee (CCC), an independent advisory body. The CCC advises – but does not decide – on the level at which carbon budgets should be set and the climate-related risks facing the UK.

The committee also produces annual assessments of “progress” and recommendations for going further, which the government is obliged to respond to, but not to accept.

Each time the secretary of state sets out their plan for a new carbon budget – taking the CCC’s advice into account – or responds to a progress report from the committee, parliament scrutinises the government’s activities.

Contrary to recent criticisms from the opposition Conservatives and the hard-right populist Reform UK, however, the act says nothing at all about how the government should meet its targets.

The only requirement is that the government’s plan should be capable of meeting its targets.

Moreover, it was the Conservatives under Cameron that had wanted to give the CCC executive and target-setting powers. This was opposed at the time by the then-Labour government.

Rachel Solomon Williams, executive director of the Aldersgate Group, notes on LinkedIn that this was a “closely debated” issue, but that, ultimately, the act puts the government “in control”:

“A closely debated aspect of the bill at the time was whether the CCC should have an executive or an advisory function. In the end, it was appointed as an expert advisory committee and the government remains entirely in control of delivery choices.”

The Conservative press release announcing Badenoch’s plan to “repeal” the act is, therefore, incorrect to state that the legislation “force[s]” governments to introduce specific policies.

(Speaking at the 2025 Conservative party conference, shadow energy secretary Claire Coutinho caricatured what she called “Ed Miliband’s…act” as requiring “1970s”-style “central planning” that “dictate[s] what products people must buy, and when”.

Just 18 months earlier, she, as energy secretary, had written of her “government’s unwavering commitment to meeting our ambitious emissions targets, including the legislated carbon budgets and the net-zero by 2050 target”.)

The press release also falsely describes the targets set under the act as “arbitrary” and falsely suggests they were set without consideration for the impact on jobs, households and the economy.

(In 2021, Badenoch herself, then a government minister, told parliament: “We will put affordability and fairness at the heart of our reforms to reach net-zero.”)

Specifically, section 10 of the act lists “matters to be taken into account” when setting carbon budgets, including the latest climate science, available technologies, “economic circumstances”, “fiscal circumstances” and the impact of any decisions on fuel poverty.

As for the net-zero target, the Intergovernmental Panel on Climate Change (IPCC) has concluded that reducing emissions to net-zero is the only way to stop global warming. The target was set on this basis, following detailed advice from the CCC that took climate science, economic and social factors into account.

The Conservatives have also taken aim at the CCC itself as part of their rejection of the Climate Change Act, highlighting the committee’s advice on meat consumption and flying.

In an echo of widely circulated conspiracy theories, Badenoch even told the Spectator that the CCC “wants us to eat insects”. This is not true.

Despite the framing by right-leaning media and politicians, the CCC’s recommendations for contentious topics such as meat consumption and reductions in flight numbers are modest.

The committee notes that “meat consumption has been falling” without policy interventions and says this will help to free up land for tree-planting. It says “demand management measures” to curb flight numbers “may” be needed, but only if other efforts to decarbonise aviation fail.

More importantly, the government decides how to meet the carbon budgets. It can – and often does – ignore recommendations from the CCC, including those on diets and airport expansion.

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The costs and benefits of the Climate Change Act

The debate over whether to tackle climate change, how quickly and to what extent has almost invariably centred on the costs and benefits of doing so.

Those opposed to climate action have, in general, sought to exaggerate the supposed costs, while playing down the losses and damages already being caused by global warming.

Yet serious efforts to weigh up the costs and the benefits have concluded – again and again and again – that it would be cheaper to cut emissions than to face the consequences of inaction.

Indeed, this was precisely the conclusion of the landmark 2006 Stern Review, to which the 2008 Climate Change Act partly owes its existence. The review said:

“[T]he evidence gathered by the review leads to a simple conclusion: the benefits of strong and early action far outweigh the economic costs of not acting.”

More specifically, it said that the cost of action “can be limited to around 1% of global GDP [gross domestic product]”, whereas the damages from climate change would cost 5% – and as much as 20% of GDP.

When the act was passed in 2008, it was again estimated that the UK would need to invest around 1% of GDP in meeting its target of cutting emissions to 80% below 1990 levels by 2050.

Since then, estimates of the cost of cutting emissions have fallen, as the decline in low-carbon technology costs has outperformed expectations. At the same time, estimates of the economic losses due to rising temperatures have tended to keep going up.

(Some years after the review’s publication, Stern said he had “got it wrong on climate change – it’s far, far worse…Looking back, I underestimated the risks.”)

When it recommended the target of net-zero by 2050, the CCC estimated that the UK would need to invest 1-2% of GDP to hit this goal. It later revised this down to less than 1% of GDP.

Most recently, the CCC revised its estimates down once again, putting the net cost of reaching net-zero at £116bn over 25 years – roughly £70 per person per year – or just 0.2% of GDP.

In July 2025, the independent Office for Budget Responsibility (OBR) went on to estimate that the UK could take an 8% hit to its economy by the early 2070s, if the world warms by 3C.

It concluded that while there were potentially significant costs to the government from reaching net-zero, these would be far lower than the costs of failing to limit warming.

Despite all this, Conservative leader Badenoch has falsely argued that the UK’s net-zero target will be “impossible” to meet without “bankrupting” the country and that the the Climate Change Act has “loaded us with costs”.

Her party has also pledged to “axe the carbon tax” on electricity generation – a significant source of government revenue – claiming that this “just adds extra costs to our bills for no reason”.

Prof Jim Watson, director of the UCL Institute for Sustainable Resources, tells Carbon Brief that the costs of climate policies are “sometimes exaggerated” and are not the main reason for high bills:

“Policies that are in place to meet the UK’s carbon targets have costs, but these costs are sometimes exaggerated. These policies are not the primary cause of the energy price shock businesses and households have experienced over the past three years.”

Watson says that high gas prices were the “main driver” of high bills and adds that shifting away from fossil fuels “will also reduce the UK’s exposure to future fossil-fuel price shocks”.

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How nearly 70 countries followed the UK’s Climate Change Act

In the interview announcing her ambition to scrap the Climate Change Act, Badenoch falsely told the Spectator that the UK was “tackl[ing] climate change…alone”. She said:

“We need to do what we can sensibly to tackle climate change, but we cannot do it alone. If other countries aren’t doing it, then us being the goody-two-shoes of the world is not actually encouraging anyone to improve.”

This is a common claim among climate-sceptic politicians and commentators, who argue that the UK has gone further than other nations and that this is unfair. Badenoch’s predecessor, Rishi Sunak, used similar reasoning to justify net-zero policy rollbacks.

The UK has indeed been a leader in passing climate legislation, but it is far from the only country taking action to tackle climate change.

The Climate Change Act was among the first comprehensive national climate laws and the first to include legally binding emissions targets.

It has inspired legislation around the world, with laws in New Zealand, Canada and Nigeria among those explicitly based on the UK model.

Indeed, 69 countries have now passed “framework” climate laws similar to the UK’s Climate Change Act, as the chart below shows. This is up from just four when the act was legislated in 2008. Of these, 14 are explicitly titled the “climate change act”.

The UK was also the first major economy to legislate a net-zero target in 2019, but since then virtually every major emitter in the world has announced the target. (Not all of these targets have been put into law, as the UK’s has.)

When the UK announced its target in June 2019, around 1% of global emissions were covered by net-zero targets. By the end of that year, France and Germany brought this up to nearly 4%.

Over the following years, major economies including China and India announced net-zero targets, meaning that around three-quarters of global emissions are now covered by such goals, as the chart below shows.

(This figure would be even higher if the Trump administration in the US, which accounts for around a tenth of annual global emissions, had not abandoned the nation’s net-zero target.)

While it is true that the UK is “only responsible for 1% of global emissions”, as Badenoch has also noted, this does not mean its actions are inconsequential. Around a third of global emissions come from countries that are each responsible for 1% of global emissions or less.

Moreover, as a relatively wealthy country that is responsible for a large share of historical emissions, many argue that the UK also has a moral responsibility to lead on climate action.

This historical responsibility is implicitly invoked by the Paris Agreement, which recognises countries’ “common but differentiated responsibilities” for current climate change.

Finally, Badenoch’s position diverges from that of recent Conservative leaders.

Theresa May and Boris Johnson spoke positively of the UK “leading the world” in low-carbon technology and expressed pride about the nation’s climate record.

They framed the UK’s success in tackling climate change as a good reason to do more, rather than less. “Green” Conservatives also argue that the UK should race to gain a competitive advantage in producing low-carbon technologies domestically.

Responding to Badenoch’s plan to scrap the act, May issued a statement criticising the “retrograde step” following nearly two decades of the UK “[leading] the way in tackling climate change”.

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What comes next under the Climate Change Act?

The debate over the future of the Climate Change Act, triggered by the Conservative pledge to repeal it, comes ahead of two key moments for the legislation.

First, the government has until the end of October 2025 to publish a new plan for meeting the sixth carbon budget (CB6), covering the five-year period from 2033-2037.

In 2021, the then-Conservative government passed legislation to cut emissions to 78% below 1990 levels during the sixth carbon budget period, centred on 2035. The government set out its “carbon budget delivery plan” for CB6 in October 2021, as part of a wider net-zero strategy.

In July 2022, however, this plan was ruled unlawful by the High Court for failing to publish sufficient details on exactly how the target would be met. The revised plan, published in March 2023, was once again found unlawful by the High Court in May 2024.

The High Court then gave the government a deadline of May 2025 to publish another version, later extended to October 2025 as a result of last year’s general election.

Second, the government has until June 2026 to legislate for the seventh carbon budget, covering the period 2037 to 2042. This legislation will be subject to a vote in parliament.

In February 2025, the CCC advised the government to set this budget at 87% below 1990 levels, in order to stay on track for the goal of net-zero by 2050, as shown in the chart below.

Both the CB6 delivery plan this October and the parliamentary vote over CB7 next June are likely to be hotly contested, with the Conservatives and Reform having come out against climate action.

After publishing two unlawful carbon budget delivery plans and ahead of a widely anticipated election loss, the Conservatives began calling for greater scrutiny around carbon budgets in 2023.

Then-prime minister Rishi Sunak said in September of that year that parliament should be able to debate plans to meet the next carbon budget, before voting on the target. He said:

“So, when parliament votes on carbon budgets in the future, I want to see it consider the plans to meet that budget, at the same time.”

Then-secretary of state Coutinho subsequently wrote that a draft delivery plan for CB7 should be published alongside draft legislation setting the level of the carbon budget. She also argued that CB7 be debated on the floor of the House, rather than in the “delegated legislation committee”.

In response, the current government has pledged to provide “further information” to parliament, ahead of the vote on CB7. In a July 2025 letter to the chair of the House of Commons Environmental Audit Committee (EAC), energy secretary Ed Miliband wrote:

“Prior to parliament’s vote, we will publish an impact assessment which will clearly articulate the full range of benefits and costs of the government’s chosen CB7 target and the cross-economy pathway to deliver it.”

However, Miliband said the government would not publish a CB7 delivery plan until “as soon as reasonably practicable after” the parliamentary vote on the level of the budget.

The EAC itself is holding an inquiry on the seventh carbon budget and how the “costs of delivering it will filter through to households and businesses”. It is likely to report back in February 2026.

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What would happen if the Climate Change Act was repealed?

If any future government wanted to repeal the Climate Change Act and its legally binding net-zero goal, it would not be a straightforward process.

The government would need to introduce a new bill in parliament just to repeal the act.

This process would involve seeking approval from both the House of Commons and the House of Lords before receiving Royal Assent to become law. Within the make-up of the current UK parliament, it is likely that such a bill would face significant challenges.

Any new law repealing the Climate Change Act would need to introduce new climate commitments of a similar nature – or else the UK would be in breach of several international laws and treaties, explains Estelle Dehon KC, a barrister specialising in climate change. She tells Carbon Brief:

“In short, repeal of the Climate Change Act without any replacement commitments of a similar type would be in breach of the UK’s international obligations under: the climate change treaties (so UNFCCC, Kyoto and Paris); international human rights law and customary international law, as well as specific sources like UN Convention on the Law of the Sea.”

Under the Paris Agreement, the UK has made pledges to cut its emissions by 2030 and 2035, known as “nationally determined contributions” (NDCs).

The UK’s NDCs are directly informed by its domestic emissions-cutting targets, known as carbon budgets. The act specifies that the government has a “duty to prepare proposals and policies for meeting carbon budgets”.

Any move in breach of international laws and treaties could be vulnerable to legal challenges, particularly in light of a recent opinion on climate change by the International Court of Justice.

Repealing the Climate Change Act could also put the UK in opposition with its international trade agreements.

The most recent trade agreement between the UK and the EU states that each party “reaffirms its ambition of achieving economy-wide climate neutrality by 2050”.

It also contains rules on “non-regression” in relation to climate protection.

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The post Factcheck: What the Climate Change Act does – and does not – mean for the UK appeared first on Carbon Brief.

Factcheck: What the Climate Change Act does – and does not – mean for the UK

Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.

This week

Shattered climate consensus

FRACKING BAN: UK energy secretary Ed Miliband has announced that the government will bring forward its plans to permanently ban fracking, in a move designed to counter a promise from the hard-right Reform party to restart efforts to introduce the practice, the Guardian said. In the same speech, Miliband said Reform’s plans to scrap clean-energy projects would “betray” young people and future generations, the Press Association reported.

ACT AXE?: Meanwhile, Kemi Badenoch, leader of the Conservatives, pledged to scrap the 2008 Climate Change Act if elected, Bloomberg reported. It noted that the legislation was passed with cross-party support and strengthened by the Conservatives.
‘INSANE’: Badenoch faced a backlash from senior Tory figures, including ex-prime minister Theresa May, who called her pledge a “catastrophic mistake”, said the Financial Times. The newspaper added that the Conservatives were “trailing third in opinion polls”. A wide range of climate scientists also condemned the idea, describing it as “insane”, an “insult” and a “serious regression”.

Around the world

• CLIMATE CRACKDOWN: The US Department of Energy has told employees in the Office of Energy Efficiency and Renewable Energy to avoid using the term “climate change”, according to the Guardian.
• FOREST DELAY: Plans for Brazil’s COP30 flagship initiative, the tropical forests forever fund, are “suffer[ing] delays” as officials remain split on key details, Bloomberg said.
• COP MAY BE ‘SPLIT’: Australia could “split” the hosting of the COP31 climate summit in 2026 under a potential compromise with Turkey, reported the Guardian.
• DIVINE INTERVENTION: Pope Leo XIV has criticised those who minimise the “increasingly evident” impact of global warming in his first major climate speech, BBC News reported.

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€44.5 billion

The  cost of extreme weather and climate change in the EU in the last four years – two-and-a-half times higher than in the decade to 2019, according to a European Environment Agency report covered by the Financial Times.

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Latest climate research

• Fossil-fuelled climate change caused around 36% of Typhoon Ragasa’s direct damage to homes and properties in southern China, according to a rapid impact attribution study | Imperial Grantham Institute – Climate Change and the Environment
• Some 86% of the global population are concerned about climate change, according to a survey of 280,000 people in 142 countries and regions | Climate Policy
• A global shift towards a “planetary health diet” could slash emissions and save tens of thousands of lives each day | EAT-Lancet Commission 2025 report

(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)

Captured

Clean energy has met 100% of Great Britain’s electricity demand for a record 87 hours this year so far, according to new Carbon Brief analysis. This is up from just 2.5 hours in 2021 and 64.5 hours in all of 2024. The longest stretch of time where 100% of electricity demand was met by clean energy stands at 15 hours, from midnight on 25 May 2025 through to 3pm on 26 May, according to the analysis.

Spotlight

‘Overshoot’ unknowns

As the chances of limiting global warming to 1.5C dwindle, there is increasing focus on the prospects for “overshooting” the Paris Agreement target and then bringing temperatures back down by removing CO2 from the atmosphere.

At the first-ever Overshoot Conference in Laxenburg, Austria, Carbon Brief asks experts about the key unknowns around warming “overshoot”.

Sir Prof Jim Skea

Chair of the Intergovernmental Panel on Climate Change (IPCC) and emeritus professor at Imperial College London’s Centre for Environmental Policy

So there are huge knowledge gaps around overshoot and carbon dioxide removal (CDR). As it’s very clear from the themes of this conference, we don’t altogether understand how the Earth would react in taking CO2 out of the atmosphere.

We don’t understand the nature of the irreversibilities and we don’t understand the effectiveness of CDR techniques, which might themselves be influenced by the level of global warming, plus all the equity and sustainability issues surrounding using CDR techniques.

Prof Kristie Ebi

Professor at the University of Washington’s Center for Health and the Global Environment

There are all kinds of questions about adaptation and how to approach effective adaptation. At the moment, adaptation is primarily assuming a continual increase in global mean surface temperature. If there is going to be a peak – and of course, we don’t know what that peak is – then how do you start planning? Do you change your planning?

There are places, for instance when thinking about hard infrastructure, [where overshoot] may result in a change in your plan – because as you come down the backside, maybe the need would be less. For example, when building a bridge taller. And when implementing early warning systems, how do you take into account that there will be a peak and ultimately a decline? There is almost no work in that. I would say that’s one of the critical unknowns.

Dr James Fletcher

Former minister for public service, sustainable development, energy, science and technology for Saint Lucia and negotiator at COP21 in Paris.

The key unknown is where we’re going to land. At what point will we peak [temperatures] before we start going down and how long will we stay in that overshoot period? That is a scary thing. Yes, there will be overshoot, but at what point will that overshoot peak? Are we peaking at 1.6C, 1.7C, 2.1C?

All of these are scary scenarios for small island developing states – anything above 1.5C is scary. Every fraction of a degree matters to us. Where we peak is very important and how long we stay in this overshoot period is equally important. That’s when you start getting into very serious, irreversible impacts and tipping points.

Prof Oliver Geden

Senior fellow and head of the climate policy and politics research cluster at the German Institute for International and Security Affairs and vice-chair of IPCC Working Group III

[A key unknown] is whether countries are really willing to commit to net-negative trajectories. We are assuming, in science, global pathways going net-negative, with hardly any country saying they want to go there. So maybe it is just an academic thought experiment. So we don’t know yet if [overshoot] is even relevant. It is relevant in the sense that if we do, [the] 1.5C [target] stays on the table. But I think the next phase needs to be that countries – or the UNFCCC as a whole – needs to decide what they want to do.

Prof Lavanya Rajamani

Professor of international environmental law at the University of Oxford

I think there are several scientific unknowns, but I would like to focus on the governance unknowns with respect to overshoot. To me, a key governance unknown is the extent to which our current legal and regulatory architecture – across levels of governance, so domestic, regional and international – will actually be responsive to the needs of an overshoot world and the consequences of actually not having regulatory and governance architectures in place to address overshoot.

Watch, read, listen

FUTURE GAZING: The Financial Times examined a “future where China wins the green race”.

‘JUNK CREDITS’: Climate Home News reported on a “forest carbon megaproject” in Zimbabwe that has allegedly “generated millions of junk credits”.
‘SINK OR SWIM’: An extract from a new book on how the world needs to adapt to climate change, by Dr Susannah Fisher, featured in Backchannel.

Coming up

• 7 October: International Energy Agency (IEA) renewables 2025 report launch
• 8-10 October: World summit of Indigenous peoples and nature, Abu Dhabi, UAE
• 9-15 October: International Union for the Conservation of Nature (IUCN) 2025 congress, Abu Dhabi, UAE

Pick of the jobs

• UK government foreign, commonwealth and development office, senior climate policy adviser | Salary: CA$93,207. Location: Calgary, Canada
• Wellcome Trust, senior research manager, climate and health | Salary: £64,800. Location: London
• Bloomberg, product manager – climate, nature and sustainability regulations | Salary: Unknown. Location: London

DeBriefed is edited by Daisy Dunne. Please send any tips or feedback to debriefed@carbonbrief.org.

This is an online version of Carbon Brief’s weekly DeBriefed email newsletter. Subscribe for free here.

The post DeBriefed 3 October 2025: UK political gap on climate widens; Fossil-fuelled Typhoon Ragasa; ‘Overshoot’ unknowns appeared first on Carbon Brief.

DeBriefed 3 October 2025: UK political gap on climate widens; Fossil-fuelled Typhoon Ragasa; ‘Overshoot’ unknowns

A controversial way of measuring how much methane warms the planet has stirred debate in recent years – particularly around assessing the climate impact of livestock farming.

The metric – known as GWP* (global warming potential star) – was designed to more precisely account for the warming impact of short-lived greenhouse gases, such as methane.

No country so far has used GWP* to measure emissions, but New Zealand is currently considering its use.

In June, a group of climate scientists from around the world wrote an open letter advising against this.

They argued that the metric “creates the expectation that current high levels of methane emissions are allowed to continue”.

Climate experts tell Carbon Brief that there is “no strong debate” on the science behind GWP* and that it can accurately assess the global warming effect of methane.

But many experts also firmly caution against its use in national climate targets, believing it could allow countries to prolong high levels of emissions at a time when they should be drastically cut.

Some researchers tell Carbon Brief that GWP* is an “accounting trick” and a “get-out-of-jail-free card for methane emitters”. A 2021 Bloomberg article called the metric “fuzzy methane math”.

Prof Myles Allen, one of the scientists who created GWP*, tells Carbon Brief that the metric is “nothing more” than one way of better understanding the climate impact of different actions as part of efforts to limit warming under the Paris Agreement. 

In this Q&A, Carbon Brief explains the science behind GWP*, why the metric is so divisive and the ways in which its use has been considered.

• What is GWP*?
• What are the main controversies around using GWP*?
  • Carbon cycle
  • ‘No additional warming’
  • Climate ambition
  • Baseline and historical emissions
  • Communication
• Do any countries currently use GWP* to measure methane emissions?
  • New Zealand
  • Australia
  • Ireland
  • Paraguay
  • UK
• What do experts think about the use of GWP*?

What is GWP*?

Global warming is caused by a build up of greenhouse gases – mainly from burning fossil fuels – trapping heat in the atmosphere.

Different gases cause differing levels of warming and remain in the atmosphere for varying lengths of time. For example, carbon dioxide (CO2), the main contributor to warming, lingers for centuries, whereas other gases last decades or even millennia.

To account for these variables, scientists use a metric known as global warming potential (GWP), which assesses the warming caused by different gases compared to CO2, which has a GWP of 1.

Using GWP, emissions of other gases are calculated in terms of their “CO2 equivalent” over a given amount of time.

In their reports, the Intergovernmental Panel on Climate Change (IPCC) set out three GWP variants measured over 20 years (GWP20), 100 years (GWP100) and 500 years (GWP500).

GWP100 is the most common approach and is used to calculate emissions under the Paris Agreement.

Methane is a short-lived gas that only remains in the atmosphere for around 12 years before breaking down. But it causes a large burst of initial warming that is around 80 times more powerful than CO2, according to the IPCC.

This means that one tonne of methane causes the same amount of warming as around 80 tonnes of CO2, when measured over a period of 20 years.

When calculated over 100 years, methane’s shorter lifetime means it causes around 30 times more warming than CO2.

Some experts have criticised the use of GWP100, saying it does not sufficiently account for the fact that methane leaves the atmosphere much more quickly than CO2 and does not actually last for 100 years. This is the issue that GWP* was designed to fix.

GWP* calculates the warming contributions of long- and short-lived gases at different rates, accounting for their varying lifetimes in the atmosphere.

One of the researchers behind GWP*, Dr Michelle Cain, explained in a 2018 Carbon Brief guest post that a constant rate of methane emissions can maintain stable atmospheric concentrations of the gas, assuming methane sinks remain constant as well.

In contrast, a constant rate of CO2 emissions “leads to year-on-year increases in warming, because the CO2 accumulates in the atmosphere”, Cain wrote. CO2 does not leave the atmosphere after a decade or so, as methane does, and continues to build over time until emissions stop.

Cain, formerly a researcher at the University of Oxford and now a senior lecturer at Cranfield University, added:

“For countries with high methane emissions – due to, say, agriculture – this can make a huge difference to how their progress in emission reductions is judged.”

Methane emissions that slowly decline or remain stable over time are calculated as contributing “no additional warming” to the planet, which is not the case with other GWP calculations.

The chart below shows simplified emissions scenarios for CO2 and methane, highlighting the different impacts they have on global warming over time.

The chart below shows how using the two different metrics – GWP* and GWP100 – affects the same emissions pathway throughout the 21st century, given the different warming impacts of greenhouse gases.

If, for example, a country emitted 4m tonnes of methane annually from 1990-2005, these emissions would now be considered “climate-neutral” using GWP*, as they are not actively contributing new warming to the atmosphere, but rather maintaining the existing levels of methane in the atmosphere in 1990.

This would not be the case under GWP100, which looks at the warming potential of emissions over the course of a century and does not account for their different atmospheric lifetimes.

GWP* can be used for other short-lived gases, such as some hydrofluorocarbons, but methane is the most significant short-lived gas when it comes to climate change.

The IPCC notes that converting methane emissions into CO2 equivalent using GWP100 “overstates the effect of constant methane emissions on global surface temperature by a factor of 3-4” and understates the impact of new methane emissions “by a factor of 4-5 over the 20 years following the introduction of the new source”.

GWP* was created by several researchers, including Prof Myles Allen, the head of atmospheric, oceanic and planetary physics at the University of Oxford. The concept was detailed in a 2016 study and first named in a 2018 study. It was further updated by the authors in 2019 and 2020.

Allen tells Carbon Brief that the researchers involved were “reluctant” to give their new metric a name, as it “was just a way of using reported numbers to calculate warming impact”. He adds:

“I think it’s really unfortunate that people have latched onto GWP*. It doesn’t matter. We could forget about GWP* entirely, we can just use a climate model to work out the warming impact…GWP* is a handy way of calculating the warming impact of activities. Nothing more.”

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What are the main controversies around using GWP*?

Efforts to cut methane emissions are widely viewed as a “quick-win” to help limit the effects of climate change in the short term.

More than 100 countries signed a pledge, launched at COP26 in 2021, to cut global methane emissions by 30% by 2030.

Cutting methane would also help to counteract an acceleration in warming due to declining aerosol emissions, which are currently masking around half a degree of warming.

Experts Carbon Brief spoke to agree on the importance of cutting methane emissions, but disagree on whether GWP* helps or hinders these efforts.

The debate around the metric centres on the possible impacts of its use, rather than the soundness of the science behind it.

Prof Joeri Rogelj, a climate science and policy professor at Imperial College London, explains:

“At the global level, at any level, the method of GWP* actually provides a good, new way to translate the trajectory of methane emissions into equivalent emissions of CO2, or emissions of CO2 that would have an equivalent warming effect…The debate is on the application.”

Allen says he is a “little frustrated” that discussions around the use of GWP* have “become so emotive”. He tells Carbon Brief:

“Every action we take has both a temporary impact on global temperature and a permanent one. How much is in both areas depends on the action. We need to know those two things in order to make decisions about choices of action in pursuit of a temperature goal…GWP* gives you a handy way of doing that.”

Below, Carbon Brief details some of the main discussion points and controversies around GWP*.

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Carbon cycle

A misleading claim frequently made about livestock is that cows do not contribute much to global warming because the methane they emit eventually returns to the land through the carbon cycle – the set of processes in which carbon is exchanged between the atmosphere, land and ocean, as well as the organisms they contain.

Those in favour of using GWP* to measure methane emissions often also stress the difference between methane emissions that come from animals – known as biogenic methane – and methane from fossil fuels.

Rogelj tells Carbon Brief that biogenic and fossil-sourced methane are “slightly different, but that difference is really second-order” when it comes to climate change.

Methane warms the planet while it is in the atmosphere, so the “climate effect is exactly the same, irrespective of which source the methane comes from”, Rogelj adds.

The differences become more significant when methane breaks down in the atmosphere and oxidises into water vapour and CO2.

CO2 that originated from a cow can be reabsorbed by plants and the land. But the CO2 resulting from fossil methane – which stems from sources such as flaring from oil and gas drilling – stays in the atmosphere. Although fossil methane has a “bit of a longer effect”, Rogelj says:

“This is a bit of a red herring, because the main effect is, of course, the effect that the methane has while it is methane and not what the carbon molecule of that methane has after [the] methane has been broken down or oxidised to CO2.”

He adds that there are ways of reducing agricultural methane, such as “diet change” or “management measures”, but no way to remove the emissions “100%”.

The graphic below shows the digestive process through which a cow emits methane.

Agriculture also causes other significant environmental harms. It is responsible for around 80% of global deforestation and is a key driver of biodiversity loss and water pollution.

Prof Frank Mitloehner, a professor and air-quality specialist at the University of California, Davis (UC Davis), is one of the main proponents of GWP*, frequently speaking about it in public presentations and discussions with the farming sector.

He tells Carbon Brief that, while animal agriculture can cause environmental harm, it is a “silly argument” to say these impacts are being ignored in carbon-cycle discussions.

He gives an example of discussions on deaths from car accidents excluding mentions of the emissions from cars, saying that these wider impacts are still important and can be discussed separately.

He adds that it is an “urban myth” that biogenic methane emissions are not a concern because of the carbon cycle.

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‘No additional warming’

Under GWP*, methane emissions stop causing new warming once they reduce by 10% over the course of 30 years – around 3% each decade, or 0.3% each year.

These emissions are then described in research and policy as causing “no additional warming”.

For example, a 2021 study from Mitloehner and other UC Davis researchers, found that methane emissions from the US cattle industry “have not contributed additional warming since 1986”, based on GWP* calculations. It also said that the dairy industry in California “will approach climate neutrality” by the 2030s, if methane emissions are cut by just 1% annually.

(According to the US Environmental Protection Agency, methane emissions from enteric fermentation – the digestive process through which cows produce the greenhouse gas – increased by more than 5% over 1990-2022.)

However, many critics take issue with the “no additional warming” concept.

The main criticism is that, although a gradually reducing herd of cattle may stabilise methane emissions, it still emits the polluting gas. If animal numbers were instead drastically reduced, this would cut methane emissions and lower warming rather than maintaining current levels.

Dr Caspar Donnison, a postdoctoral researcher at Lawrence Livermore National Laboratory in the US, says the term no additional warming is “absolutely misleading” in the context of GWP*. He tells Carbon Brief:

“You just assume, on the face of it, that this means it has a neutral impact on the climate…But ‘no additional warming’ means that you’re still sustaining the warming that the herd is causing.”

Allen says that the debate focuses on the “stock of warming versus additional warming”. He compares it to accounting for historical emissions of CO2:

“If a country got rich by burning CO2, they’ve caused a lot of warming in the past. If they reduce their CO2 emissions to zero, then people are generally happy to call what they’re doing climate-neutral, even though they may be sitting on a huge heap of historical warming caused by their CO2 emissions while they were burning [fossil fuels].

“And yet, temperature-wise, that’s exactly the same thing as having a source of methane that’s declining by 3% per decade.”

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Climate ambition

Another criticism around the use of GWP* is that countries or companies with high agricultural methane emissions could use the metric to make small emission reductions appear larger.

Dr Donal Murphy-Bokern, an independent agricultural and environmental scientist, believes that the metric can be used as a “get-out-of-jail-free card for methane emitters”. He adds:

“It’s all about saying carry on as we are; we’ll manage this by slightly reducing our emissions over a critical period in history, so as to appear at that critical period in history to be so-called ‘climate-neutral’.”

Mitloehner disagrees with this, noting that, while reductions in methane emissions appear significant under GWP*, increases also appear significant. He says:

“It is simply not true that GWP* is a get-out-of-jail-free card. It’s not. If you reduce emissions, it makes your contributions look less. If you increase emissions, it makes your contributions much worse.”

Rogelj says he has not seen GWP* being used to advocate for the “highest possible ambition” in cutting methane emissions.

However, Allen says that “no metric tells you what to do”. He adds:

“How you measure emissions and how you measure warming has absolutely no bearing on whether you think a country has an obligation to undo some of the damage to the climate they’ve caused in the past.

“This is where the ‘free-pass’ argument makes no sense to me, because the existence of a method to calculate the warming impact of your emissions allows you to make decisions about emissions in light of their warming impact, sure, but it doesn’t tell you what the outcomes of those decisions should be.”

Allen adds that the livestock sector is “unsustainable globally”, with animal numbers and methane levels still rising.

The chart below shows how atmospheric methane concentrations have increased in recent decades.

Allen tells Carbon Brief:

“Do we need to eliminate livestock agriculture to stop global warming? No…[but] we do need to start decreasing it. And if we can decrease it faster than 3% per decade then that would help reduce warming that’s caused by other sectors or, indeed, undo some of the warming that the livestock sector has caused in the past.”

Mitloehner says considerations on the fairness of using GWP* are “real from a policy standpoint and they have to be addressed from a policy standpoint”. He adds:

“But, from a scientific standpoint – and that’s where I’m coming from – I think it’s not controversial.”

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Baseline and historical emissions

The baseline year from which emissions reduction targets are set is significant, as it helps form the scope of climate ambition.

For example, high-emitting countries, such as the UK, have set 1990 as their baseline year for emissions-cutting targets, whereas many low-emitting countries may choose further back or more recent years, depending on their needs. Rogelj says:

“Because GWP* translates a change in emissions into either an instantaneous emission or instantaneous removal of CO2, your starting point becomes really important.

“If you start with very high emissions of methane and you did not in any way account for this high starting point, then even very minor, unambitious reductions in methane would result in creating credits for high-polluting countries.”

However, he notes that this is just one way of applying the metric and that there could be ways to avoid this “inequitable outcome”, such as applying GWP* globally and allocating each country a per-capita methane budget, instead of assessing based on national current or past emissions. (Rogelj and Prof Carl-Friedrich Schleussner discussed other possible GWP* equity measures in a 2019 study.)

The chart below, adapted from that study, shows how GWP* can significantly change the per-capita methane emissions of different countries. Some countries with high agricultural methane emissions, such as New Zealand, change from high to low per-capita emitters.

A 2025 study used a climate model to quantify future national warming contributions for Ireland under different emissions scenarios and found that “no additional warming” approaches, such as GWP*, are “not a robust basis for fair and effective national climate policy”.

Discussing baseline concerns, Allen says these considerations are the same for any other metric:

“It depends on how much account you want to take of [the] warming you’ve caused in the past – and at what point you want to take responsibility for the warming your actions had caused.”

He believes that most climate experts agree that it is good to understand the impact emissions have on global temperatures, but “where the controversy arises is about what you consider someone’s nominal emissions to be today”. He adds:

“This is where everybody gets upset, because if you use GWP*, then a livestock sector that’s reducing its emissions by 3% per decade – which most global-north livestock sectors are doing – it looks like their emissions are quite small.

“But that’s only a problem if you think that the main issue is working out whose fault global warming is, rather than working out what we should do about it.”

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Communication

Many experts Carbon Brief spoke to took issue with how GWP* has been discussed by some of its proponents.

Murphy-Bokern criticises how Mitloehner and other experts communicate the metric. He says:

“The confusion arises from the activities of Mitloehner, in particular, where he presents the farming community – and the industry in general – with the idea that you can magic away the warming effect of methane simply by looking at the rate of change of methane emissions.”

Mitloehner says he has no regrets about his communication of GWP*, adding that he has “always emphasised to the livestock sector that reductions of methane are important”. He tells Carbon Brief:

“I’m proud because I have been able to take the livestock sector along with the understanding that reductions are needed and that they can be part of a solution if they understand that.”

The New York Times reported in 2022 that the research centre led by Mitloehner at the University of California, Davis “receives almost all its funding from industry donations and coordinates with a major livestock lobby group on messaging campaigns”. Other reports note his discussions about GWP* with stakeholders in various countries.

In response to these reports, Mitloehner says he believes it is important to work with the sector you are researching, adding that he receives both public and private funding. He tells Carbon Brief:

“The problem is not that they [the meat industry] are investing in research and communications and extension. The problem is that they are not putting in enough, because the public sector is withdrawing from this.

“Climate research is being slashed…If the government is not paying into research to quantify and reduce emissions – and those people who are critical of what we do say ‘oh, industry shouldn’t do it’ – then, I ask you, who should?”

Colin Woodall, the chief executive of the National Cattlemen’s Beef Association, a US lobby group, said in 2022 that GWP* is the “methodology we need to make sure everybody is utilising in order to tell the true story of methane”, Unearthed reported. According to the outlet, he added:

“We’re working with our partners around the globe to ensure that everybody is working towards adoption of GWP*.”

Asked if he regrets anything about his communication of GWP*, Allen tells Carbon Brief:

“When we first introduced this – and, perhaps, this is one thing I do regret – I was, perhaps, a little naive in that I thought everybody would seize on focusing on [the] warming impact because it was, from a policy perspective, potentially much easier for the agricultural sector.

“I thought that this would actually be welcomed. But, sadly, it’s not been. And I think part of that is because of this narrative of blame.”

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Do any countries currently use GWP* to measure methane emissions?

GWP* is not yet used by any country in methane emission reporting or targets. But it has been considered by New Zealand, Ireland and other nations with high agricultural emissions.

A 2024 statement from dozens of NGOs and environmental organisations called for countries and companies not to use GWP* in their greenhouse gas reporting or to guide their climate mitigation policies. They wrote:

“The risks of GWP* significantly outweigh the benefits.”

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New Zealand

New Zealand is currently considering changing its biogenic methane target, including applying the “no additional warming” approach used in GWP*. If it does so, it could become the first country to adopt GWP*.

The nation is a major livestock producer and agriculture generates nearly half of all its greenhouse gas emissions.

The chart below shows that the agricultural sector is also responsible for more than 90% of the country’s methane emissions.

New Zealand has a legally binding target to reach net-zero greenhouse gas emissions by 2050. However, biogenic methane has separate targets to reduce by 10% by 2030 and by 24-47% by 2050, compared to a baseline of 2017 levels.

In late 2024, a review from the nation’s Climate Change Commission recommended that the government change its 2050 greenhouse gas targets, including to increase the biogenic methane goal to a 35-47% reduction by 2050.

At the same time, an independent panel commissioned by the New Zealand government reviewed how the country’s climate targets would look under the “no additional warming” approach.

The resulting report, which did not look specifically at GWP*, but used a similar concept, found that a 14-15% cut in biogenic methane by 2050 would be “consistent with meeting the ‘no additional warming’ condition”, under mid-range global emissions scenarios that keep temperatures below 2C.

The government is “currently considering” these findings, a spokesperson for the Ministry for the Environment tells Carbon Brief in a statement.

The spokesperson says that the report is “part of the body of evidence” that the government will use in its response to the Climate Change Commission’s review, which it must publish by November 2025.

Cain, the Cranfield University lecturer who co-created GWP*, wrote in Climate Home News in 2019 that New Zealand reducing biogenic methane by 24% would “offset the warming impact” of the rest of the country’s emissions, adding:

“New Zealand could declare itself climate-neutral almost immediately, well before 2050 and only because farmers were reducing their methane emissions. That’s a free pass to all the other sectors, courtesy of New Zealand’s farmers.”

A report on GWP* by the Changing Markets Foundation found that, in 2020, 16 industry groups in New Zealand and the UK “urged” the UN’s Intergovernmental Panel on Climate Change to use GWP* to assess warming impacts.

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Australia

The Guardian reported in May 2024 that Cattle Australia, a cattle producer trade group, was “lobbying the red-meat sector to ditch its net-zero target in favour of a ‘climate-neutral’ goal that would require far more modest reductions in methane emissions”.

Cattle Australia’s senior adviser and former chief executive, Dr Chris Parker, tells Carbon Brief in a statement that the organisation is “working with the Australian government to ensure methane emissions within the biogenic carbon cycle are appropriately accounted for in our national accounting systems”. He adds:

“We believe GWP* offers a more accurate way of assessing methane’s temporary place in the atmosphere and its impact on the climate. Australian cattle producers are part of the climate solution and we need policy settings to enable them to participate in carbon markets.”

Australia’s Department of Climate Change, Energy, the Environment and Water did not respond to Carbon Brief’s request for comment.

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Ireland

Internal documents assessed for the Changing Markets Foundation’s GWP* report “suggest” that Ireland’s Department of Agriculture, Food and the Marine has advocated for GWP* “at the international level”, including at the UN’s COP26 climate summit in 2021.

Allen and Mitloehner were involved in a 2022 Irish parliamentary discussion on methane, in which Allen advocated for the country to “be a policy pioneer” by using GWP* in its methane reporting alongside standard methods.

The country’s coalition government, formed earlier this year, pledged to “recognise the distinct characteristics of biogenic methane” and also “advocate for the accounting of this greenhouse gas to be re-classified at EU and international level”.

A spokesperson for Ireland’s Department of Agriculture, Food and the Marine tells Carbon Brief that this does not refer to using GWP* specifically. They say the country is “in favour of using accurate, scientifically validated and internationally accepted emission measurement metrics”, adding:

“It is important that the nature of how biogenic methane interacts in the environment is accurately reflected in how it is accounted for. This does not mean the use of the metric GWP*.”

In December 2024, Ireland’s Climate Change Advisory Council proposed temperature neutrality pathway options to the government that do not specifically refer to GWP*, but use the same concept of no “additional warming”.

The Irish Times reported that this was “in part to reduce potential disruption from Ireland’s legal commitment to achieve national ‘climate neutrality’ by 2050”.

The climate and energy minister, Darragh O’Brien, said he has “not formed a definitive view” on this, the newspaper noted, and that expert views will feed into ongoing discussions on the 2031-40 carbon budgets, which are due to be finalised later in 2025.

In an Irish Times opinion article, Prof Hannah Daly from University College Cork, described the temperature neutrality consideration as “one of the most consequential climate decisions this government will make”. She wrote that the approach “amounts to a free pass for continued high emissions” of livestock methane.

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Paraguay

Paraguay mentioned GWP* in a national submission to the UN in 2023 after agribusiness representatives “pushed” to adopt the metric, according to Consenso, a Paraguayan online newsletter.

The country’s National Directorate of Climate Change told Consenso for a separate article related to GWP* that it is “aware” of questions around the metric, but that it “has the option of using other measurement systems” for emissions reporting.

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UK

The National Farmers’ Union, the main farming representative group in England and Wales, is in favour of using GWP* to measure agricultural methane emissions.

Carbon Brief understands that the UK government is not currently considering using GWP* in addition to, or instead of, GWP100 in its emissions reporting.

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What do experts think about the use of GWP*?

Most experts Carbon Brief spoke to agreed that GWP* could be a useful metric to apply to global methane emissions, but that it is difficult to apply equitably in individual countries or sectors. Rogelj believes that are are some contexts in which GWP* could be used, but adds:

“You cannot just take targets that were set and discussed historically with one greenhouse gas metric in mind – GWP100 under the UNFCCC [United Nations Framework on Climate Change] and the Paris Agreement and all that – [and] then simply apply a different metric to it. They change meaning entirely.

“So, if one would like to use GWP*, one should build the policy targets and frameworks from the ground up to take advantage of the strengths of that metric, but also put in place safeguards that ensure that the weaknesses and limitations of that metric do not result in unfair or undesirable outcomes.”

A 2022 study says that using GWP* in climate plans “would ask countries to start from scratch in terms of their political target setting processes”, calling it a “bold ask” for policymakers.

It adds that achieving net-zero emissions, as measured with GWP*, “would only lead to a stabilisation of temperatures at their peak level”.

However, a 2024 study found that GWP* gives a “dynamic” assessment of the warming impact of emissions that “better aligns with temperature goals” than GWP100, when measuring methane emissions from agriculture.

Allen believes that criticism over the use of GWP* is similar to “saying it’s a meaningless question” to consider the warming impact of a country or company’s actions. He adds:

“That seems a very strange position to me, because we need to know how different activities are contributing to global warming because we have a temperature target.

“In saying GWP* is a bad thing, what people are actually saying is it’s a bad thing to know the warming impact of our actions, which is a very strange thing to say.”

He says that such metrics help countries to make informed decisions on climate action, but that “we can’t expect metrics to make these decisions for us”.

Murphy-Bokern notes that GWP* could be useful in modelling global, rather than national, methane emissions to avoid high-emitting countries making small methane cuts to achieve “no additional warming”, rather than significantly reducing these emissions.

He says the metric would be particularly useful if global emissions were close to zero, as a way to target the final remaining emissions. But, he adds:

“We are so far away from that very happy situation, that the discussion now with GWP* is a huge distraction from the key objective, which is to reduce emissions.”

Mitloehner – and every expert Carbon Brief spoke with – agrees with this wider point. He says:

“The main point is we need to reduce emissions. In the case of livestock, we need to reduce methane emissions. And the question is how do we get it done? And how do we quantify the impacts that [that reduction] would have accurately and fairly? The other issues are issues that politicians have to answer.”

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The post Q&A: What the ‘controversial’ GWP* methane metric means for farming emissions appeared first on Carbon Brief.

Q&A: What the ‘controversial’ GWP* methane metric means for farming emissions