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The first-ever international conference on the contentious topic of “overshoot” was held last week in a palace in the small town of Laxenburg in Austria.

The three-day conference brought together nearly 200 researchers and legal experts to discuss future temperature pathways where the Paris Agreement’s “aspirational” target to limit global warming to 1.5C is met “from above, rather than below”.

Overshoot pathways are those which exceed the 1.5C limit – before being brought back down again through techniques that remove carbon from the atmosphere.

The conference explored both the feasibility of overshoot pathways and the legal frameworks that could help deliver them.

Researchers also discussed the potential consequences of a potential rise – and then fall – of global temperatures on climate action, society and the Earth’s climate systems.

Speaking during a plenary session, Prof Joeri Rogelj, a professor of climate science and policy at Imperial College London, said that “moving into a world where we exceed 1.5C and have to manage overshoot” was an exercise in “managing failure”.

He said that it was “essential” that this failure was acknowledged, explaining that this would help set out the need to “minimise and manage” the situation and clarify the implications for “near-term action” and “long-term [temperature] reversal”.

Below, Carbon Brief draws together some of the key talking points, new research and discussions that emerged from the event.

Defining overshoot

The study of temperature overshoot has grown in recent years as the prospects of limiting global temperature rise to 1.5C have dwindled.

Conference organiser Dr Carl-Friedrich Schleussner – a senior research scholar at the International Institute for Applied Systems Analysis (IIASA) – explained the event was designed to bring together different research communities working on a “new field of science”.

He told Carbon Brief:

“If we look at [overshoot] in isolation, we may miss important parts of the bigger picture. That’s why we also set out the conference with very broad themes and a very interdisciplinary approach.”

The conference was split between eight conference streams: mitigation ambition; carbon dioxide removal (CDR); Earth system responses; climate impacts; tipping points; adaptation; loss and damage; and legal implications.

There was also a focus on how to communicate the concept of overshoot.

In simple English, “overshoot” means to go past or beyond a limit. But, in climate science, the term implies both a failure to meet a target – as well as subsequent action to correct that failure.

Today, the term is most often deployed to describe future temperature trajectories that exceed the Paris Agreement’s 1.5C limit – and then come back down.

(In the Intergovernmental Panel on Climate Change’s (IPCC’s) fifth assessment cycle, completed in 2014, the term was used to describe a potential rise and then fall of CO2 concentrations above levels recommended to meet long-term climate goals. A recent “conceptual” review of overshoot noted this was because, at the time, CO2 concentrations were the key metric used to contextualise emissions reductions).

The plot below provides an illustration of three overshoot pathways. The most pronounced pathway sees global temperatures rise significantly above the 1.5C limit – before eventually falling back down again as carbon dioxide is pulled from the atmosphere at scale.

In the second and third pathways, global temperature rise breaches the limit by a smaller margin, before either falling enough just to stabilise around 1.5C, or dropping more dramatically due to larger-scale carbon removals.

Credit: Amended from Schleussner et al (2024).

In an opening address to delegates, Prof Jim Skea, who is the current chair of the IPCC, acknowledged the scientific interpretation of overshoot was not intuitive to non-experts.

“The IPCC has mainly used two words in relation to overshoot – “exceeding” and “limiting”. To a lay person, these can sound like opposites. Yet we know that a single emissions pathway can both exceed 1.5C in the near term and limit warming to 1.5C in the long term.”

Noting that different research communities were using the term differently, Skea urged researchers to be precise with terminology and stick to the IPCC’s definition of overshoot:

“We should give some thought to communication and keep this as simple as possible. When I look at texts, I hear more poetic words like “surpassing” and “breaching”. I would urge you to keep the range of terms as small as possible and make sure that we’re absolutely using them consistently.”

In the glossary for its latest assessment cycle, AR6, the IPCC defines “overshoot” pathways as follows:

Overshoot pathways ragout

IIASA’s Schleussner stressed that not all pathways that go beyond 1.5C qualify as overshoot pathways:

“The most important understanding is that overshoot is not any pathway that exceeds 1.5C. An overshoot pathway is specific to this being a period of exceedance. It is going to come back down below 1.5C.”

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Mitigation ambition and 1.5C viability

Perhaps the most prominent topic during the conference was the implications of overshoot for global ambition to cut carbon emissions and the viability of the 1.5C limit.

Opening the conference, IIASA director general Prof Hans Joachim Schellnhuber shared his personal view that “1.5C is dead, 2C is in agony and 3C is looming”.

In a pre-recorded keynote speech, Ralph Regenvanu, Vanuatu’s minister for climate change, called for a rejection of the “normalisation of overshoot” and argued that “we must treat 1.5C as the absolute limit that it is” and avoid backsliding. He added:

“Minimising peak warming must be our lodestar, because every tenth of a degree matters.”

Prof Skea opened his keynote with some theology:

“I’m going to start with the prayer of St Augustine as he struggled with his youthful longings: ‘Lord grant me chastity and continence, but not yet.’ And it does seem that this is the way that the world as a whole is thinking about 1.5C: ‘Lord, limit warming to 1.5C above pre-industrial levels, but not yet.’”

Referencing the “lodestar” mentioned by Regenvanu, Skea warned that it is light years away and, “unless we act with a sense of urgency, [1.5C is] likely to remain just as remote”.

Speaking to Carbon Brief on the sidelines of the conference, Skea added:

“We are almost certain to exceed 1.5C and the viability of 1.5C is now much more referring to the long-term potential to limit it through overshoot.”

Schleussner told Carbon Brief that the framing of 1.5C in the conference is “one that further solidifies 1.5C as the long-term limit and, therefore, provides a backstop against the idea of reducing or backsliding on targets”.

If warming is going to surpass 1.5C, the next question is when temperatures are going to be brought back down again, Schleussner added, noting that there has been no “direct” guidance on this from climate policy:

“The [Paris Agreement’s] obligation to “pursue efforts” [to limit global temperature rise by 1.5C] points to doing it as fast as possible. Scientifically, we can determine what this means – and that would be this century. But there’s no clear language that gives you a specific date. It needs to be a period of overshoot – that is clear – and it should be as short as possible.”

In a parallel session on the “highest possible mitigation ambition under overshoot”, Prof Joeri Rogelj, professor of climate science and policy at Imperial College London, outlined how the recent ruling from the International Court of Justice (ICJ) provides guidance to countries on the level of ambition in their climate pledges under the Paris Agreement, known as “nationally determined contributions” (NDCs). He explained:

“[The ruling] highlights that the level of NDC ambition is not purely discretionary to a state and that every state must do its utmost to ensure its NDC reflects the highest possible ambition to meet the Paris Agreement long-term temperature goal.”

Rogelj presented some research – due to be published in the journal Environmental Research Letters – on translating the ICJ’s guidance “into a framework that can help us to assess whether an NDC indeed is following a standard of conduct that can represent the highest level of ambition”. He showed some initial results on how the first two rounds of NDCs measure up against three “pillars” covering domestic, international and implementation considerations.

In the same session, 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, warned that the concept of returning temperatures back down to 1.5C after an overshoot is “not a political project yet”.

He explained that there is “no shared understanding that, actually, the world is aiming for net-negative”, where emissions cuts and CDR together mean that more carbon is being taken out of the atmosphere than is being added. This is necessary to achieve a decline in global temperatures after surpassing 1.5C.

This lack of understanding includes developed countries, which “you would probably expect to be the frontrunners”, Geden said, noting that Denmark is the “only developed country that has a quantified net-negative target” of emission reductions of 110% in 2050, compared to 1990 levels. (Finland also has a net-negative target, while Germany announced its intention to set one last year. In addition, a few small global-south countries, such as Panama, Suriname and Bhutan, have already achieved net-negative.)

Geden pondered whether developed countries are a “little bit wary to commit to going to net-negative territory because they fear that once they say -110%, some countries will immediately demand -130% or -150%” to pay back a larger carbon debt.

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Carbon removal

To achieve a decline in global temperatures after an initial breach of 1.5C would require the world to reach net-negative emissions overall.

There is a wide range of potential techniques for removing CO2 from the atmosphere, such as afforestation, direct air capture and bioenergy with carbon capture and storage (BECCS). Captured carbon must be locked away indefinitely in order to be effective at reducing global temperatures.

However, despite its importance in achieving net-negative emissions, there are “huge knowledge gaps around overshoot and carbon dioxide removal”, Prof Skea told Carbon Brief. He continued:

“As it’s very clear from the themes of this conference, we don’t altogether understand how the Earth would react in taking carbon dioxide 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.”

Skea notes that the seventh assessment cycle of the IPCC, which is just getting underway, will “start to fill these knowledge gaps without prejudging what the appropriate policy response should be”.

Prof Kristie Ebi, Dr Jonathan Donges. Prof Debra Roberts, Prof Deliang Chen, Dr Matt Gidden, Dr Annika Högner and Dr Keywan Riahi at a plenary session at the Overshoot Conference.
Prof Kristie Ebi, Dr Jonathan Donges, Prof Debra Roberts, Prof Deliang Chen, Dr Matt Gidden, Dr Annika Högner and Dr Keywan Riahi at a plenary session at the Overshoot Conference. Credit: IIASA

Prof Nebojsa Nakicenovic, an IIASA distinguished emeritus research scholar, told Carbon Brief that his “major concern” was whether there would be an “asymmetry” in how the climate would respond to large-scale carbon removal, compared to its response to carbon emissions.

In other words, he explained, would global temperatures respond to carbon removal “on the way down” in the same way they did “on the way up” to the world’s carbon emissions.

Nakicenovic noted that overshoot requires a change in focus to approaching the 1.5C limit “from above, rather than below”.

Schleussner made a similar point to Carbon Brief:

“We may fail to pursue [1.5C] from below, but it doesn’t relieve us from the obligation to then pursue it from above. I think that’s also a key message and a very strong overarching message that’s going to come out from the conference that we see…that pursuing an overshoot and then decline trajectory is both an obligation, but it also is well rooted in science.”

Reporting back to the plenary from one of the parallel sessions on CDR, Dr Matthew Gidden, deputy director of the Joint Global Change Research Institute at the Pacific Northwest National Laboratory, also noted another element of changing focus:

“When we’re talking about overshoot, we have become used to, in many cases, talking about what a net-zero world looks like. And that’s not a world of overshoot. That’s a world of not returning from a peak. And so communicating instead about a net-negative world is something that we could likely be shifting to in terms of how we’re communicating our science and the impacts that are coming out of it.”

On the need for both CDR and emissions cuts, Gidden noted that the discussions in his session emphasised that “CDR should not be at the cost of mitigation ambition”. But, he added, there is still the question of how “we talk about emission reductions needed today, but also likely dependence on CDR in the future”.

In a different parallel session, Prof Geden also made a similar point, noting that “we have to shift CDR from being seen as a barrier to ambition to an enabler of even higher ambition, but not doing that by betting on ever more CDR”.

Among the research presented in the parallel sessions on CDR was a recent study by Dr Jay Fuhrman from the JGCRI on the regional differences in capacity to deploy large-scale carbon removal. Ruben Prütz, from the Potsdam Institute for Climate Impact Research, presented on the risks to biodiversity from large-scale land-based CDR, which – in some cases – could have a larger impact than warming itself.

In another talk, the University of Oxford’s Dr Rupert Stuart-Smith explored how individual countries are “depending very heavily on [carbon] removals to meet their climate targets”. Stuart-Smith was a co-author on an “initial commentary” on the legal limits of CDR, published in 2023. This has been followed up with a “much more detailed legal analysis”, which should be published “very soon”, he added.

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Impacts of overshoot

Since the Paris Agreement and the call for the IPCC to produce a special report on 1.5C, research into the impacts of warming at the aspirational target has become commonplace.

Similarly, there is an abundance of research into the potential impacts at other thresholds, such as 2C, 3C and beyond.

However, there is comparatively little research into how impacts are affected by overshoot.

The conference included talks on some published research into overshoot, such as the chances of irreversible glacier loss and lasting impacts to water resources. There were also talks on work that is yet to be formally published, such as the risks of triggering interacting tipping points under overshoot.

Speaking in a morning plenary, Prof Debra Roberts, a coordinating lead author on the IPCC’s forthcoming special report on climate change and cities and a former co-chair of Working Group II, highlighted the need to consider the implications of different durations and peak temperatures of overshoot.

For example, she explained, it is “important to know” whether the impacts of “overshoot for 10 years at 0.2C above 1.5C are the same as 20 years at 0.1C of overshoot”.

Discussions during the conference noted that the answer may be different depending on the type of impact. For heat extremes, the peak temperature may be the key factor, while the length of overshoot will be more relevant for cumulative impacts that build up over time, such as sea level rise.

Similarly, if warming is brought back down to 1.5C after overshoot, what happens next is also significant – whether global temperature is stabilised or net-negative emissions continue and warming declines further. Prof Schleussner told Carbon Brief:

“For example, with coastal adaptation to sea level rise, the question of how fast and how far we bring temperatures back down again will be decisive in terms of the long-term outlook. Knowing that if you stabilise that around 1.5C, we might commit two metres of sea level rise, right? So, the question of how far we can and want to go back down again is decisive for a long-term perspective.”

One of the eight themes of the conference centred specifically on the reversibility or irreversibility of climate impacts.

In his opening speech, Vanuatu’s Ralph Regenvanu warned that “overshooting 1.5C isn’t a temporary mistake, it is a catalyst for inescapable, irreversible harm”. He continued:

“No level of finance can pull back the sea in our lifetimes or our children’s. There is no rewind button on a melted glacier. There is no time machine for an extinct species. Once we cross these tipping points, no amount of later ‘cooling’ can restore our sacred reefs, it cannot regrow the ice that already vanished and it cannot bring back the species or the cultures erased by the rising tides.”

As an example of a “deeply, deeply irreversible” impact, Dr Samuel Lüthi, a postdoctoral research fellow in the Institute of Social and Preventive Medicine at the University of Bern, presented on how overshoot could affect heat-related mortality.

Using mortality data from 850 locations across the world, Lüthi showed how projections under a pathway where warming overshoots 1.5C by 0.1-0.3C, before returning to 1.5C by 2100 has 15% more heat-related deaths in the 21st century than a pathway with less than 0.1C of overshoot.

His findings also suggested that “10 years of 1.6C is very similar [in terms of impacts] to five years of 1.7C”.

Extreme heat also featured in a talk by Dr Yi-Ling Hwong, a research scholar at IIASA, on the implications of using solar geoengineering to reduce peak temperatures during overshoot.

She showed that a world where a return to 1.5C had been achieved through geoengineering would see different impacts from a world where 1.5C was reached through cutting emissions. For example, in her modelling study, while geoengineering restores rainfall levels for some regions in the global north, significant drying “is observed in many regions in the global south”.

Similarly, a world geoengineered to 1.5C would see extreme nighttime heat in some tropical regions that is more severe than in a 2C world with no geoengineering, Hwong added.

In short, she said, “this implies the risk of creating winners and losers” under solar geoengineering and “raises concerns about equity and accountability that need to be considered”.

After describing how overshoot features in the outlines of the forthcoming AR7 reports in his opening speech, Prof Skea told Carbon Brief that he expects a “surge of papers” on overshoot in time to be included.

But it was important to emphasise that a “lot of the science that people have been carrying out is relevant within or without an overshoot”, he added:

“At points in the future, we are not going to know whether we’re in an overshoot world or just a high-emissions world, for example. So a lot of the climate research that’s been done is relevant regardless of overshoot. But overshoot is a new kind of dimension because of this issue of focus on 1.5C and concerns about its viability.”

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Adaptation

The implications of overshoot temperature pathways for efforts to prepare cities, countries and citizens for the impacts of climate change remains an under-researched field.

Speaking in a plenary, Prof Kristie Ebi a professor at the University of Washington’s Center for Health and the Global Environment – described research into adaptation and overshoot as “nascent”. However, she stressed that preparing society for the impacts associated with overshoot pathways was as important as bringing down emissions.

She told Carbon Brief that there were “all kinds of questions” about how to approach “effective” adaptation under an overshoot pathway, explaining:

“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.”

IIASA’s Schleussner told Carbon Brief that the scientific community was only just “beginning to appreciate” the need to understand and “quantify” the implications of different overshoot pathways on adaptation.

In a parallel session, Dr Elisabeth Gilmore, associate professor in environmental engineering and public policy at Carleton University in Canada, made the case for overshoot modelling pathways to take greater account of political considerations.

“Not just, but especially, in situations of overshoot, we need to start thinking about this as much as a physical process as a socio-political process…If we don’t do this, we are really missing out on some key uncertainties.”

Current scenarios used in climate research – including the Shared Socioeconomic Pathways and Representative Concentration Pathways – are “a bit quiet” when it comes to thinking about governance, institutions and peace and conflict, Gilmore said. She added:

“Political institutions, legitimacy and social cohesion continue to shift over time and this is really going to shape how much we can mitigate, how much we adapt and especially how we would recover when adding in the dimension of overshoot.”

Gilmore argued that, from a social perspective, adaptation needs are greatest “before the peak” of temperature rise – because this is when society can build the resilience to “get to the other side”. She said:

“Orthodoxy in adaptation [research] that you always want to plan for the worst [in the context of adaptation, peak temperature rise]… But we don’t really know what this peak is going to be – and we know that the politics and the social systems are much more messy.”

Dr Marta Mastropietro, a researcher at Politecnico di Milano in Italy, presented the preliminary results of a study that used emulators – simple climate models – to explore how human development might be impacted under low, medium and high overshoot pathways.

Mastropietro noted how, under all overshoot scenarios studied, both the drop to the human development index (HDI) – an index which incorporates health, knowledge and standard of living – and uncertainty increases as the peak temperature increases.

However, she said “the most important takeaway” from the preliminary results was around society’s constrained ability to recover from damage.

“This percentage of damages that are absorbed is always less than 50%. So, even in the most optimistic scenarios of overshoot, we will not be able to reabsorb these damages, not even half of them. And this is considering a damage function which does not consider irreversible impacts like sea level rise.”

Meanwhile, Dr Inês Gomes Marques from the University of Lisboa in Portugal, shared the results of an as-yet-unpublished study investigating whether the Lisbon metropolitan area holds enough public spaces to offer heatwave relief to the population under overshoot scenarios. The 1,900 “climate refugia” counted by researchers included schools, museums and churches.

Marques noted that most of the population were found to be within one kilometre of a “climate refugia” – but noted that “nuances” would need to be added to the analysis, including a function which considers the limited mobility of older citizens.

She explained that the researchers were aiming to “establish a framework” for this type of analysis that would be relevant to both the science community and municipalities tasked with adaptation. She added:

“The main point is that we need to think about this now, because we will face some big problems if we don’t”.

Delegates attend a poster session at the Overshoot Conference. Credit: IIASA
Delegates attend a poster session at the Overshoot Conference. Credit: IIASA

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Legal implications and loss and damage

Significant attention was given throughout the conference to the legal considerations of the breach of – and impetus to return to – the Paris Agreement’s 1.5C warming limit.

This included discussions about how the international legal frameworks should be updated for an “overshoot” world where countries would need to pursue “net-negative” strategies to bring temperatures down to 1.5C.

There were also discussions around governance of geoengineering technologies and the fairness and justice considerations that arise from the real-world impacts of breached targets.

The conference was being held just months after the ICJ’s advisory decision that limiting temperature increase to 1.5C should be considered countries’ “primary temperature goal”.

IIASA’s Shleussner told Carbon Brief that the decision provided “clarity” that countries had a “clear obligation to bring warming back to 1.5C”. He added:

“We may fail to pursue it from below, but it doesn’t relieve us from the obligation to then pursue it from above.”

Prof Lavanya Rajamani, professor of international environmental law at the University of Oxford, insisted that “1.5C was very much alive and well in the legal world”, but noted there were “very significant limits” to what could be achieved through the UN Framework Convention for Climate Change (UNFCCC) – the global treaty for coordinating the response to climate change – both today and in the future.

Summarising discussions around how countries can be pushed to deliver the “highest possible ambition” in future climate plans submitted to the UN, Rajamani urged delegates to be “tempered in [its] expectations of what we’re going to get from the international regime”. She added:

“Changing the narratives and practices at the national level are far more likely to filter up to the international level than trying to do it from a top-down perspective.”

In a parallel session, Prof Christina Voigt, a professor of international law at the University of Oslo, pointed out that overshoot would require countries to aspire beyond “net-zero emissions” as “the end climate goal” in national plans.

Stabilising emissions at “net-zero” by mid-century would result in warming above 1.5C, she explained, whereas “net-negative” emissions are required to deliver overshoot pathways that return temperatures to below the Paris Agreement’s aspirational limit. She continued:

“We will need frontrunners. Leaders, states, regions would need to start considering negative-emission benchmarks in their climate policies and laws from around mid-century. There will be an expectation that developed country parties take the lead and explore this ‘negativity territory’.”

Voigt added that it was “critical” that nations at the UNFCCC create a “shared understanding” that 1.5C remains the “core target” for nations to aim for, even after it has been exceeded. One possible place for such discussions could be at the 2028 global stocktake, she noted.

She said there would need to be more regulation to scale up CDR in a way that addresses “environmental and social challenges” and an effort to “recalibrate policies and measures” – including around carbon markets – to deliver net-negative outcomes.

In a presentation exploring governance of solar radiation management (SRM), Ewan White, a DPhil student in environmental law at the University of Oxford, said the ICJ’s recent advisory opinion could be interpreted to be “both for and against” solar geoengineering.

Countries tasked with drawing up global rules around SRM in an overshoot world would need to take a “holistic approach to environmental law”, White said. In his view, this should take into account international legal obligations beyond the Paris Agreement and consider issues of intergenerational equity, biodiversity protection and nations’ duty to cooperate.

Dr Shonali Pachauri, research group leader at IIASA, provided an overview of the equity and justice implications that might arise in an overshoot world.

First, she said that delays to emissions reductions today are “shifting the burden” to future generations and “others within this generation” – increasing the need for “corrective justice” and potential loss-and-damage payments.

Second, she said that adaptation efforts would need to increase – which, in turn, would “threaten mitigation ambition” given “constrained decision-making”.

Finally, she pointed to resource consumption issues that might arise in a world of overshoot:

“The different technologies that one might use for CDR often depend on the use of land, water, other materials – and this, of course, then means competing with many other uses [of resources].”

A separate stream focused on loss and damage. Session chair Dr Sindra Sharma, international policy lead at the Pacific Islands Climate Action Network, noted that the concept of loss and damage was “fundamentally transformed” by overshoot – adding there were “deep issues of justice and equity”.

However, Sharma said that the literature on loss and damage “has not yet deeply engaged with the specific concept of overshoot” despite it being “an important, interconnected issue”.

Sessions on loss and damage explored the existence of “hard social limits” under future overshoot scenarios, insurance and the need to bring more factors into assessments of habitability, including biophysical and social-economic constraints.

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Communication challenges and next steps

At the conference, scientists and legal experts collaborated on a series of statements that summarised discussions at the conference – one for each research theme and an overarching umbrella statement.

IIASA’s Schleussner told Carbon Brief that the statements represented a “key outcome of the conference” that could provide a “framework” to guide future research.

Nevertheless, he noted that statements are a “work in progress” and set to be “further refined” following feedback from experts not able to attend the conference.

At the time of going to press, the overarching conference statement read as follows:

“Global warming above 1.5C will increase irreversible and unacceptable losses and damages to people, societies and the environment.

“It is imperative to minimise both the maximum warming and duration of overshoot above 1.5C to reduce additional risks of human rights violations and causing irreversible social, ecological and Earth system changes including transgressing tipping points.

“This is required by international law and possible by removing CO2 from the atmosphere and further reducing remaining greenhouse emissions.”

Conference organisers also pointed delegates to an open call for research on “pathways and consequences of overshoot” in the journal Environmental Research Letters. The special issue will be guest edited by a number of scientists who played a key role in the conference.

Meanwhile, communications experts at the conference discussed the challenges inherent in conveying overshoot science to non-experts, noting potential confusion around the word “overshoot” and the difficulties in explaining that the 1.5C limit, while breached, was still a goal.

Holly Simpkin, communications manager at the Potsdam Institute for Climate Impact Research, urged caution when communicating overshoot science to the general public:

“I don’t know whether ‘overshoot’ is an effective communication framing. It is an important scientific question, but when it comes to near-term action and the requirements that an ambitious overshoot pathway would ask of us, emissions are what are in our control.

“We could spend 10 more years defining this and, actually, it’s quite complex…I think it’s better to be honest about that and to try to be more simple in that frame of communication, knowing that this community is doing a wealth of work that provides a technical basis for those discussions.”

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Overshoot: Exploring the implications of meeting 1.5C climate goal ‘from above’

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Greenhouse Gases

Analysis: UK renewables enjoy record year in 2025 – but gas power still rises

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The UK’s fleet of wind, solar and biomass power plants all set new records in 2025, Carbon Brief analysis shows, but electricity generation from gas still went up.

The rise in gas power was due to the end of UK coal generation in late 2024 and nuclear power hitting its lowest level in half a century, while electricity exports grew and imports fell.

In addition, there was a 1% rise in UK electricity demand – after years of decline – as electric vehicles (EVs), heat pumps and data centres connected to the grid in larger numbers.

Other key insights from the data include:

  • Electricity demand grew for the second year in a row to 322 terawatt hours (TWh), rising by 4TWh (1%) and hinting at a shift towards steady increases, as the UK electrifies.
  • Renewables supplied more of the UK’s electricity than any other source, making up 47% of the total, followed by gas (28%), nuclear (11%) and net imports (10%).
  • The UK set new records for electricity generation from wind (87TWh, +5%), solar (19TWh, +31%) and biomass (41TWh, +2%), as well as for renewables overall (152TWh, +6%).
  • The UK had its first full year without any coal power, compared with 2TWh of generation in 2024, ahead of the closure of the nation’s last coal plant in September of that year.
  • Nuclear power was at its lowest level in half a century, generating just 36TWh (-12%), as most of the remaining fleet paused for refuelling or outages.

Overall, UK electricity became slightly more polluting in 2025, with each kilowatt hour linked to 126g of carbon dioxide (gCO2/kWh), up 2% from the record low of 124gCO2/kWh, set last year.

The National Energy System Operator (NESO) set a new record for the use of low-carbon sources – known as “zero-carbon operation” – reaching 97.7% for half an hour on 1 April 2025.

However, NESO missed its target of running the electricity network for at least 30 minutes in 2025 without any fossil fuels.

The UK inched towards separate targets set by the government, for 95% of electricity generation to come from low-carbon sources by 2030 and for this to cover 100% of domestic demand.

However, much more rapid progress will be needed to meet these goals.

Carbon Brief has published an annual analysis of the UK’s electricity generation in 2024, 2023, 2021, 2019, 2018, 2017 and 2016.

Record renewables

The UK’s fleet of renewable power plants enjoyed a record year in 2025, with their combined electricity generation reaching 152TWh, a 6% rise from a year earlier.

Renewables made up 47% of UK electricity supplies, another record high. The rise of renewables is shown in the figure below, which also highlights the end of UK coal power.

While the chart makes clear that gas-fired electricity generation has also declined over the past 15 years, there was a small rise in 2025, with output from the fuel reaching 91TWh. This was an increase of 5TWh (5%) and means gas made up 28% of electricity supplies overall.

The rise in gas-fired generation was the result of rising demand and another fall in nuclear power output, which reached the lowest level in half a century, while net imports and coal also declined.

UK electricity supplies by source 2010-2025
UK electricity supplies by source 2010-2025, terawatt hours (TWh). Net imports are the sum of imports minus exports. Renewables include wind, biomass, solar and hydro. The chart excludes minor sources, such as oil, which makes up less than 2% of the total. Source: Carbon Brief analysis of data from NESO and DESNZ.

The year began with the UK’s sunniest spring and by mid-December had already become the sunniest year on record. This contributed to a 5TWh (31%) surge in electricity generation from solar power, helped by a jump of roughly one-fifth in installed generating capacity.

The new record for solar power generation of 19TWh in 2025 comes after years of stagnation, with electricity output from the technology having climbed just 15% in five years.

The UK’s solar capacity reached 21GW in the third quarter of 2025. This is a substantial increase of 3 gigawatts (GW) or 18% year-on-year.

These are the latest figures available from the Department for Energy Security and Net Zero (DESNZ). The DESNZ timeseries has been revised to reflect previously missing data.

UK wind power also set a new record in 2025, reaching 87TWh, up 4TWh (5%). Wind conditions in 2025 were broadly similar to those in 2024, with the uptick in generation due to additional capacity.

The UK’s wind capacity reached 33GW in the third quarter of 2025, up 1GW (4%) from a year earlier. The 1.2GW Dogger Bank A in the North Sea has been ramping up since autumn 2025 and will be joined by the 1.2GW Dogger Bank B in 2026, as well as the 1.4GW Sofia project.

These sites were all awarded contracts during the government’s third “contracts for difference” (CfD) auction round and will be paid around £53 per megawatt hour (MWh) for the electricity they generate. This is well below current market prices, which currently sit at around £80/MWh.

Results from the seventh auction round, which is currently underway, will be announced in January and February 2026. Prices are expected to be significantly higher than in the third round, as a result of cost inflation.

Nevertheless, new offshore wind capacity is expected to be deliverable at “no additional cost to the billpayer”, according to consultancy Aurora Energy Research.

The UK’s biomass energy sites also had a record year in 2025, with output nudging up by 1TWh (2%) to 41TWh. Approximately two-thirds (roughly 27TWh) of this total is from wood-fired power plants, most notably the Drax former coal plant in Yorkshire, which generated 15TWh in 2024.

The government recently awarded new contracts to Drax that will apply from 2027 onwards and will see the amount of electricity it generates each year roughly halve, to around 6TWh. The government is also consulting on how to tighten sustainability rules for biomass sourcing.

Rising demand

The UK’s electricity demand has been falling for decades due to a combination of more efficient appliances and lightbulbs, as well as ongoing structural shifts in the economy.

Experts have been saying for years that at some point this trend would be reversed, as the UK shifts to electrified heat and transport supplies using EVs and heat pumps.

Indeed, the Climate Change Committee (CCC) has said that demand would more than double by 2050, with electrification forming a key plank of the UK’s efforts to reach net-zero.

Yet there has been little sign of this effect to date, with electricity demand continuing to fall outside single-year rebounds after economic shocks, such as the 2020 Covid lockdowns.

The data for 2025 shows hints that this turning point for electricity demand may finally be taking place. UK demand increased by 4TWh (1%) to 322TWh in 2025, after a 1TWh rise in 2024.

After declining for more than two decades since a peak in 2005, this is the first time in 20 years that UK demand has gone up for two years in a row, as shown in the figure below.

Annual UK electricity demand 2000-2025
Annual UK electricity demand 2000-2025, terawatt hours (TWh). The truncated y-axis shows recent changes more clearly. Source: Carbon Brief analysis of data from NESO and DESNZ.

While detailed data on underlying electricity demand is not available, it is clear that the shift to EVs and heat pumps is playing an important role in the recent uptick.

There are now around 1.8m EVs on the UK’s roads and another 1m plug-in hybrids. Of this total, some 0.6m new EVs and plug-in hybrids were bought in 2025 alone. In addition, around 100,000 heat pumps are being installed each year. Sales of both technologies are rising fast.

Estimates from the NESO “future energy scenarios” point to an additional 2.0TWh of demand from new EVs in 2025, compared with 2024. They also suggest that newly installed heat pumps added around 0.2TWh of additional demand, while data centres added 0.4TWh.

By 2030, NESO’s scenarios suggest that electricity use for these three sources alone will rise by around 30TWh, equivalent to around 10% of total demand in 2025.

EVs would have the biggest impact, adding 17TWh to demand by 2030, NESO says, with heat pumps adding another 3TWh. Data-centre growth is highly uncertain, but could add 12TWh.

Gas growth

At the same time as UK electricity demand was growing by 4TWh in 2025, the country also lost a total of 10TWh of supply as a result of a series of small changes.

First, 2025 was the UK’s first full year without coal power since 1881, resulting in the loss of 2TWh of generation. Second, the UK’s nuclear fleet saw output falling to the lowest level in half a century, after a series of refuelling breaks and outages, which cut generation by 5TWh.

Third, after a big jump in imports in 2024, the UK saw a small decline in 2025, as well as a more notable increase in the amount of electricity exported to other countries. This pushed the country’s net imports down by 1TWh (4%).

The scale of cross-border trade in electricity is expected to increase as the UK has significantly expanded the number of interconnections with other markets.

However, the government’s clean-power targets for 2030 imply that the UK would become a net exporter, sending more electricity overseas than it receives from other countries. At present, it remains a significant net importer, with these contributions accounting for 109% of supplies.

Finally, other sources of generation – including oil – also declined in 2025, reducing UK supplies by another 2TWh, as shown in the figure below.

Change in electricity supply by source between 2024 and 2025
Change in electricity supply by source between 2024 and 2025, TWh. Source: Carbon Brief analysis of data from NESO and DESNZ.

These losses in UK electricity supply were met by the already-mentioned increases in generation from gas, solar, wind and biomass, as shown in the figure above.

The government’s targets for decarbonising the UK’s electricity supplies will face similar challenges in the years to come as electrification – and, potentially, data centres – continue to push up demand.

All but one of the UK’s existing nuclear power plants are set to retire by 2030, meaning the loss of another 27TWh of nuclear generation.

This will be replaced by new nuclear capacity, but only slowly. The 3.2GW Hinkley Point C plant in Somerset is set to start operating in 2030 at the earliest and its sister plant, Sizewell C in Suffolk, not until at least another five years later.

Despite backing from ministers for small modular reactors, the timeline for any buildout is uncertain, with the latest government release referring to the “mid-2030s”.

Meanwhile, biomass generation is likely to decline as the output of Drax is scaled back from 2027.

Stalling progress

Taken together, the various changes in the UK’s electricity supplies in 2025 mean that efforts to decarbonise the grid stalled, with a small increase in emissions per unit of generation.

The 2% increase in carbon intensity to 126gCO2/kWh is illustrated in the figure below and comes after electricity was the “cleanest ever” in 2024, at 124gCO2/kWh.

Carbon intensity of UK electricity supplies
Carbon intensity of UK electricity supplies, gCO2/kWh. Source: Carbon Brief analysis of data from NESO and DESNZ.

The stalling progress on cleaning up the UK’s grid reflects the balance of record renewables, rising demand and rising gas generation, along with poor output from nuclear power.

Nevertheless, a series of other new records were set during 2025.

NESO ran the transmission grid on the island of Great Britain (GB; namely, England, Wales and Scotland) with a record 97.7% “zero-carbon operation” (ZCO) on 1 April 2025.

Note that this measure excludes gas plants that also generate heat – known as combined heat and power, or CHP – as well as waste incinerators and all other generators that do not connect to the transmission network, which means that it does not include most solar or onshore wind.

NESO was unable to meet its target – first set in 2019 – for 100% ZCO during 2025, meaning it did not succeed in running the transmission grid without any fossil fuels for half an hour.

Other records set in 2025 include:

  • GB ran on 100% clean power, after accounting for exports, for a record 87 hours in 2025, up from 64.5 hours in 2024.
  • Total GB renewable generation from wind, solar, biomass and hydro reached a record 31.3GW from 13:30-14:00 on 4 July 2025, meeting 84% of demand.
  • GB wind generation reached a record 23.8GW for half an hour on 5 December 2025, when it met 52% of GB demand.
  • GB solar reached a record 14.0GW at 13:00 on 8 July 2025, when it met 40% of demand.

The government has separate targets for at least 95% of electricity generation and 100% of demand on the island of Great Britain to come from low-carbon sources by 2030.

These goals, similar to the NESO target, exclude Northern Ireland, CHP and waste incinerators. However, they include distributed renewables, such as solar and onshore wind.

These definitions mean it is hard to measure progress independently. The most recent government figures show that 74% of qualifying generation in GB was from low-carbon sources in 2024.

Carbon Brief’s figures for the whole UK show that low-carbon sources made up a record 58% of electricity supplies overall in 2025, up marginally from a year earlier.

Similarly, low-carbon sources made up 65% of electricity generation in the UK overall. This was unchanged from a year earlier.

Methodology

The figures in the article are from Carbon Brief analysis of data from DESNZ Energy Trends, chapter 5 and chapter 6, as well as from NESO. The figures from NESO are for electricity supplied to the grid in Great Britain only and are adjusted here to include Northern Ireland.

In Carbon Brief’s analysis, the NESO numbers are also adjusted to account for electricity used by power plants on site and for generation by plants not connected to the high-voltage national grid.

NESO already includes estimates for onshore windfarms, but does not cover industrial gas combined heat and power plants and those burning landfill gas, waste or sewage gas.

Carbon intensity figures from 2009 onwards are taken directly from NESO. Pre-2009 estimates are based on the NESO methodology, taking account of fuel use efficiency for earlier years.

The carbon intensity methodology accounts for lifecycle emissions from biomass. It includes emissions for imported electricity, based on the daily electricity mix in the country of origin.

DESNZ historical electricity data, including years before 2009, is adjusted to align with other figures and combined with data on imports from a separate DESNZ dataset. Note that the data prior to 1951 only includes “major” power producers.

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Ricky Bradley named Citizens’ Climate Executive Director after strategic and legislative progress during interim leadership role

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Ricky Bradley named Citizens’ Climate Executive Director after strategic and legislative progress during interim leadership role

Dec. 22, 2025 – After a six month interim period, Ricky Bradley has been appointed Executive Director of Citizens’ Climate Lobby and Citizens’ Climate Education. The decision was made by the CCL and CCE boards of directors in a unanimous vote during their final joint board meeting of 2025. 

“Citizens’ Climate Lobby is fortunate to have someone with Ricky Bradley’s experience, commitment, and demeanor to lead the organization,” said CCL board chair Bill Blancato. “I can’t think of anyone with as much knowledge about CCL and its mission who is held in such high regard by CCL’s staff and volunteers.”

Bradley has been active with Citizens’ Climate for more than 13 years. Prior to his former roles as Interim Executive Director and Vice President of Field Operations, he has also served as a volunteer Group Leader and volunteer Regional Coordinator, all of which ground him in Citizens’ Climate’s grassroots model. Bradley has also led strategic planning and implementation efforts at HSBC, helping a large team adopt new approaches and deliver on big organizational goals.

“We are confident that Ricky has the skills to guide CCL during a challenging time for organizations trying to make a difference on climate change,” Blancato added.

Since stepping into the Interim Executive Director role in July 2025, Bradley has led Citizens’ Climate through a season of high volunteer engagement and effective advocacy on Capitol Hill. Under his leadership, CCL staff and volunteers organized a robust virtual lobby week with 300+ constituent meetings, despite an extended government shutdown, and executed a targeted mobilization to support the bipartisan passage of climate-friendly forestry legislation through the Senate Agriculture Committee.

“We have heard nothing but glowing descriptions of Ricky’s ability as a leader, as a manager, and as a team player,” said CCE board chair Dr. Sandra Kirtland Turner. “We’ve been absolutely thrilled with how Ricky’s brought the team together over the last six months to deliver on a new strategic plan for the organization.”

The strategic plan, which launched during CCL’s Fall Conference in November, details Citizens’ Climate’s unique role in the climate advocacy space, its theory of change for effectively moving federal climate legislation forward, and its strategic goals for 2026.

“Ricky has the heart of a CCLer and the strategic chops to take us into the next chapter as an organization,” Dr. Kirtland Turner said.

Bradley shared his vision for that next chapter in his conference opening remarks last month and, most recently, during the organization’s December monthly meeting.

“There’s a lot that we don’t control in today’s politics, but we do know who we are. The power of our persistent, nonpartisan advocacy is unmistakable,” Bradley said. “If we stay true to that, deepen our skills, and walk forward together, I know we’re going to meet this moment and deliver real results for the climate.”

CONTACT: Flannery Winchester, CCL Vice President of Marketing and Communications, 615-337-3642, flannery@citizensclimate.org

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Citizens’ Climate Lobby is a nonprofit, nonpartisan, grassroots advocacy organization focused on national policies to address climate change. Learn more at citizensclimatelobby.org.

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DeBriefed 19 December 2025:  EU’s petrol car U-turn; Trump to axe ‘leading’ research lab; What climate scientists are reading

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

This week

EU easing up

HITTING THE BREAKS: The EU “walked back” its target to ban the sale of petrol and diesel cars by 2035, “permitting some new combustion engine cars”, reported Agence-France Presse. Under the original plan, the bloc would have had to cut emissions entirely by 2035 on new vehicles, but will now only have to cut emissions by 90% by that date, compared to 2021 levels. However, according to the Financial Times, some car manufacturers have “soured” on the reversal.

ADJUSTING CBAM: Meanwhile, the Financial Times reported that the EU is making plans to “close loopholes” in the bloc’s carbon border adjustment mechanism (CBAM) before it goes into effect in January. CBAM is set to be the world’s first carbon border tax and has drawn ire from key trading partners. The EU has also finalised a plan to delay its anti-deforestation legislation for another year, according to Carbon Pulse.

Around the world

  • NCAR NO MORE: The Trump administration is moving to “dismantle” the National Center for Atmospheric Research in Colorado, said USA Today, describing it as “one of the world’s leading climate research labs”.
  • DEADLY FLOODS: The deadliest flash flooding in Morocco in a decade killed “at least” 37 people, while residents accused the government of “ignoring known flood risks and failing to maintain basic infrastructure”, reported Radio France Internationale.
  • FAILING GRADE: The past year was the “warmest and wettest” ever recorded in the Arctic, with implications for “global sea level rise, weather patterns and commercial fisheries”, according to the US National Oceanic and Atmospheric Administration’s 2025 Arctic report card, covered by NPR.
  • POWER TO THE PEOPLE: Reuters reported that Kenya signed a $311m agreement with an African infrastructure fund and India’s Power Grid Corporation for the “construction of two high-voltage electricity transmission lines” that could provide power for millions of people.
  • BP’S NEW EXEC: BP has appointed Woodside Energy Group’s Meg O’Neill as its new chief executive amid a “renewed push to…double down on oil and gas after retreating from an ambitious renewables strategy”, said Reuters.

29

The number of consecutive years in which the Greenland ice sheet has experienced “continuous annual ice loss”, according to a Carbon Brief guest post.


Latest climate research

  • Up to 4,000 glaciers could “disappear” per year during “peak glacier extinction”, projected to occur sometime between 2041 and 2055 | Nature Climate Change
  • The rate of sea level rise across the coastal US doubled over the past century | AGU Advances
  • Repression and criminalisation of climate and environmentally focused protests are a “global phenomena”, according to an analysis of 14 countries | Environmental Politics

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

Captured

The latest coal market report from the International Energy Agency said that global coal use will reach record levels in 2025, but will decline by the end of the decade. Carbon Brief analysis of the report found that projected coal use in China for 2027 has been revised downwards by 127m tonnes, compared to the projection from the 2024 report – “more than cancelling out the effects of the Trump administration’s coal-friendly policies in the US”. 

Spotlight

What climate scientists are curious about

This week, Carbon Brief spoke to climate scientists attending the annual meeting of the American Geophysical Union in New Orleans, Louisiana, about the most interesting research papers they read this year.

Their answers have been lightly edited for length and clarity.

Dr Christopher Callahan, assistant professor at Indiana University Bloomington

The most interesting research paper I read was a simple thought experiment asking when we would have known humans were changing the climate if we had always had perfect observations. The authors show that we could have detected a human influence on the climate as early as the 1880s, since we have a strong physical understanding of how those changes should look. This paper both highlights that we have been discernibly changing the climate for centuries and emphasises the importance of the modern climate observing network – a network that is currently threatened by budget cuts and staff shortages.

Prof Lucy Hutyra, distinguished professor at Boston University

The most interesting paper I read was in Nature Climate Change, where the researchers looked at how much mortality was associated with cold weather versus hot weather events and found that many more people died during cold weather events. Then, they estimated how much of a protective factor in the urban heat island is on those winter deaths and suggested that the winter benefits exceed the summer risks of mitigating extreme heat, so perhaps we shouldn’t mitigate extreme heat in cities. 

This paper got me in a tizzy…It spurred an exciting new line of research. We’ll be publishing a response to this paper in 2026. I’m not sure their conclusion was correct, but it raised really excellent questions.

Dr Kristina Dahl, vice president for science at Climate Central

This year was when we saw source attribution studies, such as Chris Callahan‘s, really start to break through and be able to connect the emissions of specific emitters…to the impact of those emissions through heat or some other sort of damage function. [This] is really game-changing.

What [Callahan’s] paper showed is that the emissions of individual companies have an impact on extreme heat, which then has an impact on the GDP of the countries experiencing that extreme heat. And so, for the first time, you can really say: “Company X caused this condition which then led to this economic damage.”

Dr Antonia Hadjimichael, assistant professor at Pennsylvania State University

It was about interdisciplinary work – not that anything in it is ground-shakingly new, but it was a good conversation around interdisciplinary teams and what makes them work and what doesn’t make them work. And what I really liked about it is that they really emphasise the role of a connector – the scientist that navigates this space in between and makes sure that the things kind of glue together…The reason I really like this paper is that we don’t value those scientists in academia, in traditional metrics that we have.

Dr Santiago Botía, researcher at Max Planck Institute for Biogeochemistry

The most interesting paper I’ve read this year was about how soil fertility and water table depth control the response to drought in the Amazon. They found very nicely how the proximity to soil water controls the anomalies in gross primary productivity in the Amazon. And, with that methodology, they could explain the response of recent droughts and the “greening” of the forest during drought, which is kind of a counterintuitive [phenomenon], but it was very interesting.

Dr Gregory Johnson, affiliate professor at the University of Washington

This article explores the response of a fairly coarse spatial resolution climate model…to a scenario in which atmospheric CO2 is increased at 1% a year to doubling and then CO2 is more gradually removed from the atmosphere…[It finds] a large release of heat from the Southern Ocean, with substantial regional – and even global – climate impacts. I find this work interesting because it reminds us of the important – and potentially nonlinear – roles that changing ocean circulation and water properties play in modulating our climate.

Cecilia Keating also contributed to this spotlight.

Watch, read, listen

METHANE MATTERS: In the Guardian, Barbados prime minister Mia Mottley wrote that the world must “urgently target methane” to avoid the worst impacts of climate change.

CLIMATE WRAPPED: Grist summarised the major stories for Earth’s climate in 2025 – “the good, the bad and the ugly”.

COASTING: On the Coastal Call podcast, a biogeochemist spoke about “coastal change and community resilience” in the eastern US’s Long Island Sound.

Coming up

Pick of the jobs

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 19 December 2025:  EU’s petrol car U-turn; Trump to axe ‘leading’ research lab; What climate scientists are reading appeared first on Carbon Brief.

DeBriefed 19 December 2025:  EU’s petrol car U-turn; Trump to axe ‘leading’ research lab; What climate scientists are reading

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