UK chancellor Rachel Reeves has unveiled the first spending review under the current Labour government, announcing funding for nuclear power, energy efficiency and carbon capture and storage (CCS).

A spending review establishes each ministry’s spending limits and priorities for the rest of the parliamentary term.

The Department of Energy Security and Net Zero (DESNZ) received one of the largest jumps in capital spending, despite energy secretary Ed Miliband reportedly being one of the last to agree to a spending settlement.

Before the final details had been announced, the Times was describing Miliband as one of the “biggest winners” from the process.

High-profile funding announcements in the Treasury’s spending review include £14.2bn for the Sizewell C new nuclear power plant in Suffolk, the first state-backed nuclear power station for decades.

Elsewhere, two new CCS clusters – Acorn and Viking – were allocated funding and railways across the nation were given a boost.

Below, Carbon Brief runs through the key announcements.

• Departmental spending
• Energy efficiency
• Energy infrastructure investment
  • GB Energy
  • New nuclear
  • Carbon capture and storage
• Transport
• Other announcements
  • R&D funding
  • Flood defences and farming funds
  • Foreign aid and climate finance
  • Response to climate-risks report

Departmental spending

Spending reviews are an opportunity for governments to stake out their priorities by setting the budgets for departments over the rest of this parliament.

Reeves’ spending review has been viewed by experts and media commentators as an opportunity to boost Labour’s flagging popularity and pursue some of its key manifesto commitments, including net-zero.

It covers plans for departmental “resource” spending – including day-to-day running costs – out to 2028-29 and “capital” spending out to 2029-30.

The latter includes injections of funding for infrastructure and public services, such as major clean-energy and transport projects.

In her speech launching the review, Reeves did not specifically mention the terms net-zero or climate change, but stressed the importance of achieving energy security via domestic, low-carbon power. “Clean energy” also featured prominently in the review document itself.

Overall, total departmental budgets are set to grow by 2.3% in real terms across the spending review period.

The Department for Energy Security and Net Zero (DESNZ) is expected to see a 16% increase in overall departmental spending, reaching £12.6bn in 2028-29.

(This does not include the boost in funding for Sizewell C nuclear plant, which will see a 15.6% increase thanks to a £14.2bn investment over the next five years. See: New nuclear.)

The chart below – taken from the spending review document – shows that while the absolute increase in spending on areas such as health, defence and education is higher, DESNZ is among the most highly prioritised in relative terms.

The review document emphasises that this increase in public money is necessary to mobilise private investment and “secure the UK’s electricity system with homegrown, clean power by 2030”.

Other departments that are also relevant for climate action have not seen the same overall increases in budget.

The Department for Transport (DfT) is set to see its overall departmental spending drop by 0.4%. However, the review notes that capital spending will increase, including more money for local low-carbon transport options and major rail projects.

The Department for Environment, Food and Rural Affairs (Defra) budget is also expected to fall overall, but support for “nature-friendly farming” is set to more than double over the review period.

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Energy efficiency

Leading up to the spending review, there had been speculation that the government might cut plans to invest £13.2bn on upgrading the nation’s homes under its “warm homes plan”, which had been a manifesto commitment ahead of last year’s election.

Such a move could have cost households more than £1.4bn a year in avoidable energy bills, according to analysis from thinktank the Energy and Climate Intelligence Unit (ECIU).

However, the spending review confirmed the pledged £13.2bn in funding for the scheme, covering spending between 2025-26 and 2029-30.

The government says this will help to cut bills by up to £600 per household through energy efficiency measures, heat pumps, solar panels and batteries. It will also help support tens of thousands of jobs across the country, the spending review adds.

According to innovation agency Nesta, the warm homes funding is roughly double the previous government’s commitment, amounting to a £6.6bn increase in government spending on home upgrades over the current parliament, compared with the previous one.

It will see around one-fifth of the nation’s housing stock upgraded by 2029, although to a varying degree.

Responding to the announcement, trade association Energy UK’s chief executive Dhara Vyas said in a statement:

“It’s also very important that millions of customers will see a direct benefit from today’s announcements. By reaffirming the funding to improve the energy efficiency of millions of homes and supporting the switch to cleaner heating alternatives, customers can expect warmer and more comfortable homes, cleaner air and cheaper bills – showing how the energy transition can improve their daily lives.”

Funding for the warm homes plan in the spending review follows £3.4bn in investment announced for the scheme at the autumn budget in 2024. At the time, Labour had said that this was just the “first step” in investment for decarbonisation and household energy efficiency within the scheme.

Further details for the warm homes plan will be confirmed in October, the spending review says.

Beyond energy efficiency, Reeves announced what she called the “biggest boost to investment in social and affordable housing in a generation”, confirming £39bn in funding for a 10-year affordable homes programme.

This will nearly double government spending on affordable housing, according to reporting earlier this week.

Miliband recently announced changes to the “future homes standard” that will mean almost all new homes will have to be built with rooftop solar as a default, high levels of energy efficiency and low-carbon heating, such as heat pumps.

As such, new properties built under the affordable homes programme will largely have to include energy efficiency measures and low-carbon energy technologies.

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Energy infrastructure investment

GB Energy

The spending review also confirms that it will allocate £8.3bn in funding for Great British Energy (GB Energy) and the linked GB Energy – Nuclear, another manifesto commitment.

It says this has been achieved by allocating £9.6bn in “additional financial transactions, such as loans and equity investments, to support growth”.

(It explains that “financial transactions” are designed to “allow government to invest alongside the private sector, through equity investments, loans and guarantees”. The document also says that GB Energy will be designated as a “public financial institution”.)

In addition to this top-line confirmation for GB Energy, the spending review also gives it an extra £300m in support for offshore wind supply chains.

This forms part of the “government’s investment in resilient and clean energy security, boosting domestic jobs, mobilising additional private investment and securing manufacturing facilities for critical clean energy supply chains such as floating offshore platforms”, it notes.

The spending review confirms up to £80m for port investment to support floating offshore wind deployment in Port Talbot in Wales, subject to final due diligence.

GB Energy funding follows on from Labour’s manifesto, promising investment into technologies such as floating offshore wind, as well as partnering with local authorities and the private sector to support the deployment of mature technologies.

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New nuclear

Ahead of the spending review, the chancellor announced a £14.2bn investment in the planned Sizewell C new nuclear power plant in Suffolk.

The plant is being jointly developed by the UK government with French state-owned utility firm EDF Energy, which is already building the Hinkley C plant in Somerset.

Each new plant will have a capacity of 3.2 gigawatts (GW), enough to power six million homes. During its construction, Sizewell C will provide 10,000 jobs, including 1,500 apprenticeships, according to the government.

In a statement earlier this week, energy secretary Ed Miliband said new nuclear was needed for energy security, lower bills and to help cut emissions. He said:

“We need new nuclear to deliver a golden age of clean-energy abundance, because that is the only way to protect family finances, take back control of our energy, and tackle the climate crisis.

“This is the government’s clean energy mission in action- investing in lower bills and good jobs for energy security.”

Speaking on BBC Radio 4’s Today programme following the investment announcement, Miliband stated that China would not be able to invest in the new nuclear plant in Suffolk. He further clarified that, while the majority of the investment would come from the UK government, there will also be private investment announced at a later date.

Sizewell C will be one of the first new nuclear power stations in the UK in decades, with no new nuclear power plants having opened since 1995 and all but one of the existing fleet expected to retire by the early 2030s.

The under-construction plant at Hinkley Point C is also being developed by EDF and is expected to serve as a “blueprint” for Sizewell C.

The Hinkley C plant is being funded via a “contract for difference” (CfD), under which EDF is responsible for the upfront investment costs, but will receive £92.50 per megawatt hour (MWh, 2012 prices) for each unit of electricity generated. (This will drop to £89.50/MWh in 2012 prices as a result of the Sizewell C project going ahead.)

EDF has reportedly accepted that Hinkley C will cost more than £40bn to complete, but has “rejected claims” that the Sizewell C scheme would cost a similar amount.

Sizewell C is due to be funded under the “regulated asset base” (RAB) model and so will not receive a CfD, but the details of this deal are not yet available. The final investment decision on the project is due later this summer, according to reports.

Additionally, the government announced Rolls-Royce has been selected to build small modular nuclear reactors (SMRs) following a “rigorous” two-year competition.

Rolls-Royce will partner with Great British Energy – Nuclear as part of the government’s industrial strategy, which will see £2.5bn invested over the spending review period.

The firm is expected to build three SMRs, with the first connecting to the grid “in the mid-2030s”, according to Rolls-Royce.

The spending review also included over £2.5bn for nuclear fusion. This will include support for the design and build of a prototype energy plant in Nottinghamshire.

The document notes that the government is providing a “pathway for privately led advanced nuclear technologies”, although details are not elaborated.

Great British Energy – Nuclear will shortly publish a new framework with the National Wealth Fund for exploring further investment opportunities for viable nuclear projects.

The spending review includes £13.9bn for the Nuclear Decommissioning Authority, to keep “former nuclear sites and facilities safe and secure as it decommissions sites and manages nuclear waste”.

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Carbon capture and storage

The UK has already pledged “up to” £21.7bn of funding over 25 years to support five carbon capture and storage (CCS) projects, involving “clusters” of connected facilities.

Most of this funding will come from levies on consumers, but the government has also been gradually announcing chunks of public investment to get these initiatives off the ground.

The spending review allocates another £9.4bn of capital spending by 2029. This will partly go towards “maximis[ing] deployment to fill the [CO2] storage capacity” of the first two funded clusters.

At the same time, the government also confirmed its support for the next two clusters – Acorn in north-east Scotland and Viking in the Humber in the spending review. These projects are set to be up and running in the 2030s.

The review states that the government is providing the “development funding to advance [the] delivery” of these clusters, with a final investment decision expected “later this parliament, subject to project readiness and affordability”.

Pathways set out by government advisors at the Climate Change Committee (CCC) suggest CCS is required to meet the UK’s net-zero targets.

However, the government has faced intense scrutiny over its investments in CCS. A report by the influential Public Accounts Committee earlier this year said investing public funds in this relatively undeveloped technology was a “high risk” approach.

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Transport

The spending review includes a number of commitments for regional transport projects that could help cut UK emissions, including rail upgrades, bus lanes and cycleways.

Overall, the Department for Transport (DfT) settlement will reach total funding of £31.5bn in 2028-29, a slight increase from current levels. This includes support for the HS2 high-speed rail project.

HS2, which had its second phase out to Manchester cancelled under the Conservatives in 2023, will see its funding drop over the spending period.

Meanwhile, capital spending on transport projects around the country is set to experience a 4% real-terms growth rate each year out to 2029-30.

Regional transport projects receiving funding include the TransPennine Route Upgrade between York and Manchester, with £3.5bn, as well as £2.5bn for East-West Rail between Oxford and Cambridge and £300m for rail investment in Wales.

(For comparison, despite the declining funds, HS2 will receive £25.3bn over the period.)

Other relevant investments in the spending review include a commitment to “more than double” city region transport spending per year by 2029-30, by providing a total of £15.6bn for elected mayors across England. The review says this could go towards local transport priorities, including “zero-emission buses, trams and local rail”.

Additionally, there is another £2.3bn allocated for investment in local transport grants to support “bus lanes, cycleways and congestion improvement measures” for areas outside the larger regions with mayors.

The review includes a relatively small sum – £2.6bn – of capital investment that is set aside to “decarbonise transport” as “part of the government’s clean energy mission”.

This is made up of £1.4bn to “support continued uptake” of electric vehicles, in particular vans and heavy goods vehicles (HGVs), as well as £400m for charging infrastructure and £616m for walking and cycling infrastructure.

Some of these funds will also support the production of “sustainable” aviation fuel (SAF) in the UK by extending the government’s advanced fuels fund.

The spending review also includes funding for transport projects that may not help to decarbonise the nation’s transport. Notably, there is £24bn of funding by 2030 to “maintain and improve motorways and local roads across the country”.

Also, while the project is not mentioned in the spending review document itself, Reeves’s speech mentioned “backing Doncaster airport” alongside “investment to connect our cities and our towns”. (The airport is currently closed, but there has been a local political effort to reopen it.)

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Other announcements

R&D funding

The government is increasing research and development (R&D) funding to £22.6bn per year by 2029-2030.

This will include funding for the UK’s science base, the spending review says, such as the non-departmental public body UK Research and Innovation and research initiative Horizon Europe.

Part of this funding will go to the government’s new R&D missions accelerator programme. Some £500m of public funds are intended to leverage a further £1.5bn of private investment in innovation that supports the government’s “missions”.

(One of the five key “missions” announced by the Labour government in its manifesto is to “make Britain a clean-energy superpower”.)

Additionally, R&D funding will include up to £750m for a new supercomputer at Edinburgh University, the largest in the UK. This will be used to support a broad range of fields, including climate and weather predictions and research into fusion power.

In a statement, secretary of state for Scotland Ian Murray welcomed the funding for the supercomputer, adding:

“This will see Scotland playing a leading role in creating breakthroughs that have a global benefit – such as new medicines, health advances and climate change solutions.”

Ahead of the publication of the delayed UK industrial strategy, the spending review lists relevant R&D commitments.

It says over £3bn in R&D and capital funding over the next four years will go to advanced manufacturing across the UK, “anchoring the supply chain of zero emission vehicles, batteries and ultra-low and zero-carbon emissions aircraft[s]”.

Clean-energy industries will also receive “significant additional funding”, it adds.

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Flood defences and farming funds

As part of the spending review, the government announced investment in climate adaptation and the natural environment to “increase the UK’s resilience to the effects of climate change and protect the ecosystems that underpin the economy and food security”.

This includes £2.7bn in sustainable farming and nature recovery funding until 2028-29, as well as £4.2bn to build and maintain flood defences from 2026-27 to 2028-29.

According to the spending review, farmers will benefit from £2.3bn through the farming and countryside programme and up to £400m from additional nature schemes

There will be increasing support for “nature-friendly farming” through environmental land management schemes, which will grow from £800m in 2023-24 to £2bn by 2028-29. This will be sustained by “rapidly winding down” other subsidy payments.

The spending review states that this will make a “significant contribution” to the Environment Act targets, including improvements to water and air quality and creating spaces for wildlife to support biodiversity.

Funding for both flood defences and farm schemes follows the government stating that it was facing “significant funding pressures” of almost £600m in 2024-25 in the autumn budget.

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Foreign aid and climate finance

The government announced in February that it would further cut aid spending to 0.3% of gross national income (GNI) by 2027 in order to fund higher defence spending.

This came just three months after the UK, alongside other developed countries, had committed to raising at least $300bn a year for climate action in developing countries at the COP29 climate summit.

Developed countries have traditionally used their aid budgets to meet such “climate finance” goals.

But observers have noted that scaling up climate finance to meet this new target will be difficult, as nations cut back their overseas spending and the world faces overlapping humanitarian crises.

When announcing the cut earlier this year, prime minister Keir Starmer said that the UK would retain its focus on “tackling climate change” in its aid spending. The government also acknowledged that the decision to cut aid would require “many hard choices”.

The government has a pledge to spend £11.6bn over five years on climate finance in developing countries, which ends in 2025-26. Beyond that, it is expected to announce a new pledge to feed into the $300bn goal.

The spending review does not provide details of precisely what this goal will be, or whether it will be more ambitious as other aid programmes undergo swingeing cuts.

It states that the funding plan “prioritises UK multilateral investment across issues where the international system needs to deliver at scale and to reform”, including the “climate and nature crisis”.

It also says the three departments that provide nearly all UK climate finance – the Foreign, Commonwealth and Development Office, DESNZ and Defra – will “maintain progress” on the nation’s international climate goals.

However, the amounts of aid channelled via all three of these departments will be lower in the coming years than they are now, according to the government’s figures.

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Response to climate-risks report

In a separate document published alongside the spending review, the government also set out its response to the latest “fiscal risks and sustainability” (FRS) report, published by the Office for Budget in September 2024.

Within this, the government reiterates its intention to “accelerate to net-zero”, including via its target for clean power by 2030.

The response adds that, alongside this, the government recognises that it “must also take action to build resilience and ensure the UK is well-prepared for the changing climate”.

It says that FRS identified flooding and extreme heat as areas that need particular attention, before setting out its spending commitments in these areas.

The response also confirms two important dates for UK climate-policy watchers.

First, the response says the government will, in October 2025, publish its “carbon budget delivery plan”. This will set out the plans and policies the government will put in place in order to meet the first six carbon budgets, covering the years out to 2037.

Second, it says that the government will legislate for the seventh UK “carbon budget” by June 2026. This is a legally binding limit on emissions covering five years from 2038 to 2042. The CCC has recommended an 87% reduction below 1990 levels.

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UK spending review 2025: Key climate and energy announcements

A “collapse” of key Atlantic ocean currents would cause winter temperatures to plunge across northern Europe, overriding the warming driven by human activity.

That is according to new research, published in Geophysical Research Letters, which looks at the combined impact of the shutdown of the Atlantic Meridional Overturning Circulation (AMOC) and global warming on temperatures in northern Europe.

Scientists have warned that human-caused climate change is likely causing AMOC to weaken and that continued warming could push it towards a “tipping point”.

The study suggests that, in an intermediate emissions scenario, greenhouse gas-driven warming would not be able to outweigh the cooling impact of an AMOC collapse.

In this modelled world, one-in-10 winters in London could see cold extremes approaching -20C.

Winter extremes in Oslo in Norway, meanwhile, could plummet to around -48C.

The cold temperatures are projected to be driven by the loss of heat transfer from the tropics via ocean currents, as well as the spread of sea ice to northern Europe in the winter months.

The research does not look at when AMOC might tip – instead, it focuses on scenarios in the far future when this has already happened, so as to explore what impact it would have.

Lead author Dr René van Westen, a researcher in oceanography at Utrecht University, says Europe might stand alone as the one region set to get “cooler in a warmer world”. He tells Carbon Brief:

“If the AMOC collapses, we need to prepare for substantially cooler winters. Winter extremes will be very substantial for some regions. Temperatures could go down to -50C in Scandinavia. At -40C and lower in Scandinavia – everything breaks down over there.”

The research is being published alongside an interactive map, featured below, which highlights how a collapsed AMOC under different warming scenarios could impact temperature averages, extremes and sea ice across Europe.

‘Will warming or cooling win?’

AMOC is a system of ocean currents which plays a crucial role in keeping Europe warm. It transports warm water northwards from the tropics to Europe and cold, deep waters back southwards.

The potential collapse of these ocean currents – caused by the influx of freshwater from melting ice as well as rising air temperatures – is seen by some scientists as a “tipping point” that, once triggered, would be irreversible on human timescales.

However, there is significant scientific debate around whether human-caused climate change is causing the AMOC to slow down – and whether and when it might “tip”.

(The “tipping” of AMOC is often referred to as a “collapse”, “breakdown” or “shutdown”.)

Some scientists have argued that ocean currents have been slowing down since the mid-20th century, whereas others say there has been no weakening since the 1960s.

On the risks of an approaching tipping point, some researchers have estimated a collapse could occur this century, but others have questioned the robustness of the early warning signals being interpreted as evidence of a forthcoming shutdown.

(Regular direct measurements of AMOC’s strength started in 2004. To estimate the ocean currents’ health prior to this, scientists turn to a number of methods, including looking at palaeoclimate records, running climate model “hindcasts” and analysing historical patterns in sea surface temperature.)

A paper published last year by van Westen and colleagues, which ranked second in Carbon Brief’s round-up of the most talked-about climate papers of 2024, found that the present-day AMOC is on a trajectory towards tipping.

That paper set out some of the climate impacts of such an event, including a 10-30C drop in average monthly winter temperatures in northern Europe within a century and a “drastic change” in rainfall patterns in the Amazon.

The scientist’s latest offering provides a more detailed look at how an AMOC tipping event might impact Europe, using simulations produced by the Community Earth System Model (CESM).

The research models the impact of an AMOC collapse in combination with the impacts of human-caused climate change, instead of looking at the collapse of the ocean currents in isolation.

Van Westen says the research was designed to answer the question of how warming from greenhouse gas emissions could offset cooling from an AMOC shutdown. He tells Carbon Brief:

“[A question we wanted to address was] what would happen in a scenario where we have climate change and an AMOC collapse. Will it get cooler over Europe, or will it get warmer? Will regional warming win or will the cooling win?”

Simulating AMOC ‘collapse’

To answer this question, the scientists run a raft of climate simulations, exploring different combinations of global temperature rise and AMOC collapse.

Specifically, the scientists explore the collapse of AMOC under three scenarios:

• An “intermediate” climate scenario (RCP4.5), which is in line with current global climate policies.
• A very high-emissions scenario (RCP8.5) where warming hits 4C above the pre-industrial average by 2100.
• A “pre-industrial” scenario, without any human-caused global warming.

Across all three scenarios, the researchers run multiple simulations 500 years into the future, stabilising global temperature rise at 2C and above 4C from 2100 onwards. The researchers explore scenarios where AMOC is stable and when it has tipped.

The paper does not discuss the level of warming at which AMOC might tip – instead, it focuses on a point in the future after it has occurred, when the ocean currents and the climate have “equilibrated to a new background state”.

To simulate an AMOC collapse in the climate model under the two warming pathways, the researchers apply high levels of freshwater forcing to the north Atlantic.

Van Westen acknowledges the level of freshwater forcing applied to the model to create an AMOC shutdown is “unrealistic”, but says the adjustment is necessary to override a “bias” in climate models. He explains:

“[Climate models] have an overly stable AMOC. So, we need to add this kind of freshwater flux to get the AMOC in a more unstable regime which corresponds to actual observations.”

The paper focuses largely on impacts under the intermediate scenario with AMOC collapse. Under this combination, AMOC shutdown causes some global cooling, resulting in a world that is around 2C warmer than pre-industrial levels.

Prof Stefan Rahmstorf, a professor of physics of the oceans at Potsdam University who was not involved in the research, tells Carbon Brief the new study is “highly welcome”. He explains that “not many” studies have investigated the combined impact of global warming with AMOC collapse since a paper he co-authored in 1999, and adds:

“[The new study] uses a sophisticated climate model with good regional resolution – far better than what was possible 26 years ago. The model confirms the long-standing concern that an AMOC collapse would have massive impacts on European climate, in this case focusing on temperature extremes.”

Dr Alejandra Sanchez-Franks, senior research scientist in the marine physics and ocean climate group at National Oceanography Centre, who was also not involved in the research, says the study’s conclusions should not be used to explain how the European climate will respond in the near-term to changes in the strength of AMOC. She tells Carbon Brief:

“The study uses an idealised experiment with unrealistic freshwater changes to force an AMOC collapse. Very importantly, the author’s conclusions refer to the European climate 200 years after an AMOC change and do not describe what will happen to European temperatures and sea ice in the years and decades following an AMOC collapse.

“Therefore, the study does not serve to tell us how an AMOC tipping point or collapse will affect us immediately.”

‘Out of the freezer and into the frying pan’

The most “striking” finding of the paper, according to van Westen, is that an AMOC collapse in a world that is 2C warmer will result in a Europe that is cooler than it is today.

The research notes that – under this scenario – north-west Europe is set to face “profound cooling”, characterised by more intense winter extremes.

Summer temperatures, on the other hand, would be expected to remain just slightly cooler than they would in a pre-industral climate – meaning that Europeans would experience dramatic swings in temperatures throughout the year.

Increased winter storms and greater day-to-day temperature fluctuations are also expected in this scenario. This is due to a greater temperature contrast between northern Europe and southern Europe, which would be less impacted by a weakened AMOC.

The research notes that cooling from the reduced heat transfer from ocean currents would be amplified by “extensive” sea ice expansion to the coasts of north-west Europe. (Sea ice reflects incoming solar sunlight, resulting in less heat uptake and cooler temperatures overall.)

The map below shows the extent of sea ice in February under the scenario where AMOC collapses and the world is 2C warmer. It shows how Arctic sea ice – when at its yearly maximum – would cover the coasts of Scandinavia and much of the island of Great Britain.

Prof Tim Lenton, chair of climate change and Earth system science at the University of Exeter, who was not involved in the study, tells Carbon Brief it is “hard to over-stress how different” the climate simulated by the model is from present-day conditions. He says:

“The extreme winters would be like living in an ice age. But at the same time summer temperature extremes are barely impacted – they are slightly cooler than they would be due to global warming, but still with hotter extremes than the preindustrial climate.

“This means the seasonality of the climate is radically increased. In extreme years it would be like coming out of the freezer into a frying pan of summer heatwaves.”

The research also looks at the impacts of a shutdown of AMOC in a world that is 4C warmer.

It suggests that, under this scenario, cooling related to the shutdown of ocean currents would not outweigh global warming. Northern Europe would not experience extensive sea-ice expansion or the strong cooling projected under the 2C scenario.

Instead, temperatures would be expected to increase throughout the year and particularly in the summer months. However, northern Europe would be expected to see warming below the global average.

Frigid cities

While the paper itself uses the Dutch town of De Bilt as a case study, the researchers have published projections for a range of European cities under the scenarios explored in the study.

For example, the data shows that, under AMOC collapse in a 2C-warmer world, London could experience an average winter temperature of 1.9C, roughly 17.6 freezing days each year and one-in-10-year cold extremes of -19.3C.

In the Norwegian capital of Oslo, average winter temperatures are projected to plunge to -16.5C, with maximum daily temperatures not surpassing 0C for almost half the year, or 169 days. The research suggests the Norwegian city could experience cold extremes of -47.9C.

The map below shows projected cold extremes under 2C of warming and AMOC collapse in cities in Belgium, France, Ireland, the Netherlands, Switzerland and the UK. It shows how temperatures could drop to -29.7 in Edinburgh, -19.3C in London and -18C in Paris.

Van Westen says the findings are “highly relevant for society and policymakers” because they “shift the narrative” about the direction of Europe’s future climate. He explains:

“Parts of the Netherlands and parts of the UK will experience spectacular cold extremes down to -20C or even lower. Our societal structure and our infrastructure is not built for these cold extremes.”

The paper is being published alongside an interactive map, shown below, that shows ice cover, temperature averages and extremes across the world under five of the scenarios explored in the study. These are: a pre-industrial world with a stable AMOC, a pre-industrial world with a collapsed AMOC, a 2C world with a stable AMOC, a 2C world with a collapsed AMOC and a 4C world with a collapsed AMOC.

Future research

Scientists not involved in the study said the work would need to be followed up with further exploration of the interplay between global warming and potential AMOC collapse.

Dr Bablu Sinha, leader of climate and uncertainty, marine systems modelling at the National Oceanography Centre, told Carbon Brief:

“Given that observational data is limited, theoretical climate modelling approaches need to be taken to properly investigate this topic. Van Westen and Baatsen motivate the need for more detailed investigation into the combined impacts of global warming and AMOC decline on European extreme temperatures.”

Dr Yechul Chin, researcher at Seoul National University’s climate system lab, tells Carbon Brief:

“Although [this research] demonstrates the potential for more extreme weather under combined global warming and AMOC collapse scenarios, significant uncertainties remain that must be resolved before we can quantify risks or devise robust mitigation strategies.

“Projections about AMOC have a large spread and it means that alternative AMOC trajectories and different levels of warming could substantially widen the range of possible outcomes.”

His comments are echoed by Rahmstorf from Potsdam University, who points out that the “exact outcome” for Europe hinges on the development of “two opposing trends” – global warming due to greenhouse gases and regional cooling due to AMOC weakening. He says:

“The balance between those two will depend on the speed and extent of these trends and will, therefore, depend on the emission and AMOC weakening scenarios.

“Therefore, the more scenarios will be explored with different models in future, we will see a range of different outcomes for Europe as well as other parts of the world. A large uncertainty in this respect will remain.”

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Ocean current ‘collapse’ could trigger ‘profound cooling’ in northern Europe – even with global warming

Over the past decade, research has emerged suggesting that ramping up reforestation around the world could make a substantial contribution to tackling climate change.

Studies have estimated that the CO2-absorbing power of newly planted trees could add up to mitigation “potential” of 10bn tonnes (GtCO2) per year – more than the annual emissions of the US.

Achieving this would require planting trees across 678m hectares – an area twice the size of India.

But the uncertainty around those figures is large due to a range of factors, such as where sufficient trees already exist, how much climate mitigation those trees offer and where people actually want additional trees to be planted.

In our new study, published in Nature Communications, we unpack eight years of research into reducing these uncertainties.

We have quantified, for example, how the carbon-sucking power of trees changes when you let forests grow back naturally versus planting monoculture or mixed-species plantations.

We figured out how much carbon could be removed at different price points and mapped where trees – somewhat counterintuitively – actually act to warm, rather than cool, our climate.

But, as we shrank the uncertainty, we also shrank the estimate itself.

Our research provides the most precise estimate of global reforestation area to date – 195m hectares, or 71% less than earlier estimates.

Reforesting an area this size could capture 2GtCO2 per year.

Mapping reforestation opportunity

Maps of global reforestation potential have been cited in thousands of scientific publications, inspired large-scale tree-planting movements and been used by the International Panel on Climate Change (IPCC) in its flagship reports.

However, they have also been very controversial.

Critics have pointed out, for example, that these maps failed to account for natural disturbances that prevent forest growth, ignored existing trees and overlooked the people that live, steward and often depend on those lands for their wellbeing.

In our new study, we resolved to produce a map that addresses these past critiques.

We began by searching for existing maps of reforestation “opportunity”.

Our search uncovered 89 such maps, although most of those we identified are national or sub-national. Some places – such as Brazil’s Atlantic Forest – have many maps, but we found that most of the globe was only covered by a single older, more controversial map.

The map below shows where we found existing maps at the global, regional, national and sub-national levels.

Thus, we set about creating a new global map that built upon the methods of past efforts, tackled prominent critiques and incorporated newly available layers.

Our new map accounts for albedo, for example – how restoring tree cover can, in some locations, actively heat the Earth, rather than cool it, by affecting how much sunlight is absorbed or reflected.

It excludes native grasslands and other ecosystems where carpeting the land with trees would harm biodiversity and exacerbate the risk of wildfire. And it layers in additional safeguards, such as food security, to ensure that reforestation outcomes are more likely to be beneficial to people.

These constraints left us with up to 195m hectares of reforestation opportunity across the world.

A reforestation ‘menu’

Not all reforestation opportunities are created equal – different communities may want to implement reforestation for different reasons, such as restoring floodplains or re-establishing iconic ecosystems that have been lost.

So, alongside the reforestation opportunity, our map shows other factors that communities or decisionmakers may use to help them prioritise areas for reforestation.

We show, for example, where natural regeneration may be most likely to occur and where biodiversity benefits may be greatest, given proximity to existing forest. We show where reforestation opportunity exists on slopes and floodplains – and therefore is more likely to provide benefits for the local watershed. We show places where people have strong rights and secure land tenure, to avoid exacerbating social inequities.

Perhaps unsurprisingly, it is hard to find places that tick all of these complex boxes. But, it is still possible to achieve multiple objectives in one location.

In fact, our study finds that 83% of reforestation opportunities occur close to existing forest, while 81% occur in places that are expected to have low conflicts with rural livelihoods.

More than half of the opportunity that we identify also occurs in countries with explicit restoration goals – places such as Brazil’s Atlantic Forest, where we are working with local partners and communities to restore 1.2m hectares of forest. Forest restoration there contributes to national climate goals, supports sustainable economic development and connects habitat for wildlife.

Alongside the paper, we present the Global Reforestation Hub, which allows users to explore this menu of reforestation options, drill down to reforestation potential at county level and see what opportunities meet a given set of objectives.

For example, a government interested in climate mitigation and protection from floods might use the tool to find the places within their country where both goals might be achieved via reforestation.

The screenshot below shows the Global Reforestation Hub. Countries are coloured by their total reforestation opportunity, from low (white) to high (dark blue). The table shows the amount of land available for – and the CO2 mitigation potential of – reforestation given different priorities and constraints.

Smaller can be better

Reforestation remains one of the most cost-effective climate removal options, but it cannot – and should not – happen everywhere.

While there are certainly opportunities to plant and regrow trees beyond what we have mapped here, we created these maps to show where the climate mitigation opportunities – and their co-benefits – are most concentrated.

Prioritising other motivations, such as human health, habitat for specific wildlife species or local considerations, would also increase the total reforestation opportunity area. For example, our maps don’t include the potential for reforestation in dense urban areas, but trees in those areas can be highly beneficial for human health.

Our study prioritised mapping opportunities for climate change mitigation – and we were deliberately conservative, erring on the side of caution when determining which places to include.

The result is a map that shows the places where reforestation offers both the greatest climate benefits and the fewest downsides for both people and nature.

During a year when the UN climate COP will be hosted in the most iconic forest of all, our study is less a critique of the pre-existing numbers and more an effort to create the most precise and pragmatic maps of reforestation potential. This can help ensure that we get the reforestation part of the climate equation right.

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Guest post: Why the global area for regrowing trees is 71% smaller than thought