Published

9 months ago

September 17, 2025

Alice Rush

Removing carbon dioxide (CO2) from the atmosphere is widely expected to play a key role in meeting the goals of the Paris Agreement.

But this will only be effective for slowing climate change if the CO2 can be stored securely and indefinitely.

This requires “geological carbon storage”, where captured CO2 is injected deep underground, where it can stay trapped for thousands of years.

While the current deployment of CO2 removal (CDR) technologies around the world is small, almost all facilities aim to store captured CO2 in sedimentary basins.

However, in our study in Nature, we show that current policy approaches to using these formations on a larger scale could be suffering from a false sense of abundance.

We find that – once technical, social and environmental risks are considered – the world’s available reserves of geological carbon storage are significantly more limited than most estimates suggest.

Our research shows that, of nearly 12,000bn tonnes of CO2 (GtCO2) of theoretical carbon storage capacity, just 1,460GtCO2 is risk-free.

Significantly, we find that, if all available safe carbon storage capacity were used for CO2 removal, this would contribute to only a 0.7C reduction in global warming.

In short, geological carbon storage is not limitless – on the contrary, its practical potential is a rather scarce planetary resource.

From technical potential to prudent limits

When studies estimate where carbon could be stored for the long term, they typically start by looking at all sedimentary basins worldwide to find those that are mature and stable.

However, norms of international environmental law indicate that high standards of due diligence must be applied to prevent transboundary environmental harm. As scientists, we were therefore interested in understanding how much storage capacity would be available when looking through a precautionary lens.

Our study develops the first global estimate of safe and durable carbon storage that takes into account social, environmental and technical risks – in addition to the geological qualities of the basins.

Rather than taking raw geological capacity at face value, we screen the potential locations for a number of factors:

Seismic hazards
Groundwater contamination.
Proximity to population centres.
Biodiversity protections, such as environmentally protected areas and the Arctic and Antarctic circles.
Engineering limitations, such as basin depths that are too shallow to store carbon indefinitely or too deep underground and locations too deep in the ocean.
Political feasibility, such as maritime areas outside of national jurisdictions or disputed geographical areas.

The results of our assessment are stark. We find that, out of nearly 12,000GtCO2 of theoretical carbon storage capacity in sedimentary basins, just 1,460GtCO2 can be considered robust for climate planning purposes.

We refer to this as “prudent” storage capacity.

This is an order of magnitude less than commonly-cited figures.

In 2005, the Intergovernmental Panel on Climate Change’s (IPCC’s) special report on carbon capture and storage estimated that there is a “technical potential of at least about 2,000GtCO2…of storage capacity in geological formations”.

Over the two decades since, estimates have ballooned to 10,000-40,000GtCO2, depending on the academic or industry source that is consulted.

What this means for warming limits

Our research finds that if all reserves of “prudent” storage were used solely for removing CO2 from the atmosphere, they would enable – at most – a 0.7C reduction in global temperatures.

This falls to as little as 0.4C if we conservatively take the lower end of the likely (>66%) range of how much warming or cooling we expect per tonne of CO2 emitted or removed, respectively.

For the first time, our new study provides an estimate for an upper limit for how much past warming could be reversed through geological storage.

However, under most low-carbon pathways available in the academic and technical literature and assessed by the Intergovernmental Panel on Climate Change, this prudent geological storage limit would be used up before 2200 – and some by 2100.

In many cases, storage is not used to draw down atmospheric CO2, but to balance the continued production of greenhouse gas and carbon pollution from human activities.

And yet, without sharp near-term cuts in gross emissions, the likely overshoot of the Paris Agreement’s 1.5C warming limit could prove irreversible.

Equity and responsibility

The maps below show how prudent storage capacity – for offshore (left) and onshore (right) basins – is not evenly distributed.

Two global maps side by side showing the global CO2 storage potential

The “prudent” global storage potential (in GtCO2) for offshore (left) and onshore (right) basins, by individual countries. Darker shading indicates a greater amount of storage capacity. Source: Gidden et al. (2025)

Much of it is found in large, fossil-fuel-producing nations, such as the US, Australia, Russia and Saudi Arabia. These countries are among the world’s biggest historical emitters.

(This is not a coincidence, as these nations’ fossil-fuel-based economies are the result of relatively easily reachable geological deposits.)

However, the reality that the nations most responsible for emissions also appear best placed to store them raises equity concerns. Nations who benefitted from enabling carbon pollution would now also benefit from the clean up.

Other countries, such as Brazil and the Democratic Republic of the Congo, have substantial storage, but little domestic incentive to use it unless compensated.

Meanwhile, emissions-intensive nations would now be first in line to transform themselves from extractors to large-scale injectors of carbon – and could benefit from new business opportunities, often paid for by the public purse.

However, sovereign wealth funds – state-owned investment funds, often built on fossil revenues – could play a role in financing this shift, in line with the “polluter pays” principle.

Planning for scarcity

Treating storage as a finite and scarce resource has a knock-on effect for climate policy.

For example, governments would need to decide explicitly how they intend to allocate limited carbon storage capacity – should storage capacity be used to abate residual, industrial and fossil-fuel emissions, or for CO2 that has been directly pulled from the atmosphere?

Norms of international environmental law – and the recent “advisory opinion” on climate change from the International Court of Justice – provide guidance as to what countries ought to do. The principle of harm prevention indicates that risks of climate harm should be minimised where possible.

To limit risks to implementing climate targets, carbon capture and storage (CCS) should be seen as a complement to – but not a substitute – for rapid emissions cuts. This recommendation is not new – it has long been called for by researchers looking at the trade-offs and negative side-effects of specific negative emissions technologies, including the impacts poorly governed deployment of these technologies can have on biodiversity and food security.

Our geological storage estimate represents an assessment of reserves today – but this is likely to change with time as knowledge, preferences and governance of CO2 storage change.

CDR technologies that provide alternatives to geological storage, such as mineralisation in basalt, show promise. However, these technologies remain at pilot scale, with only a few million tonnes stored to date.

Climate strategies that rely on nascent CDR technologies would not constitute a strategy that minimises risks and potential harm to today’s and future generations.

The bottom line

Geological carbon storage is not a limitless backstop – and assuming otherwise puts the world at risk of irreversibly exceeding the Paris Agreement’s 1.5C threshold for global warming.

However, at the same time, carbon storage will almost certainly play a pivotal role in any future where global “net-zero” CO2 or greenhouse gas emissions is achieved.

By acknowledging the scarcity of carbon storage – and designating reserves for essential and strategic uses – governments can limit the risks of harm to people and the planet.

The post Guest post: How the role of carbon storage has been hugely overestimated appeared first on Carbon Brief.

Guest post: How the role of carbon storage has been hugely overestimated

Climate Change

UN asks AI companies to reveal full environmental impacts

Published

10 hours ago

June 23, 2026

Alice Rush

The head of the United Nations has launched an initiative aimed at holding artificial intelligence companies accountable for their exploding environmental impacts, including their carbon emissions, the amount of water and land used for data centres, and the energy they consume.

During a speech at London Climate Action Week on Tuesday, António Guterres noted that AI can accelerate climate solutions, among other key challenges, and said its potential must be harnessed.

“But AI is also hungry for land, water and power,” he emphasised, adding that the data centres needed to run AI models already consume more electricity than most countries.

The UN Secretary-General repeated a call he first made in July 2025 for all big AI companies to commit to power every data centre with renewable energy by 2030.

Some tech firms have announced they are sourcing or building out clean energy to run their hubs, but growing power demand is also contributing to gas-fired generation in the US, according to data from Global Energy Monitor.

The International Energy Agency (IEA) estimates that data centres are set to more than double the emissions from the electricity they use between 2024 and 2030 in a high-growth scenario. But AI’s use could lead to far larger reductions in the energy sector through efficiency gains if adopted widely.

Jun 23, 2026

Energy

UN chief says fossil fuel industry must cut methane for warming “relief”

The UN Secretary-General urges drastic reductions in methane emissions, starting with the energy sector, to limit an expected overshoot of global warming beyond 1.5C

Read more
Jun 22, 2026

Comment

China’s coal-chemicals boom risks repeating the mistakes of the past

By reviving the problematic industry in the name of energy security, China runs the risk of higher emissions, stranded assets and setting back its ambitions as a clean energy leader

Read more
Jun 19, 2026

Oceans

Mombasa ocean summit drives progress on marine protection, but threats persist

At the 11th Our Ocean conference in Kenya, its founder John Kerry says the ocean must become central to climate solutions and needs to be looked after

Read more

‘No more hidden costs’

Proposing the new “AI Environmental Transparency Initiative” on Tuesday, Guterres also urged big AI firms companies to measure and publicly disclose the full environmental impact of their systems, including their carbon, water, and land footprints.

“No more hidden costs. No more shifting the burden onto those least able to bear it. It is time to come clean,” he said in a major speech on responding to the world’s twin climate and energy crises. “If AI is to help build a better future, it must be honest about what it costs us now.”

A report issued earlier this month by the UN University Institute for Water, Environment and Health noted that most current assessments of AI’s environmental cost focus on carbon emissions from training models. But, it added, this misses a substantial part of the picture.

Every kilowatt-hour of electricity for AI also carries a water footprint, from cooling and generation, and a land footprint, from infrastructure and supply chains, it said.

Explainer: Will AI data centres make or break the energy transition?

The report estimated that AI data centres globally could consume 945 terawatt-hours of electricity annually by 2030 – more power than all but five countries and roughly twice France’s 2025 consumption.

Offsetting this carbon footprint by 2030 would require growing some 6.7 billion trees over 10 years, it calculated. Producing power for the data centres would consume water equal to the basic needs of 1.3 billion people in sub-Saharan Africa for a year and take up land of more than 14,500 square kilometers, roughly twice the Jakarta metropolitan area.

The European Union said earlier this month it will develop minimum energy-efficiency standards for both new and existing data centres, with a “needs assessment” due by 2027, Reuters reported. It’s also planning ⁠a sustainability label for data centres, covering criteria including water use and clean energy supply – but that has been delayed.

US community push-back

Asked after his speech what the response had been, the UN chief said “we’ll see”, without giving more details.

But, he argued that, in his view, the push for transparency “is perfectly reasonable and even positive for the AI industry, because eventually some people will say that they consume much more than they really do”. “I think the truth is essential,” he added.

Concerns about the environmental impacts of AI and the infrastructure needed to run the technology have led to growing opposition in some communities, especially in the US.

This month, Monterey Park in Los Angeles County was the first city in the United States to enact a citywide prohibition on data centres through a voter-approved ballot measure. The developers behind a proposed centre in the area had already pulled the project in April amid an increasingly hostile local environment and regulatory uncertainty.

The vote that stopped a data center: US communities query resource-hungry AI

According to nonprofit Data Center Watch, around $64 billion-worth of data centre projects nationwide were delayed or blocked between May 2024 and March 2025 as communities pushed back against them.

Industry lobby groups argue that data centres can provide economic benefits in their host communities. According to the US-based Data Center Coalition, which represents big operators and developers, data centres generate tax revenue, support construction and technical jobs, and provide infrastructure needed for cloud computing, scientific research and AI development.

The industry has also challenged claims that data centers necessarily raise electricity costs for households.

Force for good?

The UN chief said benefits can be few in the places that are home to the data centre, while “communities are often left in the dark about the environmental impact of the infrastructure rising around them”.

Guterres said companies have an “obligation” to be clear and open about the services they are offering but also the level of resources they require.

“Transparency is essential for the decisions that communities must make – and transparency is essential even for the future of artificial intelligence, and to make sure that artificial intelligence is essentially a force for good,” he told an audience of climate professionals in London

A senior UN official told journalists ahead of Tuesday’s announcement that the AI industry has started to talk about and disclose some of their impacts, but those efforts are not yet comprehensive enough.

The hope is that the new initiative will “encourage the industry to come together and take further action on it”, the official said.

The post UN asks AI companies to reveal full environmental impacts appeared first on Climate Home News.

UN asks AI companies to reveal full environmental impacts

Climate Change

Prof Philippe Ciais: The world’s most highly cited climate scientist

Published

12 hours ago

June 23, 2026

Alice Rush

Phillipe Ciais has spent almost four decades researching the planet’s carbon cycle – and the ways in which humans have been impacting its balance.

Based at the Laboratoire des Sciences du Climat et de l’Environnement (LSCE) on the outskirts of Paris, Ciais (pronounced “see-es”) has been listed as an author on more than 1,300 peer-reviewed studies.

In fact, analysis of Carbon Brief’s Cosmos database reveals that – by some distance – he is the most highly cited climate scientist in the world.

In a wide-ranging interview, he discusses:

The post Prof Philippe Ciais: The world’s most highly cited climate scientist appeared first on Carbon Brief.

https://www.carbonbrief.org/prof-philippe-ciais-the-worlds-most-highly-cited-climate-scientist/

Climate Change

Cited 23 June 2026: Project Cosmos launch | Science ‘under attack’ at Bonn | Emissions inequality

Published

13 hours ago

June 23, 2026

Alice Rush

Welcome to Cited, your essential guide to new climate research.

In the news

SCIENCE ‘UNDER ATTACK’: Climate Home News reported that “dozens” of countries called out “coordinated attacks” aimed at “undermining the role of climate science” at UN climate talks in Bonn, Germany, last week. According to the outlet, the countries said that UN decision-making had to remain based on the “best available science”, including the reports of the Intergovernmental Panel on Climate Change. One negotiator said that India and Saudi Arabia “opposed calls in draft texts to encourage scientific work on scenarios that would minimise the magnitude and duration of any overshoot of 1.5C”, the article noted. For more, read Carbon Brief’s summary of the negotiations.

REPORT OPPOSITION: “Oil industry allies” in the US are targeting a report on extreme weather attribution, due to be published by the National Academies of Sciences, Engineering and Medicine, according to Politico. The outlet reported that the “heightened scrutiny – which involves a secretive opposition research group scouring scientists’ emails – has prompted two people to leave the 15-person panel tasked with producing the report”. Separately, the Guardian reported that the Trump administration has “reversed its decision” to dismantle the Ocean Observatories Initiative, a $368m deep-sea observation system.

SUPER EL NIÑO: BBC News reported that the US National Oceanic and Atmospheric Administration announced that El Niño had “officially begun”. Forecasts suggest the event could be among the “strongest ever recorded”, it added. Meanwhile, a “vigorous debate” is taking place about whether climate change is making the El Niño phenomenon more intense, according to the New York Times. The outlet explained that some scientists see the run of “comparatively strong” El Niño events in recent decades as an indication that “climate change is supercharging El Niño”. However, it added that “others say there is no clear evidence to support that theory”.

Research picks

Water

Global sea level rise has nearly tripled the number of days since the 1970s when coastal water levels have surpassed average tide gauge readings | Science Advances
As the Arctic warms, increased iceberg activity could “reshape” deep-sea habitats and “elevate” navigational hazards as maritime traffic expands | Nature
Sea level rise has quadrupled the frequency of extreme coastal sea-level events since the year 1900 | Nature Climate Change

Inequality

The top 10% of consumers are responsible for $1.7-5.7tn of environmental damage each year, surpassing international climate and biodiversity financing gaps | Communications Sustainability
Calculating an individual’s emissions based on their asset ownership suggests that wealthier people are responsible for an even higher share of global greenhouse gas emissions than indicated by past studies | Nature Climate Change
A plan that places equity at the “centre” of climate adaptation efforts in cities is needed to address the “stark disparities” between “affluent” and “disadvantaged” urban communities’ ability to prepare for extreme heat | PLOS Climate

Extremes

In the western US, 42% of burned area over 2001-24 occurred during, and immediately following, heatwaves | Science Advances
“Hot-to-wet” whiplash events have become more frequent across Australia over the past century, with south-eastern Australia emerging as a hotspot | Journal of Climate
Rapid urbanisation, combined with more intense rainfall from tropical cyclones, have increased people’s exposure to “extreme” rainfall from tropical cyclones across China | Journal of Hydrometeorology

Captured

Chart showing that population growth and a warming world have driven up the number of people exposed to extreme heat since the 1970s

One billion additional people face at least one day of “extreme heat stress” every year compared to the 1970s, according to research published in Nature Climate Change.

The chart shows changes in “strong” (top), “very strong” (middle) and “extreme” (bottom) heat stress, defined as a “universal thermal climate index” above 32C, 38C and 46C, respectively. The grey bar shows the percentage of the global population exposed to at least one, 30 or 90 days of heat stress in 1970. The light and dark blue bars show the number of additional people experiencing heat stress over 2015-24 due to population growth and rising global temperatures, respectively.

10%

Equivalent damage to the UK’s GDP caused by climate change if global warming reaches 4C by 2100, according to new research in Nature Climate Change. The study estimates a range of 2-20%.

Spotlight

Introducing: Project Cosmos

Carbon Brief explains how it built a major new database of climate science research and unveils a new ranking of the 500 most highly cited publications, authors and institutions in climate science.

This week, Carbon Brief launched Project Cosmos – the world’s largest and most complete database of climate change research.

The database features more than 1.8m academic papers, books and reports, capturing the vast body of human knowledge about climate change that has accumulated over more than a century of academic study.

The climate science “universe” is based on reports from the Intergovernmental Panel on Climate Change (IPCC), which are recognised as the world’s most authoritative summaries of the latest climate science.

Since its first report was published in 1990, humanity’s knowledge about human-caused climate change has ballooned. The IPCC has published six sets of reports in total – each one longer than the last.

In total, IPCC reports reference more than 100,000 other papers, books and reports. This is the core of our climate science universe. Carbon Brief then built on this core, by looking at four other sources of data. Read more about how the Cosmos database was created here.

Every single publication in the Cosmos database is linked to at least one other through references. Visualising these links reveals a “galaxy” of references. In the image above, each colour and cluster reveals different topics and densities of research. Explore the galaxy in an interactive map here.

Cosmos 500

As part of an initial wave of preliminary analysis to demonstrate the scope of the Project Cosmos database, Carbon Brief has ranked the 500 most highly cited publications, authors and institutions in the database.

The most highly cited climate scientist is Prof Philippe Ciais, who has spent almost four decades researching the planet’s carbon cycle – and the ways in which humans have been impacting its balance. Carbon Brief recently interviewed Ciais in Paris.

The US tops the tables for the most highly-cited authors and institutions. Almost half of the 500 most highly-cited authors are from US institutions. This raises particular concerns for the future of climate science, as American climate scientists and institutions are coming under attack under the Trump administration.

Experts from global south countries account for only 4% of all authors in the Cosmos 500. China stands out as the most highly-cited global south country. Meanwhile, only 10% of authors in the Cosmos 500 are women.

There are many possibilities for future avenues of research using the Cosmos database. Over time, the database could be used to reveal, for example, how interest in different areas of climate science has changed over time, plus identify potential knowledge gaps and, thus, opportunities for future research.

Carbon Brief invites researchers – including academics, journalists and analysts – to submit their own proposals for co-authored studies, literature reviews and analytical projects.

Preprints to watch

Carbon Brief’s pick of new papers still going through peer review

Regional reductions in aerosol emissions can “temporarily amplify” the likelihood of record-breaking heat events | Environmental Research: Climate
Analysis of Reddit posts suggests the Fridays for Future movement has created “wider awareness” of global warming by drawing attention to climate change and “climate actions” | npj climate action
Periods of simultaneous low wind and solar power generation, known as “renewable energy droughts”, will “intensify progressively” as the planet warms | Nature portfolio

Noticeboard

28-30 June: Seventh global conference on climate and sustainable development goal synergies, Bangkok, Thailand
29 June-1 July: Exeter climate conference, Exeter, UK
29 June-1 July: National Academy of Sciences hybrid workshop on seabed critical mineral resources, Irvine, US
30 June: Submission deadline for abstracts for MedCLIVAR conference, scheduled for 21-25 September in Limassol, Cyprus
30 June: Application deadline for postdoctoral position in ice-ocean interactions at the Physics Laboratory of Ecole Normale Supérieure de Lyon | Salary: €3,071-4,714 per month. Location: Lyon, France
30 June: Submissions open for abstracts for the pan-African conference on environment, climate change and health, scheduled for 21-24 October in Nairobi, Kenya
8 July: Application deadline for position as research officer in climate science and law at the Grantham Research Institute | Salary: £43,277-51,714. Location: London, UK
10 July: Application deadline for position as associate or senior editor at Nature Water | Salary: Unknown. Location: Shanghai, Beijing or Milan