Wednesday, September 03, 2025

Safe, practical underground carbon storage could reduce warming by only 0.7°C – almost 10 times less than previously thought




International Institute for Applied Systems Analysis




A new IIASA-led study for the first time maps safe areas that can practically be used for underground carbon storage, and estimates that using them all would only cut warming by 0.7°C. The result is almost ten times lower than previous estimates of around 6°C, which considered the total global potential for geological storage, including in risky zones, where storing carbon could trigger earthquakes and contaminate drinking water supplies. The researchers say the study shows geological storage is a scarce, finite resource and warn countries must use it in a highly targeted way.

Storing carbon deep underground has been presented as an almost limitless solution to the climate crisis. The study led by IIASA researchers in collaboration with an international team of colleagues and published in Nature, shows that the reality is far more limited than previously thought. The team has estimated a prudent global limit of around 1,460 billion tons of carbon dioxide (CO₂) that can be safely stored in geologic formations – an amount almost ten times smaller than estimates proposed by industry that have not considered risks to people and the environment.

Carbon storage is widely seen as essential for achieving climate goals, whether by capturing emissions from factories and power plants or removing CO₂ from the atmosphere. According to lead author Matthew Gidden, a senior researcher in the IIASA Energy, Climate, and Environment Program and at the Center for Global Sustainability at the University of Maryland, USA, the study’s findings highlight the need for caution:

“With this study, we can conclude that carbon storage should be treated as an exhaustible, intergenerational resource, requiring responsible management. Hard choices must be made about which countries, which sectors, and even which generations are able to utilize it. It’s critical that countries make clear in their climate action plans how they plan to use carbon storage in order to collectively achieve long-term climate goals while minimizing harm to human health, biodiversity, and sustainable development.”

The researchers first analyzed total global geological storage by mapping sedimentary basins – underground rock formations where layers of sand, mud, and other materials have built up over millions of years. These basins are prime locations for both fossil fuel deposits and potential carbon storage. The team assessed their suitability for carbon storage by considering risks such as CO₂ leaking back into the atmosphere, the possibility of triggering earthquakes during the storage process, contamination of groundwater supplies, and proximity to population centers or protected areas. Sites that were too close to the surface to store carbon reliably, too far underground, or at ocean depths that make storage too expensive and risky, were also ruled out.

When these factors are taken into account, the global storage capacity shrinks dramatically from industry estimates of around 14,000 gigatonnes.

The team also examined what these storage limits mean for the planet’s ability to cool down after overshooting temperature goals, finding that if the total available geological storage capacity would be exclusively used for CO2 removal and no further emissions would be produced by other activities at that point, a maximum 0.7°C warming reversal is possible before available safe storage sites are exhausted.

Larger engineering and industry estimates have suggested much deeper temperature drawdowns of 5°C to 6°C – and even higher in some studies – but those assessments failed to factor in risks to people and the environment and allow for much more extensive and riskier storage potential.

The authors emphasize that such comparisons highlight the stark difference between what is technically possible and what can be safely achieved. They also caution that removing carbon may not reduce warming in the same way that emitting it causes warming, and that the climate system might not return to its earlier state even if global temperatures are brought back down.

“This study should be a gamechanger for carbon storage. It can no longer be considered an unlimited solution to bring our climate back to a safe level. Instead, geological storage space needs to be thought of as a scarce resource that should be managed responsibly to allow a safe climate future for humanity. It should be used to halt and reverse global warming and not be wasted on offsetting on-going and avoidable CO2 pollution from fossil electricity production or outdated combustion engines,” explains coauthor Joeri Rogelj, Director of Research at the Grantham Institute and PM senior research scholar at IIASA.

Fossil fuel producing countries such as the United States, Russia, China, Brazil and Australia have the most potential safe storage as disused mines are the most efficient type of geological storage. The countries with the lowest risks include Saudi Arabia, the Democratic Republic of the Congo and Kazakhstan, while countries that see large decreases in potential storage space due to high risks include India, Norway, Canada and countries in the European Union. About 70% of all storage is onshore, with the remaining 30% at offshore sites.

“There are still many unknowns around geological carbon storage. The technology has been around for close to 30 years, but it still hasn’t been scaled to the levels needed to bring warming down. Identifying storage sites is a laborious process that needs to characterize very local geological properties to understand how much storage is actually possible. Previous research identified sites that can carry serious risks to humans and the environment and make rosy assumptions about how much carbon can be stored there. Our study asks and answers the opposite question: how much of the storage is actually safe and realistic to use?” Gidden says.

The team’s work also highlights questions of fairness and responsibility. Countries with the largest fossil fuel industries often have the greatest storage potential but also bear the greatest historic responsibility for emissions.

“This is not just a technical issue. It is about justice across generations and across nations. Countries that have historically contributed the most to emissions also have the most practical storage space available and must show leadership in using this resource responsibly. Decisions today will determine whether storage is used wisely or wasted,” notes coauthor Siddharth Joshi, research scholar in the Integrated Assessment and Climate Change Research Group at IIASA.

By showing carbon storage is a finite global resource, the study calls for international cooperation and careful planning. The authors identify that some scenarios used to guide policymaking assessed by the IPCC would breach this global limit before 2100, and project that almost all scenarios would do so by 2200, highlighting the difficult tradeoffs facing energy and climate planners. Policymakers will need to decide how to balance the competing demands of ongoing fossil fuel use with the need to remove carbon from the atmosphere to protect future generations.

“Carbon storage is often portrayed as a way out of the climate crisis. Our findings make clear that it is a limited tool. With current trends suggesting warming up to 3°C this century, using all of the safe geological storage wouldn’t even get us back to 2°C. Our study is a call for nations serious about meeting the Paris Agreement – they need to be clear, prudent, and practical about how they plan to use carbon storage to do so. Used strategically in conjunction with fast and deep emissions reductions, it will help us meet climate goals. But used carelessly while allowing fossil fuels to continue to proliferate, it could close off options for future generations,” says Gidden.

The authors highlight that while carbon storage remains an important part of climate solutions, it should be treated like any scarce resource – with transparency, fairness, and a long-term vision.

The team has developed an interactive website that allows policymakers, researchers, and the public to explore the findings in detail. The platform provides country-level visualizations of safe, practical carbon storage potential, helping users understand the tradeoffs and risks involved in different regions. This tool is designed to support evidence-based decision making and international cooperation on the prudent use of geological storage. Explore the story, data, and interactive maps here: https://cdr.apps.ece.iiasa.ac.at/story/prudent-carbon-storage [NOTE: Due to the embargo, the link will not be accessible until 3 September 2025 at 16:00 BST/17:00CEST/11:00am ET]

Reference
Gidden, M.J., Joshi, S., Armitage, J.J., Christ, A-B., Boettcher, M., Brutschin, E., Köberle, A.C., Riahi, K., Schellnhuber, H.J., Schleussner, C-F., Rogelj, J. (2025). A prudent planetary limit for geologic carbon storage. Nature DOI: https://doi.org/10.1038/s41586-025-09423-y [NOTE: Due to the embargo, the link will not be accessible until 3 September 202 at 16:00 BST/17:00CEST/11:00am ET]

 

About IIASA:
The International Institute for Applied Systems Analysis (IIASA) is an international scientific institute that conducts research into the critical issues of global environmental, economic, technological, and social change that we face in the twenty-first century. Our findings provide valuable options to policymakers to shape the future of our changing world. IIASA is independent and funded by prestigious research funding agencies in Africa, the Americas, Asia, and Europe. www.iiasa.ac.at

 

Global methane levels continue rising as planet heats up





University of Birmingham





The world’s methane emissions continue to rise steadily with no signs of slowing, as global trade contributes some 30% to the total amount of the greenhouse gas swirling around the planet, a new study reveals.

As major trade patterns shift, South-South transactions now dominate global supply chains with developing countries increasingly participating in global supply chains. Asia and the developing Pacific region emerge as the largest contributors to global methane emissions, driven by rapid industrialisation and population growth.

Publishing their research today (3 Sep) in Nature Communications, an international team led by researchers at the Universities of Birmingham and Groningen provides the most comprehensive analysis to date of methane emissions across 164 countries and 120 sectors from 1990 to 2023.

With a global warming potential 80 times greater than CO₂ over a 20-year period, methane mitigation offers a critical opportunity to slow climate change in the near term. The researchers discovered that only developed countries have consistently reduced emissions while maintaining economic growth - mainly through improved production efficiency.

Lead author Prof. Yuli Shan, from the University of Birmingham, commented: “Methane has a short atmospheric lifespan, which means reductions today can have an immediate impact. Our findings underscore the need for coordinated global action, especially in developing regions where emissions are rising fastest.”

The study highlights fertiliser production as a key sector for action – also calling for targeted sectoral strategies, including advanced leak detection in oil and gas extraction, improved livestock feed formulations, and enhanced waste management practices. It also advocates for smarter consumption choices, such as reducing red meat intake, which has been linked to high methane emissions.

Co-corresponding author Professor Klaus Hubacek, from the University of Groningen, commented: “This study provides a roadmap for policymakers to integrate methane into national climate strategies. It’s not just about where emissions occur, but why—and that requires looking at the entire supply chain.”

Using the latest global trade  and environmental accounts dataset, the researchers found that global trade is responsible for approximately 30% of methane emissions. Shifting trade patterns have led to increased emissions in developing countries, which often lack the technological efficiency of their developed counterparts.

While economic growth and changing consumption patterns have fuelled increases, improvements in energy efficiency and cleaner production technologies have helped offset some of the growth. Between 1998 and 2023, global average methane emission coefficients dropped by nearly 67%, reflecting significant technological progress.

Methane has contributed about 30% to global warming since pre-industrial times. Unlike CO₂, methane has a shorter atmospheric lifespan, making its reduction a fast-acting climate solution. It also contributes to air pollution, causing around one million premature deaths annually.

ENDS

Notes to editor:

  • The University of Birmingham is ranked amongst the world’s top 100 institutions. Its work brings people from across the world to Birmingham, including researchers, teachers and more than 8,000 international students from over 150 countries.
  • ‘Global methane footprints growth and drivers 1990-2023’ - Yuli Shan, Kailan Tian, Ruoqi Li, Yuru Guan, Jiamin Ou, Dabo Guan, and Klaus Hubacek is published in Nature Communications.
  • Participating institutions: University of Birmingham, UK; Chinese Academy of Sciences, Beijing; University of Cambridge, UK; University of Groningen, the Netherlands; Tsinghua University, China; and University College London, UK.

 

 

 

Premiere in New Zealand: HALO research aircraft takes a detailed look at clouds in the South Pacific and Southern Ocean



Focus on the clean atmosphere of the Antarctic region





Leibniz Institute for Tropospheric Research (TROPOS)

HALO 1 

image: 

The German research aircraft HALO has been prepared for deployment in New Zealand at its home base at the German Aerospace Center (DLR) in Oberpfaffenhofen.

view more 

Credit: Roger Riedel, DLR





Oberpfaffenhofen/Leipzig. The German research aircraft HALO is currently being prepared for deployment in New Zealand at its home base at the German Aerospace Center (DLR) in Oberpfaffenhofen: During the "HALO-South" mission, which will begin in September, researchers led by the Leibniz Institute of Tropospheric Research (TROPOS) will investigate the interaction of clouds, aerosols, and radiation over the Southern Ocean. To this end, HALO will spend five weeks conducting measurement flights over the oceans of the clean southern hemisphere from Christchurch, New Zealand. Since it went into service in 2012, HALO has only been used this far south once before. The mission in New Zealand is therefore a first: never before has a German research aircraft investigated the South Pacific and the adjacent Southern Ocean in this region. The aircraft measurements during ‘HALO-South’ are mainly funded by the German Research Foundation (DFG) with contributions from the Max Planck Institute for Chemistry (MPIC) and the German Aerospace Centre (DLR). They mark the start of intensive research cooperation between Germany and New Zealand.

 

The researchers hope that the measurements will not only provide important data for optimizing weather forecasts and climate models in the little-explored southern hemisphere, but also provide a better fundamental understanding of how the atmosphere and clouds will respond to a decline in anthropogenic emissions in the coming decades. For the team, looking into the cleaner atmosphere around Antarctica is therefore also a glimpse into the future. 

The Southern Ocean around Antarctica is one of the cloudiest regions on Earth. Current climate models are based primarily on measurements in the northern hemisphere. Since the southern hemisphere has less land mass, fewer people, and less industry, it is significantly cleaner than the northern hemisphere. Because the atmosphere in the south is cleaner, there are fewer particles on which droplets or ice crystals can form. That is why there is less ice and more liquid water droplets in the clouds there than in the north. However, atmospheric models have so far been mainly aligned to data from the northern hemisphere, which leads to uncertainties in the representation of clouds in the southern hemisphere. This discrepancy has been known for several years, but there is a lack of measurements in the south to adjust the climate models accordingly. 

 

"We hope that the large-scale HALO-South measurement campaign will enable us to make an important contribution to closing this gap," explains campaign leader Prof. Mira Pöhlker from TROPOS and the University of Leipzig. Twenty-two special measuring instruments from eight institutes will be used to study the entire cycle of cloud formation, from particle formation from precursor gases to cloud seeds and the radiation properties of clouds. "We are very pleased to have so many experienced experts on board to work together to answer questions such as: What aerosols are present in the Southern Ocean? Where do they come from? How do they change clouds?" A total of 176 flight hours are planned for the HALO-South mission. Around 50 researchers will be on site from the Leibniz Institute for Tropospheric Research (TROPOS), the Leipzig Institute for Meteorology at the Leipzig University, Johannes Gutenberg University Mainz (JGU), Goethe University Frankfurt (GUF), the Max Planck Institute for Chemistry (MPIC) in Mainz, the Karlsruhe Institute of Technology (KIT), the Institute of Atmospheric Physics of the German Aerospace Center (DLR), and the Forschungszentrum Jülich (FZJ). The aircraft is operated by the Flight Experiments (FX) facility at DLR Oberpfaffenhofen. The University of Canterbury, Christchurch, and MetService New Zealand are also participating with ground-based measurements.

 

September marks the end of winter in New Zealand and the beginning of spring in the Southern Ocean. This time of year was chosen to study the particularly clean atmosphere over the seas around New Zealand. The campaign will be embedded in parallel intensive field activities such as ground-based measurements from New Zealand and will be supported by satellite investigations. For example, the flight plan on site will be adjusted to the overflights of the ESA EarthCARE Earth observation satellite in order to fly exactly under the satellite orbit. The HALO-South mission will thus support the validation of the ESA satellite as well as the EU CleanCloud project, which investigates interactions between aerosols and clouds to improve our understanding of climate dynamics in a constantly changing world. Prof. Andreas Macke, Director of TROPOS, who initiated HALO-South in 2018, adds: "I am delighted that, with this and other projects in collaboration with international partners, will enable us to take research in the southern hemisphere to an unprecedented level."

 

The aircraft measurements taken by HALO will also be supplemented by ground measurements at the MetService New Zealand site in Invercargill in the far south of New Zealand. From September 2025 to March 2027, several remote sensing and in-situ measuring devices from TROPOS will analyze cloud properties during the "goSouth-2" measurement campaign to create a detailed contrast study between clean Antarctic air and aerosol-polluted Australian air. During HALO-South, in addition to the measurements in Invercargill, which are scheduled to last around two years, accompanying ground measurements will also be carried out by the Universities of Leipzig and Canterbury at the Tāwhaki National Aerospace Centre on the eastern side of New Zealand's South Island. There, a cloud radar and a Doppler wind lidar will contribute to recording the cloud structure that is important for the HALO-South campaign. The HALO-South mission thus marks the start of a series of intensive collaborations in the field of atmospheric research between Germany and New Zealand. The investigations around Antarctica are to be continued in 2027-2030 as part of the large-scale international research project "Antarctica InSync" with a series of Antarctic expeditions, which are currently being planned and will also play a role in atmospheric research. 

 

HALO-South will provide urgently needed insights into the relationship between aerosols and clouds in the southern hemisphere, from the formation of cloud droplets and ice to changes in the radiation budget caused by clouds, which in turn are relevant for the formation of aerosols. These findings will be extrapolated to a larger scale using satellite data and global climate models. The campaign will build on and continue previous HALO campaigns that focused either on cloud and aerosol properties or on gas and aerosol properties (ML-CIRRUS, CIRRUS-HL, ACRIDICON, CAFE-EU, CAFE-Brasil, CAFE-Pacific, EMeRGe-EU, and EMeRGe-Asia). The measurements at HALO-South are intended to cover the interaction with aerosols throughout the entire life cycle of clouds, from formation to dissipation. With this extensive measurement campaign, the researchers aim to better understand the differences between the southern and northern hemispheres in order to improve weather forecasting and climate models. They also hope to gain a better understanding of how the atmosphere of the northern hemisphere will change in an increasingly decarbonized world without fossil-fuel based emissions.

 HALO 2 

The German research aircraft HALO has been prepared for deployment in New Zealand at its home base at the German Aerospace Center (DLR) in Oberpfaffenhofen.

  

The German research aircraft HALO has been prepared for deployment in New Zealand at its home base at the German Aerospace Center (DLR) in Oberpfaffenhofen.

The German research aircraft HALO has been prepared for deployment in New Zealand at its home base at the German Aerospace Center (DLR) in Oberpfaffenhofen.


The German research aircraft HALO has been prepared for deployment in New Zealand at its home base at the German Aerospace Center (DLR) in Oberpfaffenhofen.

Credit

Tilo Arnhold, TROPOS

HALO

The HALO research aircraft is a joint initiative of German environmental and climate research institutions. HALO was funded by the Federal Ministry of Research, Technology and Space (BMFTR), the Helmholtz Association, the Max Planck Society (MPG), the Free State of Bavaria, the Jülich Research Center (FZJ), the Karlsruhe Institute of Technology (KIT), and the German Aerospace Center (DLR). 

HALO is operated by the German Research Foundation (DFG), the German Aerospace Center (DLR), the Max Planck Society (MPG), the Forschungszentrum Jülich (FZJ), the Karlsruhe Institute of Technology (KIT), and the Leibniz Institute for Tropospheric Research in Leipzig (TROPOS). The DLR is both the owner and operator of the aircraft.

 

Researchers describe for the first time brain signals associated with forgetting unpleasant memories in humans



The discovery may help improve therapies for post-traumatic stress disorder and anxiety




Universitat Autonoma de Barcelona




Suppression of fear-related memories after unpleasant experiences is very critical for adaptive behaviour, as it allows one to inhibit responses that could lead to psychiatric problems such as anxiety or depression. Recent theories propose that the extinction of these memories takes place when new, highly context-dependent memories that suppress the initial fear response are created. Electrophysiological experiments on mice support this theory, and show a relationship between certain oscillations of signals recorded in the brain regions of the amygdala and hippocampus with the learning and extinction of fear-response memories. However, this relationship has so far not been confirmed in the human brain.

In an article published recently in Nature Human Behaviour, researchers at the Universitat Autònoma de Barcelona and Ruhr-Universität Bochum, Germany, describe for the first time the electrophysiological signals associated with the extinction of aversive memories in humans.

Researchers employed a powerful technique to study the characteristics of human memory called Representational Similarity Analysis (RSA), which provides information on how brain regions represent information. “The technique allows us to achieve a more detailed and mechanistic understanding of episodic memories, overcoming traditional approaches based solely on brain activation”, explains Daniel Pacheco-Estefan, first author of the paper and researcher at the UAB Department of Basic, Developmental and Educational Psychology.

The study provides a detailed characterisation of the neural representations involved in the formation and extinction of associative memories. Researchers used a novel experimental design that included multiple cues and contexts in each phase of the experiment (memory acquisition, memory extinction and testing). This allowed them to study the representations underlying classical conditioning in humans and to validate, for the first time, hypotheses derived from studies in animal models. The study involved the participation of 49 epileptic patients who had already had electrodes implanted - for the treatment of the disease - in the brain area related to fear memories and the extinction of these memories. The patients were shown a series of neutral images (a hair dryer, a fan and a toaster), associating some of them with an unpleasant stimulus (a sound), while the brain activity was recorded. Later, the procedure was repeated, but this time without associating the images with the aversive stimulus, in order to promote the extinction of aversive memories.

Among the main findings, researchers observed an increase in theta activity - a type of oscillatory signal emitted by the brain's electrical activity - in the amygdala - a key structure in the coding of emotional states - when previously unpleasant stimuli were presented during extinction learning, suggesting a safety signal. In addition, they observed higher representational similarity between items that were punished during extinction, i.e., those that had been associated with negative sounds. “This result is consistent with previous research that has identified a generalised representational signature for unpleasant memories, which favours their involuntary reappearance in all kinds of situations in subjects who have undergone traumatic experiences”, emphasises Daniel Pacheco-Estefan.

The study also shows that extinction memories are highly dependent on the context in which they are formed. Retrieval of fear memory is more likely than that of safety memory during the test phase, when representations of extinction contexts are more pronounced and specific during extinction. For Pacheco-Estefan “this finding has relevant implications for understanding why fear memories that have already been extinguished, return once patients are out of the therapeutic context”. Nikolai Axmacher, coordinating researcher at RUB, adds: “It seems that extinction memories are stored like memories of unique episodes – for the patient, the safe situation may be regarded as an exception that is unlikely to repeat.”

Overall, these pioneering results open new paths to investigating the fundamental mechanisms of episodic and autobiographical memory in humans, and “could inspire the development of more effective therapeutic interventions in patients with post-traumatic stress or anxiety disorders”, concludes the UAB researcher.

 

Global study reveals how patients view medical AI





Technical University of Munich (TUM)





How physicians feel about artificial intelligence in medicine has been studied many times. But what do patients think? A team led by researchers at the Technical University of Munich (TUM) has investigated this for the first time in a large study spanning six continents. The central finding: the worse people rate their own health, the more likely they are to reject the use of AI. The study is intended to help align future medical AI applications more closely with patients’ needs.

Acceptance by patients is essential for the effective use of artificial intelligence in medicine, regardless of whether AI is used as a diagnostic tool, to create individual treatment plans or for other applications. The international research network of the COMFORT study therefore surveyed around 14,000 patients in 74 clinics in 43 countries. In order to cover a wide range of diseases, the survey was conducted in radiology departments that carry out X-ray, CT and MRI examinations on behalf of other specialist disciplines.

A majority – 57.6% – viewed the use of AI in medicine positively. However, some differences emerged within the cohort: men were slightly more favorable at 59.1% than women at 55.6%. Approval also rose markedly with greater familiarity with technology and higher self-rated understanding of AI. Among respondents who described themselves as highly knowledgeable about AI, 83.3% were positive about using it in medicine.

Negative view of AI in severe illness

The more severe a person’s own illness, the more negative their attitude toward AI. More than half of patients in very poor health rated medical AI “extremely negative” or “rather negative” (26.6% and 29.2%, respectively). Among those in very good health, the corresponding figures were 1.3% and 5.3%.

“The exact reasons for negative attitudes among seriously ill patients cannot be determined from our study,” says Dr. Felix Busch, assistant physician at TUM’s Institute of Diagnostic and Interventional Radiology and the study’s first author. “We suspect that experiences with the health care system, illness burden, and psychological factors play a role.”

Explainability of medical AI is crucial

Respondents expressed clear preferences for how AI should be used and designed. For 70.2%, it was important that medical AI be ‘explainable,’ allowing users to see the steps leading to its conclusions. In addition, 72.9% wanted these technologies to function as tools, with physicians making the final decisions.

Only 4.4% favored diagnoses made exclusively by AI. At the same time, just 6.6% wanted diagnoses to be made entirely without AI. These questions referred to hypothetical scenarios in which human clinicians and AI were equally accurate. “The results show that explainability must be considered from the outset,” says Felix Busch.

Basis for further studies

One methodological limitation is the survey timing in 2023. “Since then, large language models in particular have advanced considerably. Patient attitudes may have changed,” says Adjunct Teaching Professor Dr. Keno Bressem, senior lecturer and, together with Adjunct Teaching Professor Dr. Lisa Adams, senior author of the study. “Follow-up surveys are needed to test this and to align the development of medical AI with patients’ needs,” adds Dr. Lisa Adams. A follow-up study by the COMFORT consortium using the same questionnaire is already underway.

 

Publication:

Busch F, Hoffmann L, Xu L, et al. Multinational Attitudes Toward AI in Health Care and Diagnostics Among Hospital Patients. JAMA Netw Open. 2025;8(6):e2514452. doi: 10.1001/jamanetworkopen.2025.14452

Subject matter expert:

Dr. Felix Busch
Technical University of Munich
TUM University Hospital
Institute for Diagnostic and Interventional Radiology
Phone +49 89 4140 1180
felix.busch@tum.de
https://radiologie.mri.tum.de

 

TUM Corporate Communications Center contact:

Paul Hellmich
Media Relations
Tel. +49 (0) 89 289 22731
presse@tum.de
www.tum.de