A new study warns that global declines in soil moisture in the 21st century could mark a “permanent” shift in the world’s water cycle.
Combining data from satellites, sea level measurements and observations of “polar motion”, the research shows how soil moisture levels have decreased since the year 2000.
The findings, published in Science, suggest the decline is primarily driven by an increasingly thirsty atmosphere as global temperatures rise, as well as shifts in rainfall patterns.
Consequently, the researchers warn the observed changes are likely to be “permanent” if current warming trends continue.
An accompanying perspective article says the study provides “robust evidence” of an “irreversible shift” in terrestrial water sources under climate change.
The drying out of soil “increases the severity and frequency” of major droughts, with consequences for humans, ecosystems and agriculture, explains Dr Benjamin Cook, an interdisciplinary Earth system scientist working at the NASA Goddard Institute for Space Studies and Columbia University, who was not involved in the research.
He tells Carbon Brief:
“Droughts are one of the most impactful, expensive natural hazards out there, because they are typically persistent and long lasting. Everything needs water – ecosystems need water, agriculture needs water. People need water. If you don’t have enough water – you’re in trouble.”
Drying soil
Every year, around 6tn tonnes of water cycles through Earth’s land surface. When rain falls on land it gets held up in soil, wetlands, groundwater, lakes and reservoirs on its journey back to the oceans.
Soil moisture forms a critical part of the Earth’s system, helping to irrigate soil, cycle nutrients and regulate the climate.
The amount of water contained in the soil is sensitive to a range of factors, including changes in rainfall, evaporation, vegetation and climate – as well as human activity, such as intensive agriculture.
The research points to a “gradual decline” in soil moisture levels in the 21st century, kickstarted by a period of “sharp depletion” in the three years over 2000-02.
Specifically, the researchers find the depletion of soil moisture resulted in a total loss of 1,614bn tonnes (gigatonnes, or Gt) of water over 2000-02 and then 1,009Gt between 2002 and 2016.
(For context, ice loss in Greenland resulted in 900Gt of water loss over 2002-06.)
Soil moisture has not recovered as of 2021, according to the research, and is unlikely to pick up under present climate conditions.
Joint-lead author Prof Dongryeol Ryu, professor of hydrology and remote sensing at the University of Melbourne, explains to Carbon Brief:
“We observed a stepwise decline [in soil moisture] twice in the past two decades, interspersed within a continuously declining trend in soil moisture. We haven’t seen this trend earlier, so that is why this is very concerning.”
Ryu explains the decision to analyse changes to soil moisture on a global scale meant the researchers could confirm trends difficult to see in smaller geographic datasets:
“The unique thing we found through analysing these larger-scale measures is that – even if we have seen widely fluctuating ups and downs in precipitation and increasing temperature – the total water contained in the soil, as soil moisture and groundwater, has been declining gradually from around the beginning of this century.“
The maps below illustrate soil moisture changes in 2003-07 and 2008-12 against a 1995-99 baseline, as estimated by the ERA5-Land reanalysis dataset. The areas marked on the map in brown saw a drop in soil moisture and the areas marked in blue an increase in soil moisture.
The top map shows soil moisture depletion across large regions in eastern and central Asia, central Africa and North and South America over 2003-07. The lower map shows that “replenishment” in the years that followed occurred in relatively small parts of South America, India, Australia and North America.
Climate change
Ryu says the researchers “suspect that increasing temperature played an important role” in the decline in terrestrial water storage and soil moisture in the 21st century.
The study points to two factors driving gradual depletion of soil moisture over the last quarter century: fluctuations to rainfall patterns and increasing “evaporative demand”.
Evaporative demand refers to the atmosphere’s “thirst” for water, or how much moisture it can take from the land, vegetation and surface water.
Studies have highlighted how global evaporative demand has been increasing over the last two decades globally, impacting water availability, hurting crops and causing drought.
The new study notes that “increasing evaporative demand driven by a warming climate” suggests a “more consistent and widespread trend toward drying as temperatures rise”.
Ryu says the “very unusual” drop in water moisture observed over 2000-02 could be attributed to low levels of rainfall globally, which coincided with the “period when evaporative demand started increasing”.
Another – less pronounced – period of rapid soil moisture decline seen over 2015-16 can be attributed to droughts triggered by the 2014-16 El Niño event, Ryu notes.
Ryu says the study findings indicate that soil moisture can no longer bounce back from a dry year, as it has in the past:
“It used to be that when precipitation goes up again, we recover water in the soil. But because of this increasing evaporative demand, once we have strong El Niño years – which lead to much less rainfall for a year or two – it seems that we are not recovering the water fully because of increasing evaporative demand. Because of that – even if we have a wet year following dry years – the water in the soil doesn’t seem to recover.”
Cross-validation
Measuring changes in global soil moisture has historically presented a challenge to scientists, given the lack of comprehensive and direct observations of water in soil.
The researchers attempt to reduce this uncertainty by corroborating the ERA5-Land reanalysis dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF) with three geophysical measurement datasets.
ERA5’s land surface modelling system uses meteorological and other input data to estimate water within the upper few metres of the soil.
These figures were compared with data collected by the Gravity Recovery and Climate Experiment (GRACE) mission – a joint satellite mission between NASA and the German Aerospace Center.
Running since 2002, the GRACE mission tracks changes to the Earth’s gravity by collecting data on groundwater depletion, ice sheet loss and sea level rise. These observations have revealed a persistent loss of water from land to the ocean.
The scientists also cross-reference the ERA5 reanalysis data with a century-old dataset that measures fluctuations in the rotation of the Earth as the distribution of mass on the planet changes.
(The redistribution of ice and water, such as melting ice sheets and depleting groundwater, causes the planet to wobble as it spins and its axis to shift slightly. This is known as “polar motion”.)
The third set of measurements the scientists use is global mean sea level height, which is collected by satellites.
To extract soil moisture changes from this set of data, the researchers subtracted other components of sea level rise from the overall total – including Greenland ice melt, Antarctica ice melt, the impact of increasing sea surface temperature (which expands water volume) and the contribution of groundwater.
This process of elimination left researchers with an estimate of the contribution of soil moisture to global sea level rise.
The study notes that both the sea surface height and polar motion observations “support the conclusion that the abrupt change in soil moisture is genuine”.
Ryu says using global average sea level rise and “Earth wobble” to track water redistribution on land is the “main innovation” applied in the paper.
He adds the value of “reverse engineering” the ERA5 dataset is to understand how to enhance land surface modelling in the future:
“By explaining all the contributing factors to this measurement, you can understand the process. And if you understand the process, you can actually predict what’s going to happen in the future if any of these factors change in a certain manner.”
NASA’s Dr Cook says the “corroborating evidence” supplied by the paper offers a “really strong case that there has been a large-scale decline in soil moisture in recent decades”.
However, he says the relatively short reference period of the study means that identifying the cause of the decline is less clear cut:
“Whether [the decline] is permanent or not is much more uncertain…On these timescales, internal natural variability can be really, really strong. Attributing this decline to something specific – either climate change or internal variability – is much much more difficult.”
Sea level rise
A notable finding in the study’s sea level rise analysis is that terrestrial water storage may have been the dominant driver of sea level rise in the early 21st century.
Specifically, the paper notes that the decline in terrestrial water storage over 2000-02 – when soil moisture plummeted – led to global average sea level rise of almost 2mm annually.
The researchers note this rate of sea level rise is “unprecedented” and “significantly higher” than the rate of sea level rise attributed to Greenland ice mass loss, which they note is approximately 0.8mm a year.
Prof Reed Maxwell, a professor at the High Meadows Environmental Institute at Princeton University, who was also not involved in the study, says the researchers’ efforts to compare soil moisture with other global water stores was “novel” and “opens the door to future study of a more holistic global water balance”.
‘Creeping disaster’
The paper notes that land surface and hydrological models require “substantial improvement” to accurately simulate changes in soil moisture in changing climate.
Current models do not factor the impacts of agricultural intensification, nor the ongoing “greening” of semi-arid regions – both of which “may contribute” to a further decline in soil moisture, it states.
Writing in a perspectives article published in Science, Prof Luis Samaniego from the department of computational hydrosystems at the Helmholtz Centre for Environmental Research says that it is “essential” that next-generation models incorporate human-caused influences such as farming, large dams and irrigation systems.
The study posits that the “innovative methods” for estimating changes in global soil moisture presented in the study provide opportunities to “improve the present state of modelling at global and continental scales”.
More broadly, advances in scientific understanding of changes to soil moisture can help improve the world’s preparedness for drought.
Drought is often described as a “creeping disaster” – because by the time it is identified, it is usually already well under way,
Paper author Ryu explains:
“Unlike a flood and heatwaves, drought comes very very slowly – and has prolonged and delayed consequences. We better be prepared earlier than later, because once drought comes you can expect a long period of consequences.”
Dr Shou Wang, associate professor at the Hydroclimate Extremes Lab and the Hong Kong Polytechnic University, who was not involved in the study, says the research findings are “crucial” for advancing understanding of the “potential drivers and dynamics” of “unprecedented hydrological extremes in a warming climate”. He tells Carbon Brief:
“This is breakthrough work that uncovers the drivers of hydrological regime changes, which are leading to unprecedented hydrological extremes such as compound and consecutive drought-flood events.”
The post Global soil moisture in ‘permanent’ decline due to climate change appeared first on Carbon Brief.
Global soil moisture in ‘permanent’ decline due to climate change
Colombia wants countries to discuss options for a global agreement to ensure that the extraction, processing and recycling of minerals – including those needed for the clean energy transition – don’t harm the environment and human wellbeing.
The mineral-rich nation is proposing to create an expert group to “identify options for international instruments, including global and legally-binding instruments, for coordinated global action on the environmentally sound management of minerals and metals through [their] full lifecyle”.
Colombia hopes this will eventually lead to an agreement on the need for an international treaty to define mandatory rules and standards that would make mineral value chains more transparent and accountable.
The proposal was set out in a draft resolution submitted to the UN Environment Assembly (UNEA) earlier this week and seen by Climate Home News. UNEA, which is constituted of all UN member states, is the world’s top decision-making body for matters relating to the environment. The assembly’s seventh session will meet in Kenya in December to vote on countries’ proposals.
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Soaring demand for the minerals used to manufacture clean energy technologies and electric vehicles, as well as in the digital, construction and defence industries have led to growing environmental destruction, human rights violations and social conflict.
Colombia argues there is an “urgent need” to strengthen global cooperation and governance to reduce the risks to people and the planet.
Options for a global minerals agreement
The proposal is among a flurry of initiatives to strength global mineral governance at a time when booming demand is putting pressure on new mining projects.
Colombia, which produces emeralds, gold, platinum and silver for exports, first proposed the idea for a binding international agreement on minerals traceability and accountability on the sidelines of the UN biodiversity talks it hosted in October 2024.
Since then, the South American nation has been quietly trying to drum up support for the idea, especially among African and European nations.
Its draft resolution to UNEA7 contains very few details, leaving it open for countries to discuss what kind of global instrument would be best suited to make mineral supply chains more transparent and sustainable.
Does the world need a global treaty on energy transition minerals?
Colombia says it wants the expert group to build on other UN initiatives, including a UN Panel on Critical Energy Transition Minerals, which set out seven principles to ensure the mining, processing and recycling of energy transition minerals are done responsibly and benefit everyone.
The group would include technical experts and representatives from international and regional conventions, major country groupings as well as relevant stakeholders.
It would examine the feasibility and effectiveness of different options for a global agreement, consider their costs and identify measures to support countries to implement what is agreed.
The resolution also calls for one or two meetings for member states to discuss the idea before the UNEA8 session planned in late 2027, when countries would decide on a way forward.
No time to lose for treaty negotiations
Colombia’s efforts to advance global talks on mineral supply chains have been welcomed by resource experts and campaigners. But not everyone agrees on the best strategy to move the discussion forward at a time when multilateralism is coming under attack.
Johanna Sydow, a resource policy expert who heads the international environmental policy division of the Heinrich-Böll Foundation, said she had hoped that the resolution would explicitly call for negotiations to begin on an international minerals treaty.
“Treaty negotiations take a long time. If you don’t even start with it now, it will take even longer. I don’t see how in two or three years it will be easier to come to an agreement,” she told Climate Home.
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Despite the geopolitical challenges, “we need joint rules to prevent a huge race to the bottom for [mineral] standards”. That could start with a group of countries coming together and starting to enforce joint standards for mining, processing and recycling minerals, she said.
But any meaningful global agreement on mineral supply chains would require backing from China, the world’s largest processor of minerals, which dominates most of the supply chains. And with Colombia heading for an election in May, it will need all the support it can get to move its proposal forward.
‘Voluntary initiative won’t cut it’
Juliana Peña Niño, Colombia country manager at the Natural Resource Governance Institute, is more optimistic. “Colombia’s leadership towards fairer mineral value chains is a welcome step,” she told Climate Home News.
“At UNEA7, we need an ambitious debate that gives the proposed expert group a clear mandate to advance concrete next steps — not delay decisions — and that puts the voices of those most affected at the centre. One thing is clear: the path forward must ultimately deliver a binding instrument, as yet another voluntary initiative simply won’t cut it,” she said.
More than 50 civil society groups spanning Latin America, Africa and Europe previously described Colombia’s work on the issue as “a chance to build a new global paradigm rooted in environmental integrity, human rights, Indigenous Peoples’ rights, justice and equity”.
“As the energy transition and digitalisation drive demand for minerals, we cannot afford to repeat old extractive models built on asymmetry – we must redefine them,” they wrote in a statement.
Main image: The UN Environment Assembly is hosted in Nairobi, Kenya. (Natalia Mroz/ UN Environment)
The post Colombia proposes expert group to advance talks on minerals agreement appeared first on Climate Home News.
Colombia proposes expert group to advance talks on minerals agreement
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Climate Change
DeBriefed 3 October 2025: UK political gap on climate widens; Fossil-fuelled Typhoon Ragasa; ‘Overshoot’ unknowns
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
Shattered climate consensus
FRACKING BAN: UK energy secretary Ed Miliband has announced that the government will bring forward its plans to permanently ban fracking, in a move designed to counter a promise from the hard-right Reform party to restart efforts to introduce the practice, the Guardian said. In the same speech, Miliband said Reform’s plans to scrap clean-energy projects would “betray” young people and future generations, the Press Association reported.
ACT AXE?: Meanwhile, Kemi Badenoch, leader of the Conservatives, pledged to scrap the 2008 Climate Change Act if elected, Bloomberg reported. It noted that the legislation was passed with cross-party support and strengthened by the Conservatives.
‘INSANE’: Badenoch faced a backlash from senior Tory figures, including ex-prime minister Theresa May, who called her pledge a “catastrophic mistake”, said the Financial Times. The newspaper added that the Conservatives were “trailing third in opinion polls”. A wide range of climate scientists also condemned the idea, describing it as “insane”, an “insult” and a “serious regression”.
Around the world
- CLIMATE CRACKDOWN: The US Department of Energy has told employees in the Office of Energy Efficiency and Renewable Energy to avoid using the term “climate change”, according to the Guardian.
- FOREST DELAY: Plans for Brazil’s COP30 flagship initiative, the tropical forests forever fund, are “suffer[ing] delays” as officials remain split on key details, Bloomberg said.
- COP MAY BE ‘SPLIT’: Australia could “split” the hosting of the COP31 climate summit in 2026 under a potential compromise with Turkey, reported the Guardian.
- DIVINE INTERVENTION: Pope Leo XIV has criticised those who minimise the “increasingly evident” impact of global warming in his first major climate speech, BBC News reported.
€44.5 billion
The cost of extreme weather and climate change in the EU in the last four years – two-and-a-half times higher than in the decade to 2019, according to a European Environment Agency report covered by the Financial Times.
Latest climate research
- Fossil-fuelled climate change caused around 36% of Typhoon Ragasa’s direct damage to homes and properties in southern China, according to a rapid impact attribution study | Imperial Grantham Institute – Climate Change and the Environment
- Some 86% of the global population are concerned about climate change, according to a survey of 280,000 people in 142 countries and regions | Climate Policy
- A global shift towards a “planetary health diet” could slash emissions and save tens of thousands of lives each day | EAT-Lancet Commission 2025 report
(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)
Captured
Clean energy has met 100% of Great Britain’s electricity demand for a record 87 hours this year so far, according to new Carbon Brief analysis. This is up from just 2.5 hours in 2021 and 64.5 hours in all of 2024. The longest stretch of time where 100% of electricity demand was met by clean energy stands at 15 hours, from midnight on 25 May 2025 through to 3pm on 26 May, according to the analysis.
Spotlight
‘Overshoot’ unknowns
As the chances of limiting global warming to 1.5C dwindle, there is increasing focus on the prospects for “overshooting” the Paris Agreement target and then bringing temperatures back down by removing CO2 from the atmosphere.
At the first-ever Overshoot Conference in Laxenburg, Austria, Carbon Brief asks experts about the key unknowns around warming “overshoot”.
Sir Prof Jim Skea
Chair of the Intergovernmental Panel on Climate Change (IPCC) and emeritus professor at Imperial College London’s Centre for Environmental Policy
So there are huge knowledge gaps around overshoot and carbon dioxide removal (CDR). As it’s very clear from the themes of this conference, we don’t altogether understand how the Earth would react in taking CO2 out of the atmosphere.
We don’t understand the nature of the irreversibilities and we don’t understand the effectiveness of CDR techniques, which might themselves be influenced by the level of global warming, plus all the equity and sustainability issues surrounding using CDR techniques.
Prof Kristie Ebi
Professor at the University of Washington’s Center for Health and the Global Environment
There are all kinds of questions about adaptation and how to approach effective adaptation. At the moment, adaptation is primarily assuming a continual increase in global mean surface temperature. If there is going to be a peak – and of course, we don’t know what that peak is – then how do you start planning? Do you change your planning?
There are places, for instance when thinking about hard infrastructure, [where overshoot] may result in a change in your plan – because as you come down the backside, maybe the need would be less. For example, when building a bridge taller. And when implementing early warning systems, how do you take into account that there will be a peak and ultimately a decline? There is almost no work in that. I would say that’s one of the critical unknowns.
Dr James Fletcher
Former minister for public service, sustainable development, energy, science and technology for Saint Lucia and negotiator at COP21 in Paris.
The key unknown is where we’re going to land. At what point will we peak [temperatures] before we start going down and how long will we stay in that overshoot period? That is a scary thing. Yes, there will be overshoot, but at what point will that overshoot peak? Are we peaking at 1.6C, 1.7C, 2.1C?
All of these are scary scenarios for small island developing states – anything above 1.5C is scary. Every fraction of a degree matters to us. Where we peak is very important and how long we stay in this overshoot period is equally important. That’s when you start getting into very serious, irreversible impacts and tipping points.
Prof Oliver Geden
Senior fellow and head of the climate policy and politics research cluster at the German Institute for International and Security Affairs and vice-chair of IPCC Working Group III
[A key unknown] is whether countries are really willing to commit to net-negative trajectories. We are assuming, in science, global pathways going net-negative, with hardly any country saying they want to go there. So maybe it is just an academic thought experiment. So we don’t know yet if [overshoot] is even relevant. It is relevant in the sense that if we do, [the] 1.5C [target] stays on the table. But I think the next phase needs to be that countries – or the UNFCCC as a whole – needs to decide what they want to do.
Prof Lavanya Rajamani
Professor of international environmental law at the University of Oxford
I think there are several scientific unknowns, but I would like to focus on the governance unknowns with respect to overshoot. To me, a key governance unknown is the extent to which our current legal and regulatory architecture – across levels of governance, so domestic, regional and international – will actually be responsive to the needs of an overshoot world and the consequences of actually not having regulatory and governance architectures in place to address overshoot.
Watch, read, listen
FUTURE GAZING: The Financial Times examined a “future where China wins the green race”.
‘JUNK CREDITS’: Climate Home News reported on a “forest carbon megaproject” in Zimbabwe that has allegedly “generated millions of junk credits”.
‘SINK OR SWIM’: An extract from a new book on how the world needs to adapt to climate change, by Dr Susannah Fisher, featured in Backchannel.
Coming up
- 7 October: International Energy Agency (IEA) renewables 2025 report launch
- 8-10 October: World summit of Indigenous peoples and nature, Abu Dhabi, UAE
- 9-15 October: International Union for the Conservation of Nature (IUCN) 2025 congress, Abu Dhabi, UAE
Pick of the jobs
- UK government foreign, commonwealth and development office, senior climate policy adviser | Salary: CA$93,207. Location: Calgary, Canada
- Wellcome Trust, senior research manager, climate and health | Salary: £64,800. Location: London
- Bloomberg, product manager – climate, nature and sustainability regulations | Salary: Unknown. Location: London
DeBriefed is edited by Daisy Dunne. Please send any tips or feedback to debriefed@carbonbrief.org.
This is an online version of Carbon Brief’s weekly DeBriefed email newsletter. Subscribe for free here.
The post DeBriefed 3 October 2025: UK political gap on climate widens; Fossil-fuelled Typhoon Ragasa; ‘Overshoot’ unknowns appeared first on Carbon Brief.
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