Every year, understanding of climate science grows stronger.
With each new research project and published paper, scientists learn more about how the Earth system responds to continuing greenhouse gas emissions.
But with many thousands of new studies on climate change being published every year, it can be hard to keep up with the latest developments.
Our annual “10 new insights in climate science” report offers a snapshot of key advances in the scientific understanding of the climate system.
Produced by a team of scientists from around the world, the report summarises influential, novel and policy-relevant climate research published over the previous 18 months.
The insights presented in the latest edition, published in the journal Global Sustainability, are as follows:
- Questions remain about the record warmth in 2023-24
- Unprecedented ocean surface warming and intensifying marine heatwaves are driving severe ecological losses
- The global land carbon sink is under strain
- Climate change and biodiversity loss amplify each other
- Climate change is accelerating groundwater depletion
- Climate change is driving an increase in dengue fever
- Climate change diminishes labour productivity
- Safe scale-up of carbon dioxide removal is needed
- Carbon credit markets come with serious integrity challenges
- Policy mixes outperform stand-alone measures in advancing emissions reductions
In this article, we unpack some of the key findings.
A strained climate system
The first three insights highlight how strains are growing across the climate system, from indications of an accelerating warming and record-breaking marine heatwaves, to faltering carbon sinks.
Between April 2023 and March 2024, global temperatures reached unprecedented levels – a surge that cannot be fully explained by the long-term warming trend and typical year-to-year fluctuations of the Earth’s climate. This suggests other factors are at play, such as declining sulphur emissions and shifting cloud cover.
(For more, Carbon Brief’s in-depth explainer of the drivers of recent exceptional warmth.)
Ocean heat uptake has climbed as well. This has intensified marine heatwaves, further stressing ecosystems and livelihoods that rely on fisheries and coastal resources.
The exceptional warming of the ocean has driven widespread impacts, including massive coral bleaching, fish and shellfish mortality and disruptions to marine food chains.
The map below illustrates some of the impacts of marine heatwaves from 2023-24, highlighting damage inflicted on coral reefs, fishing stocks and coastal communities.
Land “sinks” that absorb carbon – and buffer the emissions from human activity – are under increasing stress, too. Recent research shows a reduction in carbon stored in boreal forests and permafrost ecosystems.
The weakening carbon sinks means that more human-caused carbon emissions remain in the atmosphere, further driving up global temperatures and increasing the chances that warming will surpass the Paris Agreement’s 1.5C limit.
This links to the fourth insight, which shows how climate change and biodiversity loss can amplify each other by leading to a decrease in the accumulation of biomass and reduced carbon storage, creating a destabilising feedback loop that accelerates warming.
New evidence demonstrates that climate change could threaten more than 3-6 million species and, as a result, could undermine critical ecosystem functions.
For example, recent projections indicate that the loss of plant species could reduce carbon sequestration capacity in the range of 7-145bn tonnes of carbon over the coming decades. Similarly, studies show that, in tropical systems, the extinction of animals could reduce carbon storage capacity by up to 26%.
Human health and livelihoods
Growing pressure on the climate system is having cascading consequences for human societies and natural systems.
Our fifth insight highlights how groundwater supplies are increasingly at risk.
More than half the global population depends on groundwater – the second largest source of freshwater after polar ice – for survival.
But groundwater levels are in decline around the world. A 2025 Nature paper found that rapid groundwater declines, exceeding 50cm each year, have occurred in many regions in the 21st century, especially in arid areas dominated by cropland. The analysis also showed that groundwater losses accelerated over the past four decades in about 30% of regional aquifers.
Changes in rainfall patterns due to climate change, combined with increased irrigation demand for agriculture, are depleting groundwater reserves at alarming rates.
The figure below illustrates how climate-driven reductions in rainfall, combined with increased evapotranspiration, are projected to significantly reduce groundwater recharge in many arid regions – contributing to widespread groundwater-level declines.
These losses threaten food security, amplifying competition for scarce resources and undermining the resilience of entire communities.
Human health and livelihoods are also being affected by changes to the climate.
Our sixth insight spotlights the ongoing and projected expansion of the mosquito-borne disease dengue fever.
Dengue surged to the largest global outbreak on record in 2024, with the World Health Organization reporting 14.2m cases, which is an underestimate because not all cases are counted.
Rising temperatures are creating more favourable conditions for the mosquitoes that carry dengue, driving the disease’s spread and increasing its intensity.
The chart below shows the regions climatically suitable for Aedes albopictus (blue line) and Aedes aegypti (green line) – the primary mosquitoes species that carry the virus – increased by 46.3% and 10.7%, respectively, between 1951-60 and 2014-23.
The maps on the right reveal how dengue could spread by 2030 and 2050 under an emissions scenario broadly consistent with current climate policies. It shows that the climate suitable for the mosquito that spreads dengue could expand northwards in Canada, central Europe and the West Siberian Plain by 2050.
The ongoing proliferation of these mosquito species is particularly alarming given their ability to transmit the zika, chikungunya and yellow fever viruses.
Heat stress is also a growing threat to labour productivity and economic growth, which is the seventh insight in our list.
For example, an additional 1C of warming is projected to expose more than 800 million people in tropical regions to unsafe heat levels – potentially reducing working hours by up to 50%.
At 3C warming, sectors such as agriculture, where workers are outdoors and exposed to the sun, could see reductions in effective labour of 25-33% across Africa and Asia, according to a recent Nature Reviews Earth & Environment paper.
Meanwhile, sectors where workers operate in shaded or indoor settings could also face meaningful losses. This drain on productivity compounds socioeconomic issues and places a strain on households, businesses and governments.
Low-income, low-emitting regions are set to shoulder a greater relative share of the impacts of extreme heat on economic growth, exacerbating existing inequalities.
Action and policy
Our report illustrates not only the scale of the challenges facing humanity, but also some of the pathways toward solutions.
The eighth insight emphasises the critical role of carbon dioxide removal (CDR) in stabilising the climate, especially in “overshoot” scenarios where warming temporarily surpasses 1.5C and is then brought back down.
Scaling these CDR solutions responsibly presents technical, ecological, justice, equity and governance challenges.
Nature-based approaches for pulling carbon out of the air – such as afforestation, peatland rewetting and agroforestry – could have negative consequences for food security, biodiversity conservation and resource provision if deployed at scale.
Yet, research has suggested that substantially more CDR may be needed than estimated in the scenarios used in the Intergovernmental Panel on Climate Change (IPCC’s) last assessment report.
Recent findings showed that a pathway where temperatures remain below 1.5C with no overshoot would require up to 400Gt of cumulative CDR by 2100 in order to buffer against the effect of complex geophysical processes that can accelerate climate change. This figure is roughly twice the amount of CDR assessed by the IPCC.
This underscores the need for robust international coordination on the responsible scaling of CDR technologies, as a complement to ambitious efforts to reduce emissions. Transparent carbon accounting frameworks that include CDR will be required to align national pledges with international goals.
Similarly, voluntary carbon markets – where carbon “offsets” are traded by corporations, individuals and organisations that are under no legal obligation to make emission cuts – face challenges.
Our ninth insight shows how low-quality carbon credits have undermined the credibility of these largely unregulated carbon markets, limiting their effectiveness in supporting emission reductions.
However, emerging standards and integrity initiatives, such as governance and quality benchmarks developed by the Integrity Council for Voluntary Carbon Markets, could address some of the concerns and criticism associated with carbon credit projects.
High-quality carbon credits that are verified and rigorously monitored can complement direct emission reductions.
Finally, our 10th insight highlights how a mix of climate policies typically have greater success than standalone measures.
Research published in Science in 2024 shows how carefully tailored policy packages – including carbon pricing, regulations, and incentives – could consistently achieve larger and more durable emission reductions than isolated interventions.
For example, in the buildings sector, regulations that ban or phase out products or activities achieve an average effect size of 32% when included in a policy package, compared with 13% when implemented on their own.
Importantly, policy mixes that are tailored to the country context and with attention to distributional equity are more likely to gain public support.
These 10 insights in our latest edition highlight the urgent need for an integrated approach to tackling climate change.
The science is clear, the risks are escalating – but the tools to act are available.
The post Guest post: 10 key climate science ‘insights’ from 2025 appeared first on Carbon Brief.
Climate change, war and mismanagement are putting Iran’s water supply under major strain, experts have warned.
The Middle Eastern country has faced years of intense drought, which scientists have found was made more intense due to human-caused climate change.
In recent years, Iranian citizens have protested against the government’s management of water supplies, pointing the blame at decades of poor planning and shortsighted policies.
As water supplies run low, authorities warned last year that several of Iran’s major cities – including the capital, Tehran – could soon face “water day zero”, when a city’s water service is turned off and existing supplies rationed.
Meanwhile, recent air strikes on desalination plants in Iran and Bahrain are driving wider questions about how the war might exacerbate water insecurity across the Middle East.
One expert tells Carbon Brief the conflict is “straining an already-fragile [water] system” within Iran.
In this article, Carbon Brief looks at how conflict is combining with climate change and unsustainable use to place pressure on Iran’s water supplies.
- How close are Iran’s major cities to a ‘water day zero’?
- What role is climate change playing?
- What other factors are involved?
- How could attacks on desalination plants impact water supplies in the Middle East?
- What policies could help Iran avoid a ‘water day zero’?
How close are Iran’s major cities to a ‘water day zero’?
Iran is one of the most water-stressed countries in the world and is currently in the grips of an unprecedented, multi-year drought.
The country’s hot and dry climate means that freshwater is scarce. However, many Iranian citizens also blame decades of government mismanagement for the present-day water shortages.
In January, the Guardian explained that over multiple decades, Iranian officials abandoned the country’s “qanat aquifer system”, which consists of tens of thousands of tunnels dug into hillsides across the country that lead to underground water storage. This system has been “supplying [Iran’s] cities and agriculture with freshwater for millennia”, the newspaper said.
To replace the aquifer system, the government built dozens of dams over the second half of the 20th century, which together hold around a quarter of the country’s total water resource, according to the Guardian. However, it added:
“But by putting major dams on rivers too small to sustain them, the authorities brought short-term relief at the cost of longer-term water loss: evaporation from reservoirs increased while upland areas were deprived of water, now trapped behind the dams.”
Yale Environment 360 noted in December that “in the past half century, around half of Iran’s qanats have been rendered waterless through poor maintenance or as pumped wells have lowered water tables within hillsides”.
Agriculture is responsible for 90% of Iran’s water use. Over 2003-19, Iran lost around 211 cubic kilometres of groundwater – around twice the country’s annual water consumption – largely due to unregulated water pumping for farming.
The images below show how Lake Urmia in the north-west of the country – once the largest lake in the Middle East – has almost completely dried up since 2001 as water that feeds that lake has been diverted.
Towards the end of 2025, Iran’s Meteorological Organisation warned that the main dams supplying drinking water to major cities, such as Tehran, Tabriz and Mashhad, were close to “water day zero”.
The term “water day zero” has been used by academics, media and governments to describe the moment when a city or region’s municipal water supply becomes so depleted that authorities have to turn off taps and implement water rationing. It has been used to describe water crises in Cape Town, South Africa and Chennai, India.
In a televised national address in November, Iranian president Masoud Pezeshkian reportedly said the government had “no other choice” but to relocate the capital due to “extreme pressure” on water, land and infrastructure systems.
(This came after the government announced in January it would relocate its capital to the southern coastal region of Makran, citing Tehran’s enduring overpopulation, power shortages and water scarcity.)
Tehran is home to 10 million people and consumes nearly a quarter of Iran’s water supplies.
The water shortages have fuelled nation-wide protests, which have been often-violently suppressed by the government.
Prof Kaveh Madani, former deputy vice-president of Iran and the director of the UN University Institute for Water, Environment and Health, tells Carbon Brief that recent rainfall means the threat of “water day zero” has subsided in Iran in recent months.
However, he stresses that a combination of climate change and “local human factors” mean “many, many places in Iran are in ‘water bankruptcy’ mode”.
“Water bankruptcy” is when water systems have been overused to the point they can no longer meet demand without causing irreversible damage to the environment, according to Madani’s own research.
What role is climate change playing?
Iran is currently facing its sixth year of consecutive drought conditions.
An update posted in November by the National Iranian American Council quoted Mohsen Ardakani – managing director of Tehran Water and Wastewater Company – as saying:
“We are entering our sixth consecutive drought year. Since the start of the 2025-26 water year (about a month ago), not a single drop of rain has fallen anywhere in the country.”
The country’s most recent “water year”, which ran from September 2024 to September 2025, was one of the driest on record. Over the 12-month period, the country recorded 81% less rainfall than the historical average.
Meanwhile, temperatures in Iran can soar above 50C in the hot season, pushing the limits of human survivability and exacerbating water loss through evaporations from reservoirs of water.
Multiple attribution studies have shown that climate change is making the country’s hot and dry conditions more intense and likely.
In 2023, the World Wealth Attribution service (WWA) carried out an analysis on the drought conditions in Iran over 2020-23.
This study investigated agricultural drought, which focuses on the difference between rainfall amounts and levels of evapotranspiration from soils and plants.
The study explored how often a drought of a similar intensity would have occurred in a world without warming and how often it could occur in the climate of 2023. The researchers found that the drought would have been a one-in-80 year event without global warming, but a one-in-five year event in 2023’s climate.
They added that if the planet continues to heat, reaching a warming level of 2C above pre-industrial temperatures, Iran could expect a drought of 2023’s severity, on average, every other year.
The graphic below illustrates these results, where a pink dot indicates the number of years in every 81 with an event like the 2020-23 drought over Iran.
The box on the left shows how often such a drought would be expected in a pre-industrial climate, in which there is no human-driven warming. The box in the centre shows 2023’s climate, which has warmed 1.2C as a result of human-caused climate change. The box on the right shows a world in which the climate is 2C warmer than in the pre-industrial period.
Two years later, WWA carried out another study on drought in Iran, this time focusing on the five-year drought over 2021-25. The authors found an “even stronger impact” of climate change than their previous analysis.
A range of other attribution studies for Iran over the past five years have concluded that climate change made heatwaves and droughts over the region more intense and likely.
Meanwhile, the World Meteorological Organization’s (WMO’s) “state of the climate in the Arab region 2024” report warned about the impact of climate change on water security across the region.
In a statement, WMO secretary general Prof Celeste Saulo warned that “droughts are becoming more frequent and severe in one of the world’s most water-stressed regions”.
What other factors are involved?
Climate change is not the only – or even the primary – driver of water scarcity in Iran.
Madani explains:
“We have both the human factors and the climatic factors…A lot of times, local human factors are much more important and significant than the global factors.”
For example, Madani says, the country has experienced large population growth, but its population is concentrated in “a very few large metropolitan” areas, meaning it can struggle to provide enough water to those places. He also points to inefficient agricultural practices and overreliance on technological solutions, including dams and desalination plants.
The vast majority of the country’s water stress comes from its agricultural sector, which accounts for more than 90% of Iran’s water use.
Dr Assem Mayar, an independent researcher focused on water resources and climate security, tells Carbon Brief that Iran’s arid climate means that it uses more water per unit area for cultivating crops than other countries. This issue is compounded by government policies promoting domestic agriculture, he says:
“[Iran’s] government tries to be self-reliant in [the] food sector, which consumes the most share of water in the country.”
Both of the country’s main water sources – surface water and groundwater – are overexploited, Mayar says.
A 2021 study on the drivers of groundwater depletion in Iran found that between 2002 and 2015, Iran’s aquifers were depleted by around 74 cubic kilometres – 1.6 times larger than the amount of water stored in Iran’s largest lake, Lake Urmia, at its highest recorded levels.
The study also found that some basins had experienced depletion rates of up to 2,600% in that timeframe.
Groundwater aquifers naturally “recharge” as water percolates down from the surface. However, a 2023 study also found that this rate of recharge has been declining since the early 2000s.
When groundwater or other resources are extracted from the ground in high quantities, the land above the aquifer can compact and the aquifers themselves can collapse, leading to “subsidence” as the land surface sinks. Iran is one of the countries with the largest subsidence rates in the world, according to a 2024 study.
In late 2025, BBC News reported that Iran had begun “cloud seeding” – injecting salt particles into clouds to promote condensation, in an effort to “combat the country’s worst drought in decades”.
The country has been employing the technique since 2008 and reports that rainfall increased by 15% in the targeted areas as a result.
However, this does little to address the root of the problem, experts tell Carbon Brief.
Prof Nima Shokri, director of the Institute of Geo-Hydroinformatics at Hamburg University of Technology, tells Carbon Brief:
“Iran’s water crisis stems primarily from decades of policy choices that prioritised ideological and geopolitical objectives over sustainable resource management. A costly foreign policy posture and prolonged international isolation have limited access to foreign investment, modern technology and diversified economic development.
“Domestically, this has translated into policies that encouraged groundwater-dependent agriculture, expanded irrigated land without enforceable extraction limits, maintained heavy energy and water subsidies and underinvested in wastewater reuse, leakage reduction and monitoring systems.”
How could attacks on desalination plants impact water supplies in the Middle East?
A pair of attacks on desalination plants has led to significant media speculation around how the conflict might exacerbate freshwater supplies, both in Iran and across the Middle East.
On Saturday 7 March, Iran accused the US of attacking a desalination plant on Qeshm Island in the Strait of Hormuz.
Describing the attack on the critical water infrastructure as “blatant and desperate crime”, foreign minister Seyed Abbas Araghchi said water supply in 30 villages had been impacted.
The next day, Bahrain government said Iran had caused “material damage” to one of its desalination plants during a drone attack.
David Michel, senior fellow for water security at the Centre for Strategic and International Studies, told the Daily Mail that attacks on water plants in Gulf states by Iran could be designed to “impose costs” that push them to intervene or call for the end of the war.
There has been a boom in desalination across the Middle East in recent decades, as water-scarce countries have turned to the technology – which transforms seawater into freshwater – to boost freshwater supplies.
Collectively, the Middle East accounts for roughly 40% of global desalinated water production, producing 29m cubic metres of water every day, according to a 2026 review. This is shown in the chart below.
Iran has more than 163 desalination plants. However, it is less reliant on these plants than smaller countries in the region with fewer water reserves.
In a 2022 policy paper, the Institut Français des Relations Internationales noted Kuwait, Qatar and Oman sourced 90%, 90% and 86% of drinking water from desalination plants, respectively.
In contrast, an official from Iran’s state-run water company told the Tehran Times in 2022 that just 3% of the country’s drinking water came from desalination plants. (Iran’s water supply is sourced primarily from groundwater and rivers and reservoirs.)
Shrokri says the ongoing conflict is “hitting water security” in Iran through “direct and indirect” attacks on critical infrastructure – including desalination plants, power stations and water networks. He adds:
“The conflict is straining an already fragile system inside Iran. The country entered the war with severe drought, depleted groundwater and shrinking reservoirs, so any disruption to energy systems, industrial facilities or supply chains can quickly cascade into water shortages.”
Shokri also highlights that attacks on desalination plants in the Gulf could have serious consequences for major cities – including Dubai, Doha and Abu Dhabi – “rely heavily” on desalinated seawater for drinking water. He says:
“Without desalination plants, large parts of the region’s modern urban system will struggle to exist. The ripple effects would extend far beyond drinking water. Sanitation systems would begin to fail, public health risks would rise and economic activity could slow dramatically.”
Experts have pointed out that attacks on electricity infrastructure could also impact provision of drinking water, given desalination plants are energy-intensive and often co-located with power plants.
Dr Raha Hakimdavar, a hydrologist at Georgetown University, told Al Jazeera that attacks on desalination plants could also impact domestic food production in the long-term, if groundwater is diverted away from agriculture and towards households.
What policies could help Iran avoid a ‘water day zero’?
Experts tell Carbon Brief that the conflict could make chronic water shortages in Iran more likely – even if hostilities are unlikely to directly force a “water day zero”.
Shokri says:
“The war could accelerate the timeline, but it didn’t create the risk of day zero. Iran’s water system was already under extreme pressure from long-term mismanagement and distorted policy priorities. Conflict simply reduces the margin for error.”
Mayar says the war is “unlikely to force day zero nationwide”, but could bring forward “localised day‑zero conditions in already stressed regions”. These effects could be felt most acutely in Iran’s islands and cities that are already “facing chronic shortages”, he continues.
Since agriculture is such a large contributor to the country’s water usage, potential solutions must focus on that sector, experts say.
Mayar says the government should “phase out subsidy policies that encourage overuse”.
In 2018, researchers at Stanford University released a “national adaptation plan for water scarcity in Iran”, as part of a programme looking at the country’s long-term sustainable development.
That report lays out two sets of adaptation actions: those that work to improve the efficiency of water use and those that end water-intensive activities. Among the specific actions recommended by the report are reusing treated wastewater, reducing irrigated farming and enhancing crop-growing productivity through technological solutions.
The adaptation report concludes:
“The underlying solution to address Iran’s water problem is obvious: consumption should be regulated and reduced, water productivity should be improved and wastewater should be treated and reused in the system.”
Meanwhile, Shokri argues that the “main obstacle” to water reform in Iran is not technical capacity, but “government-set national priorities”. He explains:
“Significant public resources are directed toward non-civil spending and external commitments, leaving limited room for sustained investment in water management and environment…Real progress will require shifting attention and resources toward water security, environmental protection and long-term economic resilience.”
The post Q&A: How climate change and war threaten Iran’s water supplies appeared first on Carbon Brief.
Q&A: How climate change and war threaten Iran’s water supplies
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