Ocean temperatures warmed by human-caused climate change fed the intense rainfall that triggered deadly floods and landslides across Asia in recent weeks, according to an analysis released on Wednesday (December 10, 2025).

The rapid study by World Weather Attribution focused on heavy rainfall from cyclones Senyar and Ditwah in Malaysia, Thailand, Indonesia and Sri Lanka starting late last month. The analysis found that warmer sea surface temperatures over the North Indian Ocean added energy to the cyclones.

Floods and landslides triggered by the storms have killed more than 1,600 people, with hundreds more still missing. The cyclones are the latest in a series of deadly weather disasters affecting Southeast Asia this year, resulting in loss of life and property damage.

“It rains a lot here but never like this. Usually, rain stops around September but this year it has been really bad. Every region of Sri Lanka has been affected, and our region has been the worst impacted,” said Shanmugavadivu Arunachalam, a 59-year-old schoolteacher in the mountain town of Hatton in Sri Lanka’s Central Province.

Warmer sea surface temperatures

Sea surface temperatures over the North Indian Ocean were 0.2° Celsius higher than the average over the past three decades, according to the WWA researchers.

Without global warming, the sea surface temperatures would have been about 1° Celsius colder than they were, according to the analysis. The warmer ocean temperatures provided heat and moisture to the storms.

When measuring overall temperatures, the world is currently 1.3° Celsius warmer than global average during pre-industrial times in the 19th century, according to the National Oceanic and Atmospheric Administration.

“When the atmosphere warms, it can hold more moisture. As a result, it rains more in a warmer atmosphere as compared to a world without climate change,” said Mariam Zachariah, with the Centre for Environmental Policy at Imperial College London and one of the report’s authors.

Using tested methods to measure climate impacts quickly

The WWA is a collection of researchers who use peer-reviewed methods to conduct rapid studies examining how extreme weather events are linked to climate change.

“Anytime we decide to do a study, we know what is the procedure that we have to follow,” said Zachariah, who added that they review the findings in house and send some of their analysis for peer review, even after an early version is made public.

The speed at which the WWA releases their analysis helps inform the general public about the impacts of climate change, according to Zachariah.

“We want people everywhere to know about why something happened in their neighbourhood,” Zachariah said. “But also be aware about the reasons behind some of the events unfurling across the world.”

The WWA often estimates how much worse climate change made a disaster using specific probabilities. In this case, though, the researchers said they could not estimate the precise contribution of climate change to the storms and ensuing heavy rains because of limitations in climate models for the affected islands.

Climate change boosts Asia’s unusually heavy rainfall

Global warming is a “powerful amplifier” to the deadly floods, typhoons and landslides that have ravaged Asia this year, said Jemilah Mahmood, with the Sunway Centre for Planetary Health, a Malaysia-based think tank that was not involved with the WWA analysis.

“The region and the world have been on this path because, for decades, economic development was prioritised over climate stability,” Mahmood said. “It’s created an accumulated planetary debt, and this has resulted in the crisis we face.”

The analysis found that across the affected countries, rapid urbanisation, high population density and infrastructure in low lying flood plains have elevated exposure to flood events.

“The human toll from cyclones Ditwah and Senyar is staggering,” said Maja Vahlberg, a technical adviser with the Red Cross Red Crescent Climate Centre. “Unfortunately, it is the most vulnerable people who experience the worst impacts and have the longest road to recovery.”

Published – December 11, 2025 08:13 am IST

Human-caused climate change worsened floods that have killed hundreds of people and displaced millions in Cameroon, Chad, Niger, Nigeria and Sudan this year, according to a study published on Wednesday.

The intense rainy season has unleashed a humanitarian crisis across large areas of the Sahel region bordering the Sahara desert.

A new analysis by the World Weather Attribution (WWA) network of scientists found warming driven by the use of fossil fuels had exacerbated the flooding in Sudan.

The researchers also said climate change would have made this year’s torrential rains around five to 20 percent more intense across the Niger and Lake Chad basins, citing a previous WWA study of similar floods in 2022.

“This is only going to keep getting worse if we keep burning fossil fuels,” said Clair Barnes from the Centre for Environmental Policy at Imperial College London.

Speaking at a briefing ahead of the study’s publication, she said such downpours “could happen every year” if global temperatures increase to two degrees Celsius (35.6 Fahrenheit) above pre-industrial levels.

“It’s pretty serious,” she said.

Downpours and storms

Global warming is not just about rising temperatures — the extra heat trapped in the atmosphere and seas has knock-on effects and can result in more intense downpours and storms.

The researchers said there was a clear link between the extreme rainfall and a warming planet.

In the study, they focused on war-torn Sudan, where millions of displaced people have been uprooted by conflict and driven into flood-prone areas.

The scientists used modelling to compare weather patterns in our world and one without human-induced warming, and found that month-long spells of intense rainfall in parts of Sudan had become heavier and more likely due to climate change.

At the current 1.3 degrees Celsius of warming, they said similar periods of rainfall are expected to occur on average about once every three years, and have become about 10 percent heavier due to climate change.

‘Incredibly concerning’

“These results are incredibly concerning,” said Izidine Pinto, one of the study’s authors and a researcher at the Royal Netherlands Meteorological Institute.

He warned that “with every fraction of a degree of warming, the risk of extreme floods will keep increasing”, and called for the UN’s COP29 climate summit to “accelerate the transition away from fossil fuels” when it meets in Azerbaijan next month.

Joyce Kimutai, a researcher at Imperial’s Centre for Environmental Policy, said the floods underscored the need for a loss and damage fund for nations devastated by climate change.

A key meeting ahead of COP29 earlier this month ended with countries making little progress over how to finance a deal for poorer nations.

“Africa has contributed a tiny amount of carbon emissions globally, but is being hit the hardest by extreme weather,” Kimutai said.

The role of climate change in the floods was compounded by other human-made problems, the researchers said, and they called for better maintenance of dams and investment in early warning systems.

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

Just a couple of decades ago, the U.N. Intergovernmental Panel on Climate Change (IPCC) argued that individual weather events could not be attributed to climate change. The science has since evolved, albeit with all its attendant uncertainties, and now we regularly hear of researchers having been able to attribute some individual extreme events to climate change.

Many scientific and data challenges persist in this exercise even as its outcomes are argued to be usable for estimating richer countries’ historic liability of climate-related ‘loss and damage’ and the legal liability of governments and corporations in precipitating adverse events like floods and droughts. However, researchers have used a variety of methods to evaluate attributability, which raises questions about whether attribution science is mature enough to be used in courts and multilateral fora.

What is the value of extreme-event attribution?

While no formal cost-benefit analysis of an attribution exercise has been reported, many experts have argued that attributions are critical for the ‘loss and damage’ (L&D) process. L&D doesn’t have a unique definition but its place in climate talks under the U.N. Framework Convention on Climate Change has come a long way in the last decade. Economically developing countries, in particular those that are ‘particularly vulnerable’, have demanded the L&D fund to pay for the havoc climate change wreaks within their borders. Obviously, the criteria by which ‘particularly vulnerable’ countries are to be identified are crucial.

For example, India is a developing country in the tropics and is highly vulnerable to climate change’s impacts. But it is unlikely that India will qualify for L&D funding, and herein lies the rub: should climate finance and green funds focus on adaptation and mitigation alone or should they administer L&D funds separately? If the latter, then will attribution exercises help? The developed world is opposed to the idea of being held legally accountable in a court for any extreme events since that could open a floodgate of lawsuits.

Against this background, our understanding of whether attribution reports can actually hold up in court as evidence of culpability is very important. A good case in point is a recently published report on heatwaves in Asia.

How were the Asian heatwaves attributed?

Last week, a team of climate scientists called World Weather Attribution (WWA) reported that heatwaves across Asia, from the west to the southeast, had been rendered nearly 45-times more likely by climate change.

It is worth understanding how these ‘rapid extreme event attributions’ are performed. The most important concept is the change in probability: in this case, the climate scientists contrasted the conditions in which the heatwaves occurred against a counterfactual world in which climate change did not happen. The conditions that prevail in the counterfactual world depend on the availability of data from our world. When there isn’t enough data, the researchers run models for the planet’s climate without increasing greenhouse gas emissions and other anthropogenic forcings. Where there was sufficient data, they use trends in the data to compare conditions today with a period from the past in which human effects on the planet were relatively minimal.

This said, the data are hardly ever sufficient, especially for rainfall, and almost never for extreme rainfall events. Climate models are also notoriously bad at properly capturing normal rainfall and worse at extreme ones. Thus, climate scientists need to address these challenges in the process of assigning probability changes to events in the past. The climate models are better at capturing temperatures and temperature-related events — but again, only at regional scales, not at very local scales.

If, some day, climate scientists are able to perform reliable hyperlocal attribution exercises, they will still be confronted by a moral question: what actions should follow? Because right now, even though the L&D fund and climate jurisprudence are becoming more visible, attribution exercises are happening as if disconnected from governments’ adaptation and mitigation strategies.

Put another way: will people and businesses move away if a place is seen as being a hotspot of extreme events? This is not just a question of science. Governments need to be able to respond to such decisions, and attribution science should in turn be sufficiently reliable.

How do scientists pick extreme events to attribute?

Another significant challenge in attribution exercises is how scientists choose the extreme events for which they will perform attribution exercises.

When evaluating the Asian heatwaves, the WWA scientists used regional scales and different definitions for different regions. They also arbitrarily considered daily, three-day or monthly average temperatures for attributing likelihoods.

Heatwaves can be exacerbated by natural factors such as an El Niño event or human factors like urbanisation and deforestation. There is also a debate as to whether irrigation affects heatwaves as well.

Further, no weather event will occur in exactly the same form twice in a place, which means an extreme event occurring in that place will likely have no precedent. This is why it is easier to reliably attribute heatwaves at the subcontinent scale but not those at the level of particular areas.

The kind of questions that climate scientists ask also matters. For example, the same analysis can produce different answers to the questions “was the intensity of a heatwave amplified by climate change?” and “was the frequency or return period of a heatwave altered by climate change?”. In the WWA report, the scientists used multiple approaches in their attribution exercise to answer the same question, and have added that the differences between them are immaterial. It is not clear whether these differences will be perceived to be material in a court of law.

How do extreme events depend on human action?

The actual impacts of extreme events depend not only on the hazard or the extreme event but also on the vulnerability and the exposure of the population affected. Similarly, the financial consequences are also affected by multiple factors. So, should an attribution exercise only focus on the hazard or should it consider the impacts as well?

This is not a trivial question, especially if L&D negotiations are to be served reliably by attributions.

Considering all these challenges, we must take stock of the international finance aspects of adaptation, mitigation, and L&D. In particular, governments should consider an agreement on historical responsibilities to fund developing countries and close adaptation gaps, build adaptation capacity, and finance mitigation for the global good.

The real world is severely resource-constrained. In a counterfactual world, where human, financial, and computational resources are infinite, attribution exercises are a beautiful scientific challenge and could serve as a productive intellectual exercise. But in the real world, we need a cost-benefit analysis based on a clear role for attribution in the overall climate action landscape.

The author is visiting professor, IIT Bombay, and emeritus professor, University of Maryland.