Climate Change Attribution

Climate Change Attribution or Extreme Event Attribution

Cheri Porter

This article appeared in the December 2025 ICAG newsletter (Issue 5)

Weather is highly variable from one year to the next and even from one day to the next. Due to the natural variability in our climate, extreme weather events come along from time to time – but by definition, they’re rare. Some large-scale drivers affect the odds of extreme events, for example in eastern Australia hot events are more likely during El Niño, floods are more likely during La Niña. The elephant in the room is climate change, altering the climate and changing the odds of these extreme events.

Climate attribution is a relatively new science which allows scientists to determine how much worse an extreme weather event was because of climate change. The first climate change attribution study was published in 2004 after a deadly heatwave the previous year had killed over 70,000 people across Europe. Researchers concluded that climate change had made this heatwave at least twice as likely.

The science is improving with each new climate attribution study. We can now make claims like, “65% of the 2,399 heat deaths across 12 major European cities in the summer of 2025 were directly linked to climate change.” And furthermore, these extreme events and deaths can now be linked to individual companies through their records of cumulative emissions. 

An extreme climate event can be found to be more (or less) likely than it would have been without climate change. For example, the Australia-wide summer high temperatures in 2012-2013 were estimated to be 2.5 to 5 times more likely due to climate change.

Or the attribution may be expressed as an event being more (or less) severe than in a world without climate change. For example, the record dry and hot October in Tasmania in 2015 was around 5-10% drier and around half a degree warmer than it would have been without climate change.

Climate change can affect the intensity and frequency of extreme weather events differently, for example the 2010 Russia heat wave was made far more likely but not more intense.

Attribution studies generally proceed in four steps: (1) measuring the magnitude and frequency of a given event based on observed data, (2) running computer models to compare with and verify observation data, (3) running the same models on a baseline "Earth" with no climate change, and (4) using statistics to analyze the differences between the second and third steps, thereby measuring the direct effect of climate change on the studied event.

Heatwaves are the easiest weather events to attribute. It is much harder to detect a climate change signal in extreme rainfall events, because they are naturally extremely variable and a human influence signal does not emerge above this natural variability.

Many prominent studies around the world have found a clear and attributable influence of human-caused climate change in increasing the odds of extreme events. To keep track of this rapidly growing field of research, Carbon Brief has mapped every published study on how climate change has influenced extreme weather and published the map here. This database shows that 16 of the 17 heat events studied in Australia were made more severe or more likely by climate change.

A valuable tool

Climate attribution studies can provide crucial information for city planners, policymakers, disaster responders, insurance companies because they highlight the types of extreme weather events that specific places can expect in the future.

There is also a role for these studies in the legal system. In a recent law suit in the European Court of Human Rights, Swiss citizens used attribution studies to argue that their government’s failure to take action on climate change had directly contributed to deaths from heatwaves. In April 2024, that court ruled that the Swiss government had failed to protect its people and must live up to its climate targets.

A recent study links cumulative emissions from individual businesses that directly profit from high emissions to increases in intensity or likelihood of extreme weather events. This is an important step into requiring accountability for these companies for their continued short-sighted profit-above-all mentality.

A lawsuit against Shell, the fossil fuel company, has been filed by the Filipino survivors of the 2021 Typhoon Rai, demanding compensation for their losses. This is the first civil claim to directly link polluting companies to deaths and personal injuries due to a climate disaster.

But for many of the scientists who do attribution studies, the highest aim of this science is to help the public appreciate how profoundly our world is changing. Ten years ago, even after the most extreme weather disasters, it was rare to hear the link to climate change discussed in any detail on the news. Today, reporters and weather forecasters can say, with strong evidence, when we are experiencing weather that is new to our world.

For more information please see these sources:

https://interactive.carbonbrief.org/attribution-studies/index.html

https://www.csiro.au/en/news/all/articles/2022/april/climate-change-attribution

https://climate.mit.edu/explainers/climate-change-attribution

https://www.theguardian.com/world/2025/oct/23/we-are-now-fighting-back-philippines-typhoon-survivors-to-sue-shell-for-climate-harms