Climate attribution: linking extreme weather
by Kirsty McCabe, FRMetS
In October 2024, World Weather Attribution published their findings that the 10 deadliest extreme weather events between 2004 and 2024 were all intensified by climate change. But how do we know that climate change is to blame? One way to find out is an attribution study. These may sound like a recent thing, but scientists have been carrying out climate attribution studies for decades, ever since the 1995 Second Assessment Report published by the Intergovernmental Panel on Climate Change.
Climate scientist Ben Santer and colleagues were some of the first to show that the observed warming pattern in the lower atmosphere over the 20th century matched the "fingerprint" of human-caused greenhouse gas emissions and could not be explained by natural variabilty alone. Unfortunately their findings were not well received at the time, but their work laid the foundations that shape our global understanding of human impacts on the climate system. And these days we can get results from attribution studies in days or weeks after an event, rather than years.
But what is involved in an attribution study? The aim is to see if climate change made an extreme weather event, like a heatwave or flood, more likely. In other words, did it make a weather event more intense or cause such events to happen more frequently?
Scientists calculate this using a combination of models, data and statistical analysis.
- First they need to gather observations about the extreme weather event, such as rainfall amounts and temperature records.
- They they need to examine historical records to determine how rare or unprecedented the event is.
- A key part of climate attribution studies is running two sets of model simulations: one of our current world that includes observed levels of greenhouse gases and human-induced climate change; and the other of a hypothetical world without the influence of human emissions, relying only on natural variability such as solar and volcanic eruptions.
- From the two different models, scientists can then determine how much more likely or severe the weather event has become due to human activities.
Several organisations and research groups worldwide carry out climate attribution studies, such as World Weather Attribution, the Intergovernmental Panel on Climate Change, Climate Central, the National Oceanic and Atmospheric Administration and the UK Met Office.
More than 150 attribution studies have been published, looking at weather events around the world. Almost all studies done on extreme heat indicate human influence. About half the studies on drought show significant human influence. A smaller but increasing number of studies on extreme rainfall detect a human signal. The picture is less clear for tropical storms and hurricanes, as the total global number of tropical cyclones may be decreasing. However, increasing sea surface temperatures increases the intensity of tropical storms, and rising sea levels increases the risk of coastal flooding.
Such findings are critical for understanding climate change impacts and guiding adaptation and mitigation strategies.
Noteable attribution studies
Central Europe Floods (September 2024)
Climate change doubled the likelihood of severe rainfall from Storm Boris, leading to deadly floods across multiple countries.
UK and Ireland Winter Storms (2023-2024)
Human-induced climate change increased rainfall by about 20%, resulting in record rainfall and significant economic losses.
Hurricane Helene (2024)
Climate change intensified rainfall by 10% and wind speeds by 11%, causing devastating floods and over 230 deaths in the USA. Hurricanes as intense as Helene are today about 2.5 times more likely in the region.
Pacific Northwest Heat Dome (2021)
Extreme heat would have been virtually impossible without climate change, breaking temperature records by a significant margin.
European Heatwave (2003)
Climate change made the deadly heatwave twice as likely, causing over 70,000 deaths across Europe.
