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Weather attribution – climate scientist Wilhelm May helps us get to grips with the concept

Photograph of a flooded playground.
Sweden is also increasingly affected by unusually intense storms. Here, a flooded playground in the city of Landskrona after the storm "Hans" in August 2023.

Have you noticed that when scientists are asked whether or not a particular extreme weather event is due to climate change, they usually respond with something like "It fits the pattern, but we can't say for sure that this particular event is worse because of climate change"? Weather attribution is a new phenomenon that is changing this. Climate scientist Wilhelm May at Lund University helps us get to grips with the concept.

Weather attribution or extreme weather attribution are concepts that are increasingly appearing in climate change reporting. It is well known that global warming is leading to more extreme weather events such as droughts, heatwaves, heavy rainfall and forest fires. However, it has been more difficult for scientists to link the strength and scale of each event to ongoing climate change. This is now changing, thanks to new scientific methods.  Wilhelm May is a climate scientist at the Centre for Environmental and Climate Science (CEC) at Lund University, with a special focus on extreme weather. He recently gave a docent lecture (see infobox) on weather attribution and why it is important.

First of all - what is weather attribution? 

- It is when scientists study how different factors have influenced a weather event, and how likely each factor is to have contributed to the event. Essentially, it involves investigating whether and how human-induced climate change has altered the intensity and likelihood of a particular weather event, or whether it has other causes, such as the El Niño weather phenomenon - a recurring natural ocean and atmospheric phenomenon that causes surface water temperatures in the Pacific Ocean to rise above normal levels.

- For example, weather attribution shows that the probability of a drought in the Amazon in 2023 increased by 37 times, and the drought became 50 per cent more intense, as a result of human-induced climate change.

Why is weather attribution important?

- It is important for several reasons. By understanding why and how extreme weather events occur, we can better predict where they will occur in the future, with increased intensity and frequency. This, in turn, gives us a better chance of managing future events and preventing their consequences, for example through climate adaptation. This is particularly important in places where social vulnerability to extreme weather events such as droughts and heavy rainfall is high.

- Being able to better answer questions about how climate change affects a particular extreme weather event also makes climate change less abstract. It helps people realise that this is not a problem for the future, but that it is affecting our lives, communities and nature right now.

What research at Lund University contributes to extreme weather attribution?

- Attribution is done using climate simulations in large climate models. The models allow us to compare the world as it is today with how it would have looked without the ongoing climate change. By feeding the model with data on a specific weather event and comparing it with historical climate data, we can calculate how the probability and intensity of a particular weather event has changed over time. 

- Lund University is involved in developing this type of climate model, not least LPJ-GUESS, with a large part of the development taking place within the framework of the MERGE research environment. LPJ-GUESS in turn contributes data to the global climate model EC-Earth, whose simulations can be used for weather attribution, among other things.

How is extreme weather attribution used in practice today?

- A leading example is the work of the World Weather Attribution (WWA) organisation. In the case of an extreme weather event, they work with researchers around the world who conduct weather observations and computer simulations immediately after an event. The studies also assess the vulnerability and exposure of affected communities to extreme weather, and the role it plays in determining the extent of its impacts. The results are published as soon as they are available to contribute to discussions on, and adaptations to, climate change and extreme weather events. 

- Another, similar organisation is ClimaMeter, which recently started in 2024. It uses shorter time series than WWA and does not have the same focus on the social vulnerability to specific events.

What are the challenges or weaknesses of extreme weather attribution?

- There is a major imbalance between the global North and the global South when it comes to attribution studies. Doing studies requires resources and data, both historical and from the current event. There is simply not as much historical data from developing countries, nor the same resources and expertise to conduct attribution studies. This is a particular problem as attribution studies are especially important for developing countries where exposure to extreme weather is often greater than in the global North.

More information

World Weather Attribution
World Weather Attribution – Exploring the contribution of climate change to extreme weather events


LPJ-GUESS – Lund University

Docent lecture

A docent lecture at the Faculty of Science at Lund University is an academic presentation that a researcher gives in connection with becoming a docent. The lecture should, among other things, demonstrate in-depth knowledge of a current topic within the applicant's subject area (but not within their own research specialisation). The title of Docent is an academic title that demonstrates that the person has achieved a high level of scientific competence.