Is it climate change or just weather?

When an extreme-weather event occurs, people often ask: Is climate change to blame? For decades, climate scientists have answered that question in general terms: that as the planet warms, we can expect many such weather events to become more frequent and extreme.

But in recent years advances in attribution science have allowed researchers to answer the question in much greater detail.

Founded in 2015 by Dr Friederike Otto and the late Dr Geert Jan van Oldenborgh, the World Weather Attribution (WWA) scientific partnership, which includes the Climate Centre, quantifies how climate change influences the intensity and likelihood of a particular extreme-weather event; and it sometimes finds it has not.

To encourage actions that will make communities and countries more resilient to future extreme weather, WWA studies also evaluate how existing human vulnerability and exposure may have worsened the impacts of the event. The results are made public as soon as they are available, often weeks or even days after the event, to inform discussions about climate change and extreme weather.

Key links
Scandinavia freeze
Attribution study

Scandinavia freeze

In early January Arctic air pushed the temperature in the northern Swedish village of Vittangi down to minus 44.6°C – the coldest recorded in Sweden, Finland or Norway (photo, Stavern) in the 21st century; a station near Oslo recorded minus 31.1°C.

But a WWA study group finds that both the five-day coldwave and one-day extreme temperature they analysed would have been yet 4°C colder in a world without climate change.

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WWA is a partnership between experts from the Climate Centre, Imperial College London, the Royal Netherlands Meteorological Institute (KNMI), and the Laboratoire des Sciences du Climat et de l’Environnement to conduct rapid attribution studies of extreme events.

The WWA network includes a wide range of scientists from around the world who join studies relevant to their geographic and thematic expertise.

WWA co-founder Dr Friederike ‘Fredi’ Otto is Senior Lecturer in Climate Science at the Grantham Institute for Climate Change and the Environment, one of Imperial College London’s six hubs for research, innovation and influence on global challenges.

KNMI’s Director (from February 2023) is Professor Maarten van Aalst, the former director of the Climate Centre; scientists Sarah Kew and Sjoukje Philip are WWA leads there.

Finally, Robert Vautard, the Director of Institut Pierre-Simon Laplace and newly appointed co-chair of the IPCC working group on the science of climate change for its seventh assessment of the global climate, rounds out the WWA core team (below, a group of WWA scientists meeting in Paris, June 2023).



The method used to conduct an attribution study consists of eight steps, described in detail in the scientific paper linked below. The first is to select and precisely define the extreme event to be studied, which provides a framework for the analysis.

Researchers determine the geographical boundaries of the most affected area, the best metrics to quantify the meteorological extreme such as maximum temperature and rainfall, and the duration of the event.

The Climate Centre’s role is chiefly to monitor potentially extreme events, with the advantage of insights gained from the Red Cross Red Crescent network in the field, helping to trigger studies using pre-established thresholds, then contributing to the definition of events and findings on vulnerability and exposure.

In 2020 the prestigious MIT Technology Review included WWA climate attribution as one of its ten “breakthrough technologies”, which matters because it provides “a clearer sense of how climate change is worsening the weather, and what we’ll need to do to prepare.”

(New York-based Roop Singh, pictured here, is the Climate Centre’s leading expert on attribution. Journalists can arrange interviews with her or her colleagues through

Attribution study

Amazon basin drought

Climate change, not El Niño, was the main driver of the severe 2023 drought in the Amazon basin, according to WWA scientists, making it 30 times more likely.

River levels were at their lowest levels in 120 years, threatening some 30 million people in Brazil, Peru, Colombia, Venezuela, Ecuador and Bolivia, disrupting transportation, isolating communities, killing wildlife, and triggering wildfires (EU photo, Bolivia, November 2023).

Read the study
Amazon basin drought

Understanding climate change and extreme weather

In this production, Fredi explains the thinking behind World Weather Attribution, which she leads and which now aims to complete around 20 studies a year. The planet is already outside the range of weather to which people are adapted to, and this is having very significant impacts, and not just in the global South, she says. The studies are done relatively quickly, Fredi explains, so that the scientists’ evidence can contribute to public discussion of events soon after they occur.

Information for the media