World Weather Attribution (WWA) is an international effort to analyze and communicate the possible influence of climate change on extreme weather events, such as storms, extreme rainfall, heat waves, cold spells, and droughts.

Recognizing society’s interest in reducing the human, economic, and environmental costs of weather-related disasters, WWA delivers timely and scientifically reliable information on how extreme weather may be affected by climate change.

WWA is a partnership of Climate Central, the University of Oxford Environmental Change Institute (Oxford ECI), the Royal Netherlands Meteorological Institute (KNMI), the University of Melbourne, and the Red Cross Red Crescent Climate Centre (the Climate Centre). Climate Central also administers WWA. WWA was initiated in late 2014 after the scientific community concluded that the emerging science of extreme event attribution could be operationalized.

Identifying a human fingerprint on individual extreme weather events —“probabilistic extreme event attribution” — has been an important goal of the scientific community for more than a decade. In 2004, Dr. Peter Stott of the UK Met Office and his colleagues, published a paper in Nature showing that climate change had at least doubled the risk of the record-breaking 2003 European summer heat wave that resulted in the deaths of tens of thousands of people.

Since then, advances in the field have prompted numerous studies, leading the Bulletin of the American Meteorological Society (BAMS) to dedicate an annual special issue to extreme event attribution for the past four years. The 2016 BAMS special issue, Explaining Extreme Events of 2015 from a Climate Perspective, stated that “The science has now advanced to the point that we can detect the effects of climate change on some events with high confidence .“ In addition, the National Academies of Sciences, Engineering and Medicine issued a report in 2016, Attribution of Extreme Weather Events in the Context of Climate Change, that states, “In the past, a typical climate scientist’s response to questions about climate change’s role in any given extreme weather event was ‘we cannot attribute any single event to climate change.’ The science has advanced to the point that this is no longer true as an unqualified blanket statement.”

WWA applies a unique scientific approach that combines observational data, analysis of a range of models, peer reviewed research, and on-the-ground reports. This innovative combination, built on existing, peer reviewed methods, enables us to conduct more rapid analyses and provide faster answers to pressing questions about high-impact events – how strong the likelihood is, for example, of similar weather-related disasters in the future.

WWA considers all types of extreme weather events, including extreme heat and cold, heavy rainfall and floods, droughts, heavy snowfall, and storm surges. In cases where the probability of the event appears to have been changed due to climate change, we quantify the size of that change in order to assess the scale of the contribution from global warming. The types of events for which a quantitative analysis can be performed will expand as new attribution techniques become available and the science matures.

“The goal of this ambitious effort is to use peer reviewed science to provide decision makers, the public, and the media with early, science-based answers to the questions of whether and to what extent global warming caused by greenhouse gas emissions played a role in an event’s probability and magnitude,” said Dr. Heidi Cullen, Climate Central’s Chief Scientist.  “Our team believes that a careful science-based assessment is extremely valuable, even in cases where we can’t provide hard numbers,“ said Dr. Maarten van Aalst, Director of the Red Cross Red Crescent Climate Centre. “It is important to recognize that “we don’t know” or “there is no significant trend” are also valid findings.” This work also helps to answer questions about trends in risk and vulnerability, and the role of human activity in extreme weather.

WWA’s mission is supported by the 2016 BAMS special issue, which concluded, “Progress in managing risks from extreme events can only be made if the foundational pillars of observations, modeling, and our understanding of the physical processes that drive extreme events and their relationship to climate change also continue to improve. Continued investments in climate science at all levels are crucial not only in the next five years, but for the foreseeable future.”

By providing a clear scientific statement, WWA injects more rigorous analysis and science-based information into coverage of — and public knowledge and discourse on — extreme weather and its relationship with climate change.