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World Weather Attribution (WWA) is an international effort designed to sharpen and accelerate the scientific community’s ability to analyze and communicate the possible influence of climate change on extreme-weather events such as storms, floods, heat waves and droughts.

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

The program — 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) — was initiated in late 2014 after discussions within the scientific community concluded that the emerging science of extreme-event attribution could be operationalized.

Climate Central coordinates the program and provides its secretariat.

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 is believed to have killed 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.

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, will enable 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.

Right now, studies of the attribution of extreme events (such as those in BAMS) require months to complete and are published long after the event.

The program will consider all types of extreme-weather events. Events that will be assessed include extreme heat and cold, heavy rainfall and floods, droughts, and also heavy snowfal and storm surges. In cases where the probability of the event appears to have been changed, we will also attempt to 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,” 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 will also help answer questions about trends in risk and vulnerability, and the role of human activity in extreme weather.

There are four possible findings of our attribution analysis of an event:

  • Global warming increased its likelihood.
  • Global warming reduced its likelihood.
  • Global warming had no detectable role.
  • Our analysis methods were unable to give information.

By providing a clear scientific statement (including about what may be uncertain), our objective is to inject more rigorous analysis and science-based information into coverage of — and public discourse on — extreme weather and its relationship with climate change.

Photo: UNICEF Philippines/2015/Jeoffrey Maitem