Environmental Change Institute, University of Oxford

Friederike Otto

ECI’s unique approach uses very large ensembles of simulations of regional climate models to run two different analyses: to represent the current climate as it was observed, and to represent the same events in the world that might have been without human-induced climate change.

This methodological approach is supported by its widespread use in submissions to the annual Bulletin of the American Meteorological Society Special Issue on Explaining Extreme Events from a Climate Perspective. This analysis used very large ensembles of a regional climate model over Europe embedded in a global circulation model to assess the change in risk of extreme precipitation under two very distinct versions of the event:

  1. the observed extreme weather event itself, and
  2. a model of the extreme weather event with the impact of anthropogenic greenhouse gas emissions removed.

Using a distributed computing framework — weather@home — members of the public facilitate multi-thousand-member ensemble weather simulation experiments at both global and regional scales.

To accelerate the attribution analysis, the ECI team has developed a novel approach based on using forecast sea surface temperatures (SSTs) instead of observed SSTs. The team used the 2014 United Kingdom floods as a case study to demonstrate the robustness of this approach.

Red Cross Red Crescent Climate Centre

Red Cross Red Crescent Climate Centre logo

Maarten van Aalst

The Climate Centre is a specialist reference center for the International Federation of Red Cross and Red Crescent Societies (IFRC) and helps the Red Cross and Red Crescent Movement and other partners reduce the impacts of climate change and extreme weather events on vulnerable people. It will use its humanitarian network to identify disasters that will be analyzed by the WWA initiative. Further analysis will help place the event in the larger context of patterns of changing risk, including trends in vulnerability and exposure. The Climate Centre team is also helping develop an index of published articles relevant to specific events and geographical regions that will be consulted when WWA assesses a specific event. This “living database” includes peer-reviewed studies on regional trends in extremes, and in hydrology, decadal variability, future projections, and other published attribution studies that will allow us to more quickly assess the state of the science.

Royal Netherlands Meteorological Institute

KNMI logo

Geert Jan van Oldenborgh

The KNMI team contributes statistical analysis tools and climate data built in the KNMI Climate Explorer for event attribution. This public web application has fits to standard and extreme value distributions with co-variates that are optimised for extreme event attribution. The group collects and updates observational data in real-time at the Climate Explorer for trend detection in the past record and computation of return periods of the extreme event using long records that reach until the event under study. It also makes available a large set of climate model output that can be used for attribution studies, and stores the data used for past attribution studies to aid reproducibility. Work is in progress to facilitate the synthesis stage of attribution studies.

World Weather Attribution

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

Recognising 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.

Recent studies have quantified the impact of climate change on the likelihood and intensity of bushfires, heatwaves and storms.

Through extensive media engagement – including the Guardian, the Daily Mail, the Times, Scientific American, CBS, BBC and many more – WWA has helped to change the global conversation around climate change, influencing adaptation strategies and paving the way for new sustainability litigation. In 2020, climate change attribution was named one of MIT Tech Review’s top ten breakthrough technologies.

WWA is a partnership of:

  • Environmental Change Institute, University of Oxford (ECI)
  • Royal Netherlands Meteorological Institute (KNMI)
  • Laboratoire des Sciences du Climat et de l’Environment (LSCE)
  • University of Princeton
  • National Center for Atmospheric Research (NCAR)
  • Red Cross Red Crescent Climate Centre (The Climate Centre).

WWA was initiated in late 2014 after the scientific community concluded that the emerging science of extreme event attribution could be operationalised. It is hosted at the Environmental Change Institute, University of Oxford, and co-led by Dr Geert Jan van Oldenborgh (KNMI) and Dr Friederike Otto (ECI).

Science partners at WWA utilise established peer-reviewed methods to perform their attribution assessments. We regularly include additional international scientists to develop greater regional capacity and geographic reach.

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, Stott et al., published a paper in Nature showing that climate change had at least doubled the risk of the record-breaking 2003 European summer heatwave 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. In a report issued in 2016 the National Academies of Sciences, Engineering and Medicine, titled:

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. Friederike Otto, of the ECI.

“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.