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How science linking climate change to extreme weather took off

Published on 04/08/2021, 5:24pm

Attribution science, which quantifies the influence of human activity on specific heatwaves, droughts and floods, has developed rapidly in the past decade

Scientists are now able to directly attribute extreme events, such as this flooding event in Bangladesh in 2019, to climate change (Photo: UNWomenAsia/Flickr)

By Isabelle Gerretsen

The UN’s climate science panel is set to publish a major report in August on the physical changes to our world occurring and projected to happen as a result of human activity, from extreme weather to ocean acidification.

It will be the first comprehensive review of the scientific literature since 2013, when the Intergovernmental Panel on Climate Change (IPCC) started its last round of assessment reports, AR5.

Attribution science, which looks at how much human activities lead to climate change, is likely to feature heavily in the report. Here we give an overview of the scientific developments of the past eight years.

AR5 concluded that human influence on the climate system is “clear.” Today scientists say climate change is, without doubt, caused by us. A 2021 study concluded that humans have caused all of the warming observed since the preindustrial period.

Since the last IPCC report, there has been an explosion of attribution studies finding that specific heatwaves, droughts, tropical cyclones and other extreme events were more likely or intense because of climate change. Recent studies have shown that extreme events such as the Siberian heat wave in 2020 would never have happened without humans pumping greenhouse gases into the air.

Since AR5, attribution science has become more “impact-oriented”, Sjoukje Philip, a climate scientist from the World Weather Attribution (WWA) group, told Climate Home News.

That means more studies focusing on the societal impacts of extreme weather events, such as the 2016 study which found that 506 of the 753 fatalities during the Paris heatwave in 2003 were a result of climate change.

“We wanted to see how much human-induced climate change contributed to mortality,” Dann Mitchell, one of the study’s authors and professor of climate change at Bristol University, told Climate Home News. “Since the last IPCC report models have become more advanced and we have better ways of collecting climate and health data,” he said.

The increase in attribution studies is due to more precise climate models and peer reviewed methods which allow scientists to rapidly and accurately analyse extreme events, according to Philip. This also helps with communication. “If you can do the attribution one week after the event, it’s still news,” she said.

Scientists are now able to carry out attribution studies within a few days of an event occurring. In some cases they can do the analysis while the event is still going on. Scientists from the WWA group published a study in 2018 showing that climate change made Europe’s heatwave twice as likely, while it was ongoing.

Half of all attribution studies focus on heatwaves, according to Mitchell. Heatwaves are relatively easy to attribute because they are “very certain and the first response to climate change” and cover a large area, which makes it easier for climate models to pick up, said Mitchell. Most of the rest look at extremes of rainfall leading to drought or floods.

Only a handful have looked at hurricanes, which are hard to model due to their complexity and limited historical data. They reached relatively weak conclusions about the scale of human influence.

That could change as new high-resolution models are being developed, said Sarah Teuling-Kew, a climate scientist at WWA. “Methods for large-scale precipitation and temperature extremes are more robust – they have been put through the tests,” she said.

The majority of attribution studies focus on events in Europe and North America. This is because these regions have the most reliable climate data available, according to Philip. “I don’t think we’ve ever done a heatwave attribution study over Africa because we never hear about it,” she said, adding that WWA scientists are collaborating with African scientists and sharing knowledge to improve modelling of the continent.

Timeline of climate attribution studies

2004: First heatwave attribution study

The study found that climate change had at least doubled the likelihood of the European heatwave in 2003, which killed more than 70,000 people.

2011: First flooding attribution study

The first study to attribute greenhouse gas emissions’ contribution to flood risk in England and Wales. The scientists concluded that emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20% and in two out of three cases by more than 90%.

2014: Likelihood of European heatwaves analysis

The study found that summer heatwaves in Europe over the past 10-15 years were 10 times more likely due to climate change

2016: Mortality study of European heatwave

The first study to directly link deaths during the 2003 European heatwave to climate change. The scientists concluded that 506 of the 735 summer fatalities in Paris in 2003, and 64 of the 315 in London were a result of climate change.

2017: Bangladesh flooding study

World Weather Attribution analysis directly linked severe flooding in Bangladesh in 2017 to climate change.

2018: Cape Town water crisis analysis

The 2017 drought which led to Cape Town’s water crisis was made three times more likely by climate change, according to analysis by World Weather Attribution scientists.

2018: Extreme heat across Asia

Extreme heat across Asia in 2016 would have been impossible without climate change, scientists concluded in 2018.

2020: Siberian heatwave impossible without climate change

The prolonged Siberian heatwave in 2020 would have been almost impossible without climate change, according to rapid attribution analysis by the World Weather Attribution group.

2021: Australian bushfire season 30% more likely

Australia’s devastating bushfire season in 2019-202 was made significantly more likely because of climate change, according to World Weather Attribution scientists. The analysis showed that climate change led to weather conditions that increased the fire risk by at least 30%.