Extreme rainfall, heatwave, drought, wild fire, flash flood, tropical cyclone...
What were once rare weather events have become a regular feature of global news bulletins. Climate change is the obvious reason, but how to prove it?
After the Russian heatwave of 2010, Dr Friederike (Fredi) Otto was discussing the ‘weather’ versus ‘climate’ issue with her colleague and friend Professor Geert Jan van Oldenborgh. Both were frustrated that a focus on short-term weather forecasts often comes at the expense of the longer-term climate view, says Otto, and that in the time it takes to bridge that gap, the link between event and cause can be deniable.
“We were fed up with major weather events happening and the scientific community staying silent because they needed the requisite time to research and peer-review. After discussions with a non-profit who were also interested in putting climate change into weather bulletins, we thought: ‘We can do this faster.’”
Thus the World Weather Attribution (WWA) initiative was born – almost.
“Our first study was the European heatwave of 2015,” recalls Otto, now Senior Lecturer in Climate Science at the Grantham Institute for Climate Change and the Environment. “And it was a steep learning curve. We crunched the numbers and produced a factsheet within a couple of days that demonstrated the influence of global warming on the heatwave.”
It turned out, however, that the numbers weren’t enough. “The media didn’t really know what to make of the figures and did not report it. So, for the next study, we also wrote a scientific paper on the same timescale, which created quite a backlash from the scientific community, who said: ‘If you can do it that quickly, it’s not real science.’” The pair also began to write web summaries and press releases that highlighted the human impacts of the weather event, working with the Red Cross Climate Centre to produce simple explainers. They published their data and methods, as well as peer-reviewed papers to build trust with the scientific community. “Gradually, we went from producing five studies a year, working all the time and very late, to growing the team and becoming more systematic. Now, we produce 14 studies a year, mainly within working hours!”
These days, the crack WWA team of 11 – five full-time researchers at the Grantham Institute and seven part-time from other organisations – has a streamlined process that can produce a full report seven to ten days after a weather event, describing if and how it was directly influenced
by climate change. “Every Monday we have a meeting with the Red Cross who have scanned humanitarian appeals and websites to assess the impact of weather events, such as how many have died, how many displaced,” says Otto.
“The London heatwave of July 2022 was a good example. We have to decide if an event qualifies as severe enough to study, and then do we have access to the climate and data models? Observations from the Met Office told us the extreme heat was forecast to continue. London is a densely populated area, and the population counted as vulnerable because it was unprepared. So we decided to produce a report.”
The next stage is to define exactly what weather event a particular case is.
“We take observed data from local meteorological services and scientists – part of a network we have built up all over the world,” says Otto. “We bring in relevant climate models, of which we can use up to 70 that are accessible.”
Here, statistician Dr Clair Barnes comes into her own, as she builds statistical models of the relationship between climate change and weather events, as well as writing computer code to automate the process of checking and analysing the climate models. “We tend to share roles, but no one else really likes the stats!” laughs Barnes. Over the week, the team stay in constant contact as they build the statistical and humanitarian picture.
Then comes the important bit – attribution. Once the team have the data they need, they run the same model but with global warming removed. Statistically, they recreate the world from around 1850, just before we started emitting greenhouse gases. That way, they can see what the event would have looked like then and how likely it would have been without climate change. “We found that the likelihood of the London heatwave happening without climate change was one in 10,000,” says Otto, “which basically means it wouldn’t have happened. We also found that climate change made the heatwave 2°C hotter, pushing temperatures above 40°C, which has caused heat stress for tens of thousands more people.” Their report hit the headlines while London was still reeling.
Thus the World Weather Attribution (WWA) initiative was born – almost.
“Our first study was the European heatwave of 2015,” recalls Otto, now Senior Lecturer in Climate Science at the Grantham Institute for Climate Change and the Environment. “And it was a steep learning curve. We crunched the numbers and produced a factsheet within a couple of days that demonstrated the influence of global warming on the heatwave.”
It turned out, however, that the numbers weren’t enough. “The media didn’t really know what to make of the figures and did not report it. So, for the next study, we also wrote a scientific paper on the same timescale, which created quite a backlash from the scientific community, who said: ‘If you can do it that quickly, it’s not real science.’” The pair also began to write web summaries and press releases that highlighted the human impacts of the weather event, working with the Red Cross Climate Centre to produce simple explainers. They published their data and methods, as well as peer-reviewed papers to build trust with the scientific community. “Gradually, we went from producing five studies a year, working all the time and very late, to growing the team and becoming more systematic. Now, we produce 14 studies a year, mainly within working hours!”
We found the likelihood of the London heatwave happening without climate change was one in 10,000.
These days, the crack WWA team of 11 – five full-time researchers at the Grantham Institute and seven part-time from other organisations – has a streamlined process that can produce a full report seven to ten days after a weather event, describing if and how it was directly influenced by climate change. “Every Monday we have a meeting with the Red Cross who have scanned humanitarian appeals and websites to assess the impact of weather events, such as how many have died, how many displaced,” says Otto.
“The London heatwave of July 2022 was a good example. We have to decide if an event qualifies as severe enough to study, and then do we have access to the climate and data models? Observations from the Met Office told us the extreme heat was forecast to continue. London is a densely populated area, and the population counted as vulnerable because it was unprepared. So we decided to produce a report.”
The next stage is to define exactly what weather event a particular case is. “We take observed data from local meteorological services and scientists – part of a network we have built up all over the world,” says Otto. “We bring in relevant climate models, of which we can use up to 70 that are accessible.”
Here, statistician Dr Clair Barnes comes into her own, as she builds statistical models of the relationship between climate change and weather events, as well as writing computer code to automate the process of checking and analysing the climate models. “We tend to share roles, but no one else really likes the stats!” laughs Barnes. Over the week, the team stay in constant contact as they build the statistical and humanitarian picture.
Then comes the important bit – attribution. Once the team have the data they need, they run the same model but with global warming removed. Statistically, they recreate the world from around 1850, just before we started emitting greenhouse gases. That way, they can see what the event would have looked like then and how likely it would have been without climate change. “We found that the likelihood of the London heatwave happening without climate change was one in 10,000,” says Otto, “which basically means it wouldn’t have happened.
We also found that climate change made the heatwave 2°C hotter, pushing temperatures above 40°C, which has caused heat stress for tens of thousands more people.” Their report hit the headlines while London was still reeling.
Attribution science communicates the impacts of planet-warming on humans and natural systems. It's a science for change.
In October to December 2022, the horn of Africa experienced its worst drought in 40 years, leaving 4.35 million people in need of humanitarian assistance. Here, as well as proving that there would not have been drought at all in a 1.2°C cooler world, and that the drought had been made 100 times more likely by human-induced climate change, the WWA team were also able to assess the impact of climate change on natural weather variations. Working with WWA’s climate scientist Dr Joyce Kimutai, Barnes built a new statistical model that could factor in the El Niño-Southern Oscillation, a natural ocean variation that affects weather, adding to understanding of climate and weather extremes. It also meant the team could prove, in 2023, that drought in the Amazon basin was caused by climate change rather than El Niño.
“We know that Africa and the Amazon are disproportionately affected by climate change because they sit in the Tropics, where weather systems are naturally more erratic,” says Kimutai. “The east African drought had an impact on food security – plants drying out, crop reduction, no water or pasture for animals so that livestock died. Livelihoods were destroyed, people went hungry.” Using WWA studies, investigative website Carbon Brief was able to estimate that 15,700 people died in Africa during 2023 from weather disasters. “And these countries are getting less resilient each time,” says Kimutai. “Developmental gains, such as roads, are literally being swept away.” Kimutai acted as a systematic observer at COP28 on behalf of the Kenya Meteorological Department, pushing the UN World Meteorological Association to support countries like Kenya, which are classed as developing rather than vulnerable. “Attribution science communicates the impacts of planet warming on humans and natural systems,” she explains. “How people live, move around and produce food and goods relate to each other. It’s a science for change. It shows us we need adaptation strategies, which means building new infrastructure that is resilient – roads that won’t get swept away, crops that are drought-resistant.”
And where we can no longer adapt, we need to address loss and damage, says Kimutai. “For instance, pastoral farmers in Kenya can no longer make a living, as their animals keep dying. They are already asking: ‘What should we do?’ We need planning and new research into geoengineered crops, but there are always other valid development priorities for governments, such as health, education and poverty eradication, for example.” The Loss and Damage Fund, which began at COP26 in Glasgow, would not have been possible without attribution science, says Otto. “Without linking climate change to a weather event you can’t have accountability. And accountability allows remuneration – and litigation.” She cites the NGO Bush Fire Survivors, which successfully sued the Australian government for lack of adaptation and mitigation strategies, and set a legal precedent: that the Australian Environmental Protection Agency had a legal duty to take action on climate change.
And for Otto, the WWA’s work also allows impact on a small, local scale that can be empowering. “Calling for heat action plans in cities, for example, is really important and can save lives – letting people know what to do in a heatwave, for example, such as closing the curtains during the day. It’s easier to canvass your local council than the UN!” But change has also been large-scale; the German government adopted a nationwide heat action plan in 2023, following WWA recommendations.
For the WWA team, there is one clear action for the world to take.
“Burning fossil fuels is what causes global warming,” says Barnes. “So if we’re still issuing oil and gas licences, we’re not doing enough.” Kimutai adds: “We need to stop making oil deals – connecting money and oil. What’s all the wealth for, if we all die?”
Imperial is the magazine for the Imperial community. It delivers expert comment, insight and context from – and on – Imperial's engineers, mathematicians, scientists, medics, coders and leaders, as well as stories about student life and alumni experiences.
This story was published originally in Imperial 56/Summer 2024.
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