How to know if a disaster is to blame for climate change – 04/12/2023 – Environment

Acre, Amazonas, Maranhão, Pará, São Paulo. In recent weeks, heavy rains have led to dozens of deaths and left thousands of families homeless in various parts of the country.

When this kind of disaster happens, a recurring question is: is this the fault of climate change? The answer is not always simple, but it can be found through climate attribution, the science that seeks to determine the influence of global warming on extreme weather events.

One of the pioneers in this relatively new field of study is German climatologist Friederike Otto of Imperial College London, who leads the World Weather Attribution (WWA) research centre. Through partnerships with scientists around the world, the initiative is dedicated to doing rapid attribution studies and assessing the role of climate change in the immediate aftermath of the extreme event.

“The first step is to find out if the event that happened was extreme”, explains Lincoln Alves, a researcher at Inpe (National Institute for Space Research) who worked with the WWA in the study on the rains that hit Pernambuco in May 2022. you need to look at the region’s historical record and see if something of this magnitude has happened before—and if so, how rare it is.

“In the case of the rains that hit São Sebastião [no litoral norte de SP] in february, for example, looking at the records since 1960, it is possible to see that it never rained 600 mm in such a short time. So it’s a rare extreme event,” he says.

The group of researchers then uses a peer-reviewed method to compare two scenarios: a real-world scenario, in which humanity has already made the planet 1.2°C warmer, and a simulated one, in which this influence does not exist.

Extreme events are part of natural climate variability and always have multiple causes. But it is possible to assemble these models because it is known the exact amount of greenhouse gases that have been thrown into the atmosphere by human activities (mainly, the burning of fossil fuels and deforestation) since the Industrial Revolution.

Thus, it is enough to create a scenario with and another without this variable and check the frequency and intensity with which that extreme event occurs in each of them. As the only difference between the two is the increase in temperature, one can point out the size of the blame for climate change in each case.

In the case of the rains that hit the Brazilian northeast last year, in less than 24 hours, between May 27th and 28th, Pernambuco received more than 70% of the expected rainfall for the entire month.

The stormy day was preceded by a week of very heavy rain, including in other states in the region. Landslides and flooding displaced at least 25,000 people and killed 133.

Analyzing this scenario, the WWA concluded that climate change increased the volume of rainfall and that pre-existing social vulnerabilities made this event even more serious.

On the other hand, when they studied the drought that led to water shortages in the Southeast from 2014 to 2015, the group concluded that climate change did not play a major role. Scientists pointed out that the impacts felt were so great due to population growth and increased water consumption in the region.

Mariam Zachariah, a researcher who is part of Otto’s team at Imperial College London, says that typically each study lasts from a few days to four weeks.

At each job, scientists who are native to the places that were affected by that climate disaster join the team. “We need station data [meteorológicas] locals and people with a local perspective to really understand what we’re doing,” she explains.

The central criterion for deciding which events to analyze is the size of the impact on the population. “In the core group, there are people both on the science side and on the vulnerability and exposure side, who are more involved in understanding the real impacts associated with extreme events,” he says.

Zachariah says this approach is intended to help plan public policy. “We do climate change analysis [em um evento extremo] and then we learn that it can happen again. So the main idea has to be that in the future we should be prepared to combat these effects as much as possible.”

In addition to case-by-case attribution studies, it is also possible to determine the influence of climate change on extreme events based on data from the UN climate panel (IPCC).

The latest report points out that the climate crisis is already exacerbating droughts, storms and extreme temperatures in different ways around the world. In Brazil, the whole country already suffers from heat waves, while the South and Southeast regions, especially, have more heavy rains, and the Northeast, a greater number of droughts.

In future scenarios of greater warming, ranging from 1.5°C to 4°C, these changes are expected to increase and spread.

_{The Planeta em Transe project is supported by the Open Society Foundations.}