The record number of wildfires in the Pantanal this June occurred under potentially more damaging climate conditions due to global warming, induced by greenhouse gas emissions, according to an index that measures wildfire severity and how difficult they are to put out. In June, the index was 40% higher than normal. The heat, drought, and winds in the largest tropical wetland on the planet were fueled by climate change, creating an environment more prone to the spread of fires at a time of year when they are not usually a problem in the biome.
Extreme events of this magnitude are likely to occur in the Pantanal every 161 years without anthropogenic global warming, but the statistical trend is now that they will repeat every 35 years. This means that climate change has increased the risk of extreme conditions occurring in the Pantanal in June by four to five times.
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These are the conclusions of a study published in early August by a team of researchers from Brazil, the United Kingdom, and the Netherlands, who worked together as part of the World Weather Attribution (WWA) initiative. The international scientific collaboration analyzes the influence of climate change on extreme events around the world, such as major droughts and torrential rains, through what are known as attribution studies.
“Changes in land use and climate change are causing wildfire patterns to change in the Pantanal. Today, the fires are more frequent and intense, and more areas are affected,” says Renata Libonati, a meteorologist from the Environmental Satellite Applications Laboratory at the Federal University of Rio de Janeiro (Lasa-UFRJ) and one of the authors of the paper. Data from Brazil’s National Institute for Space Research (INPE) indicate that around 3,300 wildfires were recorded in the Pantanal in June alone. A Lasa survey found that more than 4,100 square kilometers were burned in the biome this month (see Pesquisa FAPESP issue nº 342).
The WWA’s methodology consists of using several climate models to simulate an extreme event, such as very intense rainfall or a prolonged drought, and calculating the likelihood and intensity of the event occurring in two scenarios: with and without the current level of global warming. Since the preindustrial era of the mid-nineteenth century, the planet’s average temperature has risen by approximately 1.2 degrees Celsius (°C).
“In the past, extreme events like this in the Pantanal were treated as a result of natural climate fluctuations. Now, with our improved understanding of the climate system and advanced scientific techniques, we can use attribution studies to differentiate natural climate variations from those caused by human activity,” explains INPE climatologist Lincoln Muniz Alves, coauthor of the study. “The results of these studies increase public awareness of the causes and consequences of climate change.”
The WWA did similar research on the impact of global warming during the drought in the Amazon at the end of last year and the extreme rains that fell in Rio Grande do Sul in April and May this year (see Pesquisa FAPESP issue n° 341).
In the Pantanal, a lack of rain combined with high temperatures, low humidity, and stronger winds was a decisive factor behind the occurrence of wildfires at a time of year that they usually do not occur. “To evaluate these characteristics, we use a combination of factors that we call the fire weather index,” explains Libonati. “It quantifies the difficulty of controlling fires based on the weather conditions.”
The researchers calculated the index in the Pantanal on each day of June—accumulated in a metric called the daily severity rating (DSR)—to obtain the average fire danger for the whole month. After cross-referencing the data with projections from climate models with and without climate change, it was concluded that meteorological conditions are becoming more favorable for wildfires in the biome.
If global warming increases to 2 °C above preindustrial levels, the risk of the weather conditions that occurred in the Pantanal in June this year repeating will become even greater. They would occur every 17 years, with an intensity 17% greater than recorded in 2024.
These projections are not an exaggeration, according to German climatologist Friederike Otto of the Grantham Institute for Climate Change and the Environment at Imperial College London, head of the WWA and one of the authors of the new study. “The numbers are probably at the more conservative end of our scale. This is because [climate] models struggle to accurately estimate precipitation levels,” said Otto during an online press conference to announce the results of the Pantanal study.
The story above was published with the title “The impact of the greenhouse effect” in issue 343 of September/2024.
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