By analyzing temperature patterns at five points along the Brazilian coast over the last 40 years, scientists confirmed the impacts of global warming on the country: hotter summers, more heat waves and greater thermal amplitude throughout the day.
On the coast of Espírito Santo state, the frequency of daily occurrences of extreme temperatures and heat waves increased by 188% during the period studied; Rio Grande do Sul saw an increase of 100% and São Paulo, 84%.
Such climate extremes impact the health of people, plants and animals directly and indirectly, including changes in viral cycles.
Released in February 2022, the latest report prepared by the Intergovernmental Panel on Climate Change (IPCC) stressed that greenhouse gas emissions are increasing the frequency and intensity of extreme temperatures around the planet.
According to the report, each 1° Celsius (1.8° Fahrenheit) increase in average global temperature is expected to worsen these phenomena, which are responsible for droughts and floods as well as hunger and the deaths of countless people, animals and plants. Forecasts point to an average increase of 1.5°C (2.7°F) in temperatures by 2030 compared with the preindustrial era, even in an optimistic scenario of lower carbon emissions.
But how can we define “extreme” temperatures in a huge country like Brazil with such a diverse climate, and how can we identify patterns in these extremes to understand their effects in different regions?
Those questions are answered in a new study conducted by researchers from the Institute of the Sea (IMar) at the Federal University of São Paulo (Unifesp), which looked into extreme temperature patterns on the Brazilian coast. They measured impacts in terms of occurrences (days on which extremes occurred) and events (consecutive days with extremes, characterizing waves).
The work focused on data about air temperature collected every hour of the day over the last 40 years in five coastal areas of the country: São Luís (Maranhão), Natal (Rio Grande do Norte), São Mateus (Espírito Santo), Iguape (São Paulo) and Rio Grande (Rio Grande do Sul).
Beach in Ilha Comprida, close to Iguape, São Paulo. Image courtesy of the Ilha Comprida municipal government.
After four decades of measurements, the results of the analyses were disturbing since they pointed to an issue that had already been studied in other regions of the world, though evidence was scarce for the Brazilian coast. In the country’s south and southeast — the most affected among the regions studied — the frequency of daily occurrences of extreme temperatures and heat waves increased by 188% in Espírito Santo, 100% in Rio Grande do Sul and 84% in São Paulo during the period.
The largest high temperature variation was recorded in Iguape, on the coast of São Paulo — from 29.5°C (85.1°F) in July 2000 to 40.4°C (104.7°F) in January 2016. In Espírito Santo, maximum temperatures ranged from 28.6°C (83.5°F) in July 1987 to 37.2°C (99°F) in March 2013. In the last decade, the state saw 19 occurrences of temperatures over 35°C (95°F) — more than twice the number seen in the 1990s.
“The study confirmed that extreme events are increasingly common in Brazil’s southeast and south. We expected that. But when we look at these variations, it’s been almost three times higher in Espírito Santo over 40 years, and it’s doubled in Rio Grande do Sul. That’s a lot,” says Ronaldo Christofoletti, head of research and a professor at IMar/Unifesp, who emphasizes the originality of the work and its aim to demystify climate extremes by showing them as numbers.
“Our major contribution was to answer the most basic question: What is a climate extreme? No reference value could be found. We generated a mathematical model that allows us to define what an extreme is, considering any point on the Brazilian coast for which we have long-term data.”
Two other measurements caught scientists’ attention. The coast of Espírito Santo saw an increase not only in the frequency of heat waves, but also of cold waves. On the coast of Rio Grande do Sul, in turn, the intensity of minimum temperatures has decreased; that is, it is getting less and less cold in southern Brazil.
In the Rio Grande area, where thermometers point to a trend toward higher minimum temperatures, they fell below 3°C (37.4°F) 21 times between 1989 and 1999. The previous decade had seen such temperatures only 12 times.
“Espírito Santo is subject to cold fronts that come from the south because the state is located in a subtropical area. But if you think of Rio Grande do Sul, where extreme low temperatures have decreased, it’s very worrying,” says marine biologist and first author of the study Fábio Sanches. “When I was younger, I used to hear that we would have problems related to global warming in the future. And that’s what we showed. The weather is going crazy and climate change is here,” he concludes.