March heat was intensified by climate change – 03/27/2024 – Environment

The heat that hit Rio de Janeiro and São Paulo recently was driven by climate change, concluded a study released this week.

The results of human actions, mainly the emission of greenhouse gases when burning fossil fuels, added to natural climate variability caused a rise in temperature of up to 1°C above what was observed in past “hot weather”.

This is what a rapid attribution study by ClimaMeter points out, a platform developed by the team at the climate and environmental sciences laboratory at the University Paris-Saclay, in France. Today, the group includes scientists from several European universities. The project is experimental and aims to quickly analyze extreme events immediately after they occur.

The research evaluated the heat wave that hit part of Brazil from March 15 to 18 and led temperatures and thermal sensations to reach new records in cities such as São Paulo and Rio de Janeiro.

ClimaMeter analyzed how heat waves in the region have changed this century, in relation to the characteristics of previous decades. The research compared the average temperature from 2001 to 2023 with the period from 1979 to 2000.

The study concluded that heat waves similar to the one that occurred in March are 1°C warmer than those previously observed in the country, even occurring at the end of summer.

In the assessment of researcher Tommaso Albert, one of the study’s authors, the recent heat wave highlights the profound impact of climate change in Brazil, with an increase in health risks and significant economic implications.

In the city of São Paulo, on March 16, Saturday, a temperature of 34.7°C was recorded, the highest for the month in at least 81 years, since Inmet (National Institute of Meteorology) started to compile the statistics , in 1943. This was the hottest day of 2024 in the capital of São Paulo.

In Rio, the following day (March 17), the thermal sensation was a record, with 62.3°C recorded at the Guaratiba meteorological station.

He also highlights that the heat index — as the measurement of temperature sensation is called, which considers both air temperature and humidity — has reached unprecedented levels.

“Our analysis reveals exceptionally high perceived temperatures resulting from the convergence of abnormally warm air and increased humidity, phenomena that are expected to further intensify with ongoing climate change,” says the researcher.

Scientists also observed that similar events in the past occurred mainly in November and December, while in the current climate they are happening mainly in February and March.

Analysis of changes in urban areas reveals that Rio de Janeiro, Curitiba and São Paulo are up to 1°C warmer at present compared to the past, and the capital of São Paulo also experiences increased precipitation (up to 1 mm/day), which , along with higher temperatures, raises the heat index.

According to ClimaMeter, sources of natural climate variability, especially the PDO (Pacific Decadal Oscillation) and the AMO (Atlantic Multidecadal Oscillation), may also have influenced the recent episode.

Davide Faranda, co-author of the study, believes that the impacts of this event highlight the concept of climate justice, as marginalized communities bear the brunt of increasingly severe climate impacts.

“We are entering autumn in the Southern Hemisphere, however, it continues to be characterized by summer-like conditions or even heat waves across much of the territory. Urgent adaptation measures are needed, especially for vulnerable populations living in favelas, where the heat index exceeds officially recorded values”, he says.

At the end of last year, ClimaMeter released a report on the heat wave that hit several regions of Brazil from November 13th to 19th. In this analysis, scientists pointed out that the temperature was 1°C to 4°C warmer than it would have been in events of this type between 1979 and 2000.

The same analysis by ClimaMeter in 2023 showed that, in addition to being hotter, heat waves have become drier and with less wind, which tends to reinforce high pressure zones that prevent the approach of cold fronts with humidity and rain.