Climate crisis may have worsened heat wave in Brazil – 11/24/2023 – Daily

The heat wave that hit several regions of Brazil between November 13 and 19 was 1°C to 4°C hotter than it would have been in the past. Despite natural variations in the climate over the decades, the emission of greenhouse gases may have worsened the effects of the event, the eighth of the year and which recorded the country’s temperature record, with 44.8°C in Araçuaí (MG) .

This is what a report from ClimaMeter points out, a platform developed by the team at the climate and environmental science laboratory at Paris-Saclay University, in France. Today, the group includes scientists from several European universities. The project is experimental, and aims to quickly analyze extreme events shortly after they occur, such as the wave that ended last Sunday.

ClimaMeter’s analysis shows that, in addition to being hotter, heat waves have become drier and with less wind, and to this is added an increase in atmospheric pressure. It is worth noting that hotter and drier weather reinforces high pressure zones such as the recent wave, which prevented the approach of cold fronts with humidity and rain.

Furthermore, the occurrence of has been more frequent in November than in October and December. The analysis focused on the cities of São Paulo, Rio de Janeiro and Corumbá (MT), and uses as parameters for comparison current events, from 2001 to 2022, and those of the past, from 1979 to 2000. The choice of the starting year is due to the expansion of satellite monitoring of climate variables.

According to the report, natural variations in ocean temperature may also have influenced the intensity of the heat, such as the decadal oscillations in the Pacific and multidecadal oscillations in the Atlantic. This is because they affect atmospheric pressure, which generates cyclones or anticyclones — in the case of a heat wave.

To identify the human impact, data on temperature, rain and wind are used. “Natural variability guides atmospheric pressure patterns, which are the basis of the heat wave,” says researcher Davide Faranda of France’s National Council for Scientific Research, who leads ClimaMeter.

“Basically, the temperature is higher because of the higher concentration of CO2 in the atmosphere. In these waves we experience higher temperatures and the combined effect of less rain, because there is more pressure in that area with climate change.”

According to the report, the analysis is in line with predictions from the 2021 IPCC (UN Intergovernmental Panel on Climate Change) report, which points to an increase in the frequency and intensity of heat waves over South America, with exposure of urban populations to extreme heat.

The problems of densely urbanized areas, especially peripheral ones, such as favelas, highlighted the uneven impact of the heat wave. In São Paulo, protesters blocked roads in protest against the lack of electricity. And the largest favela in Rio de Janeiro, Rocinha, spent at least ten days without electricity, forcing residents to fetch water from natural sources at the top of the hill.

As extreme events tend to be more frequent and intense, says Faranda, it is necessary to adapt the geography of cities and the capacity to help those who are most vulnerable to these events.

“This is an important part of the story. This heat wave has affected people in different ways according to social and economic class. The time to act is now.”

There is a difference announced by the group in the study in relation to the methodology. In particular, Faranda avoids talking about attribution, a science that seeks to determine the influence of human activity on extreme weather events, and says that ClimaMeter does not work with modeling.

“When we talk about attribution, you have a single actor. What we want is to see the mutual influences of natural variability with climate change caused by humans”, says the researcher.

Thus, according to Faranda, variability is not excluded from studies. “We believe that, in this short period of time, what we can do is verify the mutual roles of variability and human action, without vectors that point 100% in one direction or the other.”