El Niño and the arrival of a cold front explain the heat in August – 08/25/2023 – Daily life

A week in August in Brazil with temperatures above 30°C in São Paulo and close to 40°C in Rio de Janeiro and the Midwest. According to experts, part of the blame for this heat in the middle of winter falls on El Niño and another on a cold air mass that has already begun to act in part of the country.

First, heat waves like the current one in August are not that uncommon, says Maria Clara Sassaki, meteorologist at Climatempo. “What impressed were the temperature expectations above the historical average and the possibility of breaking a record in São Paulo [algo que acabou não se concretizando]’ says Sassaki.

According to the meteorologist, in the 1950s temperatures as high as those seen this week in São Paulo were recorded.

The current accentuated heat was boosted by some factors, among them El Niño, which is back, according to CPTEC (Center for Weather Forecast and Climatic Studies), of Inpe (National Institute for Space Research).

El Niño is characterized by an anomalous rise in sea surface temperature (exceeding 0.5°C rise) in the equatorial Pacific Ocean region.

The study center states that, closer to the coast of South America, the increase in temperature of the water surface exceeds 3°C.

Climate models, according to CPTEC, indicate more than 90% probability that El Niño conditions will remain in the coming months and last until the end of the year. While some models indicate the possibility of a moderate El Niño (central Pacific surface temperature above 1°C), others point to a strong phenomenon (sea surface temperature above 1.5°C).

The effect of El Niño, however, does not stop at sea. The phenomenon also changes the pattern of atmospheric circulation, the transport of moisture, temperatures and rainfall, especially in tropical regions, says CPTEC.

In the Southeast region, for example, which has seen high temperatures during this week, the phenomenon leads to a moderate increase in average temperatures, especially in winter and summer, points out the weather forecast center.

“Higher temperatures in winter are meteorological phenomena of natural climate variability, especially when there is an El Niño phenomenon,” said climatologist Carlos Nobre, who cites the phenomenon is still gaining strength.

Experts point out that El Niño means that the cold air masses that would come from the South often end up more stationary over the region, without the strength to advance over the Southeast, thus being able to lead to increases in temperature in that area and potentially in the Midwest.

According to Sassaki, in addition to El Niño, the higher temperatures this week were also influenced by a situation known as pre-frontal. The idea can be summarized as follows: “Whenever we have a cold front, before it arrives, no matter when, the temperature will rise,” says Sassaki.

Helena Turon Balbino, meteorologist at Inmet (National Institute of Meteorology), also says that we are in a dry period, without rain. “Without clouds, solar radiation falls directly on the ground”, which would also contribute to higher temperatures.

Blame the climate crisis?

Experts say that one must be careful with direct associations between the climate crisis and isolated episodes, even though the knowledge is already consolidated that the climate crisis will lead to extreme events, such as more frequent and more intense heat waves.

It is possible to make such associations based on attribution studies, which analyze what would be the chance of an extreme event occurring without the presence of the climate crisis caused by us. That is, only with more complete climate modeling is it possible to give a safe answer.

In general terms, it is not enough to see that the thermometers are high to be sure that it is the fault of the climate crisis caused by human beings. This is because, as Carlos Nobre says, there is natural variability in the climate.