For several weeks now, the Southern Hemisphere has been experiencing extraordinary temperature anomalies and a scorching start to spring. This phenomenon is particularly marked in South America. According to the Brazilian National Institute of Meteorology, the cities of Cuiaba and Sao Paulo experienced the hottest start to spring in 63 years.
On September 15, the Balsas weather station in central-eastern Brazil recorded a maximum temperature of 41.5°C. Abnormally high temperatures then spread across much of the country, with thermometers topping 40°C in many areas. The heat peak occurred on September 25, with anomalies of over 7°C for the time of year in southern Bahia, eastern Goias and Mato Grosso and north-central Parana. This comes on the heels of a very warm end of winter in South America, with temperatures topping 35°C in Chile and Argentina in August.
In order to measure the influence of man-made climate warming and the rise of El Niño, numerous scientists working under the umbrella of the international World Weather Attribution network have compiled statistics and field observations and run climate models over an area stretching from Sao Paulo to Paraguay.
According to their attribution study published on Tuesday, October 10, human-induced climate change makes recent heat in South America "at least 100 times" more likely in today's climate than in a pre-industrial climate. The scientists from the Brazilian, Dutch and British meteorological institutes concluded that although El Niño may have had some influence on high temperatures, climate change is the main driver of the heat, making it much more likely and about 1.4°C to 4.3°C warmer.
To arrive at these results, the researchers compared the probability of experiencing a series of 10 such hot days in today's climate and in a pre-industrial climate that was, on average, 1.2°C cooler. And they took every precaution to remain on the conservative side, precision being made more complex by two statistical biases: the "very low" probability of an event of this type in a 19th-century climate and the lack of observations in this area.
"It is noted that the major barrier to the study of climate change in many regions of South America is still the absence or insufficiency of long time series of observational data, such as central-west and north Brazil. Most national datasets were created in the 1970s and 1980s, preventing a more comprehensive mong-term trend analysis," they write, while estimating that such episodes could still be 3.9 to 8.9 times more likely in a climate warmed by 2°C compared with the pre-industrial era.
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