Climate change made record breaking early season heat in Argentina and Paraguay about 60 times more likely

A large area centred around the central-northern part of Argentina, and also southern Bolivia, central Chile, and most of Paraguay and Uruguay, experienced record-breaking temperatures during two consecutive heatwaves in late November and early December 2022.

Several weather stations in the area recorded new maximum temperatures, which is particularly noticeable as these temperature records were reached towards the end of an unusually cold spring, when the austral summer had not even begun. During a second heatwave in early December, temperatures exceeded 40°C in 24 locations, four of them above 45°C. Rivadavia station, located near the border with Bolivia and Paraguay, recorded 46°C of maximum temperature during December 7, making the region one of the hottest in the world during that day. During the heatwave, nine locations in northern Argentina registered their highest maximum temperature of December since at least 1961.

The area is also experiencing a prolonged drought that started in 2019 and has become worse since. Drought and heat reinforce each other and exacerbate impacts on agriculture. Harvests are expected to be the worst in seven years, with great economic losses for farmers and the Argentine Treasury, as Argentina is South America’s largest exporter of wheat [Successful Farming, News Dakota, Merco Press]. As a major player in the world’s wheat market, this means further increases in global food prices [National Interest]. Direct impacts of the heatwaves included large scale power cuts and wildfire outbreaks. Heatwaves are amongst the deadliest natural hazards with thousands of people dying from heat-related causes each year (IFRC, 2020), with early season heatwaves known to be particularly deadly. However, the full impact of a heatwave is often not known until weeks or months afterwards. The heatwave was well forecasted and while Paraguay still has to develop an early warning system for heatwaves, Argentina implemented such a system in 2018 which issued amber and red alerts for most parts of the affected area prior to the heatwave.

Scientists from Argentina, Colombia, France, New Zealand, Denmark, United States of America, the Netherlands and the United Kingdom, collaborated to assess to what extent human-induced climate change altered the likelihood and intensity of these heatwaves.

Using published peer-reviewed methods, we analysed how human-induced climate change altered the likelihood and intensity of the 7-day heatwave event that occurred on 4-10 December 2022, in the most affected region (see Figure 1, black outline).

Figure 1: ERA5 near surface temperature (T2m) [℃] showing 7-day average daily maximum for the period of the 4th to 10th of December 2022. The bold black outline represents the study region, the blue dots represent major cities Buenos Aires (station 6), Rosario (station 5), Córdoba (station 4) and the crosses indicate the weather stations analysed in this report.

Main findings

  • The 2022 heatwave has led to large-scale power outages, wildfires and, in combination with the ongoing drought, poor harvests. It is estimated to have led to an increase in heat-related deaths, with the impacts unequally distributed across In different cities and municipalities across South America, people living in some areas – often poorer neighbourhoods – experience higher temperatures than others, as they lack green space, adequate thermal insulation from heat, electricity, shade, and water which can be lifelines during heatwaves.
  • South America, like the rest of the world, has experienced heatwaves increasingly frequently in recent years. The recent heatwave, averaged over 7 days over the region shown in Figure 1, has an estimated return time of 1 in 20 years in the current climate, meaning it has about a 5% chance of happening each
  • We further looked at 7 individual weather stations, to see whether the character of the heatwave differed within the study We found that at most stations the 7-day maximum temperatures observed during this heatwave have return times comparable to the region average – meaning it was equally unusual across much of the region – but the heat was more extreme towards the northwest of the region.
  • To estimate how human-caused climate change has influenced the likelihood and intensity of the observed heatwave we combine climate models with the observations-based data.
  • We find that human-caused climate change made the event about 60 times more Alternatively, a heatwave with a similar probability would be about 1.4°C less hot in a world that had not been warmed by human activities.
  • With future global warming, heatwaves like this will become even more common and hotter. If global mean temperatures rise an additional 8°C, to a total warming of 2°C, a heatwave as hot as this one would be about 4 times more likely than it is now, while a heatwave that happens approximately once in 20 years would be 0.7-1.2°C hotter than this one.
  • There is a discrepancy between the modelled and observed change in heatwave intensity in the region with the observations showing a larger While there is no doubt that future heat extremes will become even hotter than they are now, this discrepancy limits confidence in projections of the magnitude of future extremes.
  • Heatwaves this early in the season pose a substantial risk to human health and are potentially lethal. This risk is aggravated by climate change, but also by other factors such as an ageing population, urbanisation and the built environment, and individual behavior and susceptibility to the The full impact will only be known after a few weeks when the mortality figures have been analysed. Effective heat emergency plans, together with accurate weather forecasts such as those issued before this heatwave, reduce impacts and are becoming even more important in light of the rising risks.