The record-breaking heatwave that scorched western North America in June last year was among the most extreme events recorded globally, according to new research.
The team of climate scientists behind the study, led by the University of Bristol and published in the journal Science Advances, uncovered only five events around the world since 1960 that were more extreme — but they went largely unnoticed.
“This is the first study to comprehensively look at extreme heatwaves in terms of how much hotter they were compared to the local normal,” Eunice Lo, a senior research associate at the school of geographical sciences and Cabot Institute for the Environment at the University of Bristol, told Mail & Guardian.
In June last year, the Canadian town of Lytton broke local temperature records by 4.6°C, setting a national temperature record of 49.6°C.
The authors said the temperatures were “unprecedented in records from 1950 to present day” for that location. The heatwave resulted in hundreds of deaths, with associated raging wildfires causing extensive infrastructure damage and loss of crops.
The Canadian heatwave shocked the world, the study’s lead author, Vikki Thompson, said in a statement. “Yet we show there have been some even greater extremes in the last few decades. Using climate models, we also find extreme heat events are likely to increase in magnitude over the coming century — at the same rate as the local average temperature.”
The study, which calculated how extreme heatwaves were relative to the local temperature, identified the top three hottest-ever heatwaves. They were in Southeast Asia in April 1998, hitting 32.8°C, Brazil in November 1985, peaking at 36.5°C, and the southern United States in July 1980, when temperatures soared to 38.4°C.
The study “exposes several greater meteorological extremes in recent decades, some of which went largely under the radar likely due to their occurrence in more deprived countries”, said Dann Mitchell, professor in climate sciences at the University of Bristol.
Some extreme heatwaves “could have been ‘missed’ because of a lack of media attention at the time”, according to Lo.
Thompson said: “It is important to assess the severity of heatwaves in terms of local temperature variability because both humans and the natural ecosystem will adapt to this, so in regions where there is less variation, a smaller absolute extreme may have more harmful effects.”
In their paper, the scientists said although heat extremes are a natural part of climate change, they are getting hotter and longer because of human-induced climate change.
The scientists used climate model projections to anticipate heatwave trends for the rest of this century. This showed that levels of heatwave intensity are set to climb in line with increasing global temperatures.
“Heat extremes pose a threat to human and ecological health and the chance of extreme heat events has increased in most regions around the world. Excess mortality due to extreme heat is well documented, with an average of six heat-related deaths per 100 000 residents each year in North America estimated for 2000 to 2019.”
The effects of heatwaves are magnified in cities and, with nearly 70% of the worlds’ population expected to live in cities by 2050, the risks posed by extreme heat events will increase, the study said.
Although the highest local temperatures do not necessarily cause the biggest harm, they are often related. The authors describe how improving the understanding of climate extremes and where they have occurred can help prioritise measures in the most vulnerable regions.
They note that “regions that, by chance, have not had a recent extreme heatwave may be less prepared for potentially imminent events”.
Mitchell said in the statement that climate change is one of the greatest global health problems of our time.
“We have shown that many heatwaves outside of the developed world have gone largely unnoticed. The country-level burden of heat on mortality can be in the thousands of deaths, and countries which experience temperatures outside their normal range are the most susceptible to these shocks.”
Lo said: “There needs to be effort in reducing greenhouse gas emissions at all levels — from the personal level (for example, choosing to walk rather than drive) to the national and international levels (through making climate policies). We also need to adapt to rising heat, as the impacts of heat are felt even in present-day climate.”
Parts of Africa, she said, were not included in the analysis “because the climate reanalysis datasets we used showed disagreement. This means results in those areas would be less robust.”
She said the current searing heatwave in India can be considered extreme because of its high absolute temperatures and timing.
“Places that are densely populated and may not have the resources to adapt to climate change are particularly vulnerable to its impacts. India and Africa are projected to have the largest population increases in the next 50 years, meaning a lot more people will be exposed to extreme weather when it happens.”