Most intense heat waves ever identified – and some went almost unnoticed, scientists say

BRISTOL, England — The most intense heat waves ever have been identified – and some of them went nearly unnoticed just decades ago. In fact, research by scientists at the University of Bristol also shows that heat waves are projected to get even hotter in the future as climate change worsens.

Western North America experienced a record-breaking heat wave last summer. Canada logged an all-time high of 121.2 degrees Fahrenheit (49.6 degrees Celsius) in Lytton, British Columbia, on June 29 — an increase of 40.3 degrees (4.6 Celsius) from the previous peak. The new findings, published in the journal Science Advances, uncover five other heat waves around the world which were even more severe, but went largely underreported.

“The recent heat wave in Canada and the United States shocked the world. Yet we show there have been some even greater extremes in the last few decades,” says study lead author Dr Vikki Thompson, a climate scientist at the university, in a statement. “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 western North America heat wave was the most deadly weather event ever in Canada, resulting in hundreds of fatalities. Researchers say associated raging wildfires also led to extensive infrastructure damage and loss of crops.

But the study, which calculated how extreme heat waves were relative to the local temperature, shows the top three hottest-ever in the respective regions were in Southeast Asia in April 1998, which hit 91 degrees Fahrenheit (32.8 Celsius); Brazil in November 1985, peaking at 97.8 Fahrenheit (36.5 Celsius); and Southern USA in July 1980, when temperatures rose to 101.1 Fahrenheit (38.4 Celsius).

“The western North America heat wave will be remembered because of its widespread devastation,” says Thompson. “However, 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. It is important to assess the severity of heatwaves in terms of local temperature variability because both humans and the natural eco-system will adapt to this, so in regions where there is less variation, a smaller absolute extreme may have more harmful effects.”

The team of scientists also used sophisticated climate model projections to anticipate heatwave trends for the rest of this century. Their modeling indicates that levels of heat wave intensity are set to rise in line with increasing global temperatures.

Researchers also explain that although the highest local temperatures do not necessarily cause the biggest impacts, they are often related. Improving the understanding of climate extremes and where they have occurred can help prioritize measures to help tackle this in the most vulnerable regions.

Climate change is one of the greatest global health problems of our time, and we have showed that many heat waves outside of the developed world have gone largely unnoticed,” adds co-author Dann Mitchell, a professor in climate sciences. “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.”

Report by South West News Service writer Stephen Beech.