A week-long heatwave that hit parts of the United States and Canada last month would not have occurred were it not for global warming, new research has shown.
A rapid analysis by researchers said the chance of temperatures in the Pacific Northwest region coming close to 50°C has increased at least 150-fold since the end of the 19th century.
Climate scientist at the Royal Netherlands Meteorological Institute, Sjoukje Philip blamed the heatwave on climate change driven by humans.
“It was probably still a rare event, but if global warming might exceed two degrees, it might occur every five to 10 years in the future,” she said.
The heatwave between 25 June and 1 July affected cities in North America that ordinarily would not experience extremely high temperatures.
The analysis showed a transparent footprint of human-caused climate change, with the researchers comparing the observed heat with maximum daily temperatures predicted by climate models.
They also incorporated simulations of temperatures in an atmosphere unaltered by the effect of rising greenhouse-gas concentrations.
Their conclusion was that the global average temperature increase of 1.2°C since preindustrial times made the extreme heatwave at least 150 times more likely to happen.
Climate modeller Geert Jan van Oldenborgh said this analysis was more challenging than previous similar studies.
“The peak temperatures observed were up to 5°C higher than previous records in the region.
“These extremes made it hard to pin down precisely how rare a heatwave of such strength might have been in cooler periods of the past,” he said.
According to the analysis, it is possible that climate change is causing local heat extremes to become more frequent and intense than they would be in a cooler climate and that such heat waves might be more likely to happen than current models predict.
Chris Gilili is an Adamela Trust climate and economic justice reporting fellow, funded by the Open Society Foundation for South Africa