US heatwave ‘virtually impossible’ without climate change

Recent record-shattering temperatures in the US and Canada which caused deaths and wildfires would be “virtually impossible” without climate change, analysis has found. Rapid analysis of last week’s heatwave in parts of North America by an international team of climate scientists found global warming driven by human activity made it at least 150 times more likely to happen.

The scientists also warned of the possibility the climate system may have crossed a threshold where a small amount of warming was causing a faster rise in extreme temperatures, posing the risk of more deadly heatwaves.

In the heatwave, parts of the Pacific northwest saw temperatures that broke records by several degrees Celsius.

The village of Lytton in British Columbia saw a new Canadian record high of 49.6 degrees Celsius, well above the country’s previous national record of 45 degrees Celsius, and was shortly afterwards largely destroyed by wildfire.

Hundreds of deaths have been attributed to the sweltering temperatures which soared above 40 degrees Celsius in many cities in Oregon and Washington states in the US and the western provinces of Canada.

Scientists said the temperatures were so extreme they lie far outside the range of historically observed temperatures, making it hard to tell just how rare the event was.

But statistical analysis suggests the temperature highs be a one in a 1,000-year event in today’s climate, which has seen 1.2 degrees Celsius of humaninduced global warming since pre-industrial times, making it still a very rare event.

Without warming driven by greenhouse gas emissions from sources such as burning fossil fuels, it would have been at least 150 times rarer, or virtually impossible, the scientists said.

It raises serious questions whether we really understand how climate change is making heatwaves hotter and more deadly

GEERT JAN VAN OLDENBORGH Royal Netherlands Meteorological Institute