Heat put down to changing climate

The deadly heat wave that roasted the Pacific Northwest and western Canada was virtually impossible without human-caused climate change. A new quick scientific analysis found that this added a few extra degrees to record-breaking temperatures.

An international team of 27 scientists calculated that climate change increased chances of the extreme heat occurring by at least 150 times, but likely much more.

The study, which has not yet been peer reviewed, said that before the industrial era, the region's late June triple-digit heat was the type that would not have happened in human civilization. And even in today's warming world, the heat was a once-in-a-millennium event.

The heat wave gripped parts of the United States and Canada for days at the end of June, smashing records in dozens of cities with power lines melting in the heat and roads buckling. Canada broke its national temperature record thrice, peaking on June 29 at 49.6 C－a full 4.6 C higher than the previous record set in 1937. Another heat wave is expected to hit parts of Canada and the US later this week.

In Oregon alone, the state medical examiner reported 116 deaths related to the heat wave on Wednesday.

This type of extreme heat "would go from essentially virtually impossible to relatively commonplace", said Gabriel Vecchi, the study's co-author and a Princeton University climate scientist. "That is a huge change."

Impact on health

The study also found that climate change was responsible for about 2 C of the heat shock in the Pacific Northwest and Canada. Those few degrees make a big difference in human health, said Kristie Ebi, the study's co-author and a professor at the Center for Health and the Global Environment at the University of Washington.

"This study is telling us climate change is killing people," said Ebi, who endured the blistering heat in Seattle. She said it will be many months before a death toll can be calculated from June's blast of heat, but it is likely to be in the hundreds or thousands. "Heat is the number 1 weather-related killer of Americans."

According to the National Academy of Sciences, the team of scientists used a well-established and credible method to search for the role of climate change in extreme weather. They logged observations of what happened and fed them into 21 computer models and ran numerous simulations. They then simulated a world without greenhouse gases from the burning of coal, oil and natural gas. The difference between the two scenarios is the climate change portion.

"Without climate change, this event would not have happened," said Friederike Otto, the study's senior author and a climate scientist at the University of Oxford.