The heat wave in the West 'virtually impossible' without climate change

Last week’s deadly and record-breaking heat wave in parts of the Western U.S. and Canada would have been "virtually impossible" without the influence of climate change, according to a study released Wednesday by leading scientists, who said global warming made the extreme temperatures at least 150 times more likely to occur.

Hundreds of people were reported to have died because of the heat, and the majority of deaths were in British Columbia, Canada. More than 100 people died in Oregon, a death toll described as "horrific" by the state's governor, Kate Brown.

Study co-author Kristie L. Ebi of the Center for Health and the Global Environment at the University of Washington warned that "in the United States, heat-related mortality is the No. 1 weather-related killer."

Parts of the U.S. and Canada saw temperatures break records by several degrees, including a new all-time Canadian record of 121.3 degrees in the village of Lytton, which was virtually destroyed by a wildfire shortly after setting the record.

Portland, the largest city in Oregon, broke its all-time temperature record for three straight days, topping out at 116 degrees – significantly hotter than the average June highs in the 80s, according to National Weather Service data.

"Climate change is making extremely rare events such as this one become more frequent," said report co-author Sonia Seneviratne of the Institute for Atmospheric and Climate Science at ETH Zurich in a statement.

In fact, every heat wave occurring today is made more likely and more intense by climate change, the study found.

Human-caused climate change, or global warming, is caused by the burning of fossil fuels such as oil, gas and coal, which release greenhouse gases such as carbon dioxide and methane into the Earth's atmosphere and oceans.

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Heat waves are one of the deadliest natural hazards, and this one affected a population unaccustomed and unprepared for such extreme temperatures, the study said. Many homes in British Columbia, Oregon and Washington lack air conditioning.

Wednesday's study was prepared by World Weather Attribution, an international collaboration that analyzes and communicates the possible influence of climate change on extreme weather events, such as storms, extreme rainfall, heat waves, cold spells and droughts.

"We are entering uncharted territory," Seneviratne said. "The temperatures experienced in Canada last week would have broken records in Las Vegas or Spain. However, much higher temperature records will be reached if we don’t manage to stop greenhouse gas emissions and halt global warming."

Until overall greenhouse gas emissions are halted, global temperatures will continue to increase and events like these will become more frequent, the study said. For example, even if global temperature rise is limited to 3.6 degrees Fahrenheit, which could occur as soon as 2050, a heat wave like this one would occur about once every five to 10 years, the scientists found.

"As warming continues, it will become a lot less rare," the study said.

Daniel Swain, a climate scientist at UCLA who was not involved in Wednesday's study, said in a recent blog post that "global warming is greatly increasing the odds of experiencing unprecedented heat extremes."

In a tweet, Swain added that "essentially every severe to record-breaking heat event globally now has a detectable human fingerprint due to climate change. Study after study after study have shown this."

But not all scientists are convinced about the connection between global warming and the Pacific Northwest heat wave. Seattle-based meteorologist Cliff Mass, in a blog post, wrote that "human-caused global warming played a very small role in the extreme heat event that we just experienced here in the Pacific Northwest."

Mass said the heat wave was largely the result of an extraordinary confluence of natural events, adding that "the atmosphere is capable of attaining extreme, unusual conditions without any aid from our species."

A separate report released Wednesday from the European Union's Copernicus Climate Change Service found that overall, North America endured its hottest June on record. The report said temperatures were hotter this June than the record highs in June 2012.

This article originally appeared on USA TODAY: Heat wave in the West almost certainly caused by climate change