Heat Waves are Man-made

 Climate researchers have grown used to heatwaves breaking records all over the world in recent years. In their study, the team of researchers says the extreme heatwave that scorched western Canada and the US at the end of June was "virtually impossible" without climate change. If humans hadn't influenced the climate to the extent that they have, the event would have been 150 times less likely.

The deadly heatwave was a one-in-a-1,000-year event. But we can expect extreme events such as this to become more common as the world heats up due to climate change. Scientists worry that global heating, largely as a result of burning fossil fuels, is now driving up temperatures faster than models predict.

All across the region, in the US states of Oregon and Washington and in the west of Canada, multiple cities hit new records far above 40C.  Researchers say that the chances of it occurring without human-induced warming were virtually impossible.

An international team of 27 climate researchers compared the climate as it is today, with the world as it would be without human-induced warming.

"We conclude that a one-in-1000-year event would have been at least 150 times rarer in the past," said lead author Sjoukje Philip, from the Royal Netherlands Meteorological Institute. "So that's in a climate without human-induced climate change, when the climate was about 1.2C cooler than it is now. The heatwave would also have been about two degrees cooler in the past."

Co-author Dr Friederike Otto, from the University of Oxford, explained what the researchers meant when they said the extreme heat was "virtually impossible" without climate change.

"Without the additional greenhouse gases in the atmosphere, in the statistics that we have available with our models, and also the statistical models based on observations, such an event just does not occur," she explained. "Or if an event like this occurs, it occurs once in a million times, which is the statistical equivalent of never." 

Climate change: US-Canada heatwave 'virtually impossible' without warming - BBC News