Attribution analysis by an international team of leading climate scientists reveals that the unprecedented heatwaves in parts of the US and Canada last week would not have occurred without climate change as a result of human activities. Scientists say climate change caused by greenhouse gas emissions makes heat waves at least 150 times more likely.
Record temperatures are being recorded in the Pacific Northwest regions of the US and Canada. The temperature in the village of Lytton, where 49.6ºC was recorded, far exceeds Canada’s national temperature record of 45ºC. Shortly after it set the temperature record, most of the village of Lytton was destroyed by bushfire.
The extreme temperatures experienced are well outside the temperature range observed in the past. For this reason, it is difficult to determine how often extreme weather events will occur in the absence of climate change as a result of human activities and in today’s climate. But the researchers conclude that the likelihood of these extreme weather events occurring without human influence is “almost impossible.”
Researchers suggest two possible scenarios for how climate change is increasing the likelihood of extreme temperatures. The first is that, although climate change increases the likelihood of extreme heatwaves, these unusual events are rare in current climate conditions. In this scenario, extremely high temperatures occur, combined with the effects of climate change, in what is known as the ‘heat dome’, which means ongoing drought and unusual atmospheric circulation conditions. This assumption requires that, without the impact of climate change, the highest recorded temperatures would be about 2°C lower than those recorded today.
If greenhouse gas emissions are not limited, global temperatures are expected to continue to rise. This means that such incidents will occur more often. For example, scientists suggest that even when global temperature rise is limited to 2°C, a heatwave of this scale could occur every 5 to 10 years.
Scenario 2 indicates that the climate system has crossed an irreversible threshold. This scenario means that a small-scale increase in global warming could result in a rapid increase in the likelihood of extreme temperatures. That means record heatwaves last week are likely to happen more often than climate models predict.
This latest event is a warning that extreme temperatures, well above the currently expected temperature range, may occur in the 50th north latitude region. This region includes the USA, France, parts of Germany, China and Japan. Scientists underline that climate change adaptation plans should be designed for temperatures well above the range witnessed in the recent past.
The study was carried out by 27 researchers working at universities and meteorological institutions in Canada, the USA, Germany, the Netherlands, Switzerland, France and the UK under the World Weather Attribution Initiative (WWA).
Friederike Otto, from the Institute for Environmental Change at Oxford University, said: “What we have seen is unprecedented. A record of four or five degrees increase in the highest recorded temperature rise should not be broken. The extraordinary situation is the possibility that today’s extreme temperatures may occur before what we expect as a result of higher levels of global warming. It shows that we cannot ignore it.”
Geert Jan van Oldenborgh of the Netherlands Meteorological Institute said: “It was to be expected that heat waves would become more frequent and intense. However, we did not expect to see this temperature in this region. This raises the question of whether we understand deeply how climate change is making heat waves more frequent and deadly. brings it,” he says.
Sonia Seneviratne, from the Swiss Federal Institute of Technology (ETH Zürich) Institute of Atmospheric and Climate Science, said: “Climate change causes an increase in the frequency of extremely rare events such as heat waves. We are swimming in unknown waters. The extreme temperatures experienced in Canada last week, Las in Vegas or Spain