Explained: Possible reasons for the historic heatwave seen in Pacific Northwest

Explained: Possible reasons for the historic heatwave seen in Pacific Northwest
  • Published7월 10, 2021

A team of climate researchers from the World Weather Attribution said this week that the historic heatwave that was witnessed in western Canada and the US in the last days of June was impossible without human-caused climate change. Typically, scientists are wary of associating a single extreme event with climate change because of the difficulty in completely ruling out the possibility of the event having been caused by some other reason, or a result of natural variability.

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The historic heat wave

Multiple cities in the US and Canada experienced a heatwave that broke more than a few temperature records. For instance, in the village of Lytton in Canada’s British Columbia, temperatures reached a high of 49.6ºC.

In Portland city in Oregon, US temperatures as high as 46 degrees Celsius were recently recorded–just three degrees short of the internal core temperature of a cooked shrimp and a few degrees hotter than summer temperatures recorded in New Delhi–a record for the city. In Salem, barely 72 km away from Portland, the temperatures were highest at about 47 degrees Celsius on June 28.

These exceptionally high temperatures prodded some people to buy air conditioners and coolers for the first time in the affected areas and also led to a rise in sudden deaths and a sharp increase in hospital visits due to heat-related illnesses and other such emergencies.

What are climate scientists saying now?

In their analysis, scientists from the UK, US, Canada, the Netherlands, France, Germany and Switzerland collaborated to assess to what extent human-induced climate change made this heatwave hotter and more likely.

For their analysis, the scientists analysed how human-induced climate change affected maximum temperatures in cities including Seattle, Portland, and Vancouver where there is a combined total population of more than 9 million people.

Crucially, their finding notes that it is “virtually impossible” for maximum daily temperatures to rise so much without human-caused climate change. “The observed temperatures were so extreme that they lie far outside the range of historically observed temperatures. This makes it hard to quantify with confidence how rare the event was,” they note. Further, they say that in the most realistic statistical analysis, such an event is estimated to be about a “1 in 1000 year event” in today’s climate.

As per them, there are two possible reasons for the “extreme jump” in maximum temperatures. The first is that the historic heatwave is itself simply a very low probability event, which is to say that it is an extremely rare event but was aggravated because of climate change.

The second possible explanation, while not shown by the climate models used by researchers, is that the probability of such kinds of heatwaves has increased.

What do these possible explanations mean?

The researchers are saying that in the absence of human-induced climate change, the heatwave such as seen recently in the Pacific Northwest would have been 150 times rarer. They also note that this heatwave was 2°C hotter than it would have been if it had occurred at the beginning of the industrial revolution (around late 1700s) when the global average temperatures were 1.2°C cooler than what they are today.

Significantly, at the current rates of emissions, when the world is warmer by 2°C (0.8°C more than what it is today) around the 2040s, a typical heatwave type of event could be at least another degree hotter.

This is to say that an event which is considered extremely rare (occurring once in about 1000 years) could occur roughly every five to ten years. In other words, the researchers are saying that if emission levels continue to rise, which in turn would increase average global temperatures, extreme heat waves will become less rare than they are today.

So, what can be done about this?

Heat action plans can be organised as early warning systems to help people deal with such events. Secondly, there need to be some long-term plans such as cutting down on greenhouse gas emissions and also adapt to the hotter climate by modifying the built environments.

In April this year, researchers from Purdue University in the US created what they called the whitest paint yet. They claimed that buildings coated with this paint may be able to cool them off enough to reduce the need for air conditioning (because the colour white absorbs the least heat out of all the colours on the VIBGYOR spectrum. Black absorbs the most). Because the paint is so white, the researchers demonstrated outdoors that the paint can keep surfaces 19 degrees Fahrenheit cooler than their ambient surroundings at night.

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