The record-breaking 2018 summer heatwave in Japan in which more than 1,000 people died “could not have happened without human-induced global warming”, a study finds.
And the extreme heat felt in Japan last summer could “become a usual situation” within the next few decades as temperatures continue to rise, the authors say.
The research is the latest in “attribution science”, a field that aims to quantify the “fingerprint” of climate change on extreme weather events, such as heatwaves, floods and droughts.
It follows analysis published in December which found that climate change made the UK 2018 summer heatwave up to 30 times more likely.
The study is “very interesting”, but requires “further confirmation” before its conclusions can be fully accepted, a leading attribution scientist tells Carbon Brief.
Last year’s summer heatwave across many parts of the Northern Hemisphere made headlines worldwide. The heat broke temperature records from Belfast to Denver and drove wildfires in places such as Sweden, Greece and California.
In Japan, temperatures reached a record high of 41.1C in July. Early reports at the time suggested that dozens had died in the record-breaking weather. The Japanese government later reported that 1,032 people died during the month-long period.
The new study assesses the extent to which human-caused climate change could have boosted the odds of such a heatwave occuring. The results are published in Scientific Online Letters on the Atmosphere, a journal published by the Meteorological Society of Japan.
It also assesses the extent to which natural changes to the weather could have influenced the odds of such a heatwave.
At the time of the heatwave, Japan experienced a “two-tiered high-pressure system”. High-pressure systems move slowly over land, often causing persistent hot and dry conditions.
During the event, two high-pressure systems were stacked on top of each other in the troposphere, explains study lead author Dr Yukiko Imada, a senior researcher at the Japan Meteorological Agency. She tells Carbon Brief:
“A high-pressure system brings descending flows and raises the temperature. [Intense] sunshine also helps to raise the temperature. Last year, those two high pressure systems were stronger and expanded over Japan.”
To work out the extent to which global warming could have boosted the chances of such a heatwave, the authors used a climate model to compare the chances of the heatwave happening in today’s world to a hypothetical world without climate change.
To do this, the researchers produced two sets of simulations. The first set included many of the factors that can influence the climate, including human-driven greenhouse gases, volcanic eruptions and solar variability. The second set included all of these factors except for human-driven greenhouse gases.
The researchers then studied the simulations to see how often heatwaves on the same scale to that seen in 2018 occur in both the “real” world and the world without global warming.
They found that, in today’s world, a heatwave on the scale of that seen in 2018 has around a one-in-five chance of occuring. However, in a world without climate change, such a heatwave would have almost no chance of occuring, says Imada:
“Surprisingly, under the climate without global warming, the event probability reduced to almost zero. That is [to say], the last-year event could not have happened without global warming.”
The map below, which is taken from the study, gives a breakdown of the results at different points across Japan.
The map shows the difference in the number of extremely hot days expected in July in today’s world and a world without climate change across Japan. For example, red areas are found to experience up to eight more extremely hot days in July in today’s world than in a world without climate change.
Japan’s deadly 2018 heatwave ‘could not have happened without climate change’ | Carbon Brief
The record-breaking 2018 summer heatwave in Japan in which more than 1,000 people died “could not have happened without human-induced global warming”, a study finds. And the extreme heat felt in Japan last summer could “become a usual situation” within the next few decades as temperatures continue to rise, the authors say. The research is… [Read More]