Simultaneous Heatwaves Will be More Frequent Due to Climate Change
Numerous large heatwaves the size of Mongolia happened at the same time approximately every day during the warm seasons of the 2010s throughout the Northern Hemisphere, according to a study guided by scientists from the Washington State University (WSU).
Applying climate data from 1979 to 2019, the scientists learned that the number of heatwaves taking place concurrently in the mid- to high-latitudes of the Northern Hemisphere was seven times more in the 2010s than in the 1980s. On average, there were simultaneous heatwaves on 143 days each year of the 2010s — nearly every day of the 153 days of the warm months of May to September.
The simultaneous heat events also became hotter and larger: their intensity grew by 17% and their geographic extent grew to 46%.
Details of the study have been published in the Journal of Climate.
Heatwaves could result in disasters from crop failures to wildfires. Simultaneous heatwaves can increase those threats, the authors highlighted, draining the ability of nations to offer mutual aid in crises as was witnessed during the numerous wildfires in the United States, Australia and Canada related to the 2019 and 2020 heatwaves.
An earlier study also discovered that concurrent heatwaves caused approximately a 4% decrease in crop production worldwide.
The study described large heatwaves as high-temperature events spanning three days or more and covering no less than 1.6 million km2 (around 620,000 square miles), which is approximately equivalent to the size of Iran or Mongolia.
The scientists examined ERA5 data generated by the European Center for Medium-Range Weather Forecasts, which combines massive amounts of observational data from weather stations on land, aircraft and water buoys as well as data from satellites with weather forecasting capacities.
ERA5 offers complete global estimates of hourly data for different climate variables from 1979, when satellite data became available, which is why the research concentrated on this time period.
With this observational data, the scientists learned that the main driver of the heatwaves was the overall increase in global mean temperature because of climate change. The world has warmed 1 °C (about 1.8 °F) over the last 100 years with the vast majority of the increase, two-thirds, happening since 1975.
The team also discovered that increasing incidence of two hemisphere-wide circulation patterns rendered certain areas more susceptible to simultaneous heatwaves, including eastern North America, East Asia, eastern and northern Europe and eastern Siberia.
The research adds more proof for the need to control greenhouse gas emissions and alleviate climate change, the scientists said, and the unrelenting increase in temperature means the world should get ready for more simultaneous heatwaves.
Besides Rogers and Singh, authors involved in this study include Kai Kornhuber of Columbia University, Sarah Perkins-Kirkpatrick of the University of New South Wales in Australia, and Paul Loikith of Portland State University. This study received support from the National Science Foundation and the Australian Research Council.
Journal Reference:
Rogers, C.D.W., et al. (2021) Six-fold increase in historical Northern Hemisphere concurrent large heatwaves driven by warming and changing atmospheric circulations. Journal of Climate. doi.org/10.1175/JCLI-D-21-0200.1.
Source: https://wsu.edu
Study: Risk of overlapping heat waves grows
in Northern Hemisphere
Andrew Freedman
AXIOS
A resident splashes water onto their face during a heat wave in Sacramento, Calif., July 8, 2021.
The risk of large heat waves happening simultaneously in at least two parts of the Northern Hemisphere is growing due to global warming and its effects on atmospheric circulation, a new study finds.
Why it matters: The study, accepted for publication in the Journal of Climate, adds to concerns about food supply disruptions and other major societal impacts, depending on the location of the concurrent extremes.
Driving the news: The research, led by Cassandra Rogers, a post-doctoral researcher at Washington State University, examined climate data from 1979 to 2019 and found a six-fold increase in the number of simultaneous large heat waves occurring in the Northern Hemisphere warm season between the 1980s and 2010s.
During the same period, the heat events grew in size and intensified. The study was discussed Thursday at a major Earth science meeting in New Orleans.
Details: While heat waves themselves can pose huge risks to human health, with hundreds of deaths attributed to last summer’s Pacific Northwest heat wave, for example, they can also prime the environment for wildfires and affect agriculture.
A 2019 study by Columbia University’s Kai Kornhuber, a co-author of the new research, found that simultaneous heat waves caused about a 4% decrease in crop production.
That research identified specific patterns of the jet stream, which steers storms, that are associated with heat extremes that tend to occur simultaneously in different breadbasket regions.
One such pattern, for example, can cause heat waves to break out in central North America, Eastern Europe and East Asia, the study found.
What they did: This study quantified large heat waves as periods of three or more days with daily mean temperature greater than the local 90th percentile with a range roughly the size of Mongolia or Iran (about 620,000 square miles).
The researchers were able to show that the primary driver of the increase in simultaneous heat waves is the background warming of the climate, plus warming's influences on atmospheric circulation, through changes in the jet stream, for example.
What they’re saying: "The fact that we know what's happening, we know these events are going to continue to happen, is a real opportunity to actually prevent the deaths that could happen," Rogers told Axios.
"I think it's a little silver lining there, as bad as the predictions are,” she added
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