New research shows extreme heat events both in the summer and in the winter are growing in the US and Canada, while extreme extreme events in the summer and winter are decreasing.
New research in Journal of Geophysical Research: Atmospheres, Published by the American Geophysical Association, examined absolute extreme temperatures – high summer temperatures and low winter temperatures – but also examined the relatively extreme temperature events – especially low temperatures and especially hot temperatures throughout the year.
The new study found that relative and sustained heat events have increased throughout the United States and Canada since 1980. This trend is the largest in the United States, especially in Ozarks and southern Arizona, and in northern Quebec, Days that are considered very hot for the time of year, as hot days and acute in the winter.
The new study also found that relatively cold and absolute cold events fall, mainly in Alaska and northern Canada, along with patches along the Atlantic coast of the US In these areas there are fewer cases of very cold temperatures or compared to the normal range, such as in winter or during the year, As on particularly cold days in the summer.
Global surface temperature, the most commonly cited climate change index, has been expanding since the 1970s. However, extreme temperatures pose a greater ecological risk for many species than average warming, according to study authors.
The new study is one of the first to investigate relatively extreme temperature events, which change more rapidly than extreme absolute temperatures, and may have important implications for the environment, agriculture and human health, according to Scott Sheridan, a professor in the Department of Geography at Kent State University and lead author of the new study.
"Usually for this type of research we look at the highest temperatures in the summer and the lowest temperatures in winter, but we also saw that extreme temperatures that are really exceptional for this year's year can have a high impact – these are relatively extreme and unimportant," he said.
Investigation of extreme temperatures
To investigate how extreme temperatures changed over time, Sheridan and his colleague conducted a climate of hot and cold events, absolute and close, to North America, and then an analysis of how they changed since 1980.
Extremely extreme temperature events change faster than absolute extreme events, and often occur outside seasonal norms, according to the new study. In the eastern half of the United States, extreme heat events occur in the middle of winter until the beginning of spring, and extreme temperatures outside the season can result in minor winters or weaker populations.
Beyond the parts of the North Pole, the extreme cold events were almost nonexistent and harder to identify, according to the researchers.
"Temperatures and relative temperatures can trigger the so-called mismatch of phenologies, when a temperature and mismatch discrepancy can cause trees to bloom too early and birds and insects pass before there is adequate food," Sheridan said.
The most notable is the very unusual hot event in March 2012, which included constant summer heat in the middle of multiple locations. The event created a "fake spring" in which the vegetation ended prematurely, so it was not ready for the next frost, leading to major agricultural losses in some areas, according to researchers.
There is some evidence that heat events at the beginning of the season are more dangerous to humans than heat events later in the season. When people are not correlated with higher temperatures, they are more vulnerable to adverse health effects, especially for the elderly, infants, young children and people with health problems or chronic disabilities.
The study clearly highlights the importance of not only looking at high summer temperatures but also looking at relative temperatures, said Kristi Ebi, a professor of health and basic sciences at Washington University who was not involved in the study.
"Using information generated in research on regional patterns in extreme weather events, particularly extreme temperatures, early warnings can be issued that include information on what people can do to protect themselves and protect crops and ecosystems," said Avi.
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Scott Sheridan et al., Temporal Trends in Absolute Relative Temperatures and Extreme Events Across North America, Journal of Geophysical Research: Atmospheres (2018). DOI: 10.1029 / 2018JD029150