‘New normal’ in the United States is half a degree hotter than it was 20 years ago

America’s new normal temperature is 0.5 C hotter than it was just two decades ago.

Scientists have long talked about climate change — hotter temperatures, changes in rain and snowfall and more extreme weather — being the “new normal.” Data released Tuesday by the National Oceanic and Atmospheric Administration (NOAA) put hard figures on the cliché.

The new United States normal is not just hotter, but wetter in the eastern and central parts of the nation and considerably drier in the West than just a decade earlier.

Meteorologists calculate climate normals based on 30 years of data to limit the random swings of daily weather. It’s a standard set by the World Meteorological Organization. Every 10 years, NOAA updates normal for the country as a whole, as well as for states and cities, by year, month and season.

Environment Canada does the same for Canada, but its most recent dataset posted is for 1981-2010. Dave Phillips, senior climatologist at Environment Canada, said the new dataset will likely be released in the summer of 2022. However, Canada, especially the North, has been warming faster than the rest of the world.

Annual U.S. temperatures in Fahrenheit compared with the 20th-century average for each U.S. Climate Normals period from 1901-1930 (upper left) to 1991-2020 (lower right). Places where the normal annual temperature was 1.25 F (0.7 C) or more colder than the 20th-century average are darkest blue; places where normal annual temperature was 1.25 F (0.7 C) or more warmer than the 20th-century average are darkest red. (NOAA Climate.gov)

For the entire U.S., the yearly normal temperature is now 11.8 C based on weather station data from 1991 to 2020. Twenty years ago, normal was 11.3 C based on data from 1971 to 2000. The average U.S. temperature for the 20th century was 11.1 C.

The new normal annual U.S. temperature is 0.9 C hotter than the first normal calculated for 1901 to 1930.

“Almost every place in the U.S. has warmed from the 1981 to 2010 normal to the 1991 to 2020 normal,” said Michael Palecki, NOAA’s normals project manager.

Fargo, N.D., where the new normal is 0.05 C cooler than the old one, is an exception, but more than 90 per cent of the U.S. has warmer normal temperatures now than 10 years ago, Palecki said.

In Chicago and Asheville, N.C., the new yearly normal temperature jumped 0.83 C in a decade. Seattle, Atlanta, Boston and Phoenix, Ariz., saw their normal annual temperature rise by at least 0.28 C in the last decade.

Cities with the biggest changes

Charlottesville, Va., saw the biggest jump in normal temperatures among 739 major weather stations. Other large changes were in California, Texas, Virginia, Indiana, Arizona, Oregon, Arkansas, Maryland, Florida, North Carolina and Alaska.

New normals are warmer because the burning of fossil fuels is making the last decade “a much hotter time period for much of the globe than the decades” before, said Cornell University climate scientist Natalie Mahowald.

A large dust storm, or haboob, sweeps across downtown Phoenix, Ariz., in 2012 amid a drought from Oklahoma to Utah. The normal annual rainfall for Phoenix dropped 10 per cent, down to 18.2 centimetres, in the past 20 years. (Ross D. Franklin/The Associated Press)

For Phoenix, the biggest change in normal came in precipitation. The city’s normal annual rainfall dropped 10 per cent down to 18.2 centimetres. Rainfall in Los Angeles dropped 4.6 per cent.

At the same time, Asheville saw a nearly nine per cent increase in rainfall, while New York City’s rainfall rose six per cent. Seattle’s normal is five per cent wetter than it used to be.

Useful or misleading statistics?

Climate scientists are split over how useful or misleading newly calculated normals are.

Mahowald and University of Oklahoma meteorology professor Jason Furtado said updating normal calculations helps city and regional planners to prepare for flooding and drought, farmers to decide what and when to plant, energy companies to meet changing demands and doctors to tackle public health issues arising from climate change.

But Pennsylvania State University climate scientist Michael Mann said he prefers a constant baseline such as 1951 to 1980, which is what NASA uses. Adjusting normal every 10 years “perverts the meaning of ‘normal’ and ‘normalizes’ away climate change,” he said in an email.

North Carolina’s state climatologist, Kathie Dello, said, “It seems odd to still call them normals because 1991-2020 was anything but normal climate-wise.”

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