(Bloomberg) -- Rising temperatures caused by climate change have forced the U.K.’s weather agency to raise the threshold for what counts as a heatwave.

The government-backed Meteorological Office currently uses historical weather records from 1981 to 2010 to define a heatwave. That threshold is met when a target temperature is recorded for at least three consecutive days.

But climate change is already having an impact. All 10 of the U.K.’s hottest years since 1882 have occurred in the past 18 years. Met Office research found that the 2018 heatwave was 30 more times likely to occur now than in 1750 because of rising carbon dioxide levels in the atmosphere. As a result, the agency will now judge a heatwave on records from 1991 to 2020. 

Six counties in England -- Surrey, Berkshire, Buckinghamshire, Bedfordshire, Hertfordshire and Cambridgeshire -- will see their heatwave threshold rise from 27 to 28 degrees Celsius (82.4 degrees Fahrenheit). Lincolnshire will move from 26C to 27C and further north, East Riding of Yorkshire will move from 25C to 26C.

“We have to get used to a ‘new normal’ -- what we previously thought of as an unusually hot summer will soon become common,” said Professor Nigel Arnell at the Department of Meteorology in the University of Reading. “In a few years, we’ll probably have to change the definitions again otherwise we’ll have a heatwave every summer.”

©2022 Bloomberg L.P.