Climate Change to Alter Global Pattern of Mild Weather

Morgan Kelly Office of Communications ・ Princeton Environmental Institute

Scientists from Princeton University and the National Oceanic and Atmospheric Administration (NOAA) have produced the first global analysis of how climate change may affect the frequency and location of mild-weather days — and it may be soon.

In a report published Jan. 18 in the journal Climatic Change, the researchers define mild weather as temperatures between 64 and 86 degrees Fahrenheit (18 and 30 degrees Celsius); less than 0.04 inches (1 mm) of rain; and a dew point below 68 degrees F (20 degrees Celsius), which indicates low humidity. NOAA funded the work.

Within the next 20 years, the current global average of 74 mild days a year will drop by four days, and fall by another six days by the end of the century, the researchers report. However, people living in the mid-latitudes — including the northern and mountainous United States, the British Isles and Northern Europe, northeastern Asia, and southern South America and Oceana — could experience as many as 10 to 15 more days of mild weather, particularly during the spring, summer and fall.

In summer, some mid-latitude areas — including a sweep of the United States from the Mountain States through the Midwest and into the Northeast — will likely get more very hot and humid days, which translates to a decrease in mild days.

The largest decreases in mild weather will happen in tropical regions where daily occurrences of heat and humidity could rise drastically, the researchers report. The hardest hit areas are expected to be in Africa, Asia and Latin America, where some regions could see 15 to 50 fewer days of mild weather each year by 2100. The loss of mild-weather days could mean less relief from extended heat waves, which could significantly affect public health.