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Does global warming affect the coldest days or the hottest days more?

It depends on the region and the season, but broadly, cold winter days are warming faster than both hot summer days and the average global temperature. 


March 15, 2024

Global warming is usually measured by the rise in the world’s average temperature. But scientists are also working to measure the impact of climate change on something called “temperature anomalies”: periods of especially warm or cold weather that notably depart from the average. 

As climate change advances, winter cold temperature anomalies are expected to be especially impacted, according to Talia Tamarin-Brodsky, an assistant professor in MIT’s Program in Atmospheres, Oceans and Climate. In temperate regions, cold winter days are warming faster than both the average temperature and temperatures on the hottest days. 

Cold days happen when cool air drifts towards the middle of the earth from the Arctic. But in recent decades, the Arctic has warmed more than twice as fast as the rest of the world.1 That means that as climate change progresses, the temperature difference between the Arctic and warmer areas closer to the equator is shrinking, making the cold anomalies less, well, cold, says Tamarin-Brodsky. 

Still, it’s the hottest days that will actually feel the most intense, especially during summer, because those temperatures will be farther from the new average—which is also getting warmer. In the future, we’ll experience significantly more high-heat days and heatwaves

Those are the general trends, but the details are much more complicated. Different parts of the world have diverse weather and seasons, and will face different impacts of warming. Some research, for instance, has found that warm days are warming fastest near the equator, while cold days are warming fastest at higher latitudes.2

How precisely the weather will change in different parts of the globe is still an active area of research, as scientists continue to refine computer models of our future climate to deal with complex variables like cloud cover, precipitation, topography, and more. These models agree that in most places, future temperatures will be higher. But global warming is not raising temperatures evenly across the year and models do not always agree on the direction of future temperature fluctuations, says Tamarin-Brodsky. 

There is growing evidence that we will experience more temperature variation during the summer, she says.3 “We're going to have a lot more warm-temperature days, but even if you think about just relative to the new mean, you get more fluctuations around it,” says Tamarin-Brodsky.

And during the winter, research suggests that we will experience less dramatic temperature swings from the average, because cold days are warming so significantly. On the other hand, cold days in the winter may also be impacted by changes to “jet streams”: strong bands of air that carry air from west to east high up in the atmosphere. Jet streams affect the weather by carrying storms, rain and snow and warm or cold air to different parts of the world. Some studies suggest that jet streams are becoming “wavier” in certain regions due to climate change, says Tamarin-Brodsky. That greater waviness—though still highly debated among scientists—could let more Arctic air travel to lower latitudes, blasting them with extreme cold weather, even as the overall temperature increases. 

What is certain is that rising temperatures will bring more extreme weather events: not just record-breaking heatwaves, but also worsening storm events like hurricanes and heavy rain. 

How severe will these new weather extremes get? It depends where you live, but also, crucially, on how much climate pollution society adds to the atmosphere. The faster we act to control that pollution, the less extreme heat (and occasional southerly extreme cold) the future will contain. Without that action, humans will face increasingly extreme weather, since changes to the climate system we cause now will be very hard to reverse.

Thank you to Timothy Donato of Alexandria, Virginia, for the question.

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1 Rantanen, Mika, et al., "The Arctic has warmed nearly four times faster than the globe since 1979." Communications Earth & Environment, Volume 3, 2022, doi:10.1038/s43247-022-00498-3.

2 Paçal, Aytaç, et al., "Detecting Extreme Temperature Events Using Gaussian Mixture Models." Journal of Geophysical Research: Atmospheres, Volume 128, Issue 18, 2023, doi:10.1029/2023JD038906.

3 Tamarin-Brodsky, Talia, et al., "Changes in Northern Hemisphere temperature variability shaped by regional warming patterns." Nature Geoscience, Volume 13, 2020, doi:10.1038/s41561-020-0576-3.