If the Earth Is Warming, Why Is It So Cold Outside? – New York Times

A frigid morning in Chicago. Jose M. Osorio/Chicago Tribune, via Associated Press

As climate change heats up the planet, winters are warming faster than summers. But on days when the temperature tumbles below freezing, it leaves many people wondering, “If the Earth is getting warmer, how can winter still be so cold?”

President Trump is among them, and he weighs in frequently.

The answer lies in the difference between local weather and climate.

Climate refers to how the atmosphere acts over a long period of time, while weather describes what’s happening on a much shorter time scale. The climate can be thought of, in a way, as the sum of long periods of weather.

Or, to use an analogy Mr. Trump might appreciate, weather is how much money you have in your pocket today, whereas climate is your net worth. A billionaire who has forgotten his wallet one day is not poor, anymore than a poor person who lands a windfall of several hundred dollars is suddenly rich. What matters is what happens over the long term.

Even on a day when it is colder than average where you live, the world as a whole is frequently warmer than average, which you can see for yourself on these daily maps from the University of Maine.

Here is an example from a period of unusually frigid weather in December 2017, when parts of the United States were 15 to 30 degrees Fahrenheit colder than average, but the world as a whole was about 0.9 degrees Fahrenheit warmer than the 1979-2000 average:

While climate scientists expect that the world could warm, on average, roughly two to seven degrees Fahrenheit by the end of the century — depending on how quickly greenhouse-gas emissions rise — they don’t expect that to mean the end of winter altogether. Record low temperatures will still occur; they’ll just become rarer over time.

One 2009 study found that the United States saw roughly as many record highs as record lows in the 1950s, but by the 2000s there were twice as many record highs as record lows. Severe cold snaps were still happening, but they were becoming less common.

Some recent cold spells have been caused by a dreaded low-pressure system called the polar vortex. There’s growing evidence to suggest that the polar vortex is appearing outside the Arctic more frequently, because of changes in the jet stream that are attributed to the warming atmosphere. These changes help frigid air escape from the Arctic and swoop southward.

Politicians have tried to use cold snaps to prove a point before. Senator James Inhofe, Republican of Oklahoma, brought a snowball to the Senate floor in February 2015 as evidence that the Earth was not warming.

Mr. Trump, who has repeatedly denied the science of climate change, has recognized the threats where some of his properties are involved. His golf resort in Ireland intends to build two sea walls and cited the risks of global warming in one of its applications for the construction.

Mr. Trump has made a habit of airing his climate skepticism on Twitter, posting comments on “climate change” or “global warming” more than 100 times since 2011. Before his presidency, he called climate change a hoax and claimed the idea was perpetuated by the Chinese.

In 2018, he backed off that claim, saying: “I don’t think there’s a hoax. I do think there’s probably a difference. But I don’t know that it’s man-made.”

The United States government and hundreds of scientific organizations agree that human activities are primarily responsible for global warming.

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