No, this polar vortex doesn’t disprove global warming

It’s a question on many blue lips this week, as the Midwest braced for below-zero temperatures for its daily high on Wednesday: How can global warming be true when it’s so cold?

Even President Donald Trump, in a tweet late Tuesday, seemed to question the coexistence of climate change and an arctic chill over much of the U.S.

“In the beautiful Midwest, windchill temperatures are reaching minus 60 degrees, the coldest ever recorded. In coming days, expected to get even colder. People can’t last outside even for minutes. What the hell is going on with Global Warming? Please come back fast, we need you!,” Trump tweeted.

As climate scientists constantly stress, weather does not equal climate.

“Weather is day to day, week to week, and climate is the long-term average of all the weather that occurs over a long period of time, like decades,” said David Easterling, a climate scientist with the National Oceanic and Atmospheric Administration’s Center for Environmental Information in Asheville, N.C.

“You’re always going to have these occasional cold-air outbreaks, but we’ve been having fewer of them over the last few decades.”

Added John Allen, a meteorologist and climate scientist at Central Michigan University, “The way to think about this is kind of like what you had for breakfast each day, as compared to what you usually have eaten for breakfast over your entire life. So we could be in a warming trend and still experience a cold winter, or cold day.”

It’s important to remember that climate change is a global phenomenon, while weather is a local experience, Easterling said. The global atmosphere is always trying to find a temperature balance, meaning when it’s bitterly cold in Michigan or elsewhere, nearly invariably it is unusually warm in some other part of the world. And, sure enough, as we get our polar vortex on, Fairbanks, Alaska _ less than 200 miles from the Arctic Circle, had a high temperature of 24 degrees on Tuesday, well above its typical January average high temperature of 2 degrees.

“Just because it’s cool here in North America doesn’t mean this is true for other places in the world,” Allen said. “Australia is currently experiencing all-time record temperatures, exceeding 115 F, and extended heat waves. These are the features of a warming world, and it’s important to take the whole Earth into account, not just our local area. “The evidence for a warming climate is long term and extremely strong, so hence a cold day means little for that overall pattern.”

The concern with climate change is that human activities such as fossil fuel-burning are putting so-called greenhouse gases such as carbon dioxide into the atmosphere to an extent that heat that typically escapes is held in place, causing temperatures to rise globally over the long term. The four warmest years on historical record, in terms of overall global average temperatures, were the last four years, Easterling said. NASA and NOAA climate data shows the 20 warmest years on record have all occurred since 1995.

There’s even emerging evidence that climate change may make these frigid dips of arctic air down into the U.S. more possible.

“In the past there was a very strong gradient of cold air at the poles and warmer air south of the poles. That gradient kept the cold where it is, just like a strong temperature gradient in a lake keeps warm water at the surface and colder water below,” said Donald Scavia, professor emeritus of environment and sustainability at the University of Michigan.

“As the poles are warming faster than the rest of the planet, that gradient weakens, allowing the cold air currents to dip south.”

While the global conditions contributing to climate change continue, as Trump’s skepticism on the phenomenon signals the U.S. will not be playing a leading role on the topic as it has previously, at least the polar vortex is skipping town later this week. Saturday’s high temperature in Detroit is forecast to be a relatively balmy 31 degrees.