Trump is citing the polar vortex descending on the Midwest as evidence against climate change. Why is this faulty logic so common?

Steam rises from Lake Michigan in January of 2014 in Chicago, Illinois. A polar vortex descending on the Midwest in January of 2018 spurred President Donald Trump to send a tweet questioning the existence of global warming. (Photo: Scott Olson/Getty Images)

As a mass of frigid, Arctic air settled over the Midwest and Americans prepared to endure temperatures as low as 35 degrees below zero, the president of the United States took the record-breaking cold forecast as evidence against climate change.

It's a familiar—and deeply flawed—argument for President Donald Trump, who has long been a climate change skeptic. In 2013, after ice storms hit the southern U.S., Trump called global warming a "total, and very expensive, hoax"; in October of 2015, he tweeted that we could "use a big fat dose of global warming"; and in 2017, when freezing temperatures hit the Northeast, he said again that the U.S. could use a bit of that "good old Global Warming."

The president's logic is fundamentally flawed. Cold weather doesn't disprove global warming because weather and climate, though related, are not the same thing. Both describe what's happening in the atmosphere, but the main difference is the timescale. Weather is what's happening in the atmosphere right now; climate is the pattern of weather over several decades.

And the climate, current weather aside, is definitely still warming: 2018 was the fourth hottest year on record. The other top three were 2015, 2016, and 2017. The vast majority of climate scientists say that climate change is occurring and human activities are to blame. But even as the scientific understanding of climate change has grown, the topic has become increasingly polarized. Though more Americans than ever believe that climate change is happening, less than half of conservative Republicans agree. And the skeptics' strategy of muddling the climate debate with weather predates the Trump administration: In February of 2015, Senator Jim Inhofe (R-Oklahoma) infamously brought a snowball onto the Senate floor in an attempt to prove that global warming was a hoax.

Why do people like Trump and Inhofe continue to confuse weather and climate?

The trouble is scientists and the public are often working with different information. Climate scientists rely on decades of weather data, complex models, and a system of checks and balances including peer review to guard against error and bias when they come to conclusions about the climate. The public relies mainly on personal experience, and though weather is visible, climate change is often not. While you can look out your window and see a snowstorm or a hurricane, climate change is more than one single storm or hazard—it's a trend. Greenhouse gases, the main drivers of climate change, are invisible, and the average American is insulated from their consequences.

So it's not all that surprising that non-scientists so often confound weather and climate. Indeed, the president’s mistake is common: When extreme weather does strike, people do talk more about climate change, according to Matthew Sisco, a Ph.D. fellow at Columbia University. His research shows that extreme weather events, like extreme temperatures, floods, wildfires, and heavy snow, all lead to spikes in tweets about climate change.

Other research similarly shows that, when the weather is hot, more people tend to accept that climate change is happening; when it's cool out, belief in climate change decreases. One 2014 study out of Columbia, which sought to find out why local weather influences climate change judgments with a series of surveys, found that it wasn't just that people were mixing up climate and weather. When the authors surveyed people about their climate change concerns and included an explanation of the difference between short-term weather and longer-term climate, weather conditions continued to influence the responses. That's due to something called the "recency effect."

Here's how Sisco explains it: If you ask someone, "Do you believe climate change is happening?" they'll likely think back on their personal experience with the weather. Our minds more easily recall recent experiences than distant ones, and people tend to give recent memories more weight than older ones, which means the current weather will have an outsize impact on their answer.

Notably, other studies find that it's a two-way street: The weather can influence how we feel about climate change, but our preconceived notions about climate change can also influence how we remember recent weather events. According to a survey of 3,000 American adults published last year, people tend to remember extreme weather events as more or less severe based on their political leanings. "People who consumed liberal media like HuffPost or The Daily Show were more likely to say they'd experienced drought, even if the data showed that their communities hadn't," Emma Sarappo wrote in her summary of the study for Pacific Standard. "Their Republican counterparts, meanwhile, under-reported experiencing extreme weather, including the polar vortex of 2014 and 2015."

In other words, one reason cold weather always leads climate change skeptics and deniers to question whether the world is warming could be because they're primed to look for evidence that it's not. This is an example of “confirmation bias,” according to Sisco.

"Once humans believe something, they selectively seek out more evidence and interpretations of evidence that support their pre-existing beliefs," Sisco writes in an email. It's hard to break people of this bias, especially if they're not already motivated to change their minds.

"One reason is probably just because it leads to happier people," Sisco writes. "It's nice to feel right, so we have a tendency to achieve that by interpreting facts accordingly. Also, shared beliefs are part of our sense of group memberships, so it also helps groups stick together. This is to say, people may not be always motivated to undo this bias."

So if illuminating the distinction between weather and climate doesn't help, what will? Unfortunately, the science on how to convince skeptics is not so settled.