By Brad Plumer

New York Times News Service

In the summer, when heat waves scorch cities or heavy rains flood the coasts, some climate scientists and environmentalists will point out any plausible connections to global warming, hoping today’s weather will help people understand tomorrow’s danger from climate change.

Then winter comes. Like clockwork, those who want to deny the established science that humans are warming the planet will try to flip the script. In January, when large swaths of the country were gripped by bitter cold, President Donald Trump took to Twitter to mock climate fears: “Wouldn’t be bad to have a little of that good old fashioned Global Warming right now!”

Welcome to the weather wars. As battle lines harden between climate advocates and deniers, both are increasingly using bouts of extreme weather as a weapon to try to win people to their side. Weather, after all, is one of the easiest things for people to bond over or gripe about, a staple of small talk and shared experience that can make it a simple and powerful opportunity to discuss global warming.

As Trump’s words show, it’s a framing device that can be easily abused.

That raises the stakes for how scientists, who have long tried to distinguish between short-term weather fluctuations and long-term climate shifts, draw out and discuss the links between the two.

“Weather, and especially extreme weather, is how most people will experience climate change,” said Susan Joy ­Hassol, director of the science outreach nonprofit group Climate Communication. “You don’t experience the slow change in average temperature. What you experience are the changes in extreme weather that are brought about. So how we talk about that is really important.”

Some messengers have long realized emotion and immediacy can be a powerful force.

“Trump is a branding guy,” said David B. Srere, co-chief executive and chief strategy officer at Siegel+Gale, a brand consultancy. “He knows his audience and understands how to tell a clear, simple story. Climate advocates and the scientific community need to get better at understanding their audience and figure out how to tell a simple, repeatable story of their own.”

In recent years, some climate scientists have focused on trying to turn flare-ups of severe weather into teachable moments.

“This is what global warming looks like,” scientists said during the summer of 2012, a season of widespread droughts, wildfires and extreme heat advisories.

Back in 2005, after Hurricane Katrina devastated New Orleans, many researchers responded cautiously, saying it was difficult to attribute a single event to global warming.

A few noted that rising ocean temperatures could make hurricanes more destructive, on average, in the future.Even that was fairly abstract.

Over time, that messaging has shifted. Partly that’s because, as climate models have improved, scientists have been able to demonstrate more rigorously how rising greenhouse-gas emissions have made recent heat waves or droughts more intense or more likely to occur — a budding field known as “extreme weather attribution.” Scientists have refined their communication strategies, using metaphors like “loaded dice” to talk about how global warming is now making certain severe weather events more likely.

That strategy, though, can cut both ways.

Marshall Shepherd, a professor of atmospheric science at the University of Georgia, isn’t convinced the president’s tweets about cold weather have staying power.

“I see Trump’s tweets as an opportunity to discuss the science,” he said. “To the 9 or 10 percent of the population that are going to be dismissive of climate science no matter what, there’s not much you can say to them. But a lot of people out there are legitimately curious” about how global warming can be real if it’s cold out today.

There are some signs opinion is shifting. One recent survey by researchers at Yale and George Mason University found that 69 percent of Americans were “worried” about global warming, an 8-point increase from the previous spring. One possible explanation, the researchers suggested, was the spate of extreme weather disasters in 2018, from wildfires to hurricanes, along with increased efforts by scientists and even local TV weathercasters to put that in a climate context.

“For a long time, Americans saw climate change as a distant threat,” said Edward Maibach, a professor at George Mason who works on climate change communication.

Others are more cautious about interpreting these trends.

One 2017 study, for instance, found that people who experience extreme weather are, for a short period, more likely to support climate adaptation measures than they were before. The effect was modest and diminished over time.

Wanyun Shao, an assistant professor of geography at the University of Alabama, has found Democrats and Republicans perceive severe weather differently: Democrats tend to see it as part of a broader pattern of climate change, Republicans as more of an aberration.

Her research has found a consistent string of shifting weather — year after year of increasing summer heat, for instance — does start to chip away even at conservative doubt about global warming.