"We found clear and strong links between last month's record warmth in the United States, and climate change," Geert Jan van Oldenborgh, a senior researcher at the Netherlands Meteorological Institute, said in a statement.
He and five other scientists involved in the group World Weather Attribution conducted what's called a rapid attribution study to figure this out. The results were published online on Wednesday, the same day that the National Centers for Environmental Information announced that last month was officially the second-warmest February in the 123-year record for the 48 contiguous states. For 16 states east of the Rockies this past February was the hottest ever recorded.
For the first part of the attribution study, the researchers examined more than 100 years of historical temperature data for the lower 48 states. They found that the chances of a February being as warm as last month had jumped dramatically since the dawn of the 20th Century.
To figure out whether there was a climate link, the researchers turned to climate models, running multiple simulations on three different types of models. Some simulations took the impact of man-made climate change into account; others did not.
For the simulations that took into account both past and projected increases in atmospheric levels of greenhouse gases tied to fossil-fuel burning, the results showed the same consistent trend: The odds of such a warm February occurring had sharply increased over time. This is the same trend identified by the observational analysis. This was not the case, however, for the simulations run without the climate change impact.
"The model results indicate that past historical increases in greenhouse gases have raised the odds of warm Februaries in the [continental U.S.] considerably. The observed trend is compatible with the effects of human-induced emissions of greenhouse gases," the study authors wrote in their online summary.
Looking at what to expect in the future, the researchers wrote: "Since past and projected future greenhouse gas increases will continue to raise the temperatures, the frequency of winter months like February 2017 should be expected to increase over the coming decades."
The World Weather Attribution team has previously examined the climate link associated with extreme heat in Australia, heavy downpours in Louisiana and other extreme weather events in recent years.
"There's every reason to believe that climate change is impacting right now. It's not this distant issue," said Heidi Cullen, a study author and climate researcher at Climate Central. "That, I think, is just one of the reasons why we feel it's important to look at these events when they come up so we can actually provide the context."