We Have Two Record Hot Days For Every Record Cold Day, and It’s Getting Worse

Whenever there's a daily cold temperature record broken someone on the planet, climate change deniers delight in pointing to it as evidence that global warming isn't real. The reality is that even as the planet continues to warm, record cold days will still appear. But if we continue down the path of current global greenhouse gas emissions, those record cold temperatures will be outpaced by record hot days 15 to one, according to a new study.

"You say the temperature's going to warm up two or three degrees and people just shrug their shoulders and say 'so what?'" said Gerald Meehl, lead author of the paper and a senior scientist at the National Center for Atmospheric Research. "But in fact, when you look at the extremes, you see how people experience climate change."

Meehl and his colleagues made this prediction by first collecting temperature records from weather stations across the United States from 1930 through 2015, according to the study published in Proceedings of the National Academy of Sciences.

But before we dig into their findings, it's helpful to understand a statistical relationship that occurs with record temperatures. If you imagine placing a weather station in your backyard this January 1, at the end of this year you would have 365 record high temperatures and 365 record low temperatures, because these are the only temperatures you've ever recorded. Statistically, in the second year you'd have half that—182 record cold days, and 182 record hot days—according to Meehl. By year three, you'd have a third as many record days, and so on.

With this understanding, the researchers calculated a baseline of expected number of record hot and cold days for a given period of time: they chose to look at averages across ten-year periods, because the numbers can fluctuate a lot from year to year. The data reflected this expectation, until about 1980, when the number of hot days started to outpace the number of cold days.

Statistically, the ratio between record hot days and record cold days ought to be 1:1 but by 2000-2009, it was actually 2:1, meaning for every record cold day, we got two record hot days. This decade obviously isn't finished, but the ratio is continuing to widen. Meehl and his co-authors used statistical modeling to project just how wide the ratio would get if we continue along the current path and found that, by about 2065, the ratio would increase to 15:1. That means in less than 50 years, we would be having 15 record hot days for every one record cold day.

"Even with a lot of warming, we still see record minimum temperature," Meehl told me. "Winter still comes. We still have record minimum temperatures being set, but there's many more record highs. But the idea is that we're shifting the odds to a better chance of record heat and a reduced chance of record cold, that's what climate change is like."

The findings shouldn't come as a shock to anyone acutely concerned about the effects of climate change, and the good news is this increased ratio of record-breaking hot days can be slowed if we do literally anything at all to reduce our greenhouse gas emissions. But it's yet another stark reminder of the impact a warming planet will have on our lives if we don't act now.