In U.S., a cold end to a warm 2017
But 2017 was a hot year.
People across the U.S. have experienced record-low or near-record-low temperatures this week, with some of the lowest hitting International Falls, Minnesota, where the thermometer dropped to minus 36 degrees. But overall, 2017 has seen far more record highs than record lows — one of the clearest signs of global warming, scientists say.
Over the past 365 days, there have been roughly three record-high temperatures in the U.S. for every record-low temperature, according to federal data.
There’s a big difference between weather and climate, scientists say: Weather happens in the short term, while global climate systems influence weather over longer time scales.
This week’s cold snap has brought record-low temperatures, freezing rain and heavy snow to much of the United States. But 2017 is still on track to be the second- or third-hottest year ever recorded globally — and scientists say climate change is to blame.
Even as the world gets hotter on average, winter isn’t going away, and there will still be extreme cold spells, climate scientists say. Even now, most of the world outside North America is warmer than usual for this time of year. In the Arctic and Alaska, recent temperatures averaged 10-25 degrees above normal, said Zack Labe, a doctoral candidate studying Earth systems science at the University of California, Irvine.
“Climate change will not occur evenly from place to place . ... Climate is all about long-term trends,” he said in an email.
Overall, 2017 has seen far more record highs than record lows — one of the clearest signs of global warming, scientists say. In the past 365 days, there have been roughly three record-high temperatures in the U.S. for every record-low temperature, federal data show.
President Trump suggested late Thursday that this week’s cold weather undermines the science of climate change. Trump tweeted: “In the East, it could be the COLDEST New Year’s Eve
on record. Perhaps we could use a little bit of that good old Global Warming.”
But there’s a big difference between weather and climate, scientists say: Weather happens in the short term, while global climate systems influence weather over longer time scales.
Since modern record-keeping began in 1880, the 10 hottest years ever measured have all been since 1998, according to the National Oceanic and Atmospheric Administration. The three hottest years on record are 2016, 2015 and 2014, in that order. Scientists at NOAA and NASA have said 2017 is likely to snag the No. 2 or No. 3 spot on the list.
Even this week’s cold is probably being caused at least in part by global warming, said Jonathan Overpeck, a climate scientist at the University of Michigan. The Arctic is warming faster than most of the planet, leading to a dramatic decline in the amount of sea ice that covers the region in winter. That has allowed more heat to transfer from the ocean to the atmosphere, weakening the polar vortex winds over the Arctic.
Arctic warming may also be contributing to the long-term drying of the U.S. Southwest, although the science on that front is less certain, Overpeck said. Unlike most of the rest of North America, the Southwest is warmer than usual right now, and 2017 will “without a doubt” go down as one of the region’s hottest years ever, he said.
“This is contributing to our record wildfires in California, and the drying out of vegetation that’s leading to those wildfires, and the drying out of the Southwest’s water,” he said.