This is statistically the warmest time of the year for a majority of the U.S. And yet here we are talking about record cold air invading the U.S. With temperatures plunging 10°F to 30°F below normal, record low temperatures are being set across the Midwest, Ohio Valley, and parts of the Southeast.
Meanwhile, the West and Southwest are sizzling with high temperature records falling across the Northwest. Still, overall in the U.S., record lows are outpacing record highs so far this year and beat out record highs in 2013 as well. This is telling us an important climate story, but not the one that might seem obvious. Remember that we're paying attention to this week’s cold wave, not because such things are common, but because they're so uncommon.
Climate scientists are tracking the number of record lows outpacing highs because it’s become unusual in recent years. Before 2013, the last time this happened was 1993. That's significant because in a world without global warming, you’d expect to see about the same number of record highs and record lows – not every year since natural weather fluctuations make that unlikely, but on the scale of decades, highs and lows would balance out. Instead, we are seeing the opposite – record high temperatures outnumbering record lows for many decades in a row so far.
We take a look at the record high vs. record low temperature breakdown two different ways this week. The first is on an annual scale, while the second is on a decadal scale. On the decadal scale, the gap between highs and lows has been growing since the 1970s. By the decade of the 2000s, there were more than twice as many record highs as record lows. Some projections indicate that this ratio of record highs to record lows could reach 20:1 by mid-century, and a staggering 50:1 by 2100.
Even on an annual scale, you see how the stretches of both record lows and highs would eventually swing back the other way. However, that balance has clearly been shifting toward record highs since the 1970s with highs greatly outpacing lows since 2000.
With that in mind, this week’s cold snap, along with the surprising number of record lows this year and last year, could someday look like a tiny downward blip on a steadily rising temperature chart.