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The supply of cold air in the Northern Hemisphere is being evaluated using temperature data from about 5,000 feet high in the atmosphere. For about a decade, Jonathan Martin, a professor of meteorology at the University of Wisconsin, has analyzed the size of the cold pool at this level, or the area of the hemisphere covered by temperatures at or below 23 degrees (minus -5 degrees Celsius). . . This winter’s cold pool will end the winter as the second smallest on record, Martin said.
Nine of the 10 smallest winter cold pools since 1948-1949 occurred in the 2000s, continuing a trend of declining winter cold pools that Martin identified in a 2015 study. study published in Climate Magazine.
“The climate continues at the same rate of warming as it has for the last 20 years,” Martin said. “The hemisphere shows us in winter, unequivocally, that the planet is warming.”
This winter’s dwindling supply of cold air in the atmosphere has coincided with what is likely to be one of the warmest winters on record. Many places in the United States are on track for a record-breaking winter as temperatures rise to nearly 30 degrees above normal in the final days of the season. On Monday, Dallas hit a record high temperature of 93 degrees, while Minneapolis hit 65, 32 degrees above average. Chicago could reach the upper 70s on Tuesday, a record for February.
Worldwide, More than 200 countries have experienced record heat this week., according to the time historian Maximiliano Herrera. January was the eighth consecutive month to record as the warmest month on record, while 2023 was the warmest year on record on Earth for both land and oceans.
Some who are skeptical about a warming climate say surface temperatures are rising due to urbanization, changes in sensor locations and other factors that they say contaminate data. While scientists are aware of such influences and adjust surface data accordingly using methods that have been verified by peer-reviewed research, Martin says the validity of data at altitude is even harder to refute.
“These measurements are not contaminated at all by any of those developments,” Martin said. “So if you get a signal (higher in the atmosphere), you can be pretty sure that it’s a really strong signal and it doesn’t have any of those limitations (of) surface-based measurements.”
According to Martin, the annual fluctuations in the size of the cold pool also do not appear to be related to El Niño. El Niño is a periodic, natural warming of the ocean surface in the central and eastern Pacific, which scientists say has contributed to extreme surface warming over the past year.
Martin calculates the size of the Northern Hemisphere cold pool for each winter day compared to the average for that day since the winter of 1948-1949, when weather balloons began consistently collecting temperature data at altitude. From there, he ranks each winter season (December 1 to February 28) based on the average cold pool size.
Only the winter of 2014-2015 produced a smaller cold pool than the current winter. Still, the cold pool reached a record size in four days this winter, which Martin said was “pretty incredible.”
Even when the cold pool contracts, that doesn’t mean mild weather will occur everywhere in the Northern Hemisphere, Martin emphasized. When the cold pool dropped to a record low in 2014-2015, the United States experienced a prolonged period of intense cold.
“This really points out how regional our own impressions of winter can be, and how different they can be from a hemisphere perspective,” Martin said.
The cold pool declined to what Martin defines as a warm extreme (two standard deviations less than the average) on 15 days this winter, while it reached a cold extreme (two standard deviations greater than the average) on no days. The last extreme cold occurred in February 1994, making this the 29th consecutive winter without extreme cold.
The predominance of warm extremes at altitude is consistent with heat records exceeding cold records. In the United States, for example, nearly 8,000 warm weather records have been set this winter, compared to about 2,300 for cold weather.
Jason Samenow contributed to this report.