Above: Departures from average temperature across the globe for the period from December 2019 through February 2020 (northern meteorological winter), in degrees Celsius. (NOAA/NCEI)
Research groups across the world concur that this past northern winter (December-February) was the second-warmest on record globally, in records going back more than a century. The latest group to confirm this finding is NOAA, in its monthly State of the Climate report issued Friday.
The winter result was a product of the second-warmest December, warmest January, and second-warmest February in the NOAA analysis, which extends back to 1880. For those three months combined, the global temperature was 1.12°C (2.02°F) above the 20th-century average. This reading is just 0.06°C (0.1°F) behind the record set in 2015-16.
The global warmth of the past few months is especially striking given the lack of an El Niño event, which raises global air temperatures by releasing heat stored in the tropical Pacific Ocean.
Global temperatures in the record-warm winter of 2015-16 were boosted by very strong El Niño conditions. In contrast, there was no El Niño event this past winter, although temperatures in the central tropical Pacific were unusually warm.
Like NOAA, NASA also ranked the winter as the planet’s second-warmest on record. In the NASA database, December and February were the second-warmest on record, just behind 2015-16, while January 2020 tied with January 2016 as the warmest on record.
The Japan Meteorological Agency had not yet released its temperature calculations for February.
Not only was last month the planet’s second warmest February—it was the third warmest of any month in terms of departure from average, coming in 1.17°C (2.11°F) above the 20th-century average. The only higher departures on record were in February and March 2016, during the extreme El Niño event noted above.
Europe's bizarre winter warmth
The most spectacular warmth throughout winter 2019-20 was across Europe and the western two-thirds of Russia. The European Union’s Copernicus Climate Change Service (C3S) estimated that temperatures across Europe were 1.4°C (2.5°F) above the previous winter record (2015-16). The center’s data go back to 1979, but when comparing the data with other sources, C3S also said this was the warmest European winter going back to at least 1850.
The center’s data go back to 1979, but when comparing the data with other sources, C3S also said this was the warmest European winter going back to at least 1850.
The Copernicus margin of 2.5°F is phenomenally large for setting a season-long, continental-scale record. Keep in mind that the normal ups and downs of daily temperature tend to act as a buffer on any major departures from average.
It was the warmest winter on record in Russia, dating to 1891, according to a report issued last Thursday from the Hydrometcenter of Russia. Parts of western and central Russia were 10-14°F warmer than average from December through February.
The HoR report said Moscow's winter temperature, averaged from December through February, was above freezing for the first time on record.
It was also a record-warm winter in Finland, where no measurable snow was recorded from January through February in the capital, Helsinki, for the first time on record.
For the first time, the Scandinavian capitals outside of Iceland—Copenhagen, Helsinki, Oslo, and Stockholm—all got above freezing on every day in January, reported Mika Rantanen (Finnish Meteorological Institute). All-time record highs for February were shattered in at least nine European countries in the last week of the month, as documented by Rantanen.
For much more detail on the standout global and regional climate events for February, see the new post from Dr. Jeff Masters at his “Eye of the Storm” blog (ScientificAmerican.com).
What caused the warmth?
Long-term climate change is boosting winter temperatures across the world. In the NOAA database, the warmest five December-to-February periods have all occurred in the last six years.
Another factor involved this winter: an exceptionally strong positive phase of the Arctic Oscillation. The AO is an index of pressure differences between the northern subtropics and polar regions. When the AO is high, a strong pressure difference leads to a powerful west-to-east jet stream that can block frigid air masses from cruising southward to lower latitudes.
The consistently high AO kept the hemisphere’s cold air bottled up in the far north, mainly across Alaska and the Arctic Ocean. Alaska had its coldest winter in 21 years, according to NOAA. Fairbanks remained below freezing for the entire climatological winter (December-February), also for the first time in 21 years.
More warming on the way
The World Meteorological Organization (WMO) reported this month that 2019 saw the second-warmest atmosphere and the warmest oceans on record globally. The last five years (2015-19) and the last 10 years (2010-19) were both the warmest on record, said the WMO.
Each decade since the 1980s has been warmer than the prior decade.
The global temperature in 2019 was about 1.9 degrees above the estimated levels that prevailed in the mid-1800s, before widespread use of fossil fuels began to boost the amount of heat-trapping greenhouse gas in the atmosphere.
"Given that greenhouse gas levels continue to increase, the warming will continue," said UN Secretary-General and WMO Secretary-General Petteri Taalas in a news release on Tuesday.
Taalas cited the latest decadal forecast from the UK Met Office, which predicts that a new annual global air temperature record is likely in the next five years.