Local weather Change Makes Excessive Chilly A Lot Much less Seemingly As Britain Sinks To -23C – Watts Up With That?
Braemar, Aberdeenshire, which recorded the UK’s lowest temperature since 1995. Jane Barlow / PA
Simon Lee, Reading University
Great Britain and large parts of Northern Europe are in an unusually cold period thanks to the cold east wind from Siberia. On the morning of February 11, the Scottish Highlands village of Braemar recorded -23.0 ° C, the UK’s coldest temperature since 1995 and the coldest February temperature since the 1950s.
The outbreak of cold air has been dubbed “The Beast of the East Two”, the continuation of another extremely cold phase in late February to early March 2018 (although note that there have been more than two outbreaks of cold easterly winds, and much more severe ).
These two cold spells mean inconsistent winter weather for four years. In February 2019, the UK experienced a “winter heat wave” when the temperature at Kew Gardens in London reached 21.2 ° C. The following year was the wettest February in the country on a record dating back to 1862. The Ciara and Dennis winter storms produced some of the rainiest single days ever.
Extreme cold, a heat wave, a flood and another cold snap: the sequence of different extremes raises questions about climate variability and climate change.
Why the UK weather is so different
Western Europe is at the mercy of the Atlantic jet stream – a group of westerly winds that control powerful weather systems, flanked by cold air in the north and warmer air in the south. The jet stream is extremely variable and fluctuations in its strength and position are the main reason the region can have such diverse weather conditions.
In both 2021 and 2018, the jet stream was unusually weak and shifted southward, allowing cold air to flow out of the Arctic. In early 2020, the jet stream was charged, trapping the colder air and instead pushing in mild, moisture-laden air and storm systems from the Atlantic. In 2019 it buckled northward, allowing a high pressure dome to develop over Britain, causing the temperature to skyrocket.
West-east winds with a pressure level of 250 hPa (approx. 11 km) in the first eight days of February 2020 (left) and 2021 (right), with the approximate core of the jet stream being represented by a red arrow. Data from NOAA PSL via https://psl.noaa.gov/data/composites/day/
These different patterns all fall within natural climate variability. The weakened jet stream in 2018 and this year and the increased jet stream in 2020 are all related to the variability of the polar vortex of the Arctic stratosphere – practically a huge low pressure system about 30 km above the surface, the strength of which fluctuates year after year.
However, we do know that climate change is likely to make the UK winters milder and more humid, largely because warmer air can hold a lot more water. This is supported by recent observations: The 2013-14, 2015-16 and 2019-20 winters are all among the five wettest in history. Recent research has shown that climate change has also made exceptionally warm winter days – like the 20 ° C heat wave in February 2019 – about 300 times more likely, although they remain rare because the specific atmospheric configuration required is so unlikely.
So there is evidence that climate change has exacerbated the extreme heat of 2019 and the rain of 2020. But what about cold weather and climate change? It is important to remember that extremely cold weather can still occur in a warming climate. If climate change is like loading a dice, rolling a dice is still possible. Just because you roll a dice every now and then doesn’t mean that the cube isn’t loaded. To do this, you need to look at longer periods of time to see if you are rolling more sixes and fewer.
The Central England Temperature (CET) is the longest running continuous instrumental temperature record in the world with data from 1659. It gives a clear indication of how even the coldest winters of recent times pale in comparison to those of the past. A winter with an average temperature below 2 ° C occurred about once per decade. Central England has not had such a cold winter since 1978/79 – a never-before-seen gap of four consecutive decades.
Despite numerous cold spells in recent decades, nobody under the age of 42 has experienced a historically cold winter season in Central England.
Number of winters per decade with an average temperature in Central England below 2 ° C that has occurred an average of once per decade since the start of the data set but has not occurred since the 1970s. Data from Met Office Hadley Center via https://www.metoffice.gov.uk/hadobs/hadcet/
While weather extremes will continue to emerge on both ends of the spectrum as part of a natural roller coaster with jet streams, the evidence supports predictions that warmer, wetter winter weather will win.
Simon Lee, PhD student in Atmospheric Science, University of Reading
This article is republished by The Conversation under a Creative Commons license. Read the original article.
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