While the unusually high temperatures on the last day of the year grabbed the headlines, the average minimum temperatures – how low the mercury falls each night – for the month were also notably high.
Unseasonably mild conditions in mid and late December were caused by high pressure over the UK, but background warming due to climate change has made it more likely that warmth will “tip into” record-breaking territory, the Met Office said.
When we see these weather patterns, they are more likely to tip into record temperatures because of that background 1.1C of global warming
The mild end to December saw the UK reach its highest New Year’s Eve temperature on record, of 16.5C at Bala, North Wales, while maximums exceeded 15C in all four UK nations.
Some weather stations broke long-standing individual records for the month, such as Cromer in Norfolk, which saw its warmest December day in a records dating back 103 years, with 15.4C on December 30.
Met Office spokesman Stephen Dixon said: “Climate change isn’t responsible for the weather pattern we saw – we’ve had warm Decembers before and warm New Year’s Eves, but this was a record.
“What it does mean is that when we see these weather patterns, they are more likely to tip into record temperatures because of that background 1.1C of global warming.”
He added that high temperature records were being challenged nine times more than low temperatures.
Over December, notably high minimum temperatures stand out, especially in southern areas, the Met Office said.
The UK had an average minimum in December of 2.8C, which is 1.4C above the long-term average for 1991 to 2020, but well below the record 5.2C for the month set in 2015.
In southern England, average minimum temperatures were 4.3C – 2C above the average for the month – and there were some “exceptionally mild” nights with overcast conditions and air being drawn in from the Azores.
Daily minimum temperatures on New Year’s Eve widely stayed in double figures, and stations including Sheffield, Bradford and Buxton recorded their highest daily minimums in records dating back more than 100 years, at around 10C higher than the average for the month.
Average monthly minimum temperatures were dragged up by warm spells in the middle and end of the month, again due to high pressure.
But the key factor was that the weather pattern was creating cloudy conditions for many that prevented harsh frosts and kept overnight temperatures up, the Met Office said.
In the cloudy conditions, the UK had its fifth dullest December on record and the gloomiest since 1956, with an average of just 27.6 hours of sunshine, the figures from the Met Office show.
For gardeners, the dull but warm conditions have meant winter greens such as Brussels sprouts and leeks have continued to grow and camellia and Christmas roses have not been spoiled.
December 2021 was a warm and dull month for most.
🗓 Record highs on New Year's Eve
🌡 Temperatures widely above average
☁ Dullest December since 1956
Find out about this, and more, in our December weather review 👇
— Met Office (@metoffice) January 4, 2022
Guy Barter, chief horticultural adviser at the Royal Horticultural Society, said: “Weeds too have kept growing, but with dull conditions they won’t set seeds and can be spared for now to help wildlife.
“Lawns remain remarkably green but growth has been limited by a lack of light, so the lawnmower can rest a bit longer.”
Rainfall was near average for much of the UK, the monthly data shows.
A white Christmas was declared by the Met Office as areas of high ground in the north of the UK saw a flurry of snow.
Mike Kendon, from the National Climate Information Centre, said: “December will largely be remembered for the unseasonable warmth we saw in the middle and end of the month.
“As a result, we have seen relatively few days of ground frost and air frost and less of the cold weather that you’d normally expect at the start of winter, although some northern spots have seen some hard frosts.
“There were also remarkable temperature inversion conditions for several days in Scotland where the warmest and sunniest place to be was across the mountain summits.”