Its annual climate update also says that the country’s 10 hottest years have all occurred since 2002, with last year being the third warmest on record after 2014 and 2006.
As well as being among the hottest, 2020 was also the fifth wettest and eight sunniest on record, the report says.
It was the first year that annual values for rainfall, temperature and sunshine were all in the top 10 at the same time.
Sea level rise has accelerated in recent years, the report adds. The rate of sea level rise was 1.5mm a year from the start of the 20th century. However, over the period 1993-2019, it increased to over 3mm a year.
Dr Mike Kendon, lead author of the research and Met Office senior climate scientist, said the findings reinforced that the UK is already reeling from the impacts of the climate crisis.
“Our climate is changing now and that’s something we see clearly in our observations,” he told a press briefing. “The science is clear that we’re going to see more of this moving into the future.”
The Met Office’s State of the UK Climate in 2020 report, published in the International Journal of Climatology, comes in the wake of flash floods and temperature extremes in much of the country.
Last month, London was hit by serious flooding over twice in two weeks, leaving buses submerged and underground stations inundated.
The floods came just days after the Met Office issued its first ever extreme heat warning as parts of the country saw scorching temperatures above of up to 33C.
The report focuses on rainfall, temperature and other climate extremes last year.
It notes that 2020 saw the wettest February on record and some of the UK’s wettest days since records began in 1891. On Saturday 3 October – the year’s wettest day, the UK received enough rainfall to fill Loch Ness.
“A [Met Office] study has shown that the wettest day [in 2020] was made roughly two and a half times more likely as a result of climate change,” said Dr Kendon.
The year 2020 also saw the sunniest spring on record, the report says. The abnormal spring sunshine, along with mild winter conditions, played a role in the early opening of plants, the scientists added.
The report notes that first leaf dates in 2020 were on average 10 days earlier than in the period 1999-2019 for a range of common shrubs and trees.
The year also saw 10 named storms, including Ciara and Dennis – which struck in quick succession in February, causing severe flooding in Cumbria, Wales and Yorkshire.
Dr Ella Gilbert, a climate scientist at the University of Reading, said the report served as a “reminder that climate change is happening here, it’s happening now and it’s happening to all of us”.
“We are already seeing the effects of climate change on our weather and these will become more and more extreme as the climate warms further,” she said.
“All of these [extreme events] have real consequences – from flood damage to lost crops and lost lives.
“The longer we put off decisive action on climate change, the more damaging these impacts will be, with tangible impacts for us all.”
Following the Met Office amber heat warning last month, some parts of the UK experienced temperatures up to - and in excess of - 30C for a number of days.
The extreme warning, which was in place for much of Wales and southern England, was the first-ever issued by meteorologists.
People flocked to rivers, coasts and lakes to escape the heat, with a number of people drowning after getting to difficulty in the water.
Forecasters say another heatwave could hit in the middle of August.
According to a long-range Met Office forecast, temperatures are likely to be above average for the time of year.
Forecasters say high pressure from the Mediterranean Sea will push storms northward and drier weather should “spread in from the south,” bringing with it a tropical air mass, although a heatwave will require specific conditions.
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