Hotter days, tropical nights and longer warm spells on the rise

Warm spells and tropical nights are on the rise in the UK as the climate changes, a report from the Met Office focusing on weather extremes reveals.

The duration of warm spells, when temperatures are well above average for the time of year, has more than doubled between the periods 1961 -1990 and 2008 to 2017, the report which tracks trends since the 1960s shows.

Scorching summer days are getting hotter, with the hottest day of each year in the most recent decade on average 0.8C warmer than each year's hottest days in the period 1961-1990.

Hottest UK summers (mean temperature, Jun-Aug).
(PA Graphics)

And the chilliest extremes of the year are not quite as biting as they were in the past, with the lowest temperature of the year 1.7C milder in the last decade than it was in the three decades up to 1990.

Tropical nights – where minimum temperatures do not fall below 20C (68F) – are still rare in the UK, and are largely confined to southern England.

But they are being included in the report on temperature and rainfall extremes as they are likely to become more common in the future as climate change becomes more pronounced.

The data show that while the 1976 heatwave is one of the most significant heatwaves for the UK, tropical nights only really start to stand out after 1995.

The hottest day each year in the most recent decade is on average warmer than the hottest day each year between 1961-1990 (Andrew Matthews/PA)
The hottest day each year in the most recent decade is on average warmer than the hottest day each year between 1961-1990 (Andrew Matthews/PA)

Between 2008 and 2017 a cluster of tropical nights are recorded in the South East, the Midlands and South Wales.

Dr Mark McCarthy, head of the Met Office's National Climate Information Centre which produced the report, said: "Minimum overnight temperatures of over 20C in the UK are rare currently and even during this summer this threshold was only exceeded on a few occasions.

"However, with projections in climate suggesting warmer temperatures, it is useful to have this metric in place, so that future changes can be monitored."

Heavy rainfall is also on the increase, with extremely wet days up 17% in the period 2008-2017, compared to 1961-1990, the report showed.

Dr McCarthy said: "Monthly, seasonal and annual climate data provide a valuable record of the changing climate in the UK.

"However, these average figures have a tendency to mask extreme weather and climate events."

So the new report focuses on measures which record weather extremes to also show how the climate is changing, he said.

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