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How the weather got 'stuck' over the UK—and produced an unusually dry and warm spring

A weather system lingering high above the UK has produced one of the driest, warmest and brightest starts to spring on record.

was the sunniest since records began in 1910. This followed the third-sunniest March, and both months saw temperatures well above average nationwide. On May 1, the temperature reached 29.3°C in Kew Gardens in London—.

Meteorologists are of the potential for a summer drought, as the UK has seen roughly half its usual amount of rainfall for March and April. While about this year's harvest, some water companies are to help reservoir levels recover by limiting water use.

Meanwhile, have engulfed forest and moorland in areas of Scotland, Wales and England.

For several weeks, a stubborn area of high pressure over the UK has diverted the usual flow of mild, moist air from the North Atlantic like a boulder in a river. This is known as a blocking weather system.

Within it, air descends, warms and dries, which is why this weather pattern tends to be linked to heat waves and drought. Blocking is usually persistent, making it seem like the weather is stuck.

Here's how climate change may have played a role in setting up this unusual spring.

The human fingerprint

The warming climate means that unusually warm weather is . At the same time, we can expect more periods of both severe drought and extreme rainfall. Sudden changes from drought to deluge, termed , are due to the intensification of the water cycle in a warmer atmosphere that can hold more water vapor.

However, certain weather patterns are necessary to produce extreme weather. More blocking events in the future could increase the chance of heat waves or drought. But are blocking weather patterns becoming more common?

It's difficult to determine how weather patterns will change as a result of the rising concentration of greenhouse gases in the atmosphere, which is predominantly caused by the burning of fossil fuels.

Part of the difficulty arises from the fact that weather patterns vary year to year. Several years in a row with more blocking events than usual could make it seem like blocking is increasing due to climate change, but it could simply be down to chance.

As a result, it is difficult to detect the fingerprint of human activity from weather observations alone. For example, blocking weather patterns over Greenland during summer have , which can . But it isn't clear that this trend is the result of human-induced climate change.

Climate models do suggest future changes in the occurrence of blocking, however. These computer simulations, consisting of equations that describe the fundamental physics of the atmosphere, are the main tool scientists use to perform experiments that parse how the climate will behave in the future.

When scientists run climate model simulations with increased greenhouse gas concentrations, the results consistently show a . But blocking generally happens more often in real life than model simulations, which reduces the confidence scientists have in future projections.

Keeping track of the jet stream

The movement of weather systems in Earth's mid-latitudes—including over the UK—is linked to the jet stream, which is a fast-flowing river of air driven by the contrast in temperature between the poles and mid-latitudes.

Some researchers have suggested that, because the Arctic is warming faster than the tropics, the jet stream , increasing the occurrence of blocking events, contrary to what most climate models show.

Outside of the scientific community, this idea has . However, the hypothesis remains controversial among scientists, and observational evidence .

In fact, around 10 kilometers above Earth's surface, near commercial aircraft cruising altitudes, the opposite trends are occurring: the temperature difference between the Arctic and mid-latitudes is , acting to increase the strength of the jet stream.

There are considerable challenges with understanding how climate change is affecting the large-scale atmospheric patterns which drive the weather we experience. These include large natural variability and imperfect climate models. Models mostly suggest a decline in blocking events with climate change, though this remains relatively uncertain compared with other aspects of the science.

Overall, we can be confident that climate change is bringing warmer conditions in all seasons. Scientists also have strong evidence to suggest that drought conditions will become more common. These changes are already affecting food production, energy generation and water availability and these impacts will continue to worsen with climate change.