writes Gregory Kirby

Crop production in Britain will plummet if climate change sends a vital ocean current pattern past "tipping point", new research suggests.

The Atlantic Meridional Overturning Circulation (AMOC) brings heat from the tropics, making Britain warmer and wetter than it would otherwise be.

The Exeter University study shows that while a warming Britain is expected to boost food production, if the AMOC collapses it could decimate arable farming across the country.

Land area suitable for arable farming would shrink by a quarter reducing crop value by around £346 million per year.

Such a collapse - a climate change "tipping point" - would leave Britain cooler, drier and unsuitable for many crops, the study says.

The main problem would be reduced rainfall and, though irrigation could be used to compensate, the researchers said the amount of water and the costs would be too high.

Dr Paul Ritchie, of Exeter University said: "If the AMOC collapsed, we would expect to see much more dramatic change than is currently expected due to climate change.

"Such a collapse would reverse the effects of warming in Britain, creating an average temperature drop of 3.4°C and leading to a substantial reduction in rainfall of 123mm during the growing season.

"These changes, especially the drying, could make most land unsuitable for arable farming."

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Scientists said the AMOC is one reason that average temperatures in Britain are warmer than those of many places at similar latitudes.

For example, Moscow and the southern extremes of Alaska are further south than Edinburgh.

The study, published in the Nature Food journal, examines a "fast and early" collapse of the all-important current pattern.

Although the collapse is currently considered a 'low-probability' - the AMOC has weakened by an estimated 15 per cent over the last 50 years.

Professor Tim Lenton, Exeter University's Global Systems Institute lead, said worst-case scenarios must be considered when calculating risks.

He added: "Any risk assessment needs to get a handle on the large impacts if such a tipping point is reached, even if it is a low-probability event.

"The point of this detailed study was to discover how stark the impacts of AMOC collapse could be."

The study follows a recent paper by the professor and his colleagues warning of a possible "cascade" of inter-related tipping points.

Professor Lenton said the new study reinforces the message that we would be "wise" to act now to minimise the risk of passing climate tipping points.

Growing crops is generally more profitable than using land as pasture for livestock rearing, but much of northern and western Britain is unsuitable for arable farming.

Professor Ian Bateman added: "With the land area suitable for arable farming expected to drop from 32 per cent to seven per cent under AMOC collapse, we could see a major reduction in the value of agricultural output.

"In this scenario, we estimate a decrease of £346 million per year - a reduction of over ten per cent in the net value of British farming."

Speaking about the expectation that moderate warming would boost agricultural production in Britain, he added: "It's important to note that the wider effects for the UK and beyond will be very negative as import costs rise steeply and the costs of most goods climb."

The study focuses on agriculture, but AMOC collapse and the resulting temperature drop could lead to a host of other economic costs for the UK.