But with sea levels rising, a managed retreat is underway that threatens to become a full-scale rout if global temperatures rise by 3C. The UN warns that they will unless governments take far more drastic action to reduce emissions.

In short, the entire shape of eastern England would change. The iconic British Isles map, learned from an early age in schools, would look very different. Locals already quip about Peterborough, 35 miles from the shore in Cambridgeshire, becoming a seaside city.

Global warming of 3C would lock in changes that would ultimately - several decades down the line - swamp most of the farm fields and much of the coastline in this eastern county.

The growing threats of flooding, storm-surges and coastal erosion are already evident.

Lincolnshire was designated a high-risk area in the most recent national flood assessment, with 30,000 vulnerable properties. The Environment Agency advises residents to check the potential threat to their homes because many are unaware of how far inland the sea can already reach. During the great coastal flood in December 2013, the surge overwhelmed a pumping station 40 miles from the shore.

The county is a major recipient of the government's six-year £2.5bn programme to strengthen sea and flood barriers in England. This is done with a mix of soft defences (sandy shores, mudflats and wetlands to absorb wave impact) by the coast along with hard defences (concrete walls) further inland.

The authorities replenish eroded beaches such as Skegness each year with 350,000 cubic metres of of sand. Earlier this year, two new flood-alleviation reservoirs were completed in Louth and Horncastle. A public inquiry has also been held for a £100m flood barrier scheme in Boston.

Increasingly, planners are also turning to "managed retreat", which cedes previously reclaimed land. In this realignment (as the authorities prefer to call it), parts of the sea bank - for example, at North Somercotes in 2009 and Alkborough Flats in 2015 - are deliberately breached and converted back to salt marsh. This creates new wildlife habitats and adds an extra defence against flooding.

"We're conscious that climate change is happening and perhaps faster than expected so we are trying to mitigate and adapt to protect people and property. We can't stop it, but we can reduce the risk," said Alison Baptiste, director of strategy and investment at the Environment Agency.

She said the measures in place should protect most communities in the near and medium term, but 50 years from now the situation will become more challenging. "If climate change projections are accurate, we're going to have to make some difficult decisions."

The greatest hits will be on food security and the economy. Lincolnshire boasts nearly a quarter of the land used in England for horticulture and an even higher proportion for peas, beans and vegetables (pdf). Most would be swamped as coastlines are redrawn. Fishing ports and seaside towns would also disappear.

Jason Elliott, who works at a Skegness beach shop selling buckets, spades and saucy postcards said people in the town had been warned about the long-term threat.

"We've heard that the coast will move so far inland that Peterborough will become a seaside town," he said, referring to an area 35 miles from the shore. "We all assume we'll be OK for a good while, but it would be sad if one day Skegness was to go. So many people live here and so many holidaymakers have had fun here."