It was not like the Asian tsunami — not a sudden knockout that came from nowhere and that nobody could have expected. The North Sea has always been an edgy neighbour, best kept behind walls. The floods of 1953 are remembered as England's worst-ever natural disaster. From Lincolnshire to Kent, more than 300 people died, 24,000 houses were flooded and 40,000 people evacuated. But "worst ever" is a superlative example of memory loss. There were catastrophic sea floods in 1938, 1928, 1897, 1703, 1663, 1570, 1287, 1236 and 1099. In AD38, it was said, 10,000 people drowned along the east coast and in the Thames estuary.
Any day, the surge could come again. The wind piles in from the west, shovelling thick purple cloud over the faraway coast of Lincolnshire. I stand on the southern edge of the Wash, ground zero in the great inundation of 1953, looking out across this shallow, choppy inlet of the North Sea. In pubs all along the Norfolk coast, walls are hung with 50-year-old photographs showing telegraph poles jutting through swells, or boats calling at bedroom windows. On walls and bridges far inland, there are markers showing how high the water rose. On the Environment Agency's new national flood map, a blue tint shows how far it might reach next time. In the frontline villages, sirens stand ready to sound retreat.
Every year the sea here rises by six millimetres. A quarter of this is due to the long, slow tilting of the land after the last ice age; the rest is rising sea, fed by meltwater and thermal expansion as the climate warms. It might not sound much, but think what 6mm adds up to when spread across the entire expanse of ocean. Think what it will add up to in 50 years (nearly a foot). Think what such a weight of water will add to the height and power of the waves; how much further it will drive on up the valleys. In 1953 the storm surge raised sea levels in north Norfolk by 3.43 metres and at Southend by 2.74 metres. Metres! This was colossal — even now, a rise of just 60 centimetres is classified by the Met Office as a "surge event", with flood warnings issued via the Environment Agency when it coincides with a high tide.
At the time, the 1953 surge was regarded as something likely to recur on average only once every 120 years. But times and perceptions change. Sea levels have risen, storms have increased in both violence and frequency, and — though coastal defences have been strengthened — coastal dwellers near shore level are like Neapolitans under Vesuvius. It's not a question of if, but when.
The when and the what, however, wriggle through your fingers like salmon. It's a safe prediction that the nasty neighbour is going to get nastier, but the Intergovernmental Panel on Climate Change (IPCC) offers a bewilderingly wide range of possibilities. Global mean sea level in the 21st century, it says, could rise by anything between 9 and 88cm. The number of uncertainties — volume of greenhouse-gas emissions, rate of ice-melt, accuracy of climatologists' computer models, effectiveness of coastal defences — creates such a cacophony of statistical noise that you can't tell which tocsin is ringing the loudest. Around the UK, the prediction is that storms at sea will not only grow and multiply but also change track, with the result that some places (the Bristol Channel, for example) may look forward to a calmer future while others (the southern half of the North Sea) are in for a smiting.
The Met Office's expert on sea-level rise, Dr Jason Lowe of the Hadley Centre, is working on a "medium-high" emissions scenario that projects changes into the 2080s. By then, he says, a severe surge at high tide will be a much wilder beast than the equivalent storm today. Even in the relatively safe haven of the Bristol Channel it could be 20cm higher. In the English Channel it could be half a metre, and in the howling wastes of the southern North Sea an awesome 1.1 to 1.2 metres. These particular figures, admittedly, are for storms of such severity that they are likely to occur only once every 50 years. But here, too, the horizons are dissolving and re-forming.
"In the southern North Sea," says Lowe, "by the 2080s, a typical return period for what is now a 150-year event will be seven or eight years."
Add to flood risk the companion peril of erosion, and entire coasts are barnacled with anxiety. A few miles to the east and south of me, villages are poised almost literally in suspension as their cliffs tumble house by house into the sea. A couple of hundred yards to my left, two Environment Agency bulldozers are straining for the umpteen-hundredth time to reshape the shingle bank that protects the freshwater marsh, coast road and Salthouse village. Less than a fortnight later, in mid-February, their work will be undone by a storm.
Round the corner in the Thames estuary, the Office of the Deputy Prime Minister (ODPM) plans 85,000 new homes along 40 miles of flood plain. Most of this, most of the time, is kept dry by flood defences, but in February the Association of British Insurers fired a maroon. Existing defences were unlikely to be adequate in a globally warmed future, it said, and the threat in some places was so serious that houses would have to be redesigned like tropical fishermen's huts, with all their living space upstairs. Unless its members could be reassured that the tide would be tamed, the new homes would be uninsurable.
The Thames estuary is a perfect example of marine perfidy. The water may be rising, but the graph is irregular. Since its completion in October 1982, the Thames barrier has been closed against surges 90 times — a rough average of four a year. But in some years (1984, 1986, 1989, 1991, 1997) there were none at all. In the record year of 2003 there were 18. The graph shows an alpine profile of needle-sharp peaks and troughs but the trend is towards progressively higher peaks, with the three busiest years all coming since 2000. At the same time, between 1999 and 2002, the mean sea level at Sheerness rose 10cm above Met Office predictions. Londoners quaked like Venetians. How long would the barrier hold? How long before the Underground flooded? How long before the sewers, water mains, power and communications systems would be washed away? Around the water margins, straight questions float on seas of equivocation. As if to underline the uncertainty, 2004 passed with only two closures of the barrier and the water at Sheerness dropped back to its predicted level. Nobody knows why.
And yet we are encouraged to believe that the drowning of Westminster is about as likely as the Queen getting caught in a beam trawl. No part of the UK will be more heavily defended than London. The existing defences could hold out for decades, possibly even for centuries, but the risk of catastrophe becomes progressively less remote. With ODPM breathing down its neck, the Environment Agency is working on a long-term management plan for the estuary that will employ every kind of defence short of intervention from St Peter. The existing barrier will be upgraded or replaced when it reaches the end of its design life in 2030; riverside defences will be heightened; parks and nature reserves will be designed to act as spillways and storage lakes; drainage systems will be enlarged; new buildings will be made flood-resistant. There might even be a new outer barrage incorporating a road and a tidal power plant.
The agency will take its time — the first draft of its detailed plan is not expected until 2008 — but the stakes could hardly be higher. More than 1.25m people already live or work in the flood plain, and £80 billion worth of property stands at risk of damage by flood. In the flood zone are 68 London Underground and Docklands Light Railway stations, 30 mainline railway stations, three world-heritage sites, eight power stations, 16 hospitals and 400 schools. With magnificent understatement, the Environment Agency predicts that the cost of protecting all these, as well as the thousands of new homes to be built along the estuary, will be "substantial" — £4 billion is the current best estimate — and the question of who pays for it all (government? Property owners? Developers?) is not the least of the problems in search of an answer.
