Or, three. Not to mention a picture of what Britain will look like in 200 years if climate change melts the globe’s three largest ice sheets. According to today’s Scotsman, a new study suggests sea levels would rise some 275 feet. The U.K. mainland would turn into a North Sea Polynesia, with coastal towns and many cities disappearing completely. The center of London would be underwater. Hm — those zombies in 28 Days Later are starting to look like a more manageable end-of-the-world scenario by the minute.

Of course, the big queston here is: how likely is this? And that’s where respectable scientists disagree. Bill McGuire, at University College London’s Benfield Hazard Research Centre, was commissioned to carry out the work by the satellite network UKTV History for a TV series, The British Isles, A Natural History. “If the West Antarctic Ice Sheet melts, along with the continued thermal expansion of seawater, we could see London and many other coastal cities disappearing beneath the waves in the next 200 years,” he says.

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(Just to put this in perspective, my grandparents arrived in New York City about 100 years ago. So within a generation or two a handful of generations, depending on how long people live in the 21st century, McGuire is saying, we could be kayaking through Trafalgar Square.)

Tim Osborn, from the well-respected Climate Research Unit at the University of East Anglia, agrees with McGuire’s results to a point: that 275-foot rise. “In terms of the science, the values are approximately right if the ice sheets do melt, with the exception of the last prediction. The question is whether these things are likely to happen or not.”

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Apparently it’s considered pretty unlikely that the West Antarctic Ice Sheet would melt in the next two centuries, as it’s about 59 degrees Fahrenheit colder than than the other two major ice sheets, Greenland and the East Antarctic. McGuire’s study gives it one in 20 odds.