A lethal virus, humanity wiped out - then what?

It is the water that has the first impact. Take away people and the pumps that prevent our cities' underground railways and tunnels from flooding stop working. Within a day of humanity's disappearance, the world's metros fill up with fetid water. Then the animals break out of zoos and lions roam the streets before emergency cooling circuits on nuclear power plants fail, causing radioactive plumes to spread.

It is an apocalyptic vision worthy of a science fiction film. In fact, these scenes form part of a startling new documentary, Life After People, that is to be shown on the History Channel over the Easter weekend. In addition, the book The World Without Us by Alan Weisman, which follows a similar Earth-without-humans theme, has become a surprise US bestseller. Last week the National Geographic Channel screened its version of the book, Aftermath: Population Zero, in the US.

Both book and programmes envisage a world in which some non-destructive event - a lethal virus - eradicates our species overnight but leaves the rest of the planet intact. How would nature fare without us?

Answers, according to Weisman in his book, are intriguing. Within months London would suffer major flooding because the Thames Barrier no longer works. Roads would crack as plants take seed. Plastic bags and other rubbish would form mounds everywhere.

After a year human lice would become extinct. In a decade untended homes would start to disintegrate and the Panama Canal would close up, uniting North and South America. In 50 years fish stocks would recover, coral reefs regenerate and elephant populations grow 20-fold. By 300 years, dams are overflowing and collapsing. In 100,000 years carbon dioxide returns to pre-human levels. Then, in 5 billion years, Earth burns up as the Sun expands.

However, before that fiery end our nuclear legacy is likely to be our lasting monument. 'If everyone on Earth disappeared, 441 nuclear plants would briefly run on autopilot until they overheated,' says Weisman. 'The spilling of radioactivity would be formidable, and it would last, in the case of enriched uranium, into geologic time.'