Disastrous climate ‘switch’ threatens

GLOBAL warming could be returning the world to the way it was four million years ago — when sea levels were 80ft higher than they are today, scientists have warned.

The frightening forecast suggests that a climatic “switch” may soon be thrown, resulting in a seismic geothermal shift.

If the prediction is correct, later generations could find themselves living in a climate similar to that of the early Pliocene epoch, four to five million years ago.

Even though at that time the greenhouse effect of atmospheric carbon dioxide was no greater than it is today, average global temperatures were 3C warmer.

Sea levels, meanwhile, were 25 metres, or 82ft, higher. Such a rise in sea levels would have a devastating effect on human populations around the world, submerging whole islands and coastal cities.

Human evolution may have depended on the onset of drier conditions, about three million years ago, when ice started growing in the north and the Earth began to cool.

Scientists have long puzzled over the extent of global warming during the early Pliocene epoch, since it seems at odds with the modest carbon dioxide levels present at the time.

The key, some experts believe, was the appearance of a “permanent” El Nino event.

El Nino is the name given to a build up of warm surface seawater, flowing eastwards from the western Pacific, off the coasts of Ecuador and Peru.

A continual or “permanent” El Nino would have had a profound influence and warmed the whole world.

Experts writing in the journal Science argue that human-induced climate change may already be pushing the “switch” that could set up a continual El Nino.

The forecast is based on a review of Pliocene conditions, coupled with models of oceanic and atmospheric behaviour.

Key elements leading to the early Pliocene conditions were a deepening of the point at which sea temperature suddenly gets much colder, known as the thermocline, and changes in the hydrological cycle, or water circulation of the Earth.

The US scientists, led by Dr Alexey Fedorov, from Yale University in New Haven, Connecticut, wrote: “A future melting of glaciers, changes in the hydrological cycle, and a deepening of the thermocline could restore the warm conditions of the early Pliocene.”

Once a permanent El Nino has been established, removing it can take thousands or even millions of years.