A team of scientists from the United States and Canada has presented new evidence about the rapid melting of ice in the Arctic.

Data presented at a meeting of the American Geophysical Union in San Francisco indicates that all-year-round ice could disappear by the year 2040.

Mark Serreze, a scientist at the US National Snow and Ice Data Centre, warned that the effects of greenhouse warming were now becoming evident.

The scientists projected a slow, steady decline of Arctic ice as global warming continues, with a dramatic 'tipping point' in about two decades.

The research, published by the scientific journal Geophysical Research Letters, found that the extent of sea ice each September could be reduced so abruptly that, within about 20 years, it may begin retreating four times faster than at any time in the observed record.

That means that the Arctic could be ice-free in summer as early as 2040, according to computer modelling.

In one simulation, the September ice shrinks from about six million square km to two million square km in a 10-year period.

By 2040, only a small amount of perennial sea ice would remain along the north coasts of Greenland and Canada, while most of the Arctic basin would be ice-free in September.

This would have major consequences for wildlife in the region, not least polar bears which traverse ice-floes in search of food.

Loss of summer ice would seriously compromise the lifestyles of the region's indigenous peoples, though it could also bring new trading opportunities as sea routes are opened up.

On a global scale, the Earth would lose a major reflective surface and so absorb more solar energy, potentially accelerating climatic change across the world.