The Earth has been warming at a rate of 0.2 degrees celsius per decade for the last 30 years, researchers reported in Tuesday's issue of Proceedings of the National Academy of Sciences.

That brings the overall temperature to the warmest in the current interglacial period, which began about 12,000 years ago, James Hansen, head researcher of Nasa's Goddard institute for space studies in New York, said.

"This evidence implies that we are getting close to dangerous levels of human-made pollution," Hansen said on Monday.

A recent report in Nature, the scientific journal, found that 1,700 plant, animal and insect species have moved towards cooler areas at an average rate of about 4 miles per decade in the last half of the 20th century.

Hansen, who first warned of the danger of climate change decades ago, said that human-made greenhouse gases have become the dominant climate change factor.

Clear signs

The study said the recent warming had brought global temperature to a level within about one degree Celsius of the maximum temperature of the past million years.

"If further global warming reaches 2 or 3 degrees Celsius, we will likely see changes that make Earth a different planet than the one we know."

"The last time it was that warm was in the middle pliocene [last tertiary period], about three million years ago, when sea level was estimated to have been about 25 meters higher than today."

The institute said that warming had been stronger in the far north, where melting ice and snow had led to the exposure of heat-absorbing land and rocks making the area warmer.

Researchers also said that the global warming signs could be seen in the Indian and western Pacific Oceans.

Those oceans have a major effect on climate, and warming there could lead to more El Nino episodes affecting the weather, said Hansen.

Few scientists doubt that the planet has warmed significantly in recent decades, though some question the causes of the change.

The National Academy of Sciences website