COPENHAGEN (AFP) –
Scientists on Wednesday unveiled a Dow Jones-style "climate-change index" aimed at showing in user-friendly form the perils posed by man-made global warming.

The index takes a basket of complex factors -- carbon dioxide (CO2), temperature change, sea level and sea ice -- and distils them into a single figure that is more easily understandable for the public, they said.

In 1980, the index stood at 34, its creators, the International Geosphere-Biosphere Programme at the Royal Swedish Academy of Sciences, said.

But from 1997, the barometer leapt suddenly, adding dozens of points each year as evidence of climate change accumulated.

As of 2007, the index stood at 574.

"We felt people outside global-change research are not clear about the scale of the changes scientists are witnessing," said IGBP executive director Sybil Seitzinger, who presented the index on the sidelines of the UN climate talks in Copenhagen.

"The index is a response to these concerns."

In three of the years -- in 1982, 1992 and 1996 -- the index falls back, reflecting big volcanic eruptions that temporarily cooled the planet by swathing the upper atmosphere with clouds of reflective dust.

However, "the change is unequivocal, it is global and, significantly, it is in one direction," the IGBP said.

"The reason for concern becomes clear: in just 30 years, we are witnessing major planetary-scale changes."