Washington, Nov 19 (IANS) Carbon levels have reached a point of no return and may trigger disastrous climate change — unless they are reversed, scientists have warned. Their study is a departure from recent estimates that truly dangerous levels would be reached only later in this century.

“There is a bright side to this conclusion,” says James E. Hansen, the study’s co-author and director of the Goddard Institute for Space Studies, part of Columbia University’s Earth Institute.

“By following a path that leads to lower CO2, we can alleviate a number of problems that had begun to seem inevitable,” he said.

Hansen said these include expanding desertification, reduced food harvests, increased storm intensities, loss of coral reefs, and the disappearance of mountain glaciers that supply water to hundreds of millions of people.

The scientists said that CO2 should be brought down to pre-industrial levels or about 350 parts per million (ppm) - to reverse the upward spiral of current warming trends.

The level is currently at 385 ppm, and rising about two ppm each year, mainly due to the burning of fossil fuels and incineration of forests. As a result, global temperatures have been creeping upward.

The authors said that improved data on past climate changes, and the pace at which earth is changing now, especially in the polar regions, contributed to their conclusion.

The scientists are optimistic that current atmospheric CO2 could be reduced if emissions from coal, the largest contributor, are largely phased out by 2030, said a Columbia release.

Use of unconventional fossil-fuel sources such as tar sands also would have to be minimised, they say. They predict that oil use will probably decline anyway as reserves shrink.

The paper appears in the current edition of the Open Atmospheric Science Journal.