New Delhi, Jan. 20: The environment ministry today released a paper by a senior Indian space scientist that highlights the role of cosmic rays in global warming and attempts to rekindle a 13-year debate on natural factors heating the planet.
The scientific review, by Udupi Ramachandra Rao, a cosmic ray physicist and former head of the Indian Space Research Organisation (Isro), also claims the UN climate change agency overestimated the role of greenhouse gases on the observed global temperature rise.
The Earth is under a steady shower of galactic cosmic rays mainly protons and electrons which some scientists believe can help build clouds in the atmosphere. But the Suns changing magnetic field can increase or decrease cosmic ray flux.
A decrease is expected to reduce the cloud cover which would result in less solar energy being reflected back into space. This would lead to increase in the Earths temperature.
Rao, who analysed recent studies on the history of cosmic ray intensity, has said that the contribution of recent changes in galactic cosmic ray intensity to climate change is quite significant and needs to be factored into predictions of global warming.
He said greenhouse gas emissions seem to account for 0.42°C (60 per cent) of the observed global warming of 0.75°C over the past century. This, Rao said, is considerably less than predicted by the Intergovernmental Panel on Climate Change, the UN agency.
Were not denying the contribution of greenhouse gases were only trying to expand the scientific debate to look at some non-greenhouse gas factors that may also influence global warming, said Union environment minister Jairam Ramesh.
But some scientists familiar with the subject said that while there is always place for debate in science, the available evidence so far has failed to conclusively prove or disprove the link between galactic cosmic rays and clouds.
Two Danish scientists Henrik Svensmark and Friis Christensen had proposed the connection between galactic cosmic rays and clouds in 1997. But despite a number of studies since then, scientists can neither categorically rule out a connection nor conclude affirmatively about such a connection, said Veerabhadran Ramanathan, a senior atmospheric scientist at the Scripps Institution of Oceanography, University of California, San Diego.
The galactic cosmic rays have some effect but it does not appear to be a significant effect, said Juerg Beer, a physicist at the Institute of Aquatic Science and Technology in Switzerland, who was in Goa today to attend a conference on space climate.
Beer and his colleagues used chemical signatures frozen in ice cores to reconstruct the changes in cosmic ray intensity over several centuries. But they could not establish any link between clouds or climate and cosmic rays. But a debate is possible we still dont fully understand space and atmosphere, Beer said.