The idea of galactic cosmic rays being an important factor driving climate change goes back over a decade. But the evidence remains ambiguous, observed the Intergovernmental Panel on Climate Change in its Fourth Assessment Report published in 2007.
The role these cosmic rays could play has now been highlighted by a paper from the former Chairman of the Indian Space Research Organisation, U.R. Rao. The work was recently published as a Discussion Paper by the Ministry of Environment and Forests.
As the cosmic rays pass through the earth's atmosphere, they turn atoms and molecules on their path into electrically charged forms called ions. These ions then act as ?cloud condensation nuclei' to which water vapour can adhere and form cloud drops.
But during periods of increased solar activity, the intensity of cosmic rays reaching the earth is reduced. That, it is argued, will reduce the number of cloud condensation nuclei that form, thereby lessening cloud cover. With lesser clouds, more sunlight would reach the earth's surface, contributing to greater warming of the planet.
Quoting published work, Dr. Rao pointed to a nine per cent reduction in the intensity of cosmic rays during the past 150 years. He estimated that the heightened warming of the earth that resulted would amount to 60 per cent of the warming attributed to increased carbon dioxide emissions. Consequently, the contribution of increased carbon dioxide emissions to the observed global warming would be considerably less than what was estimated by the Intergovernmental Panel on Climate Change.
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