The impact of cosmic rays on global warming needs to be assessed. Are charged particles coming from beyond the solar system, known as galactic cosmic rays, affecting the pace of climate change? Possibly, but the extent to which it is happening is not clear, according to V. Ramanathan, a leading atmospheric scientist with the Scripps Institution of Oceanography at San Diego, United States.
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.
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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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In a commentary published as part of the Ministry's discussion paper, Dr. Ramanathan noted that the data in Dr. Rao's paper showed the cosmic rays decreasing in intensity from 1900 to about 1970 and levelling off thereafter. On the other hand, global average temperatures had shown a warming trend from 1900 to 1940, a slight cooling from 1940 to 1970, and with the current rapid warming trend continuing unabated since then.
The mechanism that Dr. Rao had proposed was logical, said Dr. Ramanathan when he spoke to this correspondent.
However, estimating the magnitude of its impact on global warming depended on trends in the cloud data derived from satellites. ?But we now know that this satellite data itself has huge problems,? he said.
There were many links in the chain going from cosmic rays to cloud formation, he noted. At present, studies had established only the first link in that chain ? of the comic rays producing cloud condensation nuclei. Data for other links in the chain ? of such cloud condensation nuclei changing the number of cloud drops and that, in turn, affecting cloud cover ? was still missing. Pollution and natural sources like sea salt also provided copious amounts of particles on which clouds drop could form.
Dr. Rao's paper pointed out that the magnitude of the impact of cosmic rays on global warming could be potentially large. The paper should be taken seriously and the hypothesis he had put forward tested with suitable field studies, Dr. Ramanathan said.