Study casts doubts on greenhouse heating

Study casts doubts on greenhouse heating

New Delhi: In data-based research that can influence the understanding of climate change, scientists have raised doubts about accepted theories on the extent to which solar activity heats up the earth’s atmosphere.

Solar activity, astronomers have long held, waxes and wanes over roughly 11-year cycles. Increased activity heats up the earth’s atmosphere at a faster rate.

But an analysis published in the journal Nature by scientists from Imperial College, London, using satellite data of solar radiation between 2004 and 2007, says that if accepted models that relate solar activity and Earth’s temperature are accurate, Earth’s climate should have cooled in these years.

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Observations, on the other hand, say that over the past decade, temperatures on Earth have steadily increased and are believed to be the key drivers of long-term and large-scale changes in climate.

While many scientists and multilateral bodies such as the United Nation’s Intergovernmental Panel on Climate Change (IPCC) hold that the release of industrial gases into the atmosphere is mainly responsible for the rise in temperatue, the extent to which solar activity influences the process is not clear. Estimates on the role of solar activity in raising temperatures on earth range from 2% to 25%.

It is only since 1978 that scientists have been able to observe the solar radiation spectrum via satellites and model how each radiation affects various levels of the atmosphere.

‘These observations were made during the declining phase of the previous solar cycle," said Joanna Haigh, an atmospheric physicist at Imperial College and the lead author of the study.

In a telephone interview, Haigh said her team’s observations could be a one-off case. It will take more than a decade— when solar activity is waning again—before the same measuresments can be made and compared.

“But if this not an anomaly and a trend," she added, “it could significantly alter our understanding of how solar variability affects earth’s climate."

The study also found that key kinds of radiation—ultraviolet, infrared and visible—differently affected various layers of the atmosphere and didn’t, as was supposed, heat all the layers uniformly.

Current models that extrapolate climate trends into the future do account for solar variability, but don’t account for how different wavelengths of radiation affect sections of the atmosphere.

“There’s a lot more complexity that isn’t being accounted for in current IPCC models," said Haigh.

She added that despite the anomalous observations, “fluctuations in solar radiation was unlikely to significantly account for global warming."

According to a research paper by the Stanford Solar Center, the variation in energy emitted by the sun through the 11-year cycle is only about 10%. Past studies have said that when the solar cycle is at a maximum, it puts out a larger percentage of high-energy radiation, which increases the amount of ozone in the upper atmosphere.

The increased ozone warms the upper atmosphere and the warm air affects winds all the way from the stratosphere— the atmospheric layer at 6-30 miles from earth. Changes in wind strength and direction lead to different climate patterns around the globe.

Rolando Garcia, atmospheric scientist at the National Center for Atmospheric Research in Boulder, US, said it was too early for researchers to revise their solar variability theories and models.

Several independent observations over 20 years had borne out the mechanism between solar variability and climate, he said, and more observations are needed to cancel the effects of “instrument drift", when satellites give erroneous readings as they wobble out of orbit.