Why we need to shed light, not heat on global warming issue

The world is warming up

The world is warming up. The Intergovernmental Panel on Climate Change (IPCC) has declared that the cause of the warming is human emission of certain gases into the atmosphere. The verdict of the IPCC is widely, but not universally, accepted.

A small minority of scientists reject the finding of IPCC and propose that global warming is driven by the sun. Some also charge that IPCC is driven by a political agenda. These dissidents are beginning to get a public hearing. It is important that this matter be debated openly.

The conventional scientific consensus is that global warming is caused by the enhanced greenhouse effect. The only external source of energy available to Earth is the sun. Radiation from it shines on the surface of the Earth, heating it, and the Earth radiates the heat back into the atmosphere. The atmosphere is pretty much transparent to radiation incoming from the sun, but it partially absorbs the heat radiated from the Earth and slows down its transmission to outer space. This serves to keep our Earth at an average temperature of 14 degrees, eminently suitable for life. This phenomenon is called the greenhouse effect (GE) and, if the Earth had no atmosphere, it would alternately bake by day and freeze by night - becoming thoroughly unsuitable for life.

Certain gases in our atmosphere, principally water vapour, carbon dioxide, nitrous oxide and ozone, are responsible for the GE, but most of the GE can be attributed to water vapour and cloud cover. The Earth has been warming gradually since 1850 and scientific measurements have correlated this warming with a gradual build-up of carbon dioxide in the atmosphere caused by humankind's widespread burning of fossil fuel. We know that increasing the concentration of carbon dioxide would warm the Earth, and historical records going back millions of years, gleaned from ice cores drilled deep into ice sheets, also correlate temperature with carbon dioxide concentrations. It all seems to hang nicely together and the conclusion is that our current global warming is driven by man-made emissions of carbon dioxide.

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A minority of climatologists is not convinced by this argument. They claim changes in the Earth's temperature are largely driven by cyclical changes in the sun's activity. They propose an alternative theory which says cosmic rays are driving global warming by influencing cloud cover.

Cosmic rays are high-energy particles and rays emitted by exploding stars elsewhere in our galaxy. These cosmic rays constantly rain down upon the Earth. It is proposed that these rays interact with molecules of gas (ozone, sulphur dioxide and water) in the atmosphere, disrupting their electrical balance (ionisation) and thereby seeding cloud formation. White clouds have the effect of reflecting back incoming solar radiation and cooling the Earth. If there is a diminution in incoming cosmic rays, fewer clouds will form and the Earth will warm up. This, the dissident scientists claim, is what is happening now.

The intensity of cosmic rays reaching Earth is affected by the sun's magnetic field and this varies cyclically. The stronger the field, the more it deflects away incoming cosmic rays from outer space and fewer such rays reach Earth. The cosmic ray theory proposes that the intensification of the sun's magnetic field during the 20th century deflected many cosmic rays away from Earth, resulting in fewer clouds and a warmer world. A warmer world would release more carbon dioxide from the oceans into in the atmosphere and that is why carbon dioxide atmospheric levels correlate historically with global temperature - but this was the effect of global temperature not the cause. The theory's proponents say the cosmic ray phenomenon hasn't been adequately factored into the IPCC models and therefore the IPCC predictions are inaccurate.

Two proponents of the cosmic ray theory are Nir Shaviv of the Hebrew University Jerusalem and Jan Veizer of the University of Ottawa. They have also carried out historical research and claim changes in cosmic ray flux are the major reason for Earth temperature changes over the past 500 million years. They claim changes in carbon dioxide concentrations in the historical record had only a minor effect on temperature change. If they're right, the trillions of dollars it would cost to implement the Kyoto Protocol would be largely a waste of money. The latest development has just been published online by Henrick Svensmark in the Proceedings of the Royal Society, October 3rd, 2006, in which he replicated the proposed effect of cosmic rays on aerosols in the atmosphere that help to create clouds.

I am not a climatologist and I cannot discriminate scientifically between the respective scientific arguments of both sides. However, I am bothered by charges made by Dr Richard Lindzen, a former member of IPCC, and others, that IPCC scientists are under pressure to conclude that global warming is caused by carbon dioxide emissions and that the summaries issued by IPCC well in advance of the detailed main IPCC reports often differ significantly in tone and interpretation from the detail in the main reports. The media relies largely on these easily digested summaries.

On balance, I will continue to trust the IPCC conclusions. I have read evidence that the cosmic ray theory is being seriously hyped up - solar activity has changed little over the last 30 years, but global temperature has gone up significantly. However, I am somewhat bothered by the whole thing. I would like to see open, honest scientific debate on this vital matter.

William Reville is associate professor of biochemistry and public awareness of science officer at UCC - http://understandingscience.ucc.ie.