TCS Daily


Clearing the Air

By Bob Carter - May 5, 2004 12:00 AM

The first thing to be clear about is that carbon dioxide is not a pollutant. Rather, the presence of this trace gas in Earth's atmosphere is vitally important for the growth of plants. And in extracting carbon dioxide from the atmosphere, plants in turn release the oxygen that is required for the respiration of most animal life forms, you and me included.

Over geological time periods, the amount of carbon dioxide in the atmosphere has varied between less than 100 parts per million (ppm) and several thousand ppm, the exact amount at any one time depending upon the state of the global carbon budget and the mechanisms which control its sinks and sources.

Assuming the pre-industrial 260 ppm of atmospheric carbon dioxide as a "natural" interglacial baseline, increases beyond this level have two main environmental effects. First, enhanced plant growth. And, second, a warming effect on global temperature.

The first effect is well documented, and many hundreds of experimental studies testify to the reality of enhanced plant growth, both trees and grasses, in carbon dioxide-enriched atmospheres.

The physical reality of the second effect is also beyond challenge, because carbon dioxide is a greenhouse gas (meaning that it absorbs outgoing infrared radiation from the solid earth, thereby heating the atmosphere). However, the complexity of atmospheric processes and feedback effects is such that the exact magnitude of this heating is highly uncertain.

For a doubling of atmospheric carbon dioxide, deterministic computer models predict a wide range of future temperature rises between about 1 and 6 degrees. Other arguments, based on meteorological and planetary data, suggest a temperature rise an order of magnitude less, of about 0.2 to 0.4 degrees. Third, an accurate 25-year-long record of atmospheric temperature is now available from both satellite and weather balloon measurements. These show virtually no long-term trend of temperature increase despite the increased carbon dioxide levels over the last 25 years. Finally, a recent study by Bill Ruddiman of the University of Virginia suggests that the clearance of forests and development of agriculture by neolithic and early modern peoples, since about 8,000 years ago, have caused the release of sufficient "extra" greenhouse gases (carbon dioxide and methane) into the atmosphere to have already prevented the earth's expected decline into its next glacial episode.

What, then, can we conclude from all these, sometimes conflicting, lines of evidence?

It is that, contrary to strong public belief, the effects of increasing carbon dioxide in the atmosphere are generally beneficial. Enhanced plant growth has many obvious benefits, amongst them increased natural vegetation growth in general, and increased agricultural production in particular. And to maintain or slightly increase planetary temperature is also very much a global good if -- as Ruddiman and other scientists assert -- the human production of greenhouse gases is helping to hold our planetary environment in its historic, benignly warm, interglacial mode.

This news has yet to percolate up to the policy level within western governments, most of whom are still preoccupied with the politics of the now obsolete Kyoto protocol, including in many cases advanced plans for carbon trading taxes on energy consumption. Even worse, however, major government science agencies, or senior scientists such as the U.K.'s Sir David King, are continuing to propagate the view that increases in atmospheric carbon dioxide are, of themselves, environmentally harmful.

For instance, CSIRO in Australia is making much of the fact that in 2002 and 2003 estimated Australian carbon dioxide emissions exceeded the previous ten-year average; chief research scientist, Paul Fraser, is quoted as saying that he is disturbed by this because "carbon dioxide is the main driver of climate change". No mention is made of the fact that global carbon dioxide levels have been increasing at a decreasing rate through the 1990s, nor of the known beneficial effects of increased carbon dioxide, which include stressed plants responding more and the sum of all plants providing an increasing sink which may limit the ultimate increase in atmospheric carbon dioxide to about 300 ppm above present levels. Equally ignored is the geological evidence which shows that past rises in temperature preceded by several hundred years the parallel increases in carbon dioxide, which implies that the link between carbon dioxide and climate is, at best, poorly understood. In short, propaganda now reigns over science in the public debate.

There is an urgent need for governments to shake themselves free of the partial advice provided by environmental advocacy groups and government science agencies, all of whom have a strong and often undeclared self-interest in most environmental matters. Nowhere is this need greater than in the debate over climate change.

Suspicion of the motives of those who render financial advice is the main reason the governments of most western nations turn to national audit commissions when they require impartial adjudication on financial matters. Apparently, however, the Danish government is almost alone in having set up an analogous high level audit agency to advise it on contentious environmental matters. Until other western nations follow suit by creating their own national environmental audit agencies, they will continue to flounder in science-advice tarpits of their own creation, at the same time falling victim to siren calls of environmental evangelism such as those that led to the preposterously expensive and ineffective Kyoto protocol.

Professor Bob Carter, of the Marine Geophysical Laboratory, James Cook University, is a former Director of the Australian Secretariat for the Ocean Drilling Program, the world's pre-eminent international collaborative program in environmental and geological science. He recently wrote for TCS about Climate Change: A Longer View.


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