Gauging the Greenhouse

Jan Veizer sheds light   on the controversy   about global climate   change theories.   Photo by: Colin Rowe

by Tim Lougheed

EARTH SCIENCES Professor Jan Veizer has waded into the ongoing debate over the mechanics and dynamics of global warming. In an article published in Nature on December 7, 2000, he added a detailed geological perspective on how the world’s climate has changed in the past, and how it could be changing today.

The most widely publicized views on the matter surround the key role of carbon dioxide (CO₂), which has been hailed as the “primary greenhouse gas.” Its rising concentration in the earth’s atmosphere is often credited with trapping heat and raising the planet’s average temperature. International agreements, such as the one struck in Kyoto, Japan in 1997, have suggested that this change has been caused by industrial pollution, which should be reduced to minimize the environmental impact of the warming trend.

Veizer’s paper, Evidence for decoupling of atmospheric CO₂ and global climate during the Phanerozoic eon, adds a different perspective on the matter. Co-authored with Yves Godderis and Louis M. François, of the Laboratoire de Physique Atmosphérique et Planétaire at the University of Liège in Belgium, the paper points to the unclear causes for the ice ages and warm periods that have punctuated the earth’s climate throughout the last 600 million years. Using marine fossils found in sedimentary layers from different eras, they were able to establish past ocean temperatures that agreed with semiquantitative climate reconstructions based on distribution of climate sensitive rock types. Using past CO₂ estimates from others and applying the current climate models, they then calculated temperatures for the same time intervals. The results were disappointing, with very high CO₂ levels and temperatures in the midst of ice ages.

“The climate pattern mandated by these observations may require reconsideration of the role of CO₂ as the principal driving force of climate changes on geological time scales,” they concluded.

Since the publication in Nature, some media reports, depending on their political bent, have approvingly claimed that Veizer has “deflated the greenhouse theory,” while others have taken him to task for implying that CO₂ is not a greenhouse gas. Critics have either claimed that the publication is of no relevance to the understanding of the present greenhouse or have charged him with giving industry a scientific justification to go on polluting, suggesting that our civilization’s contribution of CO₂ in the atmosphere will make little or no difference to the earth’s climate.

Veizer’s own paper makes no such claim, but an accompanying commentary in the same issue of Nature, What drives climate?, came much closer to doing so.

“Such a conclusion deserves close scrutiny, because the policy implications are huge,” wrote Pennsylvania State University geoscientist Lee Kump. “If large changes in atmospheric CO₂ in the past have not produced the climate response we thought they had, that undermines the case for reducing fossil-fuel emissions.”

Veizer did not know that Kump’s comments would be published alongside of his own work. Nevertheless, he has had to respond to queries and criticism as though he had been the author of these comments.

“I never said CO₂ was not a greenhouse gas,” he says. “But there is this one political dogma: CO₂ equals global warming, equals climate change, equals disaster. Now, the further you go along this equation, the iffier it is scientifically. But the moment you step away from this dogma you are excommunicated. You are undermining the environmental agenda.” He adds that he never intended to attack anyone who wants to preserve the physical integrity of our planet. But he does worry that if such efforts depend on incomplete or flawed science, the predictions could well prove to be inaccurate and the entire environmental agenda could be discredited.

Veizer’s work has attempted to clarify existing models of climate change by enhancing their accuracy. He and his colleagues have been working with new databases for isotopes of strontium, oxygen and carbon. Their findings have offered the first quantitative estimates of seawater temperatures at different points in the earth’s history over the last 550 million years. Combining this information with records of the major shifts in climate, he notes that CO₂ is not a driver of such changes, but simply amplifies an effect that has already been started in some other way.

In fact, he points to other research revealing that the amount of water vapour in the earth’s atmosphere is a far more influential factor in modulating major shifts in global temperatures. And while water vapour is far from alone in its impact, its importance demonstrates that the climatic system is much more complex than would be allowed by any model suggesting that CO₂ is the only reason the earth is warming today. “Water must play an important role also in the proposed half a degree Celsius warming over the past century,” says Veizer. “It is the relative importance of CO₂ and the degree of warming that is a matter of debate, not the greenhouse itself.”

He adds that he is well aware that this idea is not politically welcome. But he concludes that it is scientifically correct to say so, and he has 30 years’ worth of acclaimed research to support that opinion.

“It needs a bit of perspective, that’s all,” he says.