Retorts

Greenhouse Goes On

In reply to Dai Redshaw [Retorts, Nov] I would say, I do happen to consider that the increase in greenhouse gases probably is causing global warming. However, the best current evidence indicates that it is unlikely to exceed 0.3^oC by the end of the next century, an amount that may be undetectable because of the overwhelming influence of other climate factors. It might be considered a sufficient threat for some countries to consider emission controls, but New Zealand would surely benefit by such a temperature rise.

I prefer to obtain my information from proper scientific papers, and from the IPCC reports, rather than from the popular press (eg New Scientist), or from advocacy groups like Greenpeace who select evidence to suit their preconceived ideas.

Of the 0.5^oC global temperature rise over the last century, 0.4^oC took place between 1910 and 1940 before significant greenhouse gas emissions had taken place, so they could not have made a major contribution. This rise should therefore not be included in any model assessment. From 1940 to 1978, when a large proportion of the greenhouse gases were emitted, there was a fall in temperature of 0.1^oC. The current concerns are exclusively associated with the brief temperature rise of 0.2^oC from 1978 to 1990, which seems now to have leveled off.

The Hadley Centre model, unlike almost all of the other ones, actually fits the past temperature data. However, it predicts a large temperature difference between the Northern and Southern Hemispheres which is contrary to observation, and for its future predictions it appears to commit the same error as the rest of the models in assuming that carbon dioxide in the atmosphere is increasing by 1% a year. Since the current observed value is 0.34% a year, the predicted temperatures of this model should be divided by three.

Since the global temperature does not appear to be rising, advocacy groups are trying to find other climate phenomena which might be blamed on the greenhouse effect. Unfortunately, there is little or no theoretical justification of most of these claims.

Vincent Gray, Wellington