Feature

Greenhouse Cause And Effect

Rising carbon dioxide levels and global warming are related, but there's confusion as to which is cause and which is effect.

By P. A. Toynbee

Many people are unable to distinguish between global warming and the greenhouse effect. Global warming refers to the increase in the average global temperature. This might be of natural origin, or the result of human interference with the environment. Human-derived greenhouse warming is only one factor in the broader field of global warming.

In the past there have been increases in global temperature considerably greater than the current one, and at times when human interference could not have been the cause.

Global temperatures have been increasing since at least 1970 or so. Carbon dioxide (CO₂) levels in the atmosphere have been steadily increasing since at least 1958, when measurements began. Statistical analysis of these two increasing factors cannot help but show a correlation over recent years.

A scientific paper was published recently in Nature looking at variations in the global temperature and in atmospheric CO₂ levels. The paper concluded that these two factors can be significantly correlated over the past 30 years. Almost as an afterthought, the synopsis stated "changes in carbon dioxide content lag those in temperature by five months".

If, as is claimed, increased global temperatures were brought about by the increase in atmospheric CO₂, then variations in the latter would have to precede changes in the former. Yet it's casually mentioned as being the other way round.

It is well recognised that global temperatures decreased between 1940 and 1970, while CO₂ levels kept increasing. After that, temperatures started rising again. The increase in CO₂ was reasonably linear until about 1970, but has been accelerating since then.

This leads to the suggestion that the recent higher rate of CO₂ increase could be the result of a natural increase in global warming. The amount of CO₂ in the atmosphere is about 2,600 billion tonnes. The amount trapped in the oceans is 125,000 billion tonnes, or almost 50 times as much. As global temperatures rise, the solubility of CO₂ in the oceans decreases, and the gas is released into the atmosphere.

If global temperatures and atmospheric CO₂ levels are co-dependent, the way in which CO₂ variations lag behind temperature variations suggests that the increase in the "greenhouse gas" is the result, not the cause, of increasing global temperatures.

This may well provide an answer to many of the inconsistencies that scientists cannot explain at present.

Fellow of the Institute of Energy (UK), Peter Toynbee has spent a working life in energy research, with 20 years as director of the Coal Research Association.