Renew On Line (UK) 26

Extracts from the May-June 2000 edition of Renew
These extracts only represent about 25% of it

10. Global Warming is Real

The warming trend in average global surface temperatures over the past two decades ''is undoubtedly real and is substantially greater than the average rate of warming during the 20th century,'' according to an 11-member panel of the US National Academy of Sciences.

The panel said global temperatures increased 0.45 to 0.72 degrees Fahrenheit over the past 20 years. By comparison, temperatures increased 0.72 to 1.44 degrees F over the entire 100-year period during which records of surface temperatures have been kept.

The panel attempted to resolve the long-standing dispute over the divergencies in temperature data from ground monitors, which have shown a sharp increase in Earth's temperatures, and satellite and weather balloon observations, which have shown little or no warming. While they say that this discrepancy cannot yet fully be explained, they concluded that it ''in no way invalidates the conclusion that the Earth's temperature has been rising.'' They argued that neither set of readings was necessarily wrong, but that it was not valid to equate these two kinds of observations: in any case satellite data was only available from 1979 and the surface data was seen as more reliable.

For example, most global warming is at night, and satellites aren't good at measuring nighttime temperatures near the ground, so the satellites may have have missed some of this trend. The panel also suggested that natural causes, including two major volcanic eruptions during the past 20 years, coupled with depletion of the ozone layer, may have had a cooling effect in the upper air region.

The US Environmental Defense Fund commented that the panels conclusion on this issue 'totally deflates the argument of the so-called skeptics who had used the apparent difference between ground-based and satellite data to argue that we really didn't know whether the world is warming or not.'

However, the panel still hedged on whether the warming of the Earth's surface will continue or whether it is caused by human activities. But in any case, the panel was at pains to point out that it had not been their aim to make comments on these issues- the 20-year record was, they felt, too short to make definitive statements as to how the atmosphere is changing in the long term, and their main concern was to respond to the disparity in surface and aerial data.

Readers may remember that at least part of this discrepancy had earlier been attributed to errors in the calibration of data from monitors in some satellites- no account had been taken of their decaying orbits. But the panel seem to think that the real issue was that the satellite data reflected divergent climate trends in the upper atmosphere and on the ground: there could be different processes underway in each zone.

* According to Dr Mike Hulme from the University of East Anglia’s Climate Research Unit , in recent climate events, like the storms in France and flooding in Mozambique, ‘we are witnessing events that are now clearly tainted by human actions’ (Observer 27/2/00)