Warming trend has not been reversed, page 1

Warming trend has not been reversed

www.theaustralian.news.com.au

THE opinion piece by Phil Chapman ("Sorry to ruin the fun, but an ice age cometh", Opinion, April 22) warns of an approaching ice age but contains a number of factual errors, misleading statements and incorrect conclusions.

Chapman reports global average temperature cooled by 0.7C in 2007 and says: "If the temperature does not soon recover, we will have to conclude that global warming is over."

It is true that global data sets show a pronounced cooling from January2007 to January 2008 of slightly less than 0.7C. It is an error to state, as Chapman does, that this is unprecedented, as similar dramatic falls occurred from 1998 to 1999, and from 1973 to 1974. It should also be noted that the global average temperature has warmed substantially, by about 0.3C from January 2008 to March 2008. In addition, the annual average temperature for 2007 was within 0.1C of the average temperature in 2006 and 2005; no dramatic cooling there.

So what caused this rapid cooling during 2007, and also from 1998 to 1999, and from 1973 to 1974? What was common to all those periods? In each case, the common factor was a rapid change from El Nino to La Nina conditions, from warm temperatures in the eastern equatorial Pacific Ocean to cold temperatures in the same region, which has a significant effect on global climate patterns and global average temperature. La Nina is associated with below-normal global average temperature, and because of its influence, 2008 is likely to be about 0.3C cooler than the average of the previous few years.

Chapman did not consider La Nina as a cause of the cooling in 2007 and instead linked it to the minimum in the 11-year cycle in sunspot numbers: "The first sunspot appeared in January this year and lasted only two days. A tiny spot appeared last Monday but vanished within 24 hours. Another little spot appeared this Monday."

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