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Wednesday 23 April 2008

RAPID ROUNDUP: Is a lack of sun spots about to cause an ice age?

It has been reported in The Australian that according to geophysicist Phil Chapman, a lack of sun spot activity is causing global cooling. Here, Australian scientists and solar experts comment on the article and the role of the sun in determining global climate. The AusSMC has also prepared a resource page that helps clarify the confusion over recent cooling and includes an analysis of the issue by Robert Fawcett and David Jones at the National Climate Centre within the Bureau of Meteorology.

A number of Australian scientists are available for media interviews. If you wish to speak to an expert, don’t hesitate to contact the AusSMC on (08) 8207 7415. Feel free to use this quote in your stories.

Professor David Karoly is from the School of Earth Sciences, University of Melbourne and a lead author on the IPCC WG2 report. To read his full comment see our Science Blog page.

"The opinion piece written by Phil Chapman appears to have a number of factual errors, incorrect conclusions, and misleading statements. It is true that data sets show a pronounced cooling from January 2007 to January 2008 of a little less than 0.7C. It is an error to state that this is unprecedented, as similar dramatic falls occurred from 1998 to 1999, and from 1973 to 1974. So what caused this rapid cooling, what was common to all those periods?

In each case, the common factor was a rapid change from El Nino to La Nina conditions, warm temperatures in the eastern equatorial Pacific Ocean to cold temperatures in the same region, which has a major effect on global climate patterns and global average temperature. La Nina is associated with below normal global average temperature, and 2008 is likely to be about 0.3C cooler than the average of the previous few years, because of the influence of La Nina.

So, are variations in global average temperature directly related to sunspot numbers on a monthly, annual or decadal timescale? Certainly not on a monthly timescale and the effect, if any, on a year-to-year time scale is very small.

The major flaw in this opinion piece is trying to infer understanding of long-term climate trends from short term (one year) variations of global temperature.  It is well known (by climate scientists) that there are very large interannual variations of global temperature caused by a number of factors, including El Nino, or major volcanic eruptions, or just the chaotic variability of the climate system. It is not possible to make conclusions about long term climate trends from interannual climate variations. 

There has been a clear warming trend in global average temperature over the last 100 years, with most of this warming due to the increase in greenhouse gases in the atmosphere. This long-term increase in global average temperature will continue throughout the 21st century due to increasing concentrations of greenhouse gases in the atmosphere."

Professor Paul Cally is Professor of Solar Physics at the Centre for Stellar and Planetary Astrophysics at Monash University, Victoria.

“We tend to think of the Sun as a constant, but it is certainly not that! Solar activity varies hugely on the approximately 11-year sunspot cycle, but the strength of these cycles itself changes over the centuries. The gradual increase in solar activity through the first six decades of the 20th century is thought to have contributed up to 30% to global warming. Carbon 14 studies reveal that the Sun spent only around 10% of the last 11,400 years at such high activity levels as in the last 70 years, and very rarely for such an extended period. Conversely, the famous Maunder minimum (1645—1715) saw sunspots almost disappear from the solar surface, and coincided with the Little Ice Age in Europe and North America, when even the Thames in London regularly froze over.

But it is important to realise that in the second half of the 20th century, CO2 and other greenhouse gases in the Earth's atmosphere took over as the dominant driver of global warming. It is unlikely that even a repeat of the Maunder minimum (which will certainly happen someday) would reverse this anthropogenic effect, let alone produce a little ice age, until greenhouse gases are reduced significantly.

In any case, month-to-month or even year-to-year variations in solar activity have little effect on the Earth's climate. Only variations over several successive sunspot cycles can influence climate, though even then the exact mechanisms are not clear.”