New estimate based on the forthcoming upturn in solar activity and El Niño southern oscillation cycles is expected to silence global warming sceptics
- Duncan Clark
- guardian.co.uk, Monday 27 July 2009 15.39 BST
The world faces a new period of record-breaking temperatures as the sun's activity increases, leading the planet to heat up significantly faster than scientists had predicted over the next five years, according to a new study.
The hottest year on record was 1998, and the relatively cool years since have led to some global-warming sceptics claiming that temperatures have levelled off or started to decline. However, the new research firmly rejects that argument.
The work is the first to assess the combined impact on global temperature of four factors: human influences such as CO2 and aerosol emissions; heating from the sun; volcanic activity; and the El Niño southern oscillation, the phenomenon by which the Pacific Ocean flips between warmer and cooler states every few years.
It shows that the relative stability in global temperatures observed in the last seven years is explained primarily by the decline in incoming sunlight associated with the downward phase of the 11-year solar cycle, together with a lack of strong El Niño events. These trends have masked the warming caused by CO2 and other greenhouse gases.
As solar activity picks up again in the coming years, the new research suggests, temperatures will shoot up at 150% of the rate predicted by the UN's Intergovernmental Panel on Climate Change.
The research, to be published in a forthcoming edition of Geophysical Research Letters, was carried out by Judith Lean of the US Naval Research Laboratory and David Rind of Nasa's Goddard Institute for Space Studies. Lean said: "Our paper shows that the absence of warming observed in the last decade is no evidence that the climate isn't responding to man-made greenhouse gases. On the contrary, the study again confirms that we're seeing a long-term warming trend driven by human activity, with natural factors affecting the precise shape of that temperature rise."
Lean and Rind's research also sheds light on the extreme average temperature observed in 1998. The new paper confirms that the temperature spike of that year was caused primarily by a very strong El Niño episode. A similar episode occurring in the future could be expected to create a spike of equivalent magnitude on top of an even higher baseline, thus shattering the 1998 record.
Furthermore, the study comes within days of announcements from climatologists that the world is entering a new El Niño warm spell. This development suggests that temperature rises in the next year could be even more marked than Lean and Rind's paper suggests. A particularly hot autumn and winter could add to the pressure on policy-makers to reach a meaningful deal at December's climate-change negotiations in Copenhagen.
Bob Henson of the National Center for Atmospheric Research in Colorado said: "If El Niño continues to develop, it's quite possible that the Copenhagen meeting will take place during one of the warmest Decembers in the global record."
He added that the paper was a reminder that temperature patterns observed over periods of just a few years can be misleading when it comes to the bigger picture: "To claim that global temperatures have cooled since 1998 and therefore that man-made climate change isn't happening is a bit like saying spring has gone away when you have a mild week after a scorching Easter."
Temperature highs and lows
Hottest year of the millennium
Caused by a major El Niño event. The climate phenomenon results from warming of the tropical Pacific and causes heatwaves, droughts and flooding around the world. The 1998 event caused 16% of the world's coral reefs to die.
Most sunspots in a year since 1778
The sun's activity waxes and wanes on an 11-year cycle. The late 1950s saw a peak in activity and were relatively warm years for the period.
Coldest year of the millennium
Ash from the huge eruption the previous year of a Peruvian volcano called Huaynaputina blocked out the sun. The volcanic winter caused Russia's worst famine, with a third of the population dying, and disrupted agriculture from China to France.