<p>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. But new research firmly rejects that argument.<br /><br />The research, to be published in 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.<br /><br />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.<br /><br />The analysis shows the relative stability in temperatures 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.<br /><br />As solar activity picks up again in the coming years, the research suggests, temperatures will shoot up at 150 per cent of the rate predicted by the UN’s Intergovernmental Panel on Climate Change. <br /><br />Lean and Rind’s research also sheds light on the extreme average temperature in 1998. The paper confirms that the temperature spike that year was caused primarily by a very strong El Niño episode. <br /><br />A future episode could be expected to create a spike of equivalent magnitude on top of an even higher baseline, thus shattering the 1998 record.<br /><br />A new El Niño spell<br />The study comes within days of announcements from climatologists that the world is entering a new El Niño warm spell. This suggests that temperature rises in the next year could be even more marked than Lean and Rind’s paper suggests. <br />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 Centre for Atmospheric Research in Colorado, said: “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.”<br /><br />Temperature highs and lows<br />1998: Hottest year of the millennium<br />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 per cent of the world’s coral reefs to die.<br />1957: Most sunspots in a year since 1778<br />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.<br />1601: Coldest year of the millennium<br />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.</p>
<p>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. But new research firmly rejects that argument.<br /><br />The research, to be published in 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.<br /><br />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.<br /><br />The analysis shows the relative stability in temperatures 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.<br /><br />As solar activity picks up again in the coming years, the research suggests, temperatures will shoot up at 150 per cent of the rate predicted by the UN’s Intergovernmental Panel on Climate Change. <br /><br />Lean and Rind’s research also sheds light on the extreme average temperature in 1998. The paper confirms that the temperature spike that year was caused primarily by a very strong El Niño episode. <br /><br />A future episode could be expected to create a spike of equivalent magnitude on top of an even higher baseline, thus shattering the 1998 record.<br /><br />A new El Niño spell<br />The study comes within days of announcements from climatologists that the world is entering a new El Niño warm spell. This suggests that temperature rises in the next year could be even more marked than Lean and Rind’s paper suggests. <br />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 Centre for Atmospheric Research in Colorado, said: “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.”<br /><br />Temperature highs and lows<br />1998: Hottest year of the millennium<br />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 per cent of the world’s coral reefs to die.<br />1957: Most sunspots in a year since 1778<br />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.<br />1601: Coldest year of the millennium<br />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.</p>
