The sceptical view  - the challenge to conventional wisdom

While the consensus on the impact of greenhouse gases on global temperatures and the climate is shared among thousands of scientists and opinion formers, some still remain sceptical about the evidence.    

For example, Nigel Lawson, former UK Chancellor of the Exchequer, describes the IPCC as "something like a politically correct alarmist pressure group". He says that while the global temperature rose about half a degree during the last quarter of the 20th century, recorded temperature figures from the UK’s Hadley Centre, part of the Meteorological Office, for the first seven years of the 21st century reveal there has since been a “standstill”. "Global warming ... is not at the present time happening", he says.  The Hadley Centre has responded[1] that while the climate shows large variability year-on-year, there is an underlying rise over the longer term which is “almost certainly caused by emissions of greenhouse gases”.  The centre points to natural factors that contribute to variability, particularly the ‘El Niño’ Southern Oscillation.  The global climate is now being influenced by the cold phase of this oscillation, known as La Niña, which is cooling the global average temperature. An all-time high average temperature in 1998 has been followed by a series of years with lower average temperatures. However, despite this, as the IPCC observes, 11 of the 12 years from 1995 to 2006 were among the 12 warmest years since global records began in 1850.

Sceptics and questioners also point out that the climate is always changing. For example they cite the warm period that is recorded in mediaeval times and evidence for vineyards in Roman Britain.  However leading experts such as Sir John Houghton, who edited several IPCC reports and was Chief Executive of the UK Meteorological Office, contest the idea that changes in global average temperature over the last 50 years and as projected for the 21st century are within the range of natural climate variability as observed over the last few millennia.  Sir John says the IPCC concluded that ‘Paleoclimate information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1300 years.’

Another challenge to the conventional wisdom is that climate change is driven by solar activity. Scientists who support the IPCC agree that the sun’s behaviour does influence the climate. For example, it’s accepted by many that changes in solar output and the absence of large volcanoes are likely to have been causes for the rise in temperature between 1900 and 1940. However, scientists such as Houghton say that observations of the sun from space instruments over the past 40 years demonstrate that such influences cannot have contributed significantly to the temperature increase over the later period. Cosmic rays affecting cloud formation have also been very carefully considered by the IPCC but there is no evidence that they are significant compared with the impacts of greenhouse gases such as carbon dioxide. Direct measurements of solar output since 1978 show a steady rise and fall over the 11-year sunspot cycle but no clear upwards or downwards trend.

A television documentary, The Great Global Warming Swindle, aired in 2007, said that the wide consensus on climate change was the product of "a multibillion-dollar worldwide industry: created by fanatically anti-industrial environmentalists; supported by scientists peddling scare stories to chase funding; and propped up by complicit politicians and the media.” In response Martin Rees, President of the Royal Society, said: “ Those who promote fringe scientific views but ignore the weight of evidence are playing a dangerous game. They run the risk of diverting attention from what we can do to ensure the world's population has the best possible future.”