Weather stations which produced data pointing towards man-made global warming may have been compromised by local conditions, a new report suggests. The findings are set to cast further doubt on evidence put forward by the UN's Intergovernmental Panel on Climate Change (IPCC) which claims the science supporting rising temperatures is unequivocal.
The report co-written by Anthony Watts, an American meteorologist and climate sceptic, shows photographs of weather stations near heat-generating equipment which could be distorting their readings.
Some are next to air-conditioning units or on waste-treatment plants, while one sits alongside a waste incinerator. A weather station at Rome airport was found to catch the hot exhaust fumes emitted by taxiing jets.
Rising temperatures around the stations, which have been in use for 150 years, could also have been caused by urbanisation, the study claimed. One weather station at Manchester airport, which was built when the surrounding land was mainly fields, is now surrounded by heated buildings.
The IPCC used data from the weather stations to back up claims that greenhouse gases had already caused a 0.7C rise in temperature, and gave warnings that further warming of up to 6C by 2100 could have devastating effects on civilisation and wildlife.
But the panel has been mired in controversy since the leaking of emails from the climate change unit at The University of East Anglia, which appeared to show that data used to bolster the IPCC's claims had been manipulated.
Four major errors have also been uncovered in the second of the panel's four reports on the state of global climate change, published in 2007.
Most embarrasing for the IPCC was the inaccurate claim that the Himalayan glaciers would disappear by 2035 - hundreds of years earlier than other studies suggest - which was not backed up by any research.
The damaging new findings by Mr Watts, whose study has not been peer reviewed, are backed by Professor John Christy, a former lead author on the IPCC who specialises in atmospheric science at the University of Alabama, Huntsville.
Prof Christy has published research papers examining the effects of local factors on weather stations in California, Alabama and east Africa, which he believes drastically undermine the reliability of global temperature records.
"The story is the same for each one. The popular data sets show a lot of warming but the apparent temperature rise was actually caused by local factors affecting the local weather stations, such as land development," he said.