“The temperature records cannot be relied on as indicators of global change,” said John Christy, professor of atmospheric science at the University of Alabama in Huntsville, a former lead author on the IPCC.
The doubts of Christy and a number of other researchers focus on the thousands of weather stations around the world, which have been used to collect temperature data over the past 150 years.
These stations, they believe, have been seriously compromised by factors such as urbanisation, changes in land use and, in many cases, being moved from site to site.
Christy has published research papers looking at these effects in three different regions: east Africa, and the American states of California and Alabama.
“The story is the same for each one,” he said. “The popular data sets show a lot of warming but the apparent temperature rise was actually caused by local factors affecting the weather stations, such as land development.”