Brussels, 23 Jun 2006
According to a new report from the US National Research Council, scientists are now able to say with a high level of confidence that the last few decades of the 20th century were warmer than any other period in the last 400 years.
The report, 'Surface Temperature Reconstructions for the last 2,000 Years', was requested by the US Congress following controversy over an earlier piece of research by climatologist Michael Mann. Mr Mann and his colleagues concluded that the high temperatures recorded in the late 20th century were unprecedented in the last thousand years. Their graph showing a sharp rise in temperatures after a long period of relative stability became known as the 'hockey stick'.
Records of temperatures based on measurements by instruments only go back around 150 years, meaning climatologists have to use proxies to estimate temperatures from before this time. Proxies used include evidence from tree rings, retreating glaciers, corals, ocean and lake sediments, ice cores, and documentary sources such as old drawings of glaciers.
The Committee that wrote the report found that there was sufficient evidence from proxies to say that the last few decades of the 20th century were warmer than any comparable period in the last 400 years. They also note that the proxy data accurately reflects the 0.6 degrees Celsius warming recorded by instruments over the last century.
However, proxy data from before 1600 is relatively scarce, especially in the southern hemisphere. For this reason, the Committee agreed that while Mr Mann's conclusion about the temperatures in the period before 1600 are plausible, they cannot currently be confirmed with great certainty.
On the question of whether global warming is influenced by human activities, the report underlines the fact that surface temperature reconstructions for periods before the Industrial Revolution are only one of many lines of evidence supporting the conclusion that current warming is occurring in response to human activities, and they are not the primary evidence.
The Chair of the Committee is Gerald R North of Texas A&M University. Presenting the report, he called for greater access to datasets, to help further future research. 'Peers should have access to the information needed to reproduce published results, so that increased confidence in the outcome of the study can be generated inside and outside the scientific community,' he said. 'Paleoclimate research would benefit if individual researchers, professional societies, journal editors, and funding agencies continued their efforts to ensure that existing open access practices are followed.'
Meanwhile there was bad news for European efforts to reduce greenhouse gas emissions, as the European Environment Agency (EEA) released the EU's inventory report to the United Nations Framework Convention on Climate Change (UNFCCC). According to the report, greenhouse gas emissions in the EU rose by 18 million tonnes (0.4 per cent) between 2003 and 2004. The sectors with the largest increases were industry and transport. The only countries which actually managed to reduce their greenhouse gas emissions from 2003 to 2004 were Germany, Denmark and Finland.