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To ask Her Majesty's Government whether the rate of increase in global mean surface temperatures between 1975 and 1998 was similar to the rates of increase observed between 1860 and 1880 and between 1910 and 1940; and, if so, what the implications are for their policy on anthropogenic warming.
Observations collated at the Met Office Hadley Centre and the University of East Anglia Climate Research Unit indicate that the rate of increase in global average surface temperature between 1975 and 1998 was similar to the rates of increase observed between 1860 and 1880 and between 1910 and 1940 (approximately 0.16 degrees centigrade per decade). This observation has no implications for our policy on anthropogenic warming.
Little can be deduced from relatively short periods in the temperature record taken in isolation from the overall picture. Temperatures fluctuate in response to both man-made factors (such as emissions of greenhouse gases) and natural factors (such as volcanic eruptions, changes in solar activity and internal variability within the climate system), and different combinations of these factors can cause temperatures to change at similar rates for limited periods of time. In its assessment of the whole global temperature record from 1860, the IPCC, in its fourth assessment report, concluded that it is very likely (more than 90 per cent chance) that greenhouse gas emissions were responsible for most of the warming over the past 50 years, and likely (more than more than 66 per cent chance) that greenhouse gases caused some of the warming during the early 20th century. The IPCC also showed that in the absence of actions to limit greenhouse gas emissions, temperatures will continue to rise through the 21st century by between 1.8 and 4 degrees centigrade. This raises the prospect of dangerous levels of climate change, which the Government remain committed to avoid through concerted international and domestic actions to reduce greenhouse gas emissions. Short-term fluctuations in the historic temperature record have no implications for this policy.