Researchers at the UK Meteorological Office fed the longest continuous series of temperature measurements made by instruments anywhere in the world -- dating back to 1659 -- into computer climate models to reveal that greenhouse gas emissions are definitely linked to rising temperatures. The measurements were recorded at three sites in central England and showed that the average temperature in 1950 was about 9.4 degrees Celsius and is now about 10.4 C. According to David Karoly of the University of Oklahoma in the United States and Peter Stott of the UK's Hadley Centre, the probability that this rise was part of a natural cycle was less than 5%. When they introduced the factor of greenhouse gases produced by human activities into their computer model, it reproduced the observed temperatures almost exactly.