Mayflies and tree rings point to global warming

Three separate observations published today in the journal Nature reveal the growing strength of the case for man-made global warming, writes Steve Connor.

Norwegian scientists have found that the Arctic ice sheets are now shrinking faster than at any time since 1978, British researchers say the 20th century is the warmest for 1,000 years, and a naturalist reports that mayflies are hatching earlier. All believe the evidence is strongly in favour of climate change.

Keith Briffa, a climatologist at the University of East Anglia, says research on Siberian trees, which grow wider rings and denser wood in warm summers, shows that this century has been the warmest since AD914. The first 90 years of this century were about 0.6C hotter than the average summer temperature of the past 1,000 years, and 0.1C above the next warmest century, from 1202-1291. "We're on the boundary of what we'd expect by chance, he said."

James Stawell, an amateur naturalist, says a gamekeeper who fished the same stretch of river as him wrote at the turn of the century that the first week of June was the best time to see mayflies, but now it is between 21 and 28 May - "Some 10 days earlier".