The northern hemisphere is experiencing its warmest and most widespread climatic episode in the last 1,200 years, a study by University of East Anglia has found. The last time such conditions were noted was in 800 AD.
“Our results show that, during the late 20th century, warming affected the entire northern hemisphere and that at no point in the past 1,000 years has the northern hemisphere experienced the same widespread warming,” said Dr Timothy Osborn, one of the two researchers involved in the study.
Under the study, Osborn and his colleague Keith Briffa studied 'proxy climate records' like rings around trees, fossils and ice cores in 14 regions from the world over. An analysis of these records indicated the change in the local environment in that region over a period of time. The findings showed that the medieval warm period existed between 890 and 1170 and a major cooling period, called 'little ice age', followed between 1580 and 1850.
“The key conclusion was that the 20th century stands out as having unusually widespread warmth, compared to all of the natural warming and cooling episodes during the past 1,200 years,” Osborn said.
'Proxy climate records' are used widely to accurately determine the climate of previous centuries. In the new study, the researchers studied these records from regions like America, Europe and East Asia, covering wide bases in each region.
In 10 of the records, tree rings, which not only indicate the age of a tree but also the climatic changes it has weathered over the years, were studied. Greenland's ice cores, which are samples of ice extricated from an ice sheet, were another kinds of records taken into consideration. Since ice is a result of the incremental buildup of yearly snow layers, the ice layers in the lower part are older than the top layers and contain ice from previous years and centuries, indicating the climatic conditions of the years in they were formed.
They also contain impurities like dust, ashes and atmospheric gases and radioactive substances indicating the environment that existed then. The records from China and Japan included historical data as well as ice cores. Old diaries, some as old as 750-years old, of several people were also scrutinized to reconstruct the climate they were living in.
“These (proxy) records extend over many centuries and even thousands of years. We simply counted how many of those records indicated that, in any one year, temperatures were warmer than average for the region they came from,” Osborn said.
Hailing the study, Michael E Mann of the Earth System Science Center at the Pennsylvania State University said, “The field has come a long way, growing increasingly more rigorous in recent decades. There is enough information now to draw reasonably robust conclusions.”
But John Waterhouse of the Environmental Sciences Research Center of Anglia Ruskin University in Cambridge was skeptical about the findings of the study. According to him, there was little climate data to compare today's weather with that of previous centuries. “There's much uncertainty in past reconstructions. You've got to look at the reconstructed data in the past in light of the likely errors that those data have,” he said. Waterhouse, however, conceded that the growing heap of evidence does indicate that the “current period is the warmest for over 1,000 years”.
Mann added that the study reinforces that global warming is a reality and very much happening. “This latest paper might be the nail in the coffin for the small minority of very vocal climate change denialists who continue to challenge the conclusion that the recent warming of the Earth's surface is out of the ordinary,” he said.
The findings of the study have been published in the journal
Science.
