Northern Hemisphere Temperature Hits 2,000 Year High
NORWICH, United Kingdom, September 2, 2003 (ENS) - The Earth's Northern Hemisphere has been hotter since 1980 than at any time during the past 2,000 years, according to a comprehensive study of the planet's surface temperature by an international team of scientists.
Climate scientists Philip Jones of the University of East Anglia's Climatic Research Unit in the UK and Michael Mann of the University of Virginia, published a study in the August issue of the journal "Geophysical Research Letters," showing that late 20th century temperatures for the Northern Hemisphere are unprecedented for at least "roughly the past two millennia."
The two professors reconstructed the global climate back to the time of the pre-Christian era through a complex series of investigations.
They studied ice cores and rings in the trunks of ancient trees formed before humans kept climate records, and added historical records from more recent times in the Netherlands, Switzerland and China to their data.
Mann and Jones analyzed cores from the icecaps of Antarctica and Greenland drilled down through the ice and snow of 2,000 years, analyzing the air bubbles contained in these cores for information about the climate at the time the ice was formed.
They utilized paleoclimatic data gathered from China, Peru, Tasmania, and from Chesapeake Bay in the United States to compile a picture of prehistoric temperatures.
When all the data sets were compiled, the results supported the conclusion that human activities are responsible for a warming of the planet that amounts to at least 0.2 Celsius, or .36 degrees Fahrenheit over the past 20 years.
"You can't explain this rapid warming of the late 20th century in any other way," Jones told BBC News Online, "It's a response to a buildup of greenhouse gases in the atmosphere."
But some scientists, such as Dr. Sallie Baliunas at the Harvard-Smithsonian Center for Astrophysics, believe the Earth's complex climate system works in ways not yet understood. "No reliable evidence for a catastrophic human warming trend can be found in the best temperature data available," she said.
"You have to aggregate the records together, as we've done," said Jones. "We'd like more records, especially from the tropics - but we do think we have enough information to say the world is now warmer than it's been for 2,000 years."
Jones and Mann's findings underline the most recent report from the Intergovernmental Panel on Climate Change, which wrote in 2001, "The increase in surface temperature over the 20th century for the Northern Hemisphere is likely to have been greater than that for any century in the last thousand years."
Their research also supports a July report from the UK Meteorological Office's Hadley Centre for Climate Prediction and Research. Dr. Peter Stott, who leads the team at the Hadley Centre, said July 28, "The continental warming of the past few decades cannot be explained by natural factors such as solar changes, volcanoes or natural variability. But once we factor in the effects of human activity, we find we can explain the warming that is observed. "
Mann and Jones' research was financially supported by the National Science Foundation and the Earth Systems History program sponsored by the National Oceanic and Atmospheric Administration, as well as the U.S. Department of Energy Office of Science.