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N hemisphere hottest in 1,300 yrs

world Updated: Oct 06, 2008 19:22 IST

The past decade in the northern hemisphere was the hottest in 1,300 years, scientists said.

The research was based on the makeup of corals, sediment and ice. Information on tree rings was not included in the research, otherwise the past decade would have been called the hottest in past 1,700 years.

Global surface temperatures have increased about 0.740C (plus or minus 0.180C) since the late-19th century, and the linear trend for the past 50 years of 0.130C (plus or minus 0.030C) per decade is nearly twice that for the past 100 years, according to the National Oceanic and Atmospheric Administration website.

The warming has not been globally uniform. The recent warmth has been greatest over North America and Eurasia between 40 and 700N. Lastly, seven of the eight warmest years on record have occurred since 2001 and the 10 warmest years have all occurred since 1995, it said.

Human activity has been increasing the concentration of greenhouse gases in the atmosphere. The global concentration of CO2 in our atmosphere today far exceeds the natural range over the last 650,000 years of 180 to 300 parts per million by volume (ppmv). According to the IPCC Special Report on Emission Scenarios (SRES), by the end of the 21st century, we could expect to see carbon dioxide concentrations of anywhere from 490 to 1260 ppm (75-350% above the pre-industrial concentration), the website said.

Although it is difficult to connect specific weather events to global warming, an increase in global temperatures may in turn cause broader changes, including glacial retreat, Arctic shrinkage, and worldwide sea level rise.