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High concern

High concern signatures of the past, embedded deep inside polar ice, reveal that the current levels of greenhouse gases, such as carbon dioxide (co2) and methane, are the highest over the last 650,000 years.

An international team of scientists studied air bubbles trapped in cylindrical pieces drilled from a depth of up to 3,200 metres in the Antarctic ice sheet, as part of the ongoing European Project for Ice Coring in Antarctica (epica). They say co2 concentration has never exceeded 290 parts per million (ppm) over the past 650,000 years, which has had eight ice ages with fairly long warm periods in between. Today, co2 concentrations hover around 375 ppm. The finding punctures the claim of climate change sceptics that increasing greenhouse gas levels have more to do with natural climatic variations than with human-made changes.

epica is located in east Antarctica where low snowfall rates allow extremely old sections of ice to be accessed. About 10 per cent of an ice core's volume consists of air bubbles that contain clues about the planet's climatic history.

The findings also confirmed that co2 levels have risen 200 times faster over the last 50 years than at any other time in 650,000 years, says Thomas Stocker, a University of Bern physicist and the lead author of the study that appeared in Science (Vol 310, No 5752, November 25, 2005). The study extends the time period for which data is available by 210,000 years. The earlier ice cores drilled from Russian-controlled Vostok station in Antarctica gave information about the last 440,000 years.

The situation is similar for methane: its levels hovered around 600 parts per billion (ppb) in the past. But today's atmospheric methane concentration is well over 1,700 ppb.

Stocker attributes the high levels of greenhouse gases to the large global use of fossil fuels. "Only through the impact of humans have greenhouse gases been raised above natural levels,' says Hubertus Fischer of the Alfred Wegener Institute in Germany.

Another study, which appeared in Nature (Vol 438, No 7066, November 17, 2005), predicted severe water scarcity due to global warming. Globally, glaciers and storage packs of snow will shrink, causing water shortages and other problems that will impact millions of people, say researchers from Scripps Institution of Oceanography at the University of California, San Diego, and from University of Washington, both in the us.

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