One of the most important sources of data about the correlation between greenhouse gases (like methane and carbon dioxide) and global warming has been core samples from the ice in Antarctica. Tiny bubble of gas are dropped in the ice and they offer evidence of the composition of the atmosphere over thousands of years. Earlier this week, Nature published a study of ice core date going back about 800,000 years. Critical to the current debate on climate change, there is a strong correlation between greenhouse gases and temperature going that far back:
The newest analysis of trace gases trapped in Antarctic ice cores now provide a reasonable view of greenhouse gas concentrations as much as 800,000 years into the past, and are further confirming the link between greenhouse gas levels and global warming, scientists reported May 14 in the journal Nature.
They also show that during that entire period of time, there have never been concentrations of carbon dioxide and methane as high as the current levels, said Edward Brook, an associate professor of geosciences at Oregon State University, and author of a Nature commentary on the new studies.
"The fundamental conclusion that today's concentrations of these greenhouse gases have no past analogue in the ice-core record remains firm," Brook said in the report. "The remarkably strong correlations of methane and carbon dioxide with temperature reconstructions also stand."
The latest research, done by members of the European Project for Ice Coring in Antarctica, extend the data on trace gases back another 150,000 years beyond any studies done prior to this, Brook said. Ultimately, researchers would like to achieve data going back as much as 1.5 million years.
The tiny bubbles of ancient air trapped in polar ice cores have been used to provide records of trace gases in the atmosphere at distant points in the past, and better understand the natural fluctuations that have occurred, largely as a result of cyclical changes in Earth's orbit around the sun.
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According to the data, the current levels of primary greenhouse gases -- those that are expected to cause global warming - are off the charts.
The concentration of carbon dioxide is now a bit more than 380 parts per million, compared to a range of about 200-300 parts per million during the past 800,000 years. The current concentration of methane is 1,800 parts per billion, compared to a range of about 400-700 parts per billion during that time.
In every case during that extended period, warm periods coincide with high levels of greenhouse gases. Of some interest, the latest studies are showing that the temperature increases have been even more pronounced during the most recent 450,000 years, compared to several hundred thousand years prior to that.
"It appears there may even be very long term natural cycles that have operated on much longer periods of 400,000 years or more," Brook said. "We still have quite a bit to learn about these past cycles and all the forces that control them."
Read it all here.