Clean air trapped in polar ice from pre-industrial times is being used to measure the impact of greenhouses gases on the modern world.
A paper in the journal Nature Geoscience shows how the sensitivity of the Earth’s land biosphere to changes in temperature impacts the cycles of carbon between land, ocean and the atmosphere.
About half of the carbon dioxide emitted by human activities since 1850 has been taken out of the atmosphere by the land biosphere and the ocean.
How these sinks will behave in the future has been a significant source of uncertainty in climate projections.
The paper shows the Earth’s land biosphere takes up less carbon in a warmer climate.
Australian scientists are now drilling for ice cores from which pre-industrial era air can be extracted:
“Until now it has only been assumed that as the Earth’s surface warms the ability of land-based plants to store carbon is reduced,” says paper co-author and CSIRO senior scientist David Etheridge.
“In this study we were able to quantify the relationship. Reduced storage of carbon by the biosphere leads to higher atmospheric CO2.
“This increases the Earth’s surface temperature, which leads to even less carbon stored by the biosphere, causing a positive feedback.”
The research team measured air trapped in ice core samples from the Australian Antarctic Program’s Law Dome site where past atmospheric composition is preserved in fine detail, together with ice cores from the British Antarctic Survey.
The research focused on CO2 changes preserved in ice before, during, and after a naturally-cool period known as the Little Ice Age (1500 to 1750 AD).
The study shows that for every degree celsius of global temperature rise, the equivalent of 20 parts per million less CO2 is stored by the land biosphere.
How plants and soils respond to warming is one of the big unknowns in climate projections.
The paper is a result of a collaboration between CSIRO, the Seconda Universita di Napoli, University of Melbourne, British Antarctic Survey, University of East Anglia, Australian Antarctic Division, University of Tasmania and the Australian Nuclear Science and Technology Organisation.
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