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Earth's Past Biospheric Productivity Inferred from Oxygen Isotopes in Greenland Ice Core
Luz, B., Barkan, E., Bender, M.L., Thiemens, M.H. and Boering, K.A.  1999.  Triple-isotope composition of atmospheric oxygen as a tracer of biospheric productivity.  Nature 400: 547-550.

What was done
The authors used a series of empirically-derived mathematical relationships to develop a model of the isotopic composition of oxygen trapped in air bubbles in a Greenland ice core to estimate global biospheric productivity over the past 82,000 years.

What was learned
The authors calculated that biospheric productivity at 18,000, 26,000, 37,000, 56,000 and 82,000 years before present was, respectively, 89%, 91%, 87%, 97% and 91% of what it is "currently," at a gas age of 150 years, when the atmospheric CO2 concentration was approximately 280 ppm.

What it means
Although there are a large number of assumptions in the authors' calculations, their results suggest that biospheric productivity for the planet as a whole is currently at its highest point of the past 82,000 years, as is the air's CO2 concentration.  Assuming that atmospheric CO2 concentration is the primary determinant of biospheric productivity, we thus calculate, based on the authors' mean results for all five of the points in time they investigated, that the 73 ppm increase (from 207 to 280 ppm) in the air's CO2 concentration between "then" and "now" produced a 9.9% increase (from a then/now productivity ratio of 0.91 to 1.00) in planet-wide biospheric productivity.  Further assuming a linear relationship between these two parameters, we calculate that a 300 ppm increase in atmospheric CO2 would thus be expected to produce an approximate 40% increase in biospheric productivity, which is essentially the mean experimentally-derived value of this CO2-growth response that has been derived from the thousands of studies that have evaluated this phenomenon for hundreds of earth's plants.

Is this a great coincidence?  Or is it a vindication of what Idso (1995) has been saying for so many years now - that atmospheric CO2 fuels the biosphere, and the more of this fuel you add to the air, the more productive is the total assemblage of life on earth?  Others may try to explain away this significant comparison; but we offer no apologies for it.  It is what it is.

Idso, S.B.  1995.  CO2 and the Biosphere: The Incredible Legacy of the Industrial Revolution.  Department of Soil, Water & Climate, University of Minnesota, St. Paul, MN.

Reviewed 15 August 1999