What was done
The authors painstakingly analyzed the composition of air bubbles trapped in glacial ice cores retrieved from the Taylor Dome area of Antarctica, determined the ages of the trapped air samples, and analyzed the isotopic composition of the carbon in the air's carbon dioxide.  They then used these data to reconstruct the history of carbon exchanges among the atmosphere, oceans and land biota over the past 11,000 years.

What was learned
It was determined, with a precision that Ciais (1999) describes as "unprecedented," that the atmosphere's CO2 concentration at approximately 10,500 years before present (yr BP) was 268 ppm, that it fell to a value of 260 ppm at about 8,200 yr BP, and that it increased monotonically and "almost linearly" from that point in time to a value of 285 ppm 7,000 years later (about 1,200 yr BP).  The model calculations of the authors based on the carbon isotope data further revealed that the drawdown of atmospheric CO2 from 10,500 to 8,200 yr BP was consistent with terrestrial vegetative regrowth and soil build-up on areas previously covered by ice sheets, "as well as a climatic development towards the mid-Holocene optimum."  Thereafter, however, their results implied a gradual loss of terrestrial carbon over the next 7,000 years, which they suggested was likely "due to a change from the warmer and wetter mid-Holocene climate to colder and drier conditions."

What it means
These data clearly and convincingly demonstrate that the warm and moist period of the early Holocene has not been called the Holocene Climatic Optimum for nothing.  Indeed, this important paper shows that it was the premier period of terrestrial vegetative prowess of the present interglacial, and that earth's biosphere has been going steadily downhill ever since (or at least to the point of inception of the Industrial Revolution).  Even the 25 ppm increase in the air's CO2 content from 8,200 to 1,200 yr BP was not enough to stem the downward biological spiral induced by the slowly deteriorating climate.  But now, with an anthropogenically-induced rate of increase in atmospheric CO2 concentration that is two orders of magnitude greater, we can expect to see this situation reverse itself, as may readily be inferred from much of the material on our web site.

Reference