Contribution of increasing CO2 and climate to carbon storage by ecosystemsin the United States

The effects of increasing carbon dioxide (CO2) and climate on net carbon st orage in terrestrial ecosystems of the conterminous United States for the p eriod 1895-1993 were modeled with new, detailed historical climate informat ion. For the period 1980-1993, results from an ensemble of three models agr ee within 25%, simulating a land carbon sink from CO2 and climate effects o f 0.08 gigaton of carbon per year. The best estimates of the total sink fro m inventory data are about three times larger, suggesting that processes su ch as regrowth on abandoned agricultural land or in forests harvested befor e 1980 have effects as large as or larger than the direct effects of CO2 an d climate. The modeled sink varies by about 100% from year to year as a res ult of climate variability.