A Large Terrestrial Carbon Sink in North America Implied by Atmospheric and Oceanic Carbon Dioxide Data and Models

Abstract

Atmospheric carbon dioxide increased at a rate of 2.8 petagrams of carbon per year (Pg C year-1) during 1988 to 1992 (1 Pg = 10(15) grams). Given estimates of fossil carbon dioxide emissions, and net oceanic uptake, this implies a global terrestrial uptake of 1.0 to 2. 2 Pg C year-1. The spatial distribution of the terrestrial carbon dioxide uptake is estimated by means of the observed spatial patterns of the greatly increased atmospheric carbon dioxide data set available from 1988 onward, together with two atmospheric transport models, two estimates of the sea-air flux, and an estimate of the spatial distribution of fossil carbon dioxide emissions. North America is the best constrained continent, with a mean uptake of 1.7 +/- 0.5 Pg C year-1, mostly south of 51 degrees north. Eurasia-North Africa is relatively weakly constrained, with a mean uptake of 0.1 +/- 0.6 Pg C year-1. The rest of the world's land surface is poorly constrained, with a mean source of 0.2 +/- 0.9 Pg C year-1.

Towards robust regional estimates of CO2 sources and sinks using atmospheric transport models

“…et al, manuscript in preparation). Second, we ®nd carbon uptake over the continents of the Northern Hemisphere to be distributed relatively evenly across North America, Europe and Asia, in contrast to the distribution found in an earlier, widely cited inverse study 2 . We ®nd a temperate North American sink approximately 60% of that found in the earlier study, a small boreal North American source rather than small uptake, and a large sink for Eurasia rather than an approximately neutral¯ux.…”

“…Here we report estimates of surface± atmosphere CO 2¯u xes from an intercomparison of atmospheric CO 2 inversion models (the TransCom 3 project), which includes 16 transport models and model variants. We ®nd an uptake of CO 2 in the southern extratropical ocean less than that estimated from ocean measurements, a result that is not sensitive to transport models or methodological approaches. We also ®nd a northern land carbon sink that is distributed relatively evenly among the continents of the Northern Hemisphere, but these results show some sensitivity to transport differences among models, especially in how they respond to seasonal terrestrial exchange of CO 2 .…”

Temperature sensitivity of soil respiration and its effects on ecosystem carbon budget: nonlinearity begets surprises

“…For example, based on three ecosystem process models (Biome-BGC, Century, and TEM), Schimel et al (2000) estimated that the conterminous USA was a net carbon sink during the period from 1980 to 1993, taking up 0.08 Pg C yr − 1 on average. This was in contrast with some previous estimates (Fan et al, 1998;Brown and Schoeder, 1999). This estimated carbon sink can turn into a net carbon source if the uncertainty of temperature sensitivity of soil respiration (q) is considered.…”

A dynamic global vegetation model for studies of the coupled atmosphere‐biosphere system

“…Carbon sequestration and release by terrestrial vegetation played an important role in past climate changes, and feedback loops involving climate, greenhouse gas concentrations, and vegetation in the next century have been identified [Douville et al, 2000;Cox et al, 2000;Friedlingstein et al, 2001]. On the other hand, at least during the last decades, the biosphere seems to have been acting as a sink for a part of the human emissions of greenhouse gases, with the identification of the sink regions being a field of intensive research [e.g., Fan et al, 1998;Bousquet et al, 2000]. Understanding interannual variability and secular changes of global carbon fluxes and stocks is a primary research goal in this respect.…”