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The Carbon Balance of the Terrestrial Biosphere: Ecosystem Models and Atmospheric Observations
Author(s) -
Prentice I. Colin,
Heimann Martin,
Sitch Stephen
Publication year - 2000
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/1051-0761(2000)010[1553:tcbott]2.0.co;2
Subject(s) - biosphere , environmental science , ecosystem , terrestrial ecosystem , ecology , carbon cycle , biosphere model , balance (ability) , carbon fibers , carbon flux , earth science , biology , geology , materials science , neuroscience , composite number , composite material
Precise measurements in air are helping to clarify the fate of CO 2 released by human activities. Oxygen‐to‐nitrogen ratios in firn (the transition state from snow to ice) and archived air samples indicate that the terrestrial biosphere was approximately carbon‐neutral on average during the 1980s. CO 2 release by forest clearance during this period must have been compensated for by CO 2 sinks elsewhere on land. Direct atmospheric O 2 :N 2 measurements became available during the 1990s. These measurements indicate net terrestrial CO 2 uptake of ∼2 Pg C/yr. From the north–south O 2 :N 2 gradient, it has been inferred that about this amount was taken up by terrestrial ecosystems in the northern nontropics while additional CO 2 released by tropical‐forest clearance must have been compensated for by additional, tropical, terrestrial CO 2 sinks. These and other atmospheric observations provide independent tests of carbon‐cycle reconstructions made with process‐based terrestrial ecosystem models. Such models can account for major features of the atmospheric‐CO 2 record, including the amplitude and phase of the seasonal cycle of atmospheric‐CO 2 concentration at different latitudes, and much of the interannual variability in the rate of increase of atmospheric CO 2 . Models also predict direct effects of rising atmospheric‐CO 2 concentration on primary production, modified by feedbacks at the plant and ecosystem levels. These effects translate into a global carbon sink the right order of magnitude to compensate for forest clearance during the 1980s. The modeled sink depends on continuously increasing CO 2 to maintain disequilibrium between primary production and carbon storage. There are still substantial differences among the carbon‐balance estimates made by different models, reflecting limitations in current understanding of ecosystem‐level responses to atmospheric‐CO 2 concentration, especially with regard to the interactions of C and N cycling and interactions with land‐use change. Scenario calculations nevertheless agree that if atmospheric CO 2 continues its rise unchecked then the terrestrial sink will start to decline by the middle of the next century, for reasons including saturation of the direct CO 2 effect on photosynthesis.