North America's net terrestrial CO<sub>2</sub> exchange with the atmosphere 1990–2009
Scientific understanding of the global carbon cycle is required for developing national and international policy to mitigate fossil fuel CO<sub>2</sub> emissions by managing terrestrial carbon uptake. Toward that understanding and as a contribution to the REgional Carbon Cycle Assessment...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-01-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/399/2015/bg-12-399-2015.pdf |
| Summary: | Scientific understanding of the global carbon cycle is required for
developing national and international policy to mitigate fossil fuel
CO<sub>2</sub> emissions by managing terrestrial carbon uptake. Toward that
understanding and as a contribution to the REgional Carbon Cycle Assessment
and Processes (RECCAP) project, this paper provides a synthesis of net
land–atmosphere CO<sub>2</sub> exchange for North America (Canada, United States,
and Mexico) over the period 1990–2009. Only CO<sub>2</sub> is considered, not
methane or other greenhouse gases. This synthesis is based on results from
three different methods: atmospheric inversion, inventory-based methods and
terrestrial biosphere modeling. All methods indicate that the North American
land surface was a sink for atmospheric CO<sub>2</sub>, with a net transfer from
atmosphere to land. Estimates ranged from −890 to −280 Tg C yr<sup>−1</sup>, where
the mean of atmospheric inversion estimates forms the lower bound of that
range (a larger land sink) and the inventory-based estimate using the
production approach the upper (a smaller land sink). This relatively large
range is due in part to differences in how the approaches represent trade,
fire and other disturbances and which ecosystems they include. Integrating
across estimates, "best" estimates (i.e., measures of central tendency)
are −472 ± 281 Tg C yr<sup>−1</sup> based on the mean and standard deviation
of the distribution and −360 Tg C yr<sup>−1</sup> (with an interquartile range of
−496 to −337) based on the median. Considering both the fossil fuel
emissions source and the land sink, our analysis shows that North America
was, however, a net contributor to the growth of CO<sub>2</sub> in the atmosphere
in the late 20th and early 21st century. With North America's mean
annual fossil fuel CO<sub>2</sub> emissions for the period 1990–2009 equal to 1720 Tg C yr<sup>−1</sup>
and assuming the estimate of −472 Tg C yr<sup>−1</sup> as an
approximation of the true terrestrial CO<sub>2</sub> sink, the continent's
source : sink ratio for this time period was 1720:472, or nearly 4:1. |
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| ISSN: | 1726-4170 1726-4189 |