Assessment of model estimates of land-atmosphere CO<sub>2</sub> exchange across Northern Eurasia
A warming climate is altering land-atmosphere exchanges of carbon, with a potential for increased vegetation productivity as well as the mobilization of permafrost soil carbon stores. Here we investigate land-atmosphere carbon dioxide (CO<sub>2</sub>) cycling through analysis of net ecos...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-07-01
|
| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/4385/2015/bg-12-4385-2015.pdf |
| Summary: | A warming climate is altering land-atmosphere exchanges of carbon, with a
potential for increased vegetation productivity as well as the mobilization
of permafrost soil carbon stores. Here we investigate land-atmosphere carbon
dioxide (CO<sub>2</sub>) cycling through analysis of net ecosystem productivity (NEP)
and its component fluxes of gross primary productivity (GPP) and ecosystem
respiration (ER) and soil carbon residence time, simulated by a set of land
surface models (LSMs) over a region spanning the drainage basin of Northern
Eurasia. The retrospective simulations cover the period 1960–2009 at 0.5°
resolution, which is a scale common among many global carbon and
climate model simulations. Model performance benchmarks were drawn from
comparisons against both observed CO<sub>2</sub> fluxes derived from site-based eddy
covariance measurements as well as regional-scale GPP estimates based on
satellite remote-sensing data. The site-based comparisons depict a tendency
for overestimates in GPP and ER for several of the models, particularly at
the two sites to the south. For several models the spatial pattern in GPP
explains less than half the variance in the MODIS MOD17 GPP product. Across
the models NEP increases by as little as 0.01 to as much as 0.79 g C m<sup>−2</sup> yr<sup>−2</sup>,
equivalent to 3 to 340 % of the respective model means, over the
analysis period. For the multimodel average the increase is 135 % of the mean
from the first to last 10 years of record (1960–1969 vs. 2000–2009), with a
weakening CO<sub>2</sub> sink over the latter decades. Vegetation net primary
productivity increased by 8 to 30 % from the first to last 10 years,
contributing to soil carbon storage gains. The range in regional mean NEP
among the group is twice the multimodel mean, indicative of the uncertainty
in CO<sub>2</sub> sink strength. The models simulate that inputs to the soil carbon
pool exceeded losses, resulting in a net soil carbon gain amid a decrease in
residence time. Our analysis points to improvements in model elements
controlling vegetation productivity and soil respiration as being needed for
reducing uncertainty in land-atmosphere CO<sub>2</sub> exchange. These advances will
require collection of new field data on vegetation and soil dynamics, the
development of benchmarking data sets from measurements and remote-sensing
observations, and investments in future model development and intercomparison
studies. |
|---|---|
| ISSN: | 1726-4170 1726-4189 |