Estimated regional CO<sub>2</sub> flux and uncertainty based on an ensemble of atmospheric CO<sub>2</sub> inversions
<p>Global and regional sources and sinks of carbon across the earth's surface have been studied extensively using atmospheric carbon dioxide (CO<span class="inline-formula"><sub>2</sub></span>) observations and atmospheric chemistry-transport model (ACTM)...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/9215/2022/acp-22-9215-2022.pdf |
| Summary: | <p>Global and regional sources and sinks of carbon across the earth's
surface have been studied extensively using atmospheric carbon dioxide
(CO<span class="inline-formula"><sub>2</sub></span>) observations and atmospheric chemistry-transport model (ACTM)
simulations (top-down/inversion method). However, the uncertainties in the
regional flux distributions remain unconstrained due to the lack of
high-quality measurements, uncertainties in model simulations, and
representation of data and flux errors in the inversion systems. Here, we
assess the representation of data and flux errors using a suite of 16
inversion cases derived from a single transport model (MIROC4-ACTM) but
different sets of a priori (bottom-up) terrestrial biosphere and oceanic
fluxes, as well as prior flux and observational data uncertainties (50
sites) to estimate CO<span class="inline-formula"><sub>2</sub></span> fluxes for 84 regions over the period 2000–2020.
The inversion ensembles provide a mean flux field that is consistent with
the global CO<span class="inline-formula"><sub>2</sub></span> growth rate, land and ocean sink partitioning of
<span class="inline-formula">−</span>2.9 <span class="inline-formula">±</span> 0.3 (<span class="inline-formula">±</span> 1<span class="inline-formula"><i>σ</i></span> uncertainty on the ensemble mean) and
<span class="inline-formula">−</span>1.6 <span class="inline-formula">±</span> 0.2 PgC yr<span class="inline-formula"><sup>−1</sup></span>, respectively, for the period 2011–2020
(without riverine export correction), offsetting about 22 %–33 % and
16 %–18 % of global fossil fuel CO<span class="inline-formula"><sub>2</sub></span> emissions. The rivers carry about
0.6 PgC yr<span class="inline-formula"><sup>−1</sup></span> of land sink into the deep ocean, and thus the effective
land and ocean partitioning is <span class="inline-formula">−</span>2.3 <span class="inline-formula">±</span> 0.3 and <span class="inline-formula">−</span>2.2 <span class="inline-formula">±</span> 0.3,
respectively. Aggregated fluxes for 15 land regions compare reasonably well
with the best estimations for the 2000s (<span class="inline-formula">∼</span> 2000–2009), given
by the REgional Carbon Cycle Assessment and Processes (RECCAP), and all
regions appeared as a carbon sink over 2011–2020. Interannual variability
and seasonal cycle in CO<span class="inline-formula"><sub>2</sub></span> fluxes are more consistently derived for two
distinct prior fluxes when a greater degree of freedom (increased prior flux
uncertainty) is given to the inversion system. We have further evaluated the
inversion fluxes using meridional CO<span class="inline-formula"><sub>2</sub></span> distributions from independent
(not used in the inversions) aircraft and surface measurements, suggesting
that the ensemble mean flux (model–observation mean <span class="inline-formula">±</span> 1<span class="inline-formula"><i>σ</i></span>
standard deviation <span class="inline-formula">=</span> <span class="inline-formula">−</span>0.3 <span class="inline-formula">±</span> 3 ppm) is best suited for global and
regional CO<span class="inline-formula"><sub>2</sub></span> flux budgets than an individual inversion
(model–observation 1<span class="inline-formula"><i>σ</i></span> standard deviation <span class="inline-formula">=</span> <span class="inline-formula">−</span>0.35 <span class="inline-formula">±</span> 3.3 ppm).
Using the ensemble mean fluxes and uncertainties for 15 land and 11 ocean
regions at 5-year intervals, we show promise in the capability to track flux
changes toward supporting the ongoing and future CO<span class="inline-formula"><sub>2</sub></span> emission
mitigation policies.</p> |
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| ISSN: | 1680-7316 1680-7324 |