Assessing the lifetime of anthropogenic CO<sub>2</sub> and its sensitivity to different carbon cycle processes
<p>Although it is well-established that anthropogenic <span class="inline-formula">CO<sub>2</sub></span> emitted into the atmosphere will persist for a long time, the duration of the anthropogenic climate perturbation will depend on how rapidly the excess <...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-06-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/22/2767/2025/bg-22-2767-2025.pdf |
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| Summary: | <p>Although it is well-established that anthropogenic <span class="inline-formula">CO<sub>2</sub></span> emitted into the atmosphere will persist for a long time, the duration of the anthropogenic climate perturbation will depend on how rapidly the excess <span class="inline-formula">CO<sub>2</sub></span> is removed from the climate system by different biogeochemical processes. The uncertainty around the long-term climate evolution is therefore linked to not only the future of anthropogenic <span class="inline-formula">CO<sub>2</sub></span> emissions but also our insufficient understanding of the long-term carbon cycle. Here, we use the fast Earth system model CLIMBER-X, which features a comprehensive carbon cycle, to examine the lifetime of anthropogenic <span class="inline-formula">CO<sub>2</sub></span> and its effects on the long-term evolution of atmospheric <span class="inline-formula">CO<sub>2</sub></span> concentration. This is done through an ensemble of 100 000-year-long simulations, each driven by idealized <span class="inline-formula">CO<sub>2</sub></span> emission pulses. Our findings indicate that depending on the magnitude of the emission, 75 % of anthropogenic <span class="inline-formula">CO<sub>2</sub></span> is removed within 197–1820 years of the peak <span class="inline-formula">CO<sub>2</sub></span> concentration (with larger cumulative emissions taking longer to remove). Approximately 4.3 % of anthropogenic <span class="inline-formula">CO<sub>2</sub></span> will remain beyond 100 <span class="inline-formula">kyr</span>. We find that the uptake of carbon by land, which has only been considered to a small extent in previous studies, has a significant long-term effect, storing approximately 4 %–13 % of anthropogenic carbon by the end of the simulation. Higher-emission scenarios fall on the lower end of this range, as increased soil respiration leads to greater carbon loss. For the first time, we have quantified the effect of dynamically changing methane concentrations on the long-term carbon cycle, showing that its effects are likely negligible over long timescales. The timescale of carbon removal via silicate weathering is also reassessed here, providing an estimate (80–105 <span class="inline-formula">kyr</span>) that is significantly shorter than some previous studies due to higher climate sensitivity, stronger weathering feedbacks, and the use of a spatially explicit weathering scheme, leading to faster removal of anthropogenic <span class="inline-formula">CO<sub>2</sub></span> in the long term. Furthermore, this timescale is shown to have a non-monotonic relationship with cumulative emissions. Our study highlights the importance of adding model complexity to the global carbon cycle in Earth system models to accurately represent the long-term future evolution of atmospheric <span class="inline-formula">CO<sub>2</sub></span>.</p> |
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| ISSN: | 1726-4170 1726-4189 |