Chemistry–climate feedback of atmospheric methane in a methane-emission-flux-driven chemistry–climate model
<p>The chemical sink of atmospheric methane (CH<span class="inline-formula"><sub>4</sub></span>) depends on the temperature and on the chemical composition. Here, we assess the feedback on atmospheric CH<span class="inline-formula"><sub>4...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-05-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/5133/2025/acp-25-5133-2025.pdf |
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| Summary: | <p>The chemical sink of atmospheric methane (CH<span class="inline-formula"><sub>4</sub></span>) depends on the temperature and on the chemical composition. Here, we assess the feedback on atmospheric CH<span class="inline-formula"><sub>4</sub></span> induced by changes in the chemical sink in a warming climate using a CH<span class="inline-formula"><sub>4</sub></span>-emission-flux-driven set-up of the chemistry–climate model EMAC (ECHAM/MESSy Atmospheric Chemistry), in which the chemical feedback of CH<span class="inline-formula"><sub>4</sub></span> mixing ratios can evolve explicitly. We perform idealized perturbation simulations driven either by increased carbon dioxide (CO<span class="inline-formula"><sub>2</sub></span>) mixing ratios or by increased CH<span class="inline-formula"><sub>4</sub></span> emission fluxes. The CH<span class="inline-formula"><sub>4</sub></span> emission flux perturbation leads to a large increase of CH<span class="inline-formula"><sub>4</sub></span> mixing ratios. Remarkably, the factor by which the CH<span class="inline-formula"><sub>4</sub></span> mixing ratio increases is larger than the increase factor of the emission flux, because the atmospheric lifetime of CH<span class="inline-formula"><sub>4</sub></span> is extended.</p>
<p>In contrast, the individual effect of the global surface air temperature (GSAT) increase is to shorten the CH<span class="inline-formula"><sub>4</sub></span> lifetime, which results in a significant reduction of CH<span class="inline-formula"><sub>4</sub></span> mixing ratios in our set-up. The corresponding radiative feedback is estimated at <span class="inline-formula">−</span>0.041 and <span class="inline-formula">−</span>0.089 W m<span class="inline-formula"><sup>−2</sup></span> K<span class="inline-formula"><sup>−1</sup></span> for the CO<span class="inline-formula"><sub>2</sub></span> and CH<span class="inline-formula"><sub>4</sub></span> perturbation, respectively. The explicit response of CH<span class="inline-formula"><sub>4</sub></span> mixing ratios leads to secondary feedbacks on the hydroxyl radical (OH) and ozone (O<span class="inline-formula"><sub>3</sub></span>). Firstly, the OH response includes the CH<span class="inline-formula"><sub>4</sub></span>–OH feedback, which enhances the CH<span class="inline-formula"><sub>4</sub></span> lifetime change, and, secondly, the formation of tropospheric O<span class="inline-formula"><sub>3</sub></span> is reduced. Our CH<span class="inline-formula"><sub>4</sub></span> perturbation induces the same response of GSAT per effective radiative forcing (ERF) as the CO<span class="inline-formula"><sub>2</sub></span> perturbation, which supports the applicability of the ERF framework for CH<span class="inline-formula"><sub>4</sub></span>.</p> |
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| ISSN: | 1680-7316 1680-7324 |