Editing IPCC:AR6/WGI/Chapter-5 (section)

== 5.7 Final Remarks ==

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Key research developments to further strengthen the confidence levels in AR7 include the following:

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=== Contemporary Greenhouse Gases (GHGs) Trends and Attribution ===

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* Further constrain the CO <sub>2</sub> , CH <sub>4</sub> and N <sub>2</sub> O fluxes from land use, land-use change and forestry (including gross fluxes), and fossil fuels. Improving spatial resolution and representations of land management, such as forestry, grazing and cropping.
* Improve representation of the variability and trends in the transport of carbon through the land–ocean continuum, which has implications for partitioning the land and ocean CO <sub>2</sub> sinks.
* Improve understanding of the controls over the airborne franction and sinks rates, their trends, and future dynamics.
* Fill gaps in space and time for ocean CO <sub>2</sub> and ancillary physical and biogeochemical observations at the ocean surface and interior to reduce the biases and uncertainties in the variability and trends for air–sea fluxes and inventory changes, particularly for the Arctic and the Southern Ocean.
* Reduce uncertainties of CH <sub>4</sub> emissions from wetlands and inland waters, which are the largest source term in the global CH <sub>4</sub> budget and proportionally have the largest uncertainty, to better understand future CH <sub>4</sub> -climate feedbacks.
* Reduce uncertainties in atmospheric transport models used to estimate regional sources and sinks of GHGs as independent evidence from that of ground and inventory estimates.

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=== Ocean Acidification and Deoxygenation ===

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* Improve observations for the interplay between carbonate chemistry and a variety of biogeochemical and physical processes, including eutrophication and freshwater inflow in coastal zones to increase the robustness of future assessments of ocean acidification.
* Improve our understanding of changes in water mass ventilation associated with climate change and variability to gain further insights into future trends in ocean acidification and deoxygenation in the ocean interior.

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=== Biogeochemical Feedbacks on Climate Change ===

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* Improve understanding and representation in Earth system models of changes in land carbon storage and associated carbon–climate feedbacks including: better treatment of the CO <sub>2</sub> fertilization, nutrient-limitations, soil organic matter stabilization and turnover; land-use change; large-scale and fine-scale permafrost carbon; plant growth, mortality, and competition dynamics; plant hydraulics; and disturbance processes.
* Improve observations and process understanding of CH <sub>4</sub> and N <sub>2</sub> O source responses to climate, specifically from wetlands and permafrost thaw.
* Improve observations and process understanding of ocean N <sub>2</sub> O source responses to oxygen loss and climate, particularly in the oxygen minimum zones of the tropical oceans and eastern boundary upwelling regions.
* Improve understanding of the sensitivity of ocean carbon–climate feedbacks to physical processes that are not yet resolved by the ocean domain in ESMs.
* Improve understanding of the processes affecting the efficiency, climate sensitivity and emerging feedbacks in the ocean carbon cycle via the biological carbon pump to constrain future global ocean feedbacks.

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=== Remaining Carbon Budget to Climate Stabilization ===

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* Improve understanding of the sign and magnitude of a possible zero emissions commitment (ZEC). The ZEC affects estimates of carbon budgets derived from the transient climate response to cumulative emissions of CO <sub>2</sub> (TCRE), but not TCRE itself. ZEC is particularly relevant once global CO <sub>2</sub> emissions decline towards net zero.
* Better constraint of the airborne fraction to reduce the spread in TCRE assessment.
* Account for time scales of Earth system feedbacks over time for increased accuracy of mitigation needs once global CO <sub>2</sub> emissions reach near-zero levels.

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=== Carbon Dioxide Removal (CDR) and Solar Radiation Modification (SRM) ===

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* Run large-scale and long-term experiments and assessments to explore: the regional feasibility of CDR methods; whether they present an actual and verifiable negative regional carbon balance; and whether they result in adverse unintended consequences.
* Improve understanding of the effectiveness of CDR methods to lower atmospheric CO <sub>2</sub> and reduce warming, taking into account Earth system feedbacks.

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