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Wednesday 21 Mar 2018The Carbon cycle behaviour under low mitigation scenarios, implications of the Paris Agreement

Chris Jones - Met Office

H170 14:00-15:00

Natural carbon sinks currently absorb approximately half of the anthropogenic CO2 emitted by fossil fuel burning, cement production and land-use change. However, this airborne fraction may change in the future depending on the emissions scenario. An important issue in developing carbon budgets to achieve climate stabilisation targets is the behaviour of natural carbon sinks, particularly under low emissions mitigation scenarios as required to meet the goals of the Paris Agreement. A key requirement for low carbon pathways is to quantify the effectiveness of negative emissions technologies which will be strongly affected by carbon cycle feedbacks. I will show that Earth system models suggest signi?cant weakening, even potential reversal, of the ocean and land sinks under future low emission scenarios. For example, under the RCP2.6 concentration pathway, models project land and ocean sinks to weaken to 0.8 and 1.1 GtC yr−1 respectively for the second half of the 21st century and to −0.4 and 0.1 GtC yr−1 respectively by the end of the 23rd century. Weakening of natural carbon sinks will hinder the effectiveness of negative emissions technologies and therefore increase their required deployment to achieve a given climate stabilisation target.

Under these scenarios, the role of atmospheric CO2 on carbon sinks, rather than climate feedbacks becomes the largest uncertainty. This guides future priorities for carbon cycle research.

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