finding 14.3 : key-finding-14-3

Achieving global greenhouse gas emissions reductions before 2030 consistent with targets and actions announced by governments in the lead up to the 2015 Paris climate conference would hold open the possibility of meeting the long-term temperature goal of limiting global warming to 3.6°F (2°C) above preindustrial levels, whereas there would be virtually no chance if global net emissions followed a pathway well above those implied by country announcements. Actions in the announcements are, by themselves, insufficient to meet a 3.6°F (2°C) goal; the likelihood of achieving that goal depends strongly on the magnitude of global emissions reductions after 2030. (High confidence)

This finding is from chapter 14 of Climate Science Special Report: The Fourth National Climate Assessment: Volume I.

Process for developing key messages: Different analyses have estimated the implications for global mean temperature of the emissions reductions consistent with the actions announced by governments in the lead up to the 2015 Paris climate conference and have reached similar conclusions. Assuming emissions reductions indicated in these announcements are achieved, along with a range of climate sensitivities, these contributions provide some likelihood of meeting the long-term goal of limiting global warming to well below 3.6°F (2°C) above preindustrial levels, but much depends on assumptions about what happens after 2030.

Description of evidence base: The primary source supporting this key finding is Fawcett et al.;2c0a368b-b699-4640-98c9-7799c9e6b18a it is also supported by Rogelj et al.,c34c20b8-6d8a-41ba-8f34-1ed561aceeb8 Sanderson et al.,bf91f878-c82a-409b-8d96-e21320366a69 and the Climate Action Tracker.e210c59e-516f-4f73-9649-5b8b407e7b4f Each of these analyses evaluated the global climate implications of the aggregation of the individual country contributions thus far put forward under the Paris Agreement.

New information and remaining uncertainties: The largest uncertainty lies in the assumption of achieving emissions reductions consistent with the announcements prior to December 2015; these reductions are assumed to be achieved but could either be over- or underachieved. This in turn creates uncertainty about the extent of emissions reductions that would be needed after the first round of government announcements in order to achieve the 2°C or any other target. The response of the climate system, the climate sensitivity, is also a source of uncertainty; the Fawcett et al. analysis used the IPCC AR5 range, 1.5° to 4.5°C.

Assessment of confidence based on evidence: There is high confidence in this key finding because a number of analyses have examined the implications of these announcements and have come to similar conclusions, as captured in this key finding.

This finding was derived from figure -.2: Confidence / Likelihood

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