finding 4.2 : key-finding-4-2

Over the next two decades, global temperature increase is projected to be between 0.5°F and 1.3°F (0.3°–0.7°C) (medium confidence). This range is primarily due to uncertainties in natural sources of variability that affect short-term trends. In some regions, this means that the trend may not be distinguishable from natural variability (high confidence).

This finding is from chapter 4 of Climate Science Special Report: The Fourth National Climate Assessment: Volume I.

Process for developing key messages: The estimated warming presented in this Key Finding is based on calculations reported by Kirtman et al.2f638e6d-6ba0-4426-a196-fbc3ef435d40 The key finding that natural variability is the most important uncertainty over the near-term is based on multiple peer reviewed publications.

Description of evidence base: The estimate of projected near-term warming under continued emissions of carbon dioxide and other greenhouse gases and aerosols was obtained directly from IPCC AR5 WG1.2f638e6d-6ba0-4426-a196-fbc3ef435d40

The statement regarding the sources of uncertainty in near-term projections and regional uncertainty is based on Hawkins and Suttonc247acf0-2a87-4337-b6d7-77686d049eed cbb67d95-422d-4ffc-9fbd-dec79795f437 and Deser et al.f8119757-e6b9-4434-9e12-26fb2d2a1a3b aaae6beb-646c-41df-945d-3a2af8a72aee

New information and remaining uncertainties: As stated in the key finding, natural variability is the primary uncertainty in quantifying the amount of global temperature change over the next two decades.

Assessment of confidence based on evidence: The first statement regarding projected warming over the next two decades has medium confidence in the amount of warming due to the uncertainties described in the key finding. The second statement has high confidence, as the literature strongly supports the statement that natural variability is the primary source of uncertainty over time scales of years to decades.f8119757-e6b9-4434-9e12-26fb2d2a1a3b aaae6beb-646c-41df-945d-3a2af8a72aee f4ea5568-b3de-47ae-b725-8f7b45960040

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

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