finding 4.1 : key-finding-4-1

If greenhouse gas concentrations were stabilized at their current level, existing concentrations would commit the world to at least an additional 1.1°F (0.6°C) of warming over this century relative to the last few decades (high confidence in continued warming, medium confidence in amount of warming).

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

Process for developing key messages: The key finding is based on the basic physical principles of radiative transfer that have been well established for decades to centuries; the amount of estimated warming for this hypothetical scenario is derived from Collins et al.b3bbc7b5-067e-4c23-8d9b-59faee21e58e which is in turn based on Meehl et al.eff5ce0d-c403-455b-9358-98be45351c7b using CMIP3 models.

Description of evidence base: The basic physics underlying the impact of human emissions on global climate, and the role of climate sensitivity in moderating the impact of those emissions on global temperature, has been documented since the 1800s in a series of peer-reviewed journal articles that is summarized in a collection titled, “The Warming Papers: The Scientific Foundation for the Climate Change Forecast”.eff1b5aa-a791-4a23-a595-92ae2c629e77

The estimate of committed warming at constant atmospheric concentrations is based on IPCC AR5 WG1, Chapter 12, section 12.5.2,b3bbc7b5-067e-4c23-8d9b-59faee21e58e page 1103 which is in turn derived from AR4 WG1, Chapter 10, section 10.7.1,eff5ce0d-c403-455b-9358-98be45351c7b page 822.

New information and remaining uncertainties: The uncertainty in projected change under a commitment scenario is low and primarily the result of uncertainty in climate sensitivity. This key finding describes a hypothetical scenario that assumes all human-caused emissions cease and the Earth system responds only to what is already in the atmosphere.

Assessment of confidence based on evidence: The statement has high confidence in the sign of future change and medium confidence in the amount of warming, based on the estimate of committed warming at constant atmospheric concentrations from Collins et al.b3bbc7b5-067e-4c23-8d9b-59faee21e58e based on Meehl et al.eff5ce0d-c403-455b-9358-98be45351c7b for a hypothetical scenario where concentrations in the atmosphere were fixed at a known level.

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

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