Assessment of Approaches to Updating the Social Cost of Carbon Phase 1 Report on a Near-Term Update (2016) / Chapter Skim
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4 Climate System Modeling in the SCC-IAMs and the Role of ECS
4 Climate System Modeling in the SCC-IAMs and the Role of ECS
Pages 35-44
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From page 35... ...
model. The climate system in each of them consists of three major elements: calculation of the path of atmospheric concentrations of CO2 from greenhouse gas emissions, translation of concentrations to radiative forcing, and the response of global mean surface temperature to changes in radiative forcing.
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From page 36... ...
3.80 W/m2 3.71 W/m2 3.81 W/m2 Non-CO2 Kyoto Exogenous CH4, N2O, SF6 Exogenous Non-CO2 non-Kyoto Exogenous SO2 SO2, non-SO2 exogenous Rate temperature moves toward equilibrium is a Rate temperature moves Function of global mean Global Mean Surface function of climate towards equilibrium is a land and ocean Temperature sensitivity & surface function of climate temperatures temperature modulated by sensitivity ocean heat uptake 2-box (upper and deep Ocean Temperatures 1-box 1-box ocean) Implicit with regional damage parameters Explicit with regional calibrated to regional temperatures downscaled Regional Temperatures n/a temperatures downscaled according to latitude and based on a linear pattern landmass adjustment scale average of 14 global circulation models Components (thermal expansion, glacier and small Computed as a function of Computed as a function of ice cap melt, GIS melt, WAIS Global Mean Sea Level Rise temperature and lagged temperature and lagged melt)
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From page 37... ...
Other climate variables such as precipitation, weather variability, and extreme weather events are not modeled explicitly, although these effects may be captured implicitly in the calibration of damage response to global mean temperature change. Global mean surface temperature drives projected global average mean sea level rise in all three models and projected regional average temperatures in FUND and PAGE, which in turn drive damages.
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From page 38... ...
. Th 3, he IWG met thodology reegarding soccioeconomic and emissio modeling differs to d ons g different deg grees from each model's st tandard struccture.
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From page 39... ...
; and DICE and PAGE include non-CO2 forcin oto use H E E ng exogenou usly. To estimate climate damages beyond 2100 the IWG ex e b 0, xtrapolated t EMF 22 the based soc cioeconomic and emissio inputs fr c ons rom 2100 to 2300.
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From page 40... ...
. Role of ECS and Other Assumptions in Determining the Emissions-to Temperature Link Projecting global mean surface temperature change from projected emissions in the SCCIAMs requires sequentially translating emissions trajectories into concentrations, concentrations into radiative forcing, and radiative forcing trajectories into temperature.
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From page 41... ...
umptions incclude the projected size of the economy and popula y ation, emissiions levels, d discount rate non-ECS e, climate parameters, regional tem p r mperature dow wnscaling, th assumed sea level rise response r he rate, and the functional forms and para fu ameterizatio for the va ons arious clima damages (Anthoff and ate d Tol, 2013 2013b; Hope, 2013; Butler et al., 2014; Rose et al., 2014 Some assu 3a, H , e 4)
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From page 42... ...
The key point of comparison is whether the central projections and ranges of the simple climate models agree with those of more comprehensive Earth system models. These diagnostics should not necessarily disqualify models based on broader responses than the Earth system models, however, as the latter models are known to cluster near central estimates (e.g., Huybers, 2010; Roe and Armour, 2011)
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From page 43... ...
By driving the model directly with climate forcing, these experiments isolate the energy balance portion of the simple climate model. Although these experiments and this report focus on the climate effect of CO2 emissions, similar diagnostics can be applied to the simple climate models used in the calculation of the social cost of other climate forcers.
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