The SSP greenhouse gas concentrations and their extensions to 2500

Abstract

Abstract. Anthropogenic increases of atmospheric greenhouse gas concentrations are the main driver of current and future climate change. The Integrated Assessment community quantified anthropogenic emissions for the Shared Socioeconomic Pathways (SSP) scenarios, each of which represents a different future socio-economic projection and political environment. Here, we provide the greenhouse gas concentration for these SSP scenarios – using the reduced complexity climate-carbon cycle model MAGICC7.0. We extend historical, observationally-based concentration data with SSP concentration projections from 2015 to 2500 for 43 greenhouse gases with monthly and latitudinal resolution. CO2 concentrations by 2100 range from 393 to 1135 ppm for the lowest (SSP1-1.9) and highest (SSP5-8.5) emission scenarios respectively. We also provide the concentration extensions beyond 2100 based on assumptions in the trajectories of fossil fuels and land use change emissions, net negative emissions, and the fraction of non-CO2 emissions. By 2150, CO2 concentrations in the lowest emission scenario are approximately 350 ppm and approximately plateau at that level until 2500, whereas the highest fossil-fuel driven scenario projects CO2 concentrations of 1737 ppm and reaches concentrations beyond 2000 ppm by 2250. We estimate that the share of CO2 in the total radiative forcing contribution of all considered 43 long-lived greenhouse gases increases from today 66 % to roughly 68 % to 85 % by the time of maximum forcing in the 21st century. For this estimation, we updated simple radiative forcing parameterisations that reflect the Oslo Line by Line model results. In comparison to the RCPs, the five main SSPs (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5) are more evenly spaced in terms of their expected global-mean temperatures, extend to lower 2100 temperatures and sea level rise than the RCP set. Performing 2 pairs of 6-member historical ensembles with CESM1.2.2, we estimate the effect on surface air temperatures of applying latitudinally and seasonally resolved GHG concentrations. We find that the ensemble differences in the MAM season provide a regional warming in higher northern latitudes of up to 0.4 K over the historical period, latitudinally averaged of about 0.1 K, which we estimate to be comparable to the upper bound (∼ 5 % level) of natural variability. In comparison to the comparatively straight line of the last 2000 years, the greenhouse gas concentrations since the onset of the industrial period and this studies’ projections over the next 100 to 500 years unequivocally depict a ‘hockey-stick’ upwards shape – it is a collective choice whether the hothouse pathway is pursued or whether we manage climate damages to the SSP1-1.9 equivalent of around 1.5 °C warming.

Warmer climate projections in EC-Earth3-Veg: the role of changes in the greenhouse gas concentrations from CMIP5 to CMIP6

“…Despite the match in the instantaneous radiative forcing there are substantial changes in the emissions of individual greenhouse gases (GHG) between RCPs and SSPs (see figure 3 in Gidden et al 2019). This change in emissions translates into changes of GHG concentrations in the forcing datasets (Meinshausen et al 2019) compared to the GHG concentrations that have been used in CMIP5. Future climate projections as part of ScenarioMIP (O'Neill et al 2016) are driven by GHG concentrations, and thus changes in GHG concentration could lead to changes in the forcing for the projections.…”

“…Future climate projections as part of ScenarioMIP (O'Neill et al 2016) are driven by GHG concentrations, and thus changes in GHG concentration could lead to changes in the forcing for the projections. Meinshausen et al (2019) present an overview of GHG concentrations for the different SSPs and discuss changes to the RCPs used in CMIP5. In figure 2 we show the comparison for the GHG concentrations used in EC-Earth for CMIP5 and CMIP6.…”

“…The instantaneous radiative forcing is not changing (Gidden et al 2019) but could there still be an impact from the changes in GHG concentrations? Meinshausen et al (2019) show that the global mean temperature in their simple carbon and climate model MAGICC7 (Model for the Assessment of Greenhouse Gas Induced Climate Change) is lower at the end of the 21st century with the new SSPs compared to RCPs. However, we find a higher temperature with the EC-Earth model for CMIP6 compared to CMIP5 and therefore wonder if and how much the changes in the GHG concentration could contribute to this warming.…”

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

“…The continuing importance of reducing CH 4 is seen in the newer Coupled Model Intercomparison Product 6 scenarios that are consistent with staying below 2°C (Shared Socioeconomic Pathways, SSP1-2.6 and SSP1-1.9), and these have CH 4 mole fractions starting rapid decreases in 2020 or 2021 (Meinshausen et al, 2019) ( Figure 2). Because of the unexpected rise in CH 4 mole fractions, SSP1-1.9 and SSP1-2.6 call for an even larger 45% reduction of 2020 levels by the end of the century because of the sharp decrease in CH 4 mole fraction occurring later than proposed by RCP2.6.…”

Implementation of the CMIP6 Forcing Data in the IPSL‐CM6A‐LR Model

“…For simplicity we prescribe global annual mean mixing ratios without any temporal interpolation (i.e., only the global mean mixing ratio is used and the value is updated on 1 January of each year in experiments where greenhouse gases vary). The differences between CMIP5 and CMIP6 for CO 2 , CH 4 , and N 2 O are negligible for the historical period but are noticeable for the scenario levels that are common, for example, the RCP85 (Pathway 8.5) and SSP585 (Pathway 5‐8.5) scenarios (see Figures a–c) (Meinshausen et al, ). It should be noted that methane presents latitudinal and vertical variations that may be interesting to represent in the model in the future.…”