The shared socio-economic pathway greenhouse gas concentrations and their extensions to 2500

Authors

Malte Meinshausen, Zebedee Nicholls, Jared Lewis, Matthew Gidden, Elisabeth Vogel, Mandy Freund, Urs Beyerle, Claudia Gessner, Alexander Nauels, Nico Bauer, Josep Canadell, John Daniel, Andrew John, Paul B. Krummel, Gunnar Luderer, Nicolai Meinshausen, Stephen Montzka, Peter Rayner, Stefan Reimann, Steven Smith, Marten van den Berg, Guus Velders, Martin Kollmer, and Ray Wang

This paper draws from the integrated assessment community’s shared socio-economic pathway (SSP) scenarios and their corresponding level of anthropogenic emissions, socio-economic projections, and political environments, to provide the greenhouse gas concentrations for these SSP scenarios.

Anthropogenic increases in atmospheric greenhouse gas concentrations are the main driver of current and future climate change. The integrated assessment community has quantified anthropogenic emissions for the shared socio-economic pathway (SSP) scenarios, each of which represents a different future socio-economic projection and political environment.

Here, we provide the greenhouse gas concentrations 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 regarding 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 66 % for the present day to roughly 68 % to 85 % by the time of maximum forcing in the 21st century. For this estimation, we updated simple radiative forcing parameterizations that reflect the Oslo Line-By-Line model results. In comparison to the representative concentration pathways (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 and extend to lower 2100 radiative forcing and temperatures.

Performing two pairs of six-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 March–April–May (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. The SSP concentration time series derived in this study provide a harmonized set of input assumptions for long-term climate science analysis; they also provide an indication of the wide set of futures that societal developments and policy implementations can lead to – ranging from multiple degrees of future warming on the one side to approximately 1.5 ^∘C warming on the other.

Spatially resolved emulated annual temperature projections for overshoot pathways

This study presents a new dataset of annual temperature projections for different overshoot pathways (when the 1.5 °C of global warming limit is exceeded). The data offers a unique opportunity to study local and regional climate change impacts of a range of overshoot scenarios, including when temperature thresholds might be exceeded, and by how much.

Solar geoengineering: a note to inform discussions on physical climate impacts, risks and governance issues

With international efforts on climate action still not on track to limit warming to 1.5°C, technological fixes that aim to intentionally alter the Earth’s climate, such as solar geoengineering, might seem like appealing options for tackling global warming. But they come with questions in terms of feasibility, impacts and risks, governance and geopolitics, and who may or may not benefit.

Achieving net zero greenhouse gas emissions critical to limit climate tipping risks

Current climate policies are putting Earth on a path to a high risk of triggering climatic tipping points – even if temperatures return to below 1.5°C of global warming after a period of overshoot. A new study finds that the risk of crossing these thresholds increases with every additional 0.1 °C of overshoot above 1.5 °C and strongly accelerates above 2.0 °C. These risks can be minimised if stringent emissions reductions are taken in the next decade, and net zero greenhouse gas emissions are met and maintained.

Evaluating the near and long-term role of carbon dioxide removal in meeting global climate objectives

For 1.5°C pathways with limited overshoot, most of the mitigation between now and 2030 should come from emissions reductions (70%), with reductions from cutting non-CO2 emissions (20%) and land-based carbon dioxide removals such as afforestation and preventing deforestation (10%) making up the remainder.

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About us

Decarbonisation targets and 1.5℃ pathways

Comment

The shared socio-economic pathway greenhouse gas concentrations and their extensions to 2500

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