Toward a consistent modeling framework to assess multi-sectoral climate impacts

Efforts to estimate the physical and economic impacts of future climate change face substantial challenges. To enrich the currently popular approaches to impact analysis—which involve evaluation of a damage function or multi-model comparisons based on a limited number of standardized scenarios—we propose integrating a geospatially resolved physical representation of impacts into a coupled human-Earth system modeling framework. Large internationally coordinated exercises cannot easily respond to new policy targets and the implementation of standard scenarios across models, institutions and research communities can yield inconsistent estimates. Here, we argue for a shift toward the use of a self-consistent integrated modeling framework to assess climate impacts, and discuss ways the integrated assessment modeling community can move in this direction. We then demonstrate the capabilities of such a modeling framework by conducting a multi-sectoral assessment of climate impacts under a range of consistent and integrated economic and climate scenarios that are responsive to new policies and business expectations.


Paris Forever
Derived from an assessment of the results from the UN COP-21 meeting 2 based on Intended Nationally Determined Contributions (INDCs) of major emitting countries, with no increase in policy past 2030.

Oceans
Includes a large role for renewables and oil, and slow development of CCS. Renewables are supported by renewables portfolio standards.

Mountains
Includes a large role for renewables after 2050, larger natural gas resources, and accelerated development of CCS.

2C
Assumes a globally uniform carbon tax starting in 2020 that leads to a global temperature stabilization of 2 °C above preindustrial by 2100 Note: The scenarios are chosen for illustrative purposes. The Paris Forever scenario shows how far the current emission pledges take us since there is no agreement on the emission mitigation trajectories after 2030. We do not impose any additional climate policy after 2030 to illustrate that the current pledges are not enough to meet to goal to stay "well below 2 ºC". Energy projections in Oceans and Mountains scenarios represent the view of the industry (developed by the Shell scenarios team 3 ; also see ref. 4 for more details on the climate impacts of the Oceans and Mountains scenarios) and were implemented in the EPPA model (the human system model of the MIT IGSM) by calibrating the total primary energy use on a regional basis. While there are many potential trajectories to reach the 2 °C target, all of them require a strong policy action.
Supplementary Table 3. Summary of climate impacts by emissions scenario.

Scenario Impacts by 2100
Paris Forever 3.6 ºC warming relative to preindustrial, and rising; significant and still increasing ocean acidification and significant impact on the ocean food chain; substantial increases in PM 2.5 concentrations over India and China; between 12-16% of global population exposed to moderate water scarcity and 6-9% to extreme water scarcity by 2100, strongly depending on climate model pattern chosen; decreases in global crop productivity caused by high temperature and ozone levels.

Oceans
Stabilizing temperature increase at 2.7 ºC; reduction in ocean acidification; lower rate of increase in PM 2.5 air pollution over China and India; reduction (increase) in population exposed to water scarcity under "wet" ("dry") model; small benefits in global crop productivity from reduced ozone damages and land-use change adaptation.

Mountains
Stabilizing temperature increase at 2.4 ºC; further reduction in ocean acidification and capping the damage; further reduction (increase) in population exposed to water scarcity under "wet" ("dry") model; even lower rate of increase in PM 2.5 air pollution; increased benefits of global crop productivity.

2C
Stabilizing temperature increase at 2 ºC; stabilization of ocean pH; reduction in PM 2.5 air pollution; even further reduction (increase) in population exposed to water scarcity under "wet" ("dry") model; major benefits on crop productivity.
Note: The scenarios are chosen for illustrative purposes. The Paris Forever scenario results in substantial ocean acidification, increases in PM 2.5 air pollution, water scarcity (but strongly dependent on the climate model chosen) and climate impacts on agriculture. More stringent scenarios (Oceans and Mountains) scenarios are successful in mitigating a large portion of the impacts, even producing benefits for agriculture productivity. These projections show the significant value of policies that do not quite reach 2 °C stabilization, but fall substantially close to that target by the end of the century. The more aggressive 2C scenario provides the strongest preventative effects, but still results in sizeable climate impacts, and impacts on water scarcity is strongly dependent on the climate model chosen, and benefits to the agriculture productivity through reduced warming and ozone damage. For more details on the climate impacts on all scenarios, see ref. 4 .