A paradigm shift toward a consistent modeling framework to assess 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 and Earth system modeling framework. Large internationally coordinated exercises cannot easily respond to new policy targets. Moreover, the implementation of standard scenarios across models, institutions and research communities can yield inconsistent estimates, especially when the scenarios were designed by different modeling groups. We therefore argue for a shift in paradigm, 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. Introduction Estimating the impacts of climate change is challenging because they span a large number of economic sectors and ecosystems services, and can vary strongly by region. Many integrated assessment models (IAMs) rely on simple “box” climate models and use a damage function approach to estimate a social cost of carbon that relates changes in emissions to economic damage. These models are useful. For example, the US EPA and other government agencies use these estimates to evaluate the climate benefits of rulemakings. But this approach has also attracted criticism as the existing literature offers sparse theoretical support and provides scant empirical evidence for a specification of economic damages, especially at temperatures outside the historical range. Another widely used approach relies on model intercomparison projects (MIPs) that apply the results of detailed biogeophysical models. They can offer valuable insights into specific climate impacts (e.g., the Agricultural Model Intercomparison and Improvement Project (AgMIP) for agriculture). However, these exercises suffer from a rigid and complex framework, driven by the need for international coordination, so they must rely on a limited number of socio-economic scenarios, like the RCPs. Since the developers and the users of these scenarios come from different research groups and disciplinary communities, major inconsistencies in their implementation, such as socio-economic assumptions and ecosystem characteristics, can easily occur. For example, when a common land-use scenario is implemented in different Earth system