Incorporating High-fidelity Air Quality Simulation into Integrated Assessment Models

Abstract:

A changing climate leads to changing air quality. Greenhouse gas (GHG) emissions today will affect temperatures for centuries, with propagating effects on weather – both impacting the quality of the air we breathe. But every step of this sequence introduces new variability and uncertainty. Integrated assessment models (IAMs), which bring together parameterizations of the Earth system to support decision making, have been valuable tools in supporting emissions policy, but most ignore or greatly simplify air quality calculations and cannot represent the relationship between climate uncertainty and non-linear air quality responses. Tools which represent and propagate uncertainty in both climate and air quality are needed. These will allow us to represent how anthropogenic emissions interact with a changing system, and to design robust emissions control strategies capable of addressing climate and air quality simultaneously for an uncertain future.

We present a new integrated assessment framework which combines state-of-the-science air quality modeling with an ensemble approach, using multiple uncertain climate projections. This integrates the economic Projection and Policy Analysis computable general equilibrium model, the MIT Earth System Model, the Community Atmosphere Model, and the GEOS-Chem High Performance chemistry transport model. We quantify how a Paris treaty-compliant climate policy differs from an unrestricted scenario in its effects on emissions of GHGs and air pollutants. We propagate these changes through each ensemble member to changes in climate and air quality, providing an estimate of the relative uncertainty in each outcome.

We estimate the contribution of GHG-driven climate change to air quality degradation separately from the effects of changes in (e.g.) NOx and sulfur emissions, even when the root cause - climate policy - is the same. This includes climate-driven uncertainty and inter-annual variability in air quality. The flexibility and fidelity of our approach maximizes opportunities for insight across policy analysis, economics, climate change, and air quality. Our approach can provide robust, quantitative assessments of interactions between climate change and air pollution for proposals ranging from state-level GHG reductions to a Green New Deal.