How well do integrated assessment models represent non-CO2 radiative forcing?

Drew T Shindell,Adriana Marcucci,Andries F Hof,Mathijs J H M Harmsen,Michiel Schaeffer,Chris Hope,Detlef P Van Vuuren,Maarten Van Den Berg,Jean-Francois Lamarque,Volker Krey

doi:10.1007/s10584-015-1485-0

Abstract

This study aims to create insight in how Integrated Assessment Models (IAMs) perform in describing the climate forcing by non-CO2 gases and aerosols. The simple climate models (SCMs) included in IAMs have been run with the same prescribed anthropogenic emission pathways and compared to analyses with complex earth system models (ESMs) in terms of concentration and radiative forcing levels. In our comparison, particular attention was given to the short-lived forcers' climate effects. In general, SCMs show forcing levels within the expert model ranges. However, the more simple SCMs seem to underestimate forcing differences between baseline and mitigation scenarios because of omission of ozone, black carbon and/or indirect methane forcing effects. Above all, results also show that among IAMs there is a significant spread (0.74 W/m2 in 2100) in non-CO2 forcing projections for a 2.6 W/m2 mitigation scenario, mainly due to uncertainties in the indirect effects of aerosols. This has large implications for determining optimal mitigation strategies among IAMs with regard to required CO2 forcing targets and policy costs.

Highlights

Integrated assessment models (IAMs) are important tools to inform policy-makers about different aspects of climate policy by providing an integrated view on topics like technology development, mitigation costs and functioning of the earth system
It was concluded that the representations of the carbon cycle in IAMs mostly lie within the range of earth system models
We look at the concentration and forcing representation of simple climate models (SCMs) included in IAMs regarding CH4, N2O, ozone and aerosols and compared the outcomes of SCMs to state-of-the-art atmospheric chemistry models

Summary

Introduction

Integrated assessment models (IAMs) are important tools to inform policy-makers about different aspects of climate policy by providing an integrated view on topics like technology development, mitigation costs and functioning of the earth system. Given the complexity involved in integrating these different topics, these models need to represent the relevant aspects in a simplified way. This implies, for instance, that the earth system is represented by simplified equations often derived from results of simulations with state-of-the-art earth system models. Van Vuuren et al (2011b) presented a detailed comparison of the representation of the carbon cycle and climate system in different IAMs. It was concluded that the representations of the carbon cycle in IAMs mostly lie within the range of earth system models (referred to as Bexpert models^). It was shown that the representation of these factors leads to very different results across IAMs

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