Sensitivity of Aerosol Effective Radiative Forcing to Underlying Physical Model Parameterizations and Aerosol Processes
Abstract
Aerosol processes and, in particular, aerosol-cloud interactions cut across the traditional physical-Earth system boundary of coupled Earth system models and remain one of the key uncertainties in estimating anthropogenic radiative forcing on climate. Here, we quantify the effective radiative forcing (ERF) due to aerosols in a prototype UKESM model - the next generation UK Earth System Model. Sensitivity tests show that the aerosol ERF is large and negative in the standard model due to underlying assumptions in both the physical model and aerosol parameterizations - the result is an unrealistically weak total anthropogenic forcing over the 20th century. A number of model improvements were investigated to assess their impact on the aerosol ERF. These include; an improved representation of cloud droplet spectral dispersion, updates to the aerosol activation scheme and black carbon optical properties. One of the largest contributors to the aerosol forcing uncertainty is insufficient knowledge of the pre-industrial aerosol climate. We evaluate the contribution of uncertainties in the natural marine emissions of dimethyl sulphide (DMS) and organic aerosol to the ERF. The combination of model improvements derived from these studies weaken the aerosol ERF by up to 40% of the original value and is expected to lead to a total anthropogenic historical forcing more in-line with assessed values.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A44E..05M
- Keywords:
-
- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSESDE: 3337 Global climate models;
- ATMOSPHERIC PROCESSESDE: 3275 Uncertainty quantification;
- MATHEMATICAL GEOPHYSICS