This session has been created from sessions AS3.31 ‘Radiative effects and global aerosol forcing estimates of natural and anthropogenic aerosols’ (Convenors: Cathrine Lund Myhre, Elisabeth Andrews, Andreas Petzold, Bjørn Samset, Michael Schulz) and session AS3.32 ‘Natural Aerosols from Pre-Industrial to Present Day and into the Future’ (Convenors: Catherine Scott, Stephanie Fiedler, Kerstin Schepanski, Hugh Coe, Douglas Hamilton).

Aerosol radiative effects are an important aspect of the climate system that have both anthropogenic and natural contributions. This broad session focuses on the life cycle and radiative effects of all aerosol species present in the atmosphere.

One key topic is the radiative properties and effects of aerosols (e.g. black and brown carbon, mineral dust, biomass burning and hygroscopic aerosols) and model evaluation using aerosol observations. Today, ever more high quality data of aerosol optical properties, aerosol humidification, size distributions, aerosol light absorption and aerosol extinction vertical profiles have become available through international cooperation such as ACTRIS, GAW and NOAA networks. At the same time exhaustive global aerosol model results from multiple groups have been assembled in the AeroCom database, and rapid developments are being made in advance of CMIP6.

A better understanding of the role of natural aerosols in the atmosphere is essential for accurately determining anthropogenic radiative forcing and the climate response. In this session we will explore what we consider to be natural aerosols (i.e., primary aerosols and those formed from precursor gases emitted by natural sources, such as: wildfire, dust, volcanoes and the marine and terrestrial biospheres) and what we can observe about them in today’s atmosphere. Crucial questions include:
- How can we distinguish between truly natural aerosols and those whose emissions or formation are influenced by anthropogenic activities?
- How have the contributions of natural aerosols to atmospheric composition changed over time?
- How well do we understand the lifecycle of natural aerosols in the atmosphere in the absence of anthropogenic influence?
- Can we identify any pristine environments in the present day that can help us understand the pre-industrial atmosphere?
- How well are natural aerosols represented in Earth System Models and which observations can be used to evaluate them?

We welcome contributions relating to the use of observations and/or modelling to inform us about past, present-day and future aerosol-climate interactions.