Measuring cloud and aerosol interactions

Improving cloud simulations to reduce climate modelling uncertainties in the NZESM

We now have a good understanding of how sensitive temperature and precipitation are to greenhouse gases. Improvements in the simulation of clouds at Southern high-latitudes have played a large role in recent improvements in climate model projections of the future. However, the warmer projections produced in the most recent simulations have raised questions about whether they’re the result of other newly exposed errors.

Climate models, including the New Zealand Earth System Model (NZESM), still likely contain some remaining biases from poor simulations of clouds and how they capture interactions between aerosols and clouds. Tiny particles that make up aerosols are important for cloud development, helping cloud water droplets grow which are needed to start ice crystal formation. These small particles, which are related to pollutants and dust, have low concentrations in the Southern hemisphere. This means the clouds we see over Aotearoa are often quite different to those in the Northern hemisphere. For example, here, we often observe liquid water clouds in subzero environments because of a lack of aerosol particles, with records of water droplets in clouds at temperatures down to -38^oC. These detailed chemical and physical processes need to be understood and represented in models to make projections more accurate. 

Phase 1: This project will develop the understanding required to improve cloud simulations by analysing the treasure trove of previously collected datasets across the Southern Ocean and Aotearoa. Satellite data will also be utilised to gain a better understanding of how aerosols impact cloud formation. Existing data will allow us to determine how clouds simulated in models differ from reality. 

Phase 2: We will make targeted observations of clouds and our environment in Aotearoa, onboard ships in the Southern Ocean and in Antarctica, to gain the knowledge needed to reduce model uncertainties around Aotearoa. This will make climate projections both more accurate and robust, and will enable higher quality climate adaptation planning.