A Phase II Project funded under the Deep South National Science Challenge

Project Leaders: Adrian McDonald (University of Canterbury) and Mike Harvey (NIWA)

Clouds have a surprisingly large effect on our climate. Cloud cover reflects sunlight back into space that would otherwise be absorbed by oceans, potentially raising their temperatures. Despite their significant influence on climate, clouds still represent the largest source of uncertainty in modern climate model simulations. For example, the frequency of clouds over the Southern Ocean is often underestimated, causing models to project warmer sea surface temperatures than observed. Models also often misrepresent the composition of clouds because of the importance of small particles, called aerosols, which act as the starting points for cloud droplets and ice to form. These deficiencies lead climate models to project the strength and position of the Southern Hemisphere storm tracks incorrectly.

The strength and position of these storm tracks impact New Zealand directly via their influence on rainfall, in addition to bringing extreme weather events. It is vital that our models represent clouds well so we can increase certainty in our climate projections for New Zealand.

This project aims to develop and analyse observational data sets to evaluate and understand the representation of clouds, their properties, and aerosols in NZESM to reduce known model deficiencies and biases. The focus of this work will be on known deficiencies in the simulation of cloud and aerosols in NZESM identified in Phase 1 of the Deep South Challenge (DSC). An improved representation of clouds and aerosols will lead to better and more reliable climate projections for New Zealand. By reducing uncertainties in future climate projections, this project contributes to the DSC mission of enabling New Zealanders to adapt, manage risk, and thrive in a changing climate by providing better information (i.e. NZESM projections) on how New Zealand’s climate is changing.