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The challenge

Climate models aren’t getting the full picture when it comes to the Southern Hemisphere

Earth systems climate models provide the most reliable way to help us understand how our climate will change into the future. They are used generate climate model projections and weather forecasts to answer questions such as how fast the atmosphere is warming.

The Kennaook / Cape Grim Baseline Air Pollution Station is located in remote north-western Tasmania and provides vital information about changes to the atmospheric composition of the Southern Hemisphere.

Because of its large role in the climate system, it is important that the Southern Ocean is well-represented in Earth systems climate models.

The Southern Ocean exerts a profound influence on Earth's climate and is often referred to as the "engine room" for weather and climate systems. It contains vast areas of uninterrupted water which leads to the exchange of heat and gas between the air and the sea, taking heat from near the surface and transferring it into the deep ocean.

Clouds in this region can cool the surface of the Southern Ocean by reflecting sunlight and heat back to space. They can also trap heat that is in the air or that has radiated from the surface, thereby warming the atmosphere.

Currently, climate models aren't getting the full picture when it comes to the Southern Ocean as they contain model 'biases' around aerosols and clouds. One of the issues is that climate models assume that clouds in the Southern Hemisphere have the same properties as those found elsewhere.

Scientists know that cloud properties are different in the Southern Hemisphere because of the different types of sources of airborne aerosol particles in this region, as compared to the Northern Hemisphere. Dust blown from deserts and pollution particles can trigger 'ice-clouds' in the Northern Hemisphere. But over the Southern Ocean, the air is cleaner, so water droplets stay in a liquid state. The main aerosols that form 'super-cooled' clouds here are derived from biological sources (e.g. phytoplankton).

Super-cooled clouds aren't currently accurately accounted for in climate models. This means that climate models predict that too much sunlight reaches the ocean in this region.

Our response

Capturing a full seasonal cycle of aerosol and cloud observations over the Southern Ocean

Over the vast Southern Ocean, aerosols and their interactions with clouds are difficult to observe. We need to know more about the interaction of aerosols and clouds in the climate system of the Southern Hemisphere: what is their distribution, how and where do aerosols affect the formation of clouds, do the clouds exist as super-cooled liquid or ice clouds, and how much moisture can the clouds ultimately release via precipitation (rainfall).

A new collaborative research project involving Australia and the United States, commencing in April 2024, will gather never-before-seen atmospheric data from north-west Tasmania at Kennaook / Cape Grim. The research project is called "CAPE-k", standing for "Clouds And Precipitation Experiment at Kennaook".

The remotely situated Kennaook / Cape Grim Baseline Monitoring Station is the ideal location for studying aerosol and cloud interactions. The pristine air travelling from the mid-latitudes is situated in the exact same band (40 °S) where climate models currently struggle to represent low-altitude cloud formation. This location, combined with the station's long-term continuous data record provides the ideal location to undertake continuous detailed observations over a full seasonal cycle (17 months).

The Kennaook / Cape Grim station is positioned just south of the isolated north-west tip (Woolnorth Point) of Tasmania.

The results

International collaboration to help deliver more precise climate projections

The science underway at Kennaook / Cape Grim will contribute to a more comprehensive understanding of Earth's climate system and energy balance.

The project is a collaboration between the CSIRO, Bureau of Meteorology, and United States Department of Energy's Atmospheric Radiation Measurement (ARM) user facility.

New observation data from this project will be integrated with the long-term atmospheric data record from the Kennaook / Cape Grim Baseline Air Pollution Station, which spans back to 1977.

Improving our understanding of Southern Ocean aerosols and clouds could lead to improved tracking of how fast the Earth is heating (via climate projections) and more accurate climate projections and weather forecasts.

The ARM User Facility make all data from this project publicly available at their website.

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