SWAIS2C: Sensitivity of the West Antarctic Ice Sheet to 2 degrees celsius

The Paris Agreement presents an ambitious goal: to keep global warming less than 2°C above pre-industrial levels. But these targets present a massive challenge, as global average temperature is already 1°C above pre-industrial levels and rising.

Due to polar ice melt, global average sea level will rise, but not uniformly across the planet. Local and regional sea level change depends on where ice and water are distributed around the Earth’s surface, and how this changes as the polar ice melts and is added to the ocean.

We know sea level will rise at least 30cm over the next several decades, potentially displacing many millions of people living in low lying coastal areas. If Antarctica’s ice shelves and the West Antarctic Ice Sheet collapse, global sea level will rise up to five metres. We need to understand the environmental conditions that will cause WAIS to collapse, when it will happen and just how fast it can retreat.

The West Antarctic Ice Sheet (WAIS) is presently losing mass at an accelerating rate, but the response of the WAIS to a projected 2°C (or more) global warming remains a significant uncertainty in sea level rise projections. WAIS is inherently more susceptible to collapse than the East Antarctic Ice Sheet as it sits on land well below sea level and its margin is exposed to a warming ocean. Of particular concern is that the submarine land surface on which the WAIS sits deepens from the ice sheet margin towards its centre and has potential for runaway and unstoppable retreat, if the large fringing ice shelves that help to hold it in place collapse, ice flow increases, and gravity ‘takes over’.

Our research aims to understand the timing of past Ross Ice Shelf collapse and WAIS retreat, and the local and regional environmental conditions that drove these changes during past warmer-than-present climatic conditions.

During the last interglacial period (125,000 to 120,000 years ago), global temperatures were 1°C - 1.5°C warmer than pre-industrial times, similar to those that now appear to be unavoidable, and we will see in the coming decades even as we strive to reduce atmospheric carbon emissions. Due to ice melt, sea level was as much as six metres higher than present day. This extra freshwater in the ocean came from Earth’s large ice sheets but it’s not yet clear how much came from Greenland and how much from Antarctica.

We aim to answer the key question: Did the West Antarctic Ice Sheet melt during previous warm interglacial periods?

To do this, we will collect geological records from the centre of West Antarctica.

West Antarctica is largely ice-covered, which means its geological archives are hidden. Scientific drilling is vital to access valuable archives of past climate and ice sheet behaviour.

We are embarking on an ambitious drilling and research programme with international collaborators to obtain the sedimentary history at two locations (Kamb Ice Stream and Crary Ice Rise) near the modern grounding zone of the West Antarctic Ice Sheet. In this location, along the Siple Coast in the West Antarctic interior, the West Antarctic Ice Sheet first lifts off from the sea floor and begins to float.

Our team of engineers has developed a new ice and sediment drilling system. We will first melt a hole through floating ice with a hot water drill. Then a purpose-built light-weight sediment coring system will drill over a hundred meters into the sea floor. This transportable system is capable of recovering ~200 metres of sediment from beneath the sea floor in places where the combined depth of the ice shelf (or sea ice) and water column is over 1000 metres thick.

The drilling team and a small group of scientists will be on site in Antarctica to recover sedimentary cores that will be shipped to a research facility in New Zealand. Planning is underway, site surveys are complete, and drilling at the Kamb Ice Stream site will begin 2023, followed by drilling at another site at the Crary Ice Rise site in 2024.

A larger team of international scientists will gather at the end of each drilling season to study the sediments and reveal environmental secrets currently hidden beneath the ice. The new records will be used to reconstruct past climate conditions and will tell us how the West Antarctic Ice Sheet behaved in the past. We can then test the climate and ice sheet models that we use to project, understand and foresee our possible future.

This new information will allow us to take a huge step forward as we strive to learn just how sensitive West Antarctica is to a warmer climate. We will find out whether our efforts to reduce greenhouse gas emissions can save the Ross Ice Shelf and West Antarctic Ice Sheet and limit global sea level rise.