advertisement
Projected sea level rise will have widespread effects in Australia and around the world. But current projections of ice sheet melt are so wide that developing ways for societies to adapt will be incredibly expensive and difficult.
Ice loss from the Antarctic and Greenland ice sheets was the largest contributor to sea level rise in recent decades. Even if all greenhouse gas emissions ceased today, the heat already in the ocean and atmosphere would cause substantial ice loss and a corresponding rise in sea levels. But exactly how much, and how fast, remains unclear.
This lack of information is one of the main sources of uncertainty in the models used to estimate ice mass loss.
At the moment, quantifying how much the Greenland and Antarctic ice sheets will contribute to sea level rise primarily involves an international scientific collaboration known as the “Ice Sheet Model Intercomparison Project for CMIP6”, or ISMIP6, of which we are part.
The project includes experts in ice sheet and climate modelling and observations. It produces computer simulations of what might happen if the polar regions melt under different climate scenarios, to improve projections of sea level rise.
The project also investigates ice sheet–climate feedbacks. In other words, it looks at how processes in the oceans and atmosphere will affect the Antarctic and Greenland ice sheets, including whether the changes might cause them to collapse – leading to large and sudden increases in sea level.
This and other constraints mean the rate of progress in ice sheet modelling has been insufficient to date, and so active ice sheet models are not included in climate models.
Scientists must instead make projections using the ice sheet models in isolation. This hinders scientific attempts to accurately simulate the feedback between ice and climate.
For example, it creates much uncertainty in how the interaction between the ocean and the ice shelf will affect ice mass loss, and how the very cold, fresh meltwater will make its way back to global oceans and cause sea level rise, and potentially disrupt currents.
The study also outlines a pessimistic, but still plausible, basal melt scenario for Antarctica in which sea levels could be five times higher than in the main scenarios.
The breadth of such findings underpinned sea level projections in the latest IPCC report. The Antarctic ice sheet once again represented the greatest source of uncertainty in these projections.
The below graph shows the IPCC’s latest sea level projections. The shaded area reflects the large uncertainties in models using the same basic data sets and approaches. The dotted line reflects deep uncertainty about tipping points and thresholds in ice sheet stability.
IPCC reports are intended to guide global policy-makers in coming years and decades. But the uncertainties about ice melt from Antarctica limit the usefulness of projections by the IPCC and others.
It’s crucial that ice sheet models are improved, tested robustly against real-world observations, then integrated into the next generation of international climate models – including those being developed in Australia.
Sea levels will continue rising in the coming decades and centuries. Ice sheet projections must be narrowed down to ensure current and future generations can adapt safely and efficiently.
(The report is jointly authored by Chen Zhao, a Research associate, at University of Tasmania and Rupert Gladstone, a Adjunct professor, University of Lapland. This is an opinion piece and the views expressed above are the author’s own. The Quint neither endorses nor is responsible for them. This article was originally published on The Conversation. Read the original article here.)
Published: undefined