An international team of researchers has produced the most precise estimate yet of historical melting of the Antarctic ice sheet using historical data collected from various locations in Australia, providing more realistic predictions of future sea level rise. The Antarctic ice sheet is the largest mass of ice on Earth, containing more than 30 million cubic kilometers of water.
Researchers have refined their forecasts of melting Antarctic ice sheets and their impact on future sea levels, narrowing the predicted rise to 5-9 centimeters by 2100. This more accurate estimate is critical for future policy and planning, especially in coastal and low-elevation areas. (artist's concept)
Predicting the future requires historical analysis
Therefore, the melting of the Antarctic ice sheet could have catastrophic effects on future sea levels. To find out just how big the impact was, the research team, including Dr Mark Hoggard from the Australian National University, turned to the past.
Dr Hoggard said: "If we want to know what will happen over the next 100 years, we need to have an accurate model of how the ice sheet responds to climate change. Previous predictions of Antarctica's contribution to global mean sea level rise were that by 2100, Antarctica's sea levels would sea levels would have risen by 20 to 52 centimeters. But by better understanding sea levels during the mid-Pleistocene, our study lowers this estimate to 5 to 9 centimeters, the period 3 million years ago that is thought to be the closest to expected conditions during this century."
Methods and findings
Dr Hoggard said accurate determination of sea levels during this period could help reveal how the Antarctic ice sheet behaved in the past and, therefore, how it might behave in the future. To determine historical sea levels, researchers first looked at Australia's geological record, looking for coral fossils and other sea level markers to show how high the coastline once was. "It's not a perfect approach, as fossil marks are affected not only by the movement of sea water, but also by movement of land. Over millions of years, Earth's plates move up and down, a process known as dynamic topography. If you were to stand on Australia's coastline today and see our Sea levels are rising, and that could go either way. It could be that the sea levels are actually rising, or it could be that the land you're standing on is sinking, and for the first time we've corrected for these up-and-down motions across the continent, so we can see where the sea-level markers really are," Dr. Hoggard said.
According to previous estimates, Australia's mid-Pleistocene sea level was 6 to 60 meters higher than today's sea level. Sea level can now be more accurately determined to be 16 meters, with the Antarctic ice sheet possibly contributing 9.8 meters.
The researchers attribute the accuracy of these predictions to major advances in science over the past decade: "Thanks to better models, increased computing power, and a deeper understanding of geological processes, our ability to map the movement of tectonic plates in the Earth's mantle has been revolutionized. Now, this is probably the best reconstruction we've ever had."
Reducing this uncertainty will make modeling of future sea level rise more accurate. While lower estimates of sea level rise from the Antarctic ice sheet are good news, researchers note that there is still a lot of work to be done.
Dr Hoggard said: "If you live in a Pacific island nation like Tuvalu, where the highest point is only 4.6 meters above sea level, small changes in baseline sea level can have devastating effects when a disaster event such as a hurricane or storm surge comes. Ensuring we have more accurate models can help improve policy, especially when looking at coastal and low-lying communities where changes of just a few centimeters in sea level can have an impact."