Scientists from the University of Leeds, the University of California San Diego, and University of Maryland reviewed decades of satellite measurements to reveal how and why Antarctica’s glaciers, ice shelves, and sea ice are changing.
Their report, published June 14 in a special issue of the journal Nature on Antarctica, explains how ice shelf thinning and collapse have triggered an increase in the continent’s sea level contribution. The study “Trends and connections across the Antarctic cryosphere” also explains that although the total area of sea ice surrounding Antarctica has shown little overall change during the satellite era, there are signs of a longer-term decline when mid-twentieth century ship-based observations are considered.
Helen Amanda Fricker, a glaciologist at Scripps Institution of Oceanography at UC San Diego, contributed to that study. She is also a co-author of a review paper in the same issue that considers the consequences for Antarctica’s future under two climate scenarios.
“Even though Antarctica is far from most human civilization, its ice sheet is losing mass to the ocean, and is an increasing contribution to sea-level rise, which will have large impacts on coastlines all around all the world,” said Fricker, who is currently on sabbatical at the Institute of Marine and Antarctic Science in Hobart, Australia. “The future we choose could determine when we need to rebuild airports, cities and infrastructure so that we can become resilient to such changes.”
The review, “Choosing the future of Antarctica,” presents two narratives of what the continent might be like in the year 2070. Fricker and the rest of the review authors are winners of the prestigious Tinker-Muse Prize for Science and Policy in Antarctica and experts in a range of disciplines, including biology, oceanography, glaciology, geophysics, climate science, and policy.
The team considers a scenario in which greenhouse gas emissions remain unchecked and another in which ambitious action is taking to limit them. They describe two resulting plausible outcomes. In the former, global sea-level rise accelerates and a lowering of the pH of the oceans alters marine ecosystems. In the latter, ecosystems remain intact and human pressures on Antarctica are collectively managed through international governance.
Satellite data gathered over decades provide a baseline for such future projections. In the University of Leeds-led analysis of records going back to the mid 20th Century, Fricker and colleagues found evidence that the drift of Antarctic glaciers toward the ocean is accelerating.
The biggest changes have occurred in places where ice shelves – the continent’s protective barrier – have either thinned or collapsed. In West Antarctica, ice shelves are being eaten away by warm ocean water, and those in the Amundsen and Bellingshausen seas are up to 18 percent thinner than in the early 1990s. At the Antarctic Peninsula, where air temperatures have risen sharply, ice shelves have collapsed as their surfaces have melted. Altogether, 34,000 square kilometres (13,000 square miles) of ice shelf area has been lost since the 1950s.
“Although breakup of the ice shelves does not contribute directly to sea-level rise – since ice shelves, like sea ice, are already floating – we now know that these breakups have implications for the inland ice: without the ice shelf to act as a natural buffer, glaciers can flow faster downstream and out to sea,” said Fricker.
In the Amundsen Sea, for example, ice-shelf thinning of up to six meters (20 feet) per year has triggered a 1.5-kilometer (1-mile) -per-year acceleration of the Pine Island and Thwaites glaciers. These glaciers have the potential to raise sea levels by more than a meter, and are now widely considered to be unstable.
Satellite observations have meanwhile provided an increasingly detailed picture of the sea ice cover, allowing scientists to map the extent, age, motion and thickness of the ice.
The combined effects of climate variability, atmosphere and ocean circulation, and even ice shelf melting have driven regional changes, including reductions in sea ice in the Amundsen and Bellingshausen seas.
“Antarctica is way too big to survey from the ground, and we can only truly understand the trends in its ice cover by looking at the continent from space,” said lead author Andrew Shepherd, from the School of Earth and Environment, at Leeds.
“The waxing and waning of the sea ice controls how much sunlight is reflected back to space, cooling the planet,” said co-author Sinéad Farrell, from the Earth System Science Interdisciplinary Center at the University of Maryland. “Regional sea ice loss impacts the temperature and circulation of the ocean, as well as marine productivity.”
New missions, such as Sentinel-3, the recently launched Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), and ICESat-2 to be launched in September, will continue to give researchers insights into the disappearing ice in even greater detail.
About the University of Leeds
The University of Leeds is one of the largest higher education institutions in the UK, with more than 33,000 students from more than 150 different countries, and a member of the Russell Group of research-intensive universities.
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About the College of Computer, Mathematical, and Natural Sciences
The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 9,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $175 million. cmns.umd.edu
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Scripps Institution of Oceanography at the University of California San Diego, is one of the oldest, largest, and most important centers for global science research and education in the world. Now in its second century of discovery, the scientific scope of the institution has grown to include biological, physical, chemical, geological, geophysical, and atmospheric studies of the earth as a system. Hundreds of research programs covering a wide range of scientific areas are under way today on every continent and in every ocean. The institution has a staff of more than 1,400 and annual expenditures of approximately $195 million from federal, state, and private sources. Scripps operates oceanographic research vessels recognized worldwide for their outstanding capabilities. Equipped with innovative instruments for ocean exploration, these ships constitute mobile laboratories and observatories that serve students and researchers from institutions throughout the world. Birch Aquarium at Scripps serves as the interpretive center of the institution and showcases Scripps research and a diverse array of marine life through exhibits and programming for more than 430,000 visitors each year. Learn more at scripps.ucsd.edu and follow us at Facebook, Twitter, and Instagram.
About UC San Diego
At the University of California San Diego, we constantly push boundaries and challenge expectations. Established in 1960, UC San Diego has been shaped by exceptional scholars who aren’t afraid to take risks and redefine conventional wisdom. Today, as one of the top 15 research universities in the world, we are driving innovation and change to advance society, propel economic growth, and make our world a better place. Learn more at www.ucsd.edu.