Two Pronged Global Warming Could Cause Rapid West Antarctica Melt

Summary: Current two pronged global warming could cause a rapid West Antarctica melt that is still stoppable, according to a Nature study published March 30.

Image, based on analysis of weather station and satellite data, depicts Antarctic warming trend from 1957 through 2006; dark red identifies West Antarctica as most warmed region per decade; orange = smaller warming trend; white = no observable change: Image courtesy Trent Schindler, NASA Goddard Space Flight Center Scientific Visualization Studio, Freely available for re-publication or re-use, via NASA Earth Observatory

Limiting the average global temperature rise to 2 degrees Celsius would stop the greenhouse gas-driven, two-pronged attack by atmospheric and oceanic warming currently threatening a super rapid West Antarctica melt by 2100, according to a study published online March 30, 2016, in Nature.

“Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated,” lead author Robert M. DeConto, professor of geosciences at the University of Massachusetts Amherst, and co-author David Pollard, senior scientist at Pennsylvania State University’s Earth and Environmental Systems Institute, state in the article’s abstract.

Three Representative Carbon Pathway (RCP) scenarios evaluate the factor of greenhouse gas emissions on the 1950 to 2500 timeline of the Antarctic contribution to sea-level rises. Scenarios range from mitigated to unabated greenhouse gas emissions.

The worst case scenario, RCP8.5, based on uncurbed greenhouse gas emissions, predicts a rapid West Antarctica melt that includes the onset of a major ice sheet retreat around 2050.

The ice sheet-climate model’s RCP2.6 scenario, however, balances the drastically rapid West Antarctica melt predicted by RCP8.5. The optimistic RCP2.6 scenario limits the average global temperature to a rise of only 2 degrees Celsius and flatlines, registering no rises in Antarctic contribution to global mean sea level (GMSL), across the 450-year-timeline from 2050 to 2500.

The ice sheet-climate model developed by the two paleoclimatologists sweeps backward and forward across time. The model suggests future scenarios based upon insights gleaned from past simulations. Sea-level estimates for the Last Interglacial Period (LIG) and the Pliocene Epoch (PO), as points on a warm past timeline, calibrate the ice sheet-climate model that is applied to the three long-term future Representative Carbon Pathway (RCP) scenarios. The Antarctic ice sheet’s apparent instability, driven by super sensitivity to climate warming, emerges as the major player in sea-level rises.

DeConto and Pollard find in their abstract that “Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6 to 9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability.”

To clarify a melting Antarctic ice sheet’s contributions to sea-level rises, the ice sheet-climate model considers rapid ice melting processes, or mechanisms, specific to the Last Interglacial and to the Pliocene. Maximum rates of collapse into the ocean by vertical ice cliffs characterize the contribution of Antarctica’s melting retreat to sea-level rises of 6 to 9 meters (19.68 to 29.5 feet) during the Last Interglacial Period. Ocean temperature-driven melt rates of the sub-ice-shelf and hydrofracturing, or water-caused crevassing, of low-lying floating ice shelves explain a melting Antarctica’s contribution to the Pliocene’s sea-level rises of 10 to 30 meters (32.8 to 98.4 feet). Atmospheric warming drives Antarctic hydrofracturing via the pools of surface meltwater and rainfall associated with warming air temperatures.

The breakup of hydrofractured ice shelves exposes grounding line ice cliffs that extend below sea level to their deep bedrock seat and rise to dizzying heights above sea level. Removal of the protective buttress afforded by the ice shelves that fringe the Antarctic ice sheet exploits ice cliffs' vulnerability to collapse, under the pressure of their great weight, into the ocean.

The mechanisms of atmospherically-warmed, fractured ice shelves and of ocean-warmed, unstable ice cliffs are known processes. DeConto and Pollard’s ice sheet-climate model is the first to incorporate the “previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs” as analytical values for simulations.

The researchers find that the two-pronged attack from atmospheric warming as well as oceanic warming could cause a rapid West Antarctica melt in a future simulation covering 550 years from 1950 to 2500. High greenhouse gas emissions drive atmospheric warming’s takeover from oceanic warming as the main cause of rapid Antarctic ice loss. Oceanic warming, however, delays recovery.

DeConto and Pollard’s conclude with the finding that “it is the long thermal memory of the ocean that will inhibit the recovery of marine-based ice for thousands of years after greenhouse gas emissions are curtailed.”

Antarctica, a landmass enclosed by oceans (as opposed to the Arctic, an ocean enclosed by landmasses), is seen as a tipping point, with its enormous melted potential for raising global sea levels, in greenhouse gas-driven climate change: Nature News&Comment @NatureNews, via Twitter March 30, 2016

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Antarctica warming, 1957 to 2006; image, based on analysis of weather station and satellite data, depicts Antarctic warming trend from 1957 through 2006; dark red identifies West Antarctica as most warmed region per decade; orange = smaller warming trend; white = no observable change: Image courtesy Trent Schindler, NASA Goddard Space Flight Center Scientific Visualization Studio, Freely available for re-publication or re-use, via NASA Earth Observatory @ https://earthobservatory.nasa.gov/images/36736/antarctic-warming-trends;
(former URL @ http://earthobservatory.nasa.gov/IOTD/view.php?id=36736&src=ve)

Antarctica, a landmass enclosed by oceans (as opposed to the Arctic, an ocean enclosed by landmasses), is seen as a tipping point, with its enormous melted potential for raising global sea levels, in greenhouse gas-driven climate change: NatureNews&Comment @NatureNews, via Twitter March 30, 2016, @ https://twitter.com/NatureNews/status/715238446474858498

For further information:

DeConto, Robert M., and David Pollard. “Contribution of Antarctica to past and future sea-level rise.” Nature 531 (31 March 2016): 591-597. DOI:10.1038/nature17145
Available @ http://www.nature.com/nature/journal/v531/n7596/full/nature17145.html

NatureNews&Comment @NatureNews. "Antarctic model raises prospect of unstoppable ice collapse." Twitter. March 30, 2016.
Available @ https://twitter.com/NatureNews/status/715238446474858498

Penn State Research Communications. "Melt Antarctica." YouTube. March 30, 2016.
Available @ https://www.youtube.com/watch?v=U8aT_EVW778