Studies: Ice Melt from Carbon Dioxide Increase Could Raise Sea Level 100 Feet
Atmospheric carbon dioxide levels expected during the 21st century would equal
those from a geologic era that saw
contraction of the Antarctic Ice Sheet and a substantial rise in sea level, according
to two studies published Feb. 22 in the
Proceedings of the National Academy of Sciences.
A new climate and ice sheet model reported in one study projects the sea level
to rise approximately 100 feet if the current
carbon dioxide level of 400 parts per million increases to 500 ppm, as predicted
by the Intergovernmental Panel on Climate
Change.
Scientists with the Antarctic Geological Drilling Program, or ANDRILL, reached
the conclusions after extracting and examining
a 3,375-foot-long drill-core sample of rock from beneath Antarctica’s McMurdo Sound.
The core sample gave researchers access to layers of sedimentary rock deposited
between 20 and 14 million years ago.
Analyzing this rock record for numerous factors that included geochemical signatures,
sediment properties and changes in fossil types allowed the scientists to meticulously
reconstruct many shifts in water temperature, ice coverage and sea level that occurred
throughout the period. Dr. Sophie Warny’s research group (CENEX-The Center for Excellence
in Palynology) at LSU was in charge these past 7 years of analyzing the fossils of
pollen, spores and organic-walled algae for this international project (see Warny
et al., 2009; Feakins et al., 2012; Griener et al., 2013; Griener et al., 2015; Griener
and Warny, 2015). The project provided funding for 7 LSU graduate students.
During times when carbon dioxide concentrations reached 500 ppm, ice retreated at least 50 miles inward from the Antarctic coast as the Ross Sea warmed about 5 degrees Celsius above its current temperature, according to one study.
“These changes happened in the past; they’re going to happen again in the future,” said co-author David Harwood, professor at the University of Nebraska-Lincoln and research director of ANDRILL’s Science Management Office. “Carbon dioxide driving Earth’s warming in the past and future is just a fact of how the greenhouse gases work. We now have a clear example of how ice sheets can behave under elevated levels projected for the next century.”
Harwood said geological evidence suggests that the planet is already overdue for a 40-foot rise in sea level, based on the carbon dioxide increase from 280 to 400 ppm catalyzed by the Industrial Revolution. That shift occurred so rapidly by geologic standards that Earth’s ice sheets have yet to fully respond as they did in the past, he said.
The team’s findings also informed the development of a computer model that can simulate large-scale contractions of Antarctic ice, a feat that Harwood said previous models struggled to achieve. Both the drill-core sample and the ice sheet-climate models demonstrated substantial changes in ice volume under only modest increases in carbon dioxide.
Though previous research has indicated the vulnerability of ice shelves and marine-based ice sheets, the new PNAS studies have shown that even land-based portions of the East Antarctic Ice Sheet were vulnerable to past warming similar to that projected over the next several decades.
“You’ve got to go back in time to make the models better at forecasting the future,” Harwood said. “By testing and grounding our models on past warm periods, which we might see equivalents of in our near future, we can then understand how this might all play out. This work has allowed the models to mature to the point that they can understand the dynamics of an ice sheet in its many complexities and give a clearer view of the timing and magnitude of change.”
While cautioning that establishing a definitive timeframe for ice melt and sea level rise remains difficult, Harwood said the new model has called for the phenomena to occur at “alarming rates” that exceed prior projections.
“We’re talking about 2 to 3 thousand years (to see a 100-foot rise), whereas previous models might have called for a slower rate of change,” he said. “The models give us important windows into the future. Taken together, the results from these two studies demonstrate that the Antarctic Ice Sheet can respond to elevated atmospheric carbon dioxide levels similar to those projected for the near future.”
Funded in part by the U.S. National Science Foundation and the Antarctic research
programs of New Zealand, Italy and Germany, the ANDRILL Program involved more than
100 researchers. The PNAS study “Antarctic Ice Sheet Sensitivity to Atmospheric CO2
Variations in the Early to Mid-Miocene” was authored by researchers from more than
20 institutions, led by Richard Levy of GNS Science in New Zealand. Its companion
study, “Dynamic Antarctic Ice Sheet During the Early to Mid-Miocene,” was led by Edward
Gasson from the University of Massachusetts Amherst.
Warny, S., Askin, R., Hannah, M., Mohr, B., Raine, I., Harwood, D.M., Florindo, F., and the SMS Science Team, 2009. Palynomorphs from a sediment core reveal a sudden remarkably warm Antarctica during the middle Miocene. Geology, 37(10): 955–958; doi: 10.1130/G30139A.1.
Feakins, S.J., Warny, S., and Lee, J.-E., 2012. Hydrologic cycling over Antarctica during the Middle Miocene warming. Nature Geoscience, 5, 557–560. Published online 17 June 2012. DOI: 10.1038/NGEO1498
Griener, K., Nelson, D. and Warny, S., 2013. Decreased moisture availability on the Antarctic Peninsula during the late Eocene. Palaeogeography, Palaeoclimatology and Palaeoecology, 383-384: 72-78.
Griener, K., Warny, S., Askin, R.E., Acton, G., 2015. Early to middle Miocene vegetation history of Antarctica supports eccentricity-paced warming intervals during the Antarctic icehouse phase. Global and Planetary Change, 127: 67-78. http://dx.doi.org/10.1016/j.gloplacha.2015.01.006
Griener, K. and Warny, S., 2015. Nothofagus pollen grain size as a proxy for long-term climate change: an applied study on Antarctic Eocene, Oligocene, and Miocene cores. Review of Palaeobotany and Palynology, 221:138–143
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