Antarctic ice shelves are shrinking mainly due to frequent small calving events, while major iceberg break-offs remain rare and unchanged in frequency.
A recent study by geologists and geographers at the University of Florida provides new insights into the impact of climate change on Antarctic ice shelves. The research confirms widespread ice shelf loss due to rising temperatures but finds that the frequency and size of major iceberg calving events have remained relatively stable.
This study was led by Assistant Professor of Geological Sciences Emma MacKie, Ph.D., and Assistant Professor of Geography Katy Serafin, Ph.D., along with a collaborator at the Colorado School of Mines.
“Our results suggest that the primary threat to our ice shelves is ‘death by a thousand cuts’ via small calving events, rather than catastrophic extremes,” said MacKie.
Understanding Iceberg Calving
Calving, when chunks of ice break off from ice shelves to form icebergs, is common and increasingly influenced by climate change. For extremely large icebergs, this process is typically slow, often starting with small rifts that spread across the ice shelf before fully breaking off.
These rifts can be detected as they form and grow using satellite data, but their random nature and the risks associated with sending scientists to observe them in person make it extremely difficult to predict when future rifts or calving events may occur. Major calving events are particularly challenging to study. While smaller calving events occur frequently, large events — where over 100 square kilometers of ice break away — are exceptionally rare.
This study is the first of its kind to focus on these large calving events. Even with 47 years’ worth of satellite data from 1976 to 2023, the team was still faced with a small sample size. This challenge was addressed with extreme value theory, a type of statistical analysis used when studying rare natural disasters like major earthquakes, extreme floods, or volcanic eruptions. As an expert on extreme flooding, Serafin was no stranger to this type of data analysis.
“Statistical models relating event size and frequency are tools that have been used for estimating rare flood events, like a 100-year flood, for decades,” said Serafin. “Now that satellite imagery can more consistently track large calving events, we thought we’d test whether we could apply the same tools for understanding how likely these massive calving events are.”
Predictions for Future Iceberg Sizes
Using this method, the team analyzed extreme calving events found in the satellite record and developed a model to predict the likelihood of these events over time. While creating their models, researchers also developed scenarios to predict how large calving events could be. By their estimates, a once-in-a-decade iceberg could be as large as 6,100 square kilometers, only slightly larger than an extreme calving event in 2017, when an iceberg roughly the size of Delaware broke off the Antarctic ice sheet. A once-in-a-century event event could produce an iceberg about 45,000 square kilometers, slightly larger than the entire country of Denmark.
“A once-in-a-century iceberg would be several times larger than any in the observational record and would have a significant impact on ice-sheet stability and ocean processes,” said MacKie.
The team found no evidence that large icebergs have increased in size over the last half-century, with the peak iceberg surface areas occurring between 1986 and 2000. This indicates that extreme calving events do not correlate with climate change, although overall ice shelf loss has increased due to climate change. While extreme calving events continue to be rare and may be part of a larger natural cycle, more numerous small calving events have dominated Antarctic ice shelf loss over the last half-century.
Reference: “47 Years of Large Antarctic Calving Events: Insights From Extreme Value Theory” by Emma J. MacKie, Joanna Millstein and Katherine A. Serafin, 29 November 2024, Geophysical Research Letters.
DOI: 10.1029/2024GL112235
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1 Comment
“This study is the first of its kind to focus on these large calving events.” They summarize their observations with, “Calving, …, is common and increasingly influenced by climate change.” However, they temper that with, “The research confirms widespread ice shelf loss due to rising temperatures but finds that the frequency and size of major iceberg calving events have remained relatively stable.” The assertions about the correlation of small icebergs with ‘climate change’ is not as strongly supported as the lack of correlation with climate change. They reinforce that with, “This indicates that extreme calving events do not correlate with climate change, …”
Interestingly, this University of Florida press release does not make the explicit point that the study was for all of Antarctica. Therefore, I went to the provided DOI link to read the actual paper. What I confirmed was that the study was for all of Antarctica. However, what stood out was that most of the calving, and in particular the largest, were located in West Antarctica. This is interesting in light of the lack of correlation with “climate change” because it is generally known that West Antarctica has more known volcanoes than East Antarctica, and also contains regions of high geothermal heat flow.
This suggests that even the smaller icebergs may be the result of geothermal hot spots in the west, rather than from warmer air caused by an increase in the well-mixed CO2. If one were to complain that the small icebergs are the result of ‘warm’ water eroding the base of the grounded ice, then there is a problem of explaining why warm, generally buoyant water is found several hundred feet below the surface of the water. The point being, “How did the CO2-warmed air result in warming the water below the surface?”