Giant icebergs are not the main threat to Antarctica’s stability 

A new study led by geologists and geographers from the University of Florida provides new insights into Antarctic ice shelves and how they respond to climate change. 

While warming temperatures are clearly driving a widespread loss of ice shelves, the study reveals that major iceberg calving events have not significantly increased in frequency or size. 

Instead, smaller, more frequent calving events, which the authors describe as “death by a thousand cuts,” appear to be the main culprits in Antarctic ice shelf decline.

The findings have been published in the journal Geophysical Research Letters, and the research team was led by assistant professor of geological sciences Emma MacKie and assistant professor of geography Katy Serafin (both from the University of Florida), along with a collaborator from 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,” MacKie said.

Rising temperatures and Antarctic ice shelves 

Calving refers to the process by which chunks of ice detach from ice shelves to form icebergs. While this process has long been known to occur naturally, the role of climate change in speeding it up has attracted increasing scientific attention. 

The most striking aspect of this new study is its finding that extreme, large-scale iceberg break-offs – although they capture headlines – are not happening more frequently or growing in magnitude due to global warming.

Throughout their survey, the researchers primarily observed a broad retreat of ice shelves associated with rising temperatures. However, these large calving events – where an iceberg exceeds 100 square kilometers – remain relatively rare.

Large calving events are rare

The team delved into 47 years’ worth of satellite data, spanning 1976 to 2023, to uncover patterns in the frequency and size of large calving events. Despite this extensive timeframe, major calving events still numbered too few for standard statistical methods to paint a clear picture. 

To address this, the team turned to extreme value theory, a statistical approach commonly used to study rare natural disasters like major floods or earthquakes.

Katy Serafin – an expert on extreme flooding – applied these established methods to the ice shelf data. “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,” she explained.

“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.”

Giant icebergs are not increasing

By applying extreme value theory to the available data, the researchers calculated the likelihood and potential size of large calving events. 

They estimated that a once-in-a-decade iceberg could be around 6,100 square kilometers, comparable to a giant iceberg that broke off in 2017 (roughly the size of Delaware), while a once-in-a-century iceberg could measure as much as 45,000 square kilometers, an area larger than 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.

Despite these theoretical extremes, the researchers found no upward trend in the frequency or size of these major events over the last five decades. 

Interestingly, the largest icebergs observed appeared between 1986 and 2000, suggesting that these rare break-offs are not directly tied to rising temperatures.

The real threat: Small calving events

While dramatic, large icebergs do not seem to be increasing in tandem with climate change, smaller, more frequent calving events appear to be gradually eroding Antarctica’s ice shelves.

The cumulative impact of these numerous small break-offs seems to be the main driver of ice shelf loss over the past 50 years.

This ongoing reduction in ice shelves – amplified by warmer conditions – poses long-term concerns for ice sheet stability and global sea levels.

Climate models and sea level rise

The study’s findings carry significant consequences for climate modeling and predictions of sea level rise.

Contrary to public perceptions focusing on massive icebergs breaking away, the slow, continuous loss of ice could represent the more serious danger to polar regions.

Understanding these smaller, frequent calving events can help scientists improve models that forecast the future of ice shelves and enable policymakers to formulate more precise strategies for addressing the ramifications of ice melt.

Dynamics of Antarctic ice shelves

By revealing that large calving events are not growing in size or frequency, the study comes up with a new narrative on how Antarctic ice shelves are declining. 

The emphasis shifts to the accumulative toll of small-scale calving. This highlights the value of long-term observational data and specialized statistical methods, such as extreme value theory, for discerning broader patterns in rarely observed phenomena.

Ultimately, the results warn that rapid warming, while not accelerating catastrophic iceberg release, is facilitating a steady thinning of ice shelves – a trend that remains a serious concern for Antarctica’s stability and the worldwide consequences of sea level rise.

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