Antarctic Ice Melt

Icecaps in the Antarctica with icebergs melting in the sea Photo by  Sarah Atoui licensed from 123rf.com

Pro: Antarctic Ice Melt is Dangerous

Climate Change is causing accelerated ice loss in Antarctica and Greenland. This is causing sea level rise to increase dangerously. This rising sea level threatens the homes and livelihoods of 100’s of millions of people living on coasts and low-lying islands. NASA presents this graph showing sea level rise plotted by satellite data, and suggests

Downloaded from NASA Global Climate Change4 Accessed 6/19/2020

From USA Today

Greenland and Antarctica have lost 6.4 trillion tons of ice in the past three decades; unabated, this rate of melting could cause flooding that affects hundreds of millions of people by the end of the century, NASA said in a statement.

Satellite observations showed that the regions are losing ice six times faster than they were in the 1990s, according to a new study.

If the current melting trend continues, the regions will be on track to match the “worst-case” scenario of the United Nation’s Intergovernmental Panel on Climate Change, (IPCC) of an extra 6.7, (17 centimeters) inches of sea level rise by 2100.

“That’s not a good news story,” study lead author Andrew Shepherd from the University of Leeds in the United Kingdom, told the BBC

From NASA

Observations from 11 satellite missions monitoring the Greenland and Antarctic ice sheets have revealed that the regions are losing ice six times faster than they were in the 1990s.

The findings, published online March 12 in the journal Nature from an international team of 89 polar scientists from 50 organizations, are the most comprehensive assessment to date of the changing ice sheets. The Ice Sheet Mass Balance Intercomparison Exercise team combined 26 surveys to calculate changes in the mass of the Greenland and Antarctic ice sheets between 1992 and 2018.



Con: Why Antarctica And Greenland Ice Melt is Not Serious:

Antarctica and Greenland are indeed losing ice mass, which is corroborated by a modest rise in annual sea levels.  However, this has been the case since the end of the last glacial maximum between 20 thousand and 19 thousand years ago.  At the height of this glacial period, gigantic ice sheets over a mile thick, covered all of the Artic, Canada and the US from approximately Seattle to New York City.  These tremendous ice sheets also covered much of Northern Europe and Asia as well as regions in Southern South America.  Antarctica and Greenland also had more extensive and deeper ice sheets than today.  Since the last glacial maximum, over the past 20 thousand years, virtually all of these ice sheets have melted away, leaving only Antarctica and Greenland and thousands of relatively tiny glaciers still in existence.  This is normal melting during interglacial periods that generally last approximately 10 to 30,000 years. The last four have averaged about 20 thousand years. (we are approximately 17,000 years into our current interglacial period).  This melting has occurred during each of the past 11 interglacial periods.  In fact, over the past 800,000 years, approximately 60-75% of the time the world has had extensive ice sheets over the Northern and Southern reaches of the North and South hemispheres.  Which means that about 25-40% of the time over the past 800,000 years earth has experienced the warm climate that we’ve experienced over the past 11,000 years.

This interglacial melting has caused an increase in sea levels. The deglaciation spanned approximately 14,000 years, starting about 20,000 years ago.  The vast majority of these ice sheets disappeared in the period between 12,000 and 6.8-6,000 years ago, when the earth experienced warming several degrees greater than we experience today.  In the past 8,000 years, the world has been generally cooling a bit, with intermittent spikes of warming and cooling.  Starting around 1450 the world experienced a significant decline in global temperatures that lasted about 400 years, ending in about 1850.  This period is called the Little Ice Age.  Since the end of the Little Ice Age, the world has been warming and the remaining massive ice sheets in Greenland and Antarctica continue to experience fractional melting as a result. 

It would require several thousands of years of detailed ice mass data to accurately determine the natural trends and fluctuations of Antarctic and Greenland ice masses that would allow an accurate comparison to ice mass fluctuations since the 1.3 part per ten thousand increase in atmospheric carbon dioxide since 1850.  This is the period during which human activity contributed CO2 to the atmosphere, most of which occurred since 1940.

Despite the lack of long-term historical data, short term data contradicts theories of rapidly increasing ice mass loss due to increases in atmospheric CO2 levels. 

Thirty years ago, Antarctica was barely losing ice mass, and this remains so. In 2019 and 2020, media outlets began claiming the Antarctic ice cap is melting six times faster than 30 years ago. “Six times” almost no ice loss remains almost no ice loss. When recent ice loss measurements are compared to the full entire Greenland and Antarctic ice caps, the loss is so small that it is barely detectable.

Writing in the journal Nature, scientists at Columbia University and the University of Victoria, British Columbia report,

The Antarctic continent has not warmed in the last seven decades, despite a monotonic increase in the atmospheric concentration of greenhouse gases. ”The scientists also observe that over the past several decades, “Antarctic sea ice area has modestly expanded.”

https://www.nature.com/articles/s41612-020-00143-w

Sea-level measurements also contradict claims that Antarctic ice loss threatens coastal flooding. NASA satellite instruments, with readings dating back to 1993, show global sea level rising at a pace of merely 1.2 inches per decade, which is not significantly different than sea-level rise from the mid-1800s to the 1950s, a period prior to the 1 part per 10,000 increase in atmospheric CO2, which is otherwise considered the cause of the melting. 

Summary: NASA and subsequent media stories have said this about Greenland and Antarctic ice: “The two regions have lost 6.4 trillion tons of ice in three decades; unabated, this rate of melting could cause flooding that affects hundreds of millions of people by 2100.” However, that is an imperceptible amount relative to the vast amounts of Greenland and Antarctic ice mass. As shown in the right graph in Figure 1, below, the total ice loss each year is a nearly undetectable three ten-thousandths of one percent (0.0003%) of the Antarctic ice mass. Despite statements of certainty, this loss is well within the range of measurement error.

Figure 1: comparison of satellite data for Antarctic ice mass loss. Cumulative ice mass loss on the left, and that same data compared to the total mass of ice on the right. Data source: http://imbie.org (IMBIE is an international collaboration of polar scientists, providing improved estimates of the ice sheet contribution to sea level rise.)
Graphs originally by Willis Eshenbach, adapted and annotated by Anthony Watts

The hype is a typical overreaction to a small fluctuation which is not statistically significant.


References/Further reading:

  1. Greenland, Antarctica Melting Six Times Faster Than in the 1990s source: NASA press release. Accessed 03/28/20 https://www.nasa.gov/feature/jpl/greenland-antarctica-melting-six-times-faster-than-in-the-1990s
  2. Ice loss in Antarctica and Greenland increased sixfold in the last 30 years Source: Livescience, Accessed 3/28/20 https://www.livescience.com/antarctica-greenland-ice-shelf-loss.html
  3. NASA Global Climate Change: https://climate.nasa.gov/vital-signs/sea-level/
  4. The data plotted in the graphs above is from the ice sheet mass balance inter-comparison exercise (IMBIE), a joint exercise by NASA and the European Space Agency. http://imbie.org/about-the-project/
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