Expected Sea Level Rise Could Double From Prior Expectations

In April, 2018, the Guardian reported research by the UK Centre for Polar Observation and Modeling indicating that climate change was having a greater effect on the melt rate of the Antarctic ice sheets than previously thought and, as such, would “likely prompt global projections of sea-level rise to be revised upward.”

Fast forward a year to Monday, May 20, 2019.

A new study published in the PNAS (Proceedings of the National Academy of Sciences) indicated that previous projections of sea level rise not only understate the problem but could actually double if the increase in greenhouse gas emissions continues unabated. That is a clarion call for action for those willing to listen. Business as usual could “result in land loss of 1.79 million square kilometers, including critical regions of food production, and displacement of up to 187 million people.” Those numbers are not intended as hyperbolic scare tactics.

Unfortunately, we live in a world becoming more nationalistic and tribal at a time when it needs to be more global and inclusive in order to stave off the future crisis at our shorelines. Perhaps, it’s becoming more nationalistic and tribal to preemptively avoid the social, political, and economic structural changes required of a global and inclusive response to the crisis.

The authors point out that advances in understanding ice sheet models since the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (AR5) in 2014 has increased our awareness of the uncertainties and difficulties of predicting outcomes with respect to the implications of the melting ice sheets and the rise of sea levels. To paraphrase a former US Secretary of Defense, this means that science has developed greater awareness over the last five years of the “known unknowns”.

They also point out that “limiting attention to the likely range (i.e., of sea level rise), as was the case of AR5 may be misleading and will likely lead to a poor evaluation of the true risks.” No doubt, the next five years will lead to more unsavory revelations as the likely consequences of business as usual become clearer, and more extreme, based on more advanced predictive modeling.

Finally, they focus our current inadequate understanding of the changing climate on the dynamics of the large ice fields of Greenland and Antarctica. This lack of understanding makes it very difficult to accurately predict the rate of ice sheet melting and its impact on sea level rise. A consequence of that lack of understanding, unfortunately, is greater uncertainty about the future and sea level rise. For example, an article in USA Today indicated that approximately 25% of the West Antarctic ice sheet is now unstable. It reported that “some areas are losing ice five times faster than they were in the 1990’s”. Models based on satellite data have shown the increasing impact of the melting ice sheets on sea level rise since the 1990’s.

The conclusion of the authors of the PNAS study is that “we should plan on a 2 meter rise in sea level by 2100”, if business as usual continues. That is their best prediction factoring in the continued melting of the Greenland and Antarctic ice sheets. It is also double the upper value outlined in AR5, which was published in 2014. That was only 5 years ago. Do the arithmetic and its likely implications. It does not bode well for future generations who will have to live with our failure.

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