Friday, September 4, 2015

Rate of Sea Level Rise Has Doubled Since 2014. Trend or Outlier?

During the past year and a half, the rate of sea level rise has doubled. Sea level has risen at a rate that projects out to over 0.2" per year.  The sea level rise over the last 20 months has jumped from the previous two decades rate of 0.1".  Given that there is a great deal of variability in the rate of in sea level rise on a short term basis, it's hard to judge whether the sea level rise is accelerating, or if this increase is just a short term aberration.  As shown in the chart below, while the trend in sea level is clearly upward, there is a great deal of variability on a year to year basis. During the past two decades, any big jumps or declines in sea level rise have been followed by reversion to the trend line.

If the sea level rise is carried out to an additional decimal point, the sea level has been rising at a rate of 3.2 mm ( 0.12") per year over the past couple of decades. Thus, being more precise, the rate of sea level rise since the start of 2014 has increased from 0.12" to more than 0.24" annually.  (for reference 0.1" is equivalent to 2.54 mm)

For a finer level of detail, monthly reports on sea level rise are provided by CSIRO

The rate of sea level rise has enormous implications for long term planning purposes. If the rate of sea level rise reverts to the mean and continues at 0.1" per year, then it may be decades before rising sea levels cause massive problems. If an annual sea level rise of 0.2" is the new normal, then there is likely to be a dramatic increase in tidal and storm related flooding in less than two decades. And if the rate of sea level rise continues to accelerate, as the vast majority of climate researchers predict, sea level could rise by 8" or more by mid century. 

Sea level rise offers a dramatic example of why proposed actions to reduce greenhouse gas emissions are so controversial. The majority of today's voters may well be dead before the impacts of rising sea level become catastrophic, sometime between 2050 and 2100. Given the uncertain long term benefits of various actions to reduce fossil fuel burning, and the immediate economic pain to be caused, solution aversion is an understandable reaction. Of course, for those that care about the world that they are leaving to their grandchildren and/or hope to still be around in 2050, continuing down the current path of annual global emission of 9 billion metric tons of CO2 is frightening.

With the past year and a half  being the hottest in recorded history, it's not surprising that there has been an increase in the rate of sea level rise. The high recent temperatures are in part due to El Nino. Thus, once El Nino conditions end, there may be a small decrease in global temperatures and sea level rise.  However, on a long term basis, climate researchers predict that the rate of sea level rise will accelerate. As shown in the following chart, the projected rise in sea level becomes a huge problem after 2050. If these projections are correct, the current refugee problem in Europe could become exponentially worse as coastal areas become uninhabitable.

The costs of dealing with rising seas will be enormous. Miami has already spent $15 million on pumps to keep tidal waters from rising on city streets and plans on spending an additional $500 million. Miami's spending may only be a pittance compared to the future cost of defending against coastal flooding. The authors of a study published in Nature Climate Change suggest that spending
of $50 billion per year will be required through 2050 to defend against coastal flooding.


Climate researchers have warned that sea levels rise is accelerating. It's logical to conclude that glacial and arctic ice melt will occur at a more rapid rate in a warming world. Time will tell whether the acceleration in sea level rise started picking up speed in 2014.

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