Sea Level Rises and the Precautionary Principle

September 18, 2014 Stephen Murgatroyd
Sea level rises are said to be the most serious consequence of climate change. According to the draft IPCC’s fifth assessment draft leaked recently, sea levels are likely to rise by between 29 and 82 centimeters by the end of the century, compared to 18-59 centimeters anticipated in the 4th Assessment report published in 2007 – the IPCC thinks things are getting worse. Satellite measurement shows that sea levels have risen (app) 6 cm since 1990. If we see a 6 cm rise every 15 years (app) we will see a rise of (app.) 34 cm by 2100.



A paper published recently in Global and Planetary Change finds global sea level rise has decelerated by 44% since 2004 to a rate equivalent to only 7 inches (17.8 cm) per century. According to the authors, global mean sea level rise from 1993-2003 was at the rate of 3.2 mm/yr (± 0.4 mm/yr), but sea level rise "started decelerating since 2004 to a rate of 1.8 ± 0.9 mm/yr in 2012."  The IPCC’s fourth assessment looks more likely to be the “best case” at this time rather than the more recent IPCC analysis.


Some suggest that these estimates are far too low. National Geographic said this in its November 2013 issue:


“Climate scientists now estimate that Greenland and Antarctica combined have lost on average about 50 cubic miles of ice each year since 1992—roughly 200 billion metric tons of ice annually. Many think sea level will be at least three feet [91 cm] higher than today by 2100. Even that figure might be too low.”


- the 91 cm figure being much higher than the IPCC anticipate.



The World Bank analysis also assumes a higher rate than the IPCC. A recent study of the likely impact of sea level rise on coastal cities suggests that the mean sea level will rise between 0.2 meters and 0.4 meters (19. 8 cm to 39.9 cm) by 2050. This both larger and faster than other estimates.



James Hansen, the doyen of climate change scientists, sees ocean level rise as even more alarming.  He has suggested that sea level rises could be between 15 and 20 feet – that is between 457 cm and 356 cm – since the IPCC models take inadequate account of ice sheet melting.


Not to be outdone, Ben Strauss from Climate Change Central in the US suggests in a recent study that by the end of this century, if global climate emissions continue to increase, the climate system may lock in 23 feet of sea-level rise." 23 feet is 701 cm – way beyond all consensus models. He basis this on a calculation of sea level rises linked to the level of CO2 emissions and the predicted temperature rises these levels of CO2 will cause.  Strauss sees the IPCC as “enormously cautious”.


Meantime, the ultimate skeptical ocean scientist is Nils-Axel Molner. He has been studying sea level rises for most of his career and he dismisses most of the concerns out of hand.  Indeed, he suggests that there is no discernable rise in sea level beyond that normally expected for the last fifty years.


So, what to do? If you are a policy maker you have an international body suggesting that sea level rise could be somewhere between 26 and 32 cm by the end of the century. Then you have respected scientists who claim “special expert knowledge” suggesting that this is by far too cautious and is more likely to be around 700 cm. Yet another suggests not to panick, since nothing is happening. What is clear is that we don’t know – the science is very unsettled.


One place has already made its decision. Kiribati – a small island in the Pacific – is seeking to buy land in Fiji so that it can relocate its population of 113,000. One member of this community is seeking asylum in Australia as a result of these developments. Other countries are seeking reparations from the developed world to pay for sea defenses – this is a major argument behind the $100 billion annual fund being demanded in Poland as part of this weeks annual climate change jamboree (COP19).



Outgoing New York Mayor Bloomberg, whose own team of scientists suggest that sea level rises in the New York area could be as much as 73 cm by 2050, has proposed an investment of just over $19 billion in strengthening  the sea walls and flood defenses of New York city. New York is just one of twenty five cities around the world to be investing in these strategies.



The precautionary principle seems to apply. If you have responsibility for a coastal city or a community in a floodplain, there is a need to plan and to take such precautionary measures as seem appropriate and affordable. While precaution can be expensive, dealing with the aftermath of flooding is even more expensive.




But the next time you hear a politician say that the science is settled, just smile. It isn’t.

Written by Stephen Murgatroyd - contact stephen.murgatroyd@shaw.ca for permissions.
Previous Article
Science and Public Policy

How should science shape public policy?This is not a theoretical question....

Next Article
Typhoon Haiyan

Typhoon Haiyan is a terrible storm – one of the worst for some time. We...