John’s Blog/Newsletter: SEA LEVEL RISE NOW

Just this week a good article of scientific research was published, that intended to clarify rates of sea level rise. Unfortunately, for the public, it added to the confusion. In fact a quick read of the story in the New York Times, would lead someone to believe that sea level rise is SLOWER than previously thought, yet Discovery News coverage indicated that sea level rise is HIGHER than previously thought. Which is it? In the last few days many have asked me to explain the article, the inconsistency and what it really means.

Over the last century the best calculations for global, average sea level (SL) has been about 7-8 inches, or 18-20 centimeters. First it is worth recalling what causes sea levels to rise. Melting in the size of glaciers and the two ice major sheets–Greenland and Antarctica — is the largest factor. Expansion of seawater as it warms is also significant, causing about half the increase in the last century as the ocean has warmed. Smaller impacts would be changes in the amount of water on the continents in the form of lakes, reservoirs, and even moisture in the soils.

Land subsidence, or uplift, can also be a very significant adjustment. From New Orleans, to Virginia Beach, to Venice-Italy, Jakarta, and Tokyo most of the apparent rise in SL has actually come from the land going down. In other words where SL is measured from observing stations on land, and the land becomes 12 inches lower, the global 8 inch rise is effectively 20 inches higher. For example, in Jakarta, in the last three decades they have had more than ten feet (3 meters) of SL rise just from the land subsiding. Virginia Beach has had about two feet of SL rise, just due to land subsidence in the last hundred years.

Historically, most of our sea level measurements have come from tide gauges like the one shown here, in operation since 1844 in France. There are hundreds around the world — with some not much more sophisticated than a measuring stick, shielded from waves by a buffering structure like the one shown. They were not intended to track changes in SL, but rather to observe the patterns and magnitudes of heights of tide change, daily and with the lunar and planetary cycles. They did their primary job very well in most places tracking about three feet, or a meter, of routine cycles.

In recent years we have also looked to that same global group of tide gauges to get insight into long term changes in sea level, but the accuracy was limited given all the variations in land subsidence and uplift, and changes in wave patterns, and ocean currents in the hundreds of systems around the world some as old as the one shown here. Refining the accuracy to the scale of one inch world wide is not only pushing the limits, but beyond the limit of what is realistic for this pre-satellite technology.

For the last two decades, going back to the launch of the Topex/Poseidon “Oceanographer” Satellite in 1992 measurement of global ocean height entered a new era of accuracy — truly global coverage, and consistency. Thus the really accurate record for sea level only goes back two decades.

What this new research published this week in NATURE (Hay, Morrow, et al) says is this: A better refinement of the global tide gauge data, looking at adjustments such as land subsidence, indicates that the amount of global average SL rise in the era before the sattelites was about 5 inches, not 6 inches. [Note: this post was revised on 1-18-15 to adjust the numbers of inches to better reflect the metric measurements in the new research. The principles are unchanged. Our initial conversions were rounded off in a way that makes them a little inaccurate.]

It seems perfectly reasonable that the old system of mechanical gauges did not give information down to the level on a one inch (few cm) accuracy as a global standard for a century. So the OLD amount of SL rise, was a tad less than thought.

But the implication is significant. The highly accurate data in the last two decades showing an increase of approximately 2.4 inches, then shows a much greater rate of increase in SL compared to the five inches, pre-1990 data. (In other word, 2.4 inches is a much greater rate of increase, compared to 5 inches, than it is to 6 inches.)

So in effect both headlines are correct — but very confusing. Sea level rise over the last hundreds years was slightly less than believed. But the current rate of increase, and the trend, is actually faster, or steeper than believed. [Credit for pointing out the inconsistencies in the headlines this week goes to friend Carl Nettleton a communications pro.]

This seems like a twist on the old “glass half empty or glass half full” metaphor, with which I usually end my presentations.

Few people appreciate the following facts, which are the really important bottom line takeaways about sea level:

1. Sea level is rising and accelerating. The trend will continue for centuries, regardless of efforts to slow the warming, with energy efficiency, GHG reduction, etc., due to the heat that is already trapped in the oceans. The effects will be extremely disruptive to our economies, communities, and way of life. (If we do not take the steps to slow the rate of warming, the chance for catastrophic SL rise this century, increases substantially.)
2. We must seriously begin planning now for major SLR that will become obvious by mid-century and beyond. Now is the time to realize that the shoreline will move far inland forcing us to either retreat or build higher.
3. Sea level will vary dramatically from one location to another due to land subsidence, topographic features, changing ocean currents, and geologic structure.

Anyone with investments in coastal areas — and on tidal rivers — would be wise to consider the effects and implications, BEFORE the wider market does. There will be losses ahead, but also opportunities. As always, those with the ability to see what is “on the horizon” or in this case, just beyond the horizon, can be better prepared.

The headlines this week about the revised sea level history went global. Sadly, as noted above, it seems to have created more misunderstanding than understanding.

Please consider sharing this information with friends and on blogs. For more information about sea level rise and my consulting and speaking services visit my website www.johnenglander.net.