Sea Level Shenanigans
The Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) projected that global sea level will rise by up to 60 cm by 2100 due to global warming. The cause of this rise is twofold: expansion of ocean waters as they warm and additional water from glaciers melting. Despite nearly stable sea levels over the past 3,000 years, a number of low-lying and island nations have seized on the imminent flood as a reason to demand reparations from developed nations. In reality, most of the areas in the world that are suffering from inundation are threatened because of human actions, but not global warming. Damming and rerouting of rivers combined with over-pumping of ground water has led to subsidence in many areas—in other words, the seas are not rising, the land is sinking.
As reported in a review article in Science, authored by Robert J. Nicholls and Anny Cazenav, global sea levels have risen throughout the 20th century but key uncertainties remain. Mean sea level has remained nearly stable since the end of the last deglaciation. The rate of sea level rise over much of the last 6,000 years has been an almost-imperceptible 1.4 millimeters per year (about 6 inches per century). Based on tide gauge measurements, sea level has risen by an average of 1.7 ± 0.3 mm/year since 1950. Since the early 1990s, sea level rise (SLR) has been measured by high-precision altimeter satellites. Between 1993 and 2009, the mean rate of SLR was reported as 3.3 ± 0.4 mm/year. Naturally, to climate change alarmists, this suggests that SLR is accelerating because of warming climatic conditions.
With ~10% of the world population living in low-elevation coastal zones, figuring out what is truly causing the seas to rise in some areas is an area worthy of study. In “Sea-Level Rise and Its Impact on Coastal Zones,” Nicholls and Cazenay sum up the present state of scientific understanding:
Satellite altimetry shows that sea level is not rising uniformly. In some regions (e.g., western Pacific), sea level has risen up to three times faster than the global mean since 1993. Spatial patterns in sea-level trends mainly result from nonuniform ocean warming and salinity variations, although other factors also contribute, including the solid Earth response to the last deglaciation and gravitational effects and changes in ocean circulation due to ongoing land ice melting and freshwater input. Spatial patterns in ocean thermal expansion are not permanent features: They fluctuate in space and time in response to natural perturbations of the climate system; as a result, we expect that the sea-level change patterns will oscillate on multidecadal time scales. IPCC AR4 projections suggest appreciable regional variability around the future global mean rise by 2100 in response to nonuniform future ocean warming, but agreement between the models is poor.
More plainly said, there are a few wrinkles in the IPCC scenario. First, sea level is not rising at the same rate everywhere. In fact, in some places it appears to be falling. This is partly because of the normal action of plate tectonics, the movement of Earth's crustal plates. This results in some areas being uplifted, and others forced downward. And, as glacial ice melts, a great burden is removed from the continental land mass supporting it. This can cause significant change in relative sea levels.
“For example, relative sea level is presently falling where land is uplifting considerably, such as the northern Baltic and Hudson Bay—the sites of large (kilometer-thick) glaciers during the last glacial maximum,” state the authors. “In contrast, relative sea level is rising more rapidly than climate-induced trends on subsiding coasts.” Fluctuation is also caused by the interaction of wind and ocean, and changes in the ocean gyres. The nonuniformity of change can be seen in the map below.
Regional sea-level trends from satellite altimetry.
Other factors not mentioned when the threat of climate change induced sea level rise is discussed are non–climate-related anthropogenic processes. Ground subsidence due to oil and groundwater extraction, or reduced sediment supply to river deltas caused by dam building, are more frequently to blame. As stated in the Science review:
In many regions, human activities are exacerbating subsidence on susceptible coasts, including most river deltas [e.g., the Ganges-Brahmaputra, Mekong, and Changjiang deltas]. The most dramatic subsidence effects have been caused by drainage and groundwater fluid withdrawal; over the 20th century, coasts have subsided by up to 5 m in Tokyo, 3 m in Shanghai, and 2 m in Bangkok. To avoid submergence and/or frequent flooding, these cities now all depend on a substantial flood defense and water management infrastructure. South of Bangkok, subsidence has led to substantial shoreline retreat of more than 1 km, leaving telegraph poles standing in the sea.
Sadly, even after presenting the facts given above, the authors just can't resist reaching into the scaremonger's bag for some old and discredited examples of supposed AGW induced sea rise. “Low islands such as the Maldives or Tuvalu face the real prospect of submergence and complete abandonment during the 21st century,” the authors fatuously report. This flies in the face of evidence from sea level expert N. A. Morner, who has worked extensively in the Maldives and has repeatedly stated that the local sea level has not changed significantly in decades (see “New perspectives for the future of the Maldives”). According to Morner et al.:
Novel prospects for the Maldives do not include a condemnation to future flooding. The people of the Maldives have, in the past, survived a higher sea level of about 50–60 cm. The present trend lack signs of a sea level rise. On the contrary, there is firm morphological evidence of a significant sea level fall in the last 30 years. This sea level fall is likely to be the effect of increased evaporation and an intensification of the NE-monsoon over the central Indian Ocean.
Furthermore, a recent study by Auckland University geographer Paul Kench has shown that many low-lying Pacific islands are growing, not sinking. Kench measured 27 islands, where local sea levels have risen at an average rate of 2mm a year over the past 60 years, and found that just four had diminished in size. The islands of Tuvalu, Kiribati and the Federated States of Micronesia are among those which have grown, because of coral debris and sediment.
Does this look like a safe place to live?
Nicholls and Cazenay are not the only researchers to get sea level change wrong. Recently Mark Siddall, Thomas F. Stocker and Peter U. Clark withdrew their letter, “Constraints on future sea-level rise from past sea-level change,” from publication in the journal Nature Geoscience. That paper presented projections of future sea-level rise based on simulations of the past 22,000 years of sea level history using a simple, empirical model linking sea level rise to global mean temperatures. One of their main conclusions was that the model's results supported the projections of sea level rise reported in the Fourth Assessment Report (AR4) of the IPCC.
It seems that using an inappropriate time step in their model led to inconsistencies in their results. “Thus we no longer have confidence in our projections for the twentieth and twenty-first centuries, and for this reason the authors retract the results pertaining to sea-level rise after 1900,” those researchers state in their withdrawal notice. Once again, computer modeling has turned on those it has in thrall.
To be fair, Nicholls and Cazenay admit that estimating sea level change is a total crap shoot. “The extent of future SLR remains highly uncertain—more so than in 2007, when the IPCC AR4 was published,” they state in the article summary: “More attention must also focus on the nonclimate components of SLR, especially for coasts more susceptible to subsidence, such as deltas. Nonclimate processes tend to be larger where there are high concentrations of people and economic activity, and hence have a high impact potential.”
Plate tectonics can cause changes in sea level.
Like most things associated with Earth's environment, sea levels are not static. They are constantly changing, as is the climate itself. The bottom line is this: if you live in a coastal region you had best be willing to adapt to changing sea levels. If you want to live on an island paradise, you need to accept that every 50 to 100 years a cyclone will come along and try to erase it from the map.
Part of sea level change may, indeed, be caused by human activity, but not because of anthropogenic global warming. Damming and rerouting rivers diminishes water flowing to the sea; over-pumping buried aquifers and draining oil fields can cause subsidence. At the same time uplift and subduction, changing wind and currents, erosion and the deposit of sediments all play a larger, natural part. So when climate change alarmists start ranting about the inexorable rise of the world's oceans, realize that it is just another scare tactic being used to frighten the uninformed public—sea level shenanigans meant to promote the warmist agenda.
Be safe, enjoy the interglacial and stay skeptical.
Paradise is fleeting at best.