A major U.S. government global warming report due out this week predicts that sea levels could rise as high nearly seven feet by the end of this century, imperiling millions of Americans who live within feet of high-tide levels.
Government scientists say that the rate of sea level rise has doubled since 1992 and is projected to “rise by another 1 to 4 feet in this century.” But this is only the lower end of how much sea levels could rise.
“A wider range of scenarios, ranging from 8 inches to 6.6 feet of rise by 2100, has been suggested for use in risk-based analyses,” according to the Obama administration’s National Climate Assessment (NCA).
“In the U.S., millions of people and many of the nation’s assets related to military readiness, energy, transportation, commerce, and ecosystems are located in areas at risk of coastal flooding because of sea level rise and storm surge,” the NCA said.
Rising sea levels are only some of the problems the NCA warns will come from man-made global warming. Other dangers from a warming world include increasing droughts, storms, floods and tornadoes.
But NCA says that sea level rises pose a special risk because the “U.S. population growth has been greatest in coastal zones and in the arid Southwest, areas that already have been affected by increased risks from climate change.”
“After at least two thousand years of little change, sea level rose by roughly 8 inches over the last century, and satellite data provide evidence that the rate of rise over the past 20 years has roughly doubled,” the NCA continued.
“In the U.S., millions of people and many of the nation’s assets related to military readiness, energy, transportation, commerce, and ecosystems are located in areas at risk of coastal flooding because of sea level rise and storm surge,” the NCA added.
This frightening future can be averted, says the NCA, if mankind phases out its use of fossil fuels — which make up almost 90 percent of the world’s energy needs. In the U.S., more than 80 percent of power is generated by fossil fuels.
NCA’s claim about rising sea levels, however, runs counter to emerging data on the topic. First, satellite data compiled by the University of Colorado shows that sea levels have not been rising faster in the last two decades. While local sea levels may have risen faster or even fallen, there has been no overall acceleration of sea level rises.
“We now have satellite measurements for 20 years which indicate a steady rise of about 3 mm per year, and during that time no acceleration,” said Lennart Bengtsson, a senior research fellow at the Environmental Systems Science Centre at the University of Reading, on the Swedish blog Stockholms Initiativet.
“However, it is important to be clear that this is an average and that there were considerable local variations related to tectonic changes, among others, after the last ice age,” Bengtsson added. “The isostatic adjustment that needs to be done in order to obtain useful data are being evaluated by the experts now. As you can see from the graph, it is clear that we need a relatively long time to obtain a realistic trend, but 20 years is certainly enough.”
Even the United Nations Intergovernmental Panel on Climate Change data, which NCA draws from, shows there has been no acceleration in rising sea levels.
“It is very likely that the mean rate was [1.7 millimeters per year] between 1901 and 2010 for a total sea level rise of [0.19 meters],” according to the IPCC’s latest assessment. “Between 1993 and 2010, the rate was very likely higher at [3.2 millimeters per year]; similarly high rates likely occurred between 1930 and 1950.”
“It is likely that global mean sea level has accelerated since the early 1900s, with estimates ranging from 0.000 to 0.013 [millimeters per year],” IPCC added.
Second, some scientists have even suggested there is no relationship between carbon dioxide emissions and sea levels. NCA argues that CO2 heats the ocean and causes sea levels to rise, but a study published in the Journal of Geodesy last year found that sea levels have not risen any faster.
The study found that the sea level has only risen by 1.7 millimeters per year over the last 110 years, all while carbon dioxide concentrations in the air have risen by a third. This suggests that rising carbon concentrations have not impacted the rate at which sea levels are rising.
“For the last 40-50 years strong observational facts indicate virtually stable sea level conditions,” said Nils-Axel Mörner, former head of the Paleogeophysics and Geodynamics department at Stockholm University. “The Earth’s rate of rotation records a mean acceleration from 1972 to 2012, contradicting all claims of a rapid global sea level rise, and instead suggests stable, to slightly falling, sea levels.”
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