(CNSNews.com) - The National Climate Assessment released today by the White House says that as a result of climate change the sea level could rise 8 inches, 11 inches, 4 feet or 6.6 feet by the year 2100, but that a rise of less than 8 inches or more than 6.6 feet is "considered implausible."
“Scientists are working to narrow the range of sea level rise projections for this century,” said the report.
“Recent projections show that for even the lowest emissions scenarios, thermal expansion of ocean waters and the melting of small mountain glaciers will result in 11 inches of sea level rise by 2100, even without any contribution from the ice sheets in Greenland and Antarctica,” it said.
“This suggests that about 1 foot of global sea level rise by 2100 is probably a realistic low end,” the report concludes. “On the high end, recent work suggests that 4 feet is plausible. In the context of risk-based analysis, some decision makers may wish to use a wider range of scenarios, from 8 inches to 6.6 feet by 2100.
“In particular, the high end of these scenarios may be useful for decision makers with a low tolerance for risk,” says the report. “Although scientists cannot yet assign likelihood to any particular scenario, in general, higher emissions scenarios that lead to more warming would be expected to lead to higher amounts of sea level rise.”
The report explains the “uncertainties” the arise in trying to predict future changes in the sea level.
“The key issue in predicting future rates of global sea level rise is to understand and predict how ice sheets in Greenland and Antarctica will react to a warming climate,” says the report. “Current projections of global sea level rise do not account for the complicated behavior of these giant ice slabs as they interact with the atmosphere, the ocean and the land. Lack of knowledge about the ice sheets and their behavior is the primary reason that projections of global sea level rise includes such a wide range of plausible future conditions.
“Early efforts at semi-empirical models suggested much higher rates of sea level rise (as much as 6 feet by 2100),” says the report. “More recent work suggests that a high end of 3 to 4 feet is more plausible.
“It is not clear, however,” says the report, “whether these statistical relationships will hold in the future or that they are appropriate in modeling past behavior, thus calling their reliability into question. Some decision-makers may wish to consider a broader range of scenarios such as 8 inches or 6.6 feet by 2100 in the context of risk-based analysis.”
“Sea level rise lower than 8 inches or higher than 6.6 feet is considered implausible by 2100,” says the report.
Under the worst case scenario, according to the report, 5,790 square miles of U.S. territory could be inundated by 2050.
“More than 5,790 square miles and more than $1 trillion of property and structures are at risk of inundation from sea level rise of two feet above current sea level--an elevation which could be reached by 2050 under a high rate of sea level rise of approximately 6.6 feet by 2100, 20 years later assuming a lower rate of rise (4 feet by 2100) … and sooner in areas of rapid land subsidence. Roughly half of the vulnerable property value is located in Florida, and the most vulnerable port cities are Miami, Greater New York, New Orleans, Tampa-St. Petersburg, and Virginia Beach.”
In a letter releasing the report, John P. Holdren, director of the White House Office of Science and Technology Policy, and Kathryn D. Sullivan, administrator of the National Oceanic and Atmospheric Adminstration, said that the findings of experts who produced the report "describe the current state" of climate science and will help policymakers in responding to climate change.
"Their findings and key messages not only describe the current state of that science but also the current and future impacts of climate change on major U.S. regions and key sectors of the U.S. economy," wrote Holdren and Sullivan. "This information establishes a strong base that government at all levels of U.S. society can use in responding to the twin challenges of changing our policies to mitigate further climate change and preparing for the consequences of the climate changes that can no longer be avoided."