Rapidly rising sea levels that inundate the coastlines where billions of people live is one of the more worrisome concerns associated with climate change. A new report in Nature suggests that the rate of melting of crucial Antarctic ice sheets has tripled during the past 25 years and is accelerating sea level rise. The melting is the result of warmer ocean waters undermining glaciers grounded on sea bottoms around Antarctica and increased surface melt from warmer air temperatures. If all of the glaciers on the southern continent were to melt then sea level would rise by 58 meters (190 feet).
In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change suggested that average sea level rose by 7.5 inches between 1901 and 2010. The IPCC also reported that sea level very likely rose at a rate of about 1.7 millimeters (0.07 inch) per year between 1901 and 2010, but had accelerated to 3.2 millimeters (0.13 inch) between 1993 and 2010. If the rate does not increase, that would imply that sea level would rise by an average of 10 inches by 2100. In fact, that is the IPCC’s low end estimate while its high end projection is nearly 39 inches depending on how much extra carbon dioxide is emitted into the atmosphere during the rest of this century.
A February study in the Proceedings of the National Academy of Sciences based on satellite altimeter data that sea level rise at 3 millimeters per year has accelerated at a rate of 0.084 millimeters since 1993. If sea level continues to change at this rate and acceleration, the researchers estimate that average sea-level rise by 2100 will be closer to 24 inches than 10 inches in 2100.
In the new Nature report, a team of researchers has reviewed 24 different studies on the melting trends in Antarctic ice sheets. Overall, they find that since 1992, the frozen continent has lost about 2.7 trillion tons of ice into the oceans raising sea level by an additional about 7.6 millimeters (0.3 inch) during that period. Basically, the current rate of melting in Antarctica has boosted the sea level rise by 0.3 millimeters per year since 1992. However, the losses in the last five years have tripled over what they were in the first five years of the period. This roughly suggests that Antarctica glacial melting is now adding about 0.5 millimeters per year to sea level rise.
So adding that to 3.2 millimeters yields an annual increase of 3.7 millimeters annually. At a constant rate that would increase average sea level to nearly 12 inches by the end of this century. Not good, but hardly a catastrophe.
The IPCC’s high end projection of 39 inches implies that sea level rise would have to average 12 millimeters (0.48 inch) per year from now until 2100. In its article on the new Nature study, the Washington Post reports, “In a controversial 2016 study, former NASA scientist James Hansen and a team of colleagues found that Earth’s sea level could rise above one meter (or 3.3 feet) within 50 years if polar ice-sheet loss doubles every 10 years. A tripling every decade, were it to continue, would reach that volume of sea level rise even sooner.”
That would imply an annual sea level increase of more than 20 millimeters (0.78 inches) per year; 7 times the current ratae and more than ten times the rate experienced during the 20th century. But as the Post notes, “There is no proof the current rate of change in Antarctica will continue. Scientists can’t see the future, but they do fear continuing and even worsening losses.”
from Hit & Run https://ift.tt/2JTRPnV