MALAYBALAY CITY (MindaNews/17 May)—Sea level rise has become irreversible, scientists said at the Weather and Climate Forum in Paris last month. And on May 12, a news item in www.newsweek.com quoted scientists as having said that “vast glaciers in West Antarctica seem to be locked in an irreversible thaw linked to global warming that may push up sea levels for centuries.”
The Newsweek report simply affirmed what the experts said at the forum in Paris, as the collapse of the West Antarctic ice sheet is seen as a major contributor to sea level rise in the future, although most of us would not experience it in our lifetime. Eric Rignot of the University of California, lead author of the report published by Newsweek, said the ice melt in Antarctica has passed “a point of no return.”
In both instances, the scientists agreed on one thing: the main culprit is the accumulation of man-made greenhouse gases or GHGs (mainly carbon dioxide) in the atmosphere, which drive global temperatures up. As the Intergovernmental Panel on Climate Change said in its latest assessment report, “Ocean thermal expansion and glacier melting have been the dominant contributors to 20th century global mean sea level rise.”
“If emissions continue to grow without mitigation,” it added, “we will reach a point at which no amount of adaptation would have an effect.”
Consider too the retreat of ice sheets from Greenland, which like Antarctica, also contributes significantly to sea level rise. Combine the impact of the ice loss in the two regions, and that leaves humanity with no option but to take drastic mitigation and adaptation measures.
Ice sheets in Greenland and Antarctica serve as the largest reservoirs of freshwater on earth, thus their behavior as shaped by man-made activities as well as geological and other natural factors have contributed to dips and rises in sea level across time, the IPCC said. What happens in these [no longer so frozen] regions is a deceptively simple cause-effect equation: Increases in ice mass through snowfall mean a fall in global mean sea level while increases in ice melt and outflow cause its rise.
“Over the course of this century, however, sources of mass loss appear set to exceed sources of mass gain, so that a continuing positive contribution to global sea level can be expected,” the IPCC noted.
Skeptics about the role of GHGs in global warming and its attendant effects on climate and sea level would argue that the earth is just going through a repeat of a cycle that had occurred in the past.
Indeed, climatologists themselves have found out that the earth had undergone warm periods about three million years ago that caused sea level to rise. It is estimated that such increase must have exceeded five meters but not more than 10 meters above present when global mean temperature was up to 2°C warmer than pre-industrial. The IPCC said this implies “substantial contributions from the Greenland and Antarctic ice sheets.”
However, the IPCC added that from the late 19th century to the early 20th century the rates of global mean sea level rise were higher than those during the previous two millennia. “Ocean thermal expansion and glacier melting have been the dominant contributors to 20th century global mean sea level rise.”
“It is very likely that the rate of global mean sea level rise during the 21st century will exceed the rate observed during 1971– 2010…due to increases in ocean warming and loss of mass from glaciers and ice sheets,” it predicted.
But while ocean warming and melting of glaciers and ice sheets are globally the biggest contributors to sea level rise, changes in the local sea level may be due more to factors such as climatic shifts and tectonics. The IPCC said that “some processes can also lead to land motion that is rapid but highly localized.” It cited the case of Manila where “the greater rate of rise relative to the global mean is dominated by land subsid¬ence caused by intensive groundwater pumping,” adding this is common in many coastal regions, particularly in large river deltas.
The IPCC clarified however that these factors only prevail over a relatively short period of time, and that in the long run climate change is the main contributor to sea level change in most regions.
The Philippines’ eastern seaboard in particular is at risk owing to the country’s location relative to the center of the Earth or what scientists call the geocentric sea level. “In the western Pacific Ocean, rates were about three times greater than the global mean value of about 3 mm per year from 1993 to 2012. In contrast, those in the eastern Pacific Ocean are lower than the global mean value, with much of the west coast of the Americas experiencing a fall in sea surface height over the same period,” the IPCC explained. [To be continued]
(MindaViews is the opinion section of MindaNews. H. Marcos C. Mordeno can be reached at [email protected])