By Ajith Lawrence
Monsoon means trouble along the coastline of Kerala. It is a time of strong wind and high waves. Fishing activities become very difficult and angry waves carve away chunks of coastal land. Often fishing hamlets face huge losses as they lose houses, playgrounds and space to park boats.
Scientists say this trend might become even worse as Indian Ocean sea levels are rising unevenly and threatening local communities in some densely populated coastal areas and islands. A new study published recently in Nature Geoscience notes that sea level rise – partly a result of climate change – is particularly high along the coastlines of the Bay of Bengal and the Arabian Sea. The new study led by scientists at the University of Colorado at Boulder and the National Center for Atmospheric Research (NCAR), USA, says that the sea level rise – which may aggravate monsoon flooding in Bangladesh and India – could have future impacts on both regional and global climate.
The study noted that the key player in the whole process is the Indo-Pacific warm pool, an enormous, bathtub-shaped area spanning a region of the tropical oceans from the east coast of Africa to the International Date Line in the Pacific. It has warmed up by about 0.5 degrees Celsius, in the past 50 years, primarily because of human-generated emissions in greenhouses gases. “If future anthropogenic warming effects in the Indo-Pacific warm pool dominate natural variability… north Indian Ocean may experience significantly more sea level rise than the global average,” said lead author Weiqing Han of the atmospheric and oceanic sciences department at Boulder.
While many spots in the Indian Ocean region are experiencing sea level rise, sea level is lowering in other areas. “Global sea level patterns are not geographically uniform,” says NCAR scientist Gerald Meehl, a co-author. Closer home, Indian scientists have acknowledged that there has been a sea level rise of an average two millimetres a year or 20 centimetres a century. That is in tune with the global average. However, there are indications that the rise could be faster at some areas.
Dr. C.K. Rajan Director(Rtd) centre for Monsoon Studies Kochin University of Science and Technology, says that high-tides and tidal ingressions could be an issue. “Melting of polar caps and land-based glaciers is the first and foremost direct consequence of Global warming,” he notes. “The polar ice cap is melting at the rate of 1 per cent per year. The Arctic ice thickness has decreased 40 per cent since the 1960s. Observations summarized indicate that global sea level had already increased to 20cm during the 20th century – ten times higher than the average rate of rise over the past 2000 years.” If the warming continues in this same rate, the global sea level would rise by almost 10 cm by middle of the present century, he notes. There are different scenarios – and some fear a greater rise in sea levels.
Dr N P Kurian, head of marine sciences division at the Centre for Earth Science Studies (CESS), Thiruvananthapuram notes that sea level rise could lead to more erosion. It is a major worry for many areas especially barrier islands in Kerala that are sandwiched between the Arabian Sea and the backwaters. Places like Anchuthengu in Thiruvananthapuram and some of the tsunami-hit areas of Kollam and Alappuzha districts could be at risk, he said. The science of erosion is complex. In gentle slopes a small rise in the sea level produces a large inland shift of the shoreline. When buildings, roads, and seawalls block this natural shift, the beaches and shorelines erode, especially during storm events, as Intergovernmental Panel on Climate Change (IPCC) has noted.
The Nature Geoscience paper indicates that in order to anticipate global sea level change, researchers also need to know the specifics of regional sea level changes. There are indications that locally sea level rise could be faster. Speaking at the Indian Science Congress in January, secretary in the Department of Ocean Development Sailesh Nayak said that studies suggested a faster pace of sea level rise along the Indian coast during 2004 – ’08. While at the central government level there are scientific efforts to understand the phenomenon, local action is dismal and ad hoc. While there is general talk about climate change and sea level rise as a rationale to build more seawalls the overall issue is largely unaddressed. As Kurian comments: “The threat perception has still not gone into our planning process.”