Erosion and climate change

Sri Lanka is adrift in the Indian ocean

by Kumar David

We are a small island cast away and adrift in the Indian Ocean. What happens, in climatological terms to this island and its people depend entirely on global warming scenarios driven by other heavy energy consuming nations; roughly in order of consumption China, US, India, Russia, Japan, Canada, Germany, South Korea, Brazil and France. The biggest seven polluters (in order of CO2 release) are almost the same; China, US, India, Russia, Japan, Germany and South Korea.

What will happen on the shores of this pitiful island abandoned in the Indian Ocean mirrors the fate of many islands, the East African Coast and the Sundarban mangrove wetlands of Bangladesh. The outcome depends on different scenarios that may evolve in the aforementioned high energy consuming and CO2 polluting countries. These are defined by Representative Concentration Pathways defined by the Intergovernmental Panel for Climate Change (IPCC). RCP 4.5 is a moderate scenario in which emissions peak around 2040 and then decline. RCP 8.5 is the highest baseline emissions scenario in which emissions continue to rise throughout the twenty-first century. There is good reason to fear things are not going well and that the struggle to limit global temperature rise in this Century to 1.5 degrees C has been lost. The consequences for the world and for a relatively small island like Sri Lanka could be catastrophic.

Many islands will disappear if the sea rises even a few hundred feet. Rising sea levels literally pose an existential threat to: Kiribati, Maldives, Vanuatu, Tuvalu, Solomon Islands, Grand Bahamas, Nassau, Samoa, Nauru, Palau, Micronesia, Cook Islands (New Zealand), Marshall Islands, French Polynesia, Tangier Island (Virginia, USA), Shishmaref Island (Alaska, USA).

The graph reproduced from the IPCC or Intergovernmental Panel on Climate Change and many similar assessments of rising sea levels are more frightening than sobering – particularly the RCP 8 case. Overall, the consequences apart from rising sea level are shrinking glaciers, severe storms, increased drought, loss of species, food shortage and health risks. The social consequences are poverty, displacement and conflict. If we go on as at present global temperature may rise by as much as 2.8 degrees C above pre Industrial Revolution values unless green-house gas emissions are reduced now, not by the end of the Century and the inability to do so may unleash a scenario similar to that at the end of the last ice-age. Myths of a great flood about 11,500 years ago, that is at the end of the last ice-age are commonplace in all ancient cultures such as Mesopotamia, Zoroastrian, ancient pre-Hindu Indian, Greek, Chinese and Cheyenne- a North American Great Plains tribe – cultures.

Expert opinion among historians and climatologists converges on the view that the Great Flood myths were associated with melting of the polar ice-caps none of this was of anthropogenic origin. The rise of sea-level anticipated in the course of this century is entirely due to human activity. [See for example IPCC 2019: Summary for Policymakers on Ocean and Cryosphere in a Changing Climate; and Fox-Kemper et al, Chapter 9: Ocean, Cryosphere and Sea Level Change, Working Group I, Sixth Assessment Report of the IPCC].

The rise and fall of sea-level during the last 100,000-years, is associated with the ice ages. The recent or Last or Late Global Maximum when glaciers covered the earth was about 30,000 years ago. Water was trapped in ice in the Arctic and Antarctic, Northern America, Europe, and Asia so sea levels were low. Then in the early Holocene (the present geological age starting 12,000 years ago) as the ice-caps melted for geological reasons, sea level rose about 300 feet. This rise in sea level and associated climatic changes (giving rise to the Great Flood myths) may have contributed to the Neolithic Revolution (agricultural revolution) in the Fertile Crescent. This is a quick summary of my amateurish but extensive background reading and I hope my non-expert readers find it helpful. The converse point is that even without our human folly a FALL in global sea level may occur once in thousands of years due to purely geological causes. I will return to this converse theme to entertain my Sri Lankan readers at the end of this short column. Please hold on for bit – thanks.

Rising global sea-level endangers many island nations and coastal communities. The 2011 Tōhoku earthquake and tsunami magnitude 9.0–9.1 megathrust undersea earthquake which devasted the Tohoku region of northern Hokaido on March 11, 2011 had its epicentre at a depth of 29 km in the Pacific Ocean, 72 km east of the coast, and is recorded as the strongest earthquake in the history of Japan. It resulted in 16,000 deaths and 6,000 injuries. Hundreds of ghost stories, some of the forlorn un-dead searching for a resting place still circulate in the wake of the event. Cities under partial or severe threat include Dhaka, Bangladesh (population 22.4 million); Lagos, Nigeria (population 15.3 million); Bangkok, Thailand (population 9 million could land drowned or unusable). The sea-level rise in coastal Indian cities will lead to road networks becoming submerged in Bombay, Cochin, Mangalore, Madras, Visakhapatnam and Thiruvananthapuram by mid-century.

Now allow me to sign off with a comment that will interest people interested or amused by Ravana legends and pertinent to the peopling of the island tens of thousands of years ago by migrations that would have included Balangoda Man and his ilk. Children are taught that the seasons depend on the axial tilt (obliquity) between the earth’s axis of rotation and the orbital plane (tilt with respect to the plane of rotation around the sun). However, this obliquity changes over a period of about forty thousand years (axial precession). This and other factors will cause sea levels to rise and fall over millions of years and when it falls the island will become an extension of the Indian landmass as it was from time to time every tens of thousands of years.

About 30,000 years ago sea-level dropped sharply and the island was connected to India forming one continental landmass over which large scale migrations would certainly have taken place. However, this obliquity changes over a period of about forty thousand years (axial precession). This and other factors will cause sea levels to fall again in many years and the island will once again become connected to the Indian landmass as it was every tens of thousands of years. Anthropologists and expert historians may sneer but for simple folk like you and me that’s a good enough working hypothesis. Conclusion? The Ravana legends, the ancestors of Balangoda man, the Veddas and the other early settlers of the island surely had an independent pre-Sinhala origin of their own.