The biggest ‘giant’ is surely the Intergovernmental Panel of Climate Change. Founded in 1988, IPCC has concluded that the fossil-driven civilisation is altering our planet profoundly by releasing carbon dioxide and other heat trapping gases, called greenhouse gases, into the atmosphere. The world’s temperatures have already warmed by up to 1.20 C since pre-industrial levels and the impact of this warming is visible in the form of extreme climatic developments, the rising sea levels by about eight inches, and the diminishing Arctic sea ice. Even if we stop the burning of fossil fuels, the existing greenhouse gases would continue to warm the Earth for centuries. The IPCC is unequivocal in its assertion that at 1.50 C the world would reach critical thresholds beyond which natural ecosystems would change fundamentally
Such catastrophes as an earthquake, a fire, or an explosion can change our lives. But there is also a slow motion catastrophe, sparked by the dependence on fossil fuels. This has warmed the atmosphere and oceans and melted glaciers and continental ice sheets, and has consequently sea levels. Indeed, the sea levels would continue to rise for centuries even if we cap global warming at 1.50 C. The problem confronts not only countries but also generations. The people who are going to be most severely affected by human-induced climate change are yet unborn. Indeed, the future generations are very likely to countenance a hotter world and rising seas. To quote Dr John Church, one of the world’s leading experts on sea-level rise, “Much of society’s past development has occurred in a period of relatively stable sea level. The world is now moving out of this period and future coastal planning and development must consider the inevitable increase of the regional sea level.”
Global warming affects the sea level in two ways. It is causing the oceans to absorb a lot of extra heat (up to 90 per cent). This expands the volume of water. Trapped within a basin hemmed by the continents, the water has nowhere to go but move upwards. The thermal expansion accounts for around a third of the current sea-level rise. The rest comes from the melting of land-based ice sheets and glaciers. So far it has been mostly mountain glaciers. Melting mountain glaciers contribute another third. By 2100 they will probably add a few inches to sea level ~ but not feet. They don’t contain that much ice. The major concern for the future is the giant ice sheets in Greenland and Antarctica. The Greenland ice sheet is now a small contributor, but its surface has started melting in summer ~ a worrisome sign. The ice sheet contains enough water to increase the sea level by nearly 25 feet. East Antarctica seems fairly stable. But a warming ocean is undermining parts of West Antarctica’s ice sheet. Its future, like Greenland’s, is very uncertain.
One of the biggest wild cards is the massive Thwaites Glacier in West Antarctica. A few years ago NASA sponsored a series of flights over the region, using ice-penetrating radar to map the seafloor topography. A 2000-ft-high undersea ridge holds the glacier in place, slowing its slide into the sea. A rising sea could allow more water to seep in between the ridge and the glacier. In the opinion of Richard Alley, a glaciologist and a member of the IPCC: ‘It involves the physics of the ice fracture that we really don’t understand.’ The sea level began to rise in the late 19th century as the Earth started getting warmer. Since the beginning of the 20th century, the average global sea level has been rising. Precise data gathered from real-time satellite radar measurements reveal an accelerating rise of 7.5 cm from 1993 to 2017, which is a trend of roughly 30 cm per century. Between 1993 and 2018, thermal expansion of oceans contributed 42 per cent to the sea level rise; the melting glaciers, 21 per cent; Greenland, 15 per cent; and Antarctica, 8 per cent. In 2007 the IPCC issued a report predicting a maximum of 60 cm (2 feet) of sea-level rise by the end of the 21st century. In its Fifth Assessment Report (in 2013) the IPCC projected that the continued warming of the planet, without major reductions in emissions, would see global water rising by between 52 cm and 98 cm by 2100. However, a conservative estimate of the long-term projections is that each Celsius degree of temperature rise triggers a sea-level rise of approximately 2.3 meters over a period of two millennia.
A disproportionate percentage of the world’s largest cities are located near the sea. In fact, 50 per cent of the world population lives within fifteen miles of the coast, and according to the US National Academy of Sciences, ‘Coastal populations around the world are also growing at a phenomenal pace. Already, nearly two-thirds of the world’s population lives on or within 100 miles of a coastline. Estimates are that in three decades, nearly 75 per cent of the world’s population will live along coasts. In much of the developing world, the coastal population are exploding.’ The sea level will not rise uniformly everywhere on Earth, and it will even drop in some locations. Local factors such as tectonic effects and subsidence of the land, tides, current storms play vital roles. Sea-level rise can affect the people in coastal and island regions. Widespread coastal flooding is expected with several degrees of warming sustained for millennia. There are risks of strong storm-surges, devastating tsunamis, displacement of populations, loss and degradation of agricultural land and damage to cities. Natural environments like marine ecosystems are also affected, with fish, birds and plants losing part of their habitat.
Sea levels along the Indian coast are projected to rise by 3.5 inches to as high as 34 inches by the end of the century posing a threat to vast stretches of the western coastline as well as the deltas in eastern India. The deltas of the Ganga, Krishna, Godavari, Cauvery, and Mahanadi on the east coast may be threatened, along with irrigated land and a number of urban and other settlements. The projected rise of the sea-level may threaten river systems, food security and cause flooding. The projected rise may also result in coastal groundwater turning saline, endangering the wetlands.
Rising sea levels and tidal erosion are eating up the Sundarbans. As many as 13 islands of the region face serious trouble and three of them ~ Lohachora, Ghoramara and New Moore (South Talpatti in Bangladesh) ~ have already submerged into the Bay of Bengal. The swelling sea levels have posed the problem of environmental refugees and the homes of at least 70,000 people might disappear. The region can be linked to the Titanic that hit the iceberg. The water is pouring in; it is a sinking ship. People will be compelled to move northwards.