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Rising seas ~ II

India has lost 235 square kilometres of land to coastal erosion between 1990 and 2016, placing people’s livelihoods and homes in jeopardy.

JAYDEV JANA | New Delhi |

The Antarctic ice sheet is the largest mass of ice in the world, holding around 60 percent of the world’s fresh water. Scientists are grappling with exactly how global warming will affect this great ice sheet. Scientific understanding of ice sheet processes, and of the variability of the forces that affect ice sheets, is incredibly limited. This is largely because the ice sheets are in very remote and harsh environments and difficult to access. However, research has identified so-called ‘basal melt’ as the most significant driver of Antarctica ice loss. Basal melt refers to the melting of ice shelves from underneath, and in the case of Antarctica, interaction with the ocean are thought to be main cause.

While a few areas of the frozen continent’s gigantic ice sheet have been growing, overall Antarctica is losing ice. East Antarctica seems fairly stable. But parts of West Antarctica’s ice are being undermined by a warming ocean. One of the biggest wild cards in all sea-level-rise scenarios is the massive Thwaites Glacier in West Antarctica. A few years ago NASA sponsored a series of flights over the region that used ice-penetrating radar to map the sea floor topography. The flights revealed that a 2000-ft-high undersea ridge holds the Thwaites Glacier in place, slowing its slide into the sea. A rising sea could allow more water to seep between ridge and glacier and eventually unmoor it. But no one knows when or if that will happen.

Melting ice is not limited to the polar areas. Mountain glaciers around the world are melting faster now than at any time in the past 5,000 years because of unprecedented period of global warming. Ice cores taken from mountains as far as the Andes of South America and the Himalayas of Asia have revealed how climate change is leading to a fullscale retreat of the world’s tropical glaciers, according to a study. Scientists have warned that human activities over the past 100 years have nudged the global climate beyond a critical threshold which could see most of the highest ice caps disappearing within the near future. Melting glaciers in South America and Asia not only contributes to rising sea levels, they are also vital sources of fresh water for many millions of people who live within their range at lower altitudes.

Interestingly, the most dramatic evidences have been gathered from around 28 sites where the retreating ice has exposed the ancient plants that have been frozen and preserved for between 5,000 and 6,000 years by the glacier’s base. This means that the climate at the ice cap has not been warmer than it is today in the last 5,000 years or more. If it had been, then the plants would have been decayed, as explained by Lonnie Thompson of Ohio State University. According to him “Global climate can change abruptly … that’s serious.” Twenty thousand years ago, the sea level was 110 meters (about 350 feet) lower than it is today, exposing much of the present continental shelves. 14,000 years ago the sea level increased 4 to 5 metres per century for several consecutive centuries ~ an average rate of one metre every 20 or 25 years. Since 1880, the Global mean sea level has risen about 8-9 inches (21-24 centimetres).

In 2020, global mean sea level was 91.3 millimetres (3.6 inches) above the 1993 average, making it the highest annual average in the satellite record. The last time Earth was free of ice was more than 34 million years ago, in the Eocene epoch. Alligators swam in Arctic swamps. But the planet slowly cooled as CO2 rained from the air and was locked up in seafloor sediments. Continental ice sheets formed first in Antarctica, but over the past few million years they have repeatedly surged across northern continents too. We’re presently living in an interglacial period, which began about 10,000 years ago. There are more than five million cubic miles of ice on Earth, and no one really knows how long it would take to melt it all.

Some scientists opined that it would probably be more than 5,000 years. But if we burn all the coal, oil, and gas, adding some five trillion more tons of carbon to the atmosphere, we will very likely create an ice-free planet. It would be a hot planet, with an average temperature of perhaps 80oF. Large swathes of it might become too hot for humans; the desert would doubtless expand. Sea level would rise by 216 feet. Compared with other continents, Africa would lose less of its land to the ultimate sealevel catastrophe. Australia would gain a new inland sea ~ but it would lose much of narrow coastal strip where four out of five Australians now live. Land now inhabited by more than 600 million Chinese would flood as would all of Bangladesh and much of coastal India.

The Amazon Basin and Paraguay River Basin would become Atlantic inlets. These are a few examples of the catastrophes. An increase in the sea level could cause an inundation of some lowlands, accelerated coastal erosion, increased coastal flooding and storm damage, damage to coastal structures, and saltwater intrusion into freshwater estuarie sand aquifers. Because bridges and harbour facilities are designed for certain water levels, some will be rendered useless and some will have to be modified as a consequence of sea level increase. Because beach profiles tend to be flatter than the land just above sea level, a rise in the sea level will cause erosion of land areas several times the areas initially inundated, and the inundation of the entire barrier islands off coastlines.

Beach resort areas will suffer significant losses of buildings. With a higher sea level, storm surges will operate from a higher base and do significantly more damage. Higher sea levels will force the groundwater table upwards, adding to flooding problems and cause salt water to extend farther up to the estuaries and intrude into groundwater sources. The paper, published in Nature Communications, finds that currently 267 million people worldwide live on land less than 2 meters above sea level. It is predicted that by 2100, with one meter sea level rise and zero population growth, the number could increase to 410 million people. It has also been shown that 62 percent of the most at-risk land is concentrated in the tropics, with Indonesia having the largest extent of land at risk worldwide. These projections showed even more risk in the future, with 72 percent of the atrisk population in the tropics, and 59 percent in tropical Asia alone.

India has lost 235 square kilometres of land to coastal erosion between 1990 and 2016, placing people’s livelihoods and homes in jeopardy. According to the Internal Displacement Monitoring Centre, about 3.6 million Indians were displaced annually between 2008 and 2018, most as a result of flooding from monsoon rains that are the heaviest in South Asia in absolute terms. Crucially, warming between the two poles in the last interglacial did not happen simultaneously. But under today’s GHGs-driven climate change, warming and ice loss are happening in both regions at the same time. There is a catastrophe that is playing out in slow motion, measured out over the course of years, decades, and centuries. And it’s happening now. The startling conclusion is that if the present generation is unable to take care of the present, they will not be able to contribute for the future. The future generation would inherit a hotter world and rising seas.