HISTORY has a habit of repeating itself but at an unprecedented rate as of today. Combined researchers at University College London and the University of Bremen have studied thousands of sediment samples drilled from ocean beds to discover how temperatures have risen and fallen over the last 66 million years. The publication of their results in ‘Science’ reveals that the present pace of global warming, resulting from manmade emissions, will increasingly lead to a ‘hot house’ phase, last seen 45 million years ago and well before man appeared on Earth.
Clearly anthropogenic change is affecting two key elements that add structure to our world’s climates; the volume of ice at our polar extremities and greenhouse gas concentrations. It has been estimated that within the next two to three centuries the average global surface temperatures will rise between 4 and 12 degrees Celsius, leading to extensive flooding of lowland coastal areas.
A recent UN report suggests that, on the current trend, temperatures will rise by 3.4 to 3.9 degrees Celsius by the end of this century. This will inevitably lead to a sea level rise of up to nine metres thus inundating coastal areas worldwide together with more violent storms in the tropics with some equatorial areas becoming uninhabitable.
The causes of rising sea levels
Interestingly sea levels were first officially recorded at the fishing port of Newlyn in West Cornwall, England, only 3km away from where I was born. The average global sea level has been rising by 0.3 metres over the last century but is accelerating year by year. The causes of this are exacerbated by human induced global warming, forcing the expansion of seawater, a major collector of carbon dioxide emissions, amounting in total to 42 per cent of sea level rises. Another major cause is the melting of the Arctic Ocean and the Greenland and Antarctic ice caps. The effects of the latter’s meltwater pulses are gradually being revealed.
What of the world’s ice caps and frozen oceans?
Antarctica’s ice holds 70 per cent of the world’s freshwater. The East Antarctic Ice Sheet stores enough ice to raise global sea levels by over 53 metres and is increasingly losing ice. It is West Antarctica that is experiencing a faster outflow of ice. There, the Thwaites Glacier, flowing into the Amundsen Sea, is underlain by a complex web of deep sea floor passages which funnel warmer waters to penetrate beneath the ice mass thus leading to faster thawing from below. With its vast extent of 191,660 sq km this glacier is losing ice at an amazing rate, possibly leading to a sea level increase of over six metres.
The Greenland Icecap, 3km deep in places, feeding its numerous glaciers, is the largest contributor to sea level rise over the last decade. In northeast Greenland, some 109 sq km of the Nioghalvfjerdsfjorden glacier has broken as of September, thus supporting scientists’ claims that increasing temperatures are leading to a gradual disintegration of this ice cap thereby adding to a progressive rise in sea levels. Again, a loss of a shelving glacier as it enters the warmer seas leads to an increase in glacier movement bearing in mind the simple equation that output equals input thus lowering the thickness of the ice cover.
The loss of sea ice in the Arctic Ocean is unparalleled. In July, the sea ice coverage amounted to 7.28 million sq km, the lowest in satellite records for this month. This was a loss of 23 per cent below the average from 1981 to 2010. Our present year, in the same month, saw the Northern Sea Route on the Siberian side of the Arctic Ocean totally ice free with a total loss of Arctic sea ice of 3.6 million sq miles. Currently the linear rate of decline of July sea ice cover amounts to nearly 8 per cent per decade.
Arctic sea ice is profoundly influenced by the seasonality of the atmosphere and the ocean. Increasing global temperatures and resultant changes in wind directions, including storms over ice packs, lead to their break up. Such storms can churn up warmer waters thus drawing warmer water from the ocean depths to the surface leading to the melting of sea ice. Sea ice cover is mostly influenced by the transport of much warmer waters from lower latitudes. Branches of warmer waters from the North Atlantic Drift sea current enter the Arctic Ocean via the Greenland, Iceland and Norwegian Seas. As this water is saltier and thus more than dense than the Arctic waters, it flows underneath it thereby warming it up by releasing its heat and melting the sea ice from below. Similarly, warmer waters from can enter the Arctic Ocean from the Pacific Ocean via the Kuro Siwo warm current through the Bering Straits separating Siberia from Alaska. As the Bering Strait has a maximum depth of only 100 metres more warm water can rush into the Arctic. The UK Meteorological Office, after extensive studies, warn us that the Arctic Ocean will be free of sea ice by 2035!
From the rapid changes in ice loss in these three examples, we can appreciate that these critical components of our Earth’s climate system have far reaching impacts beyond the polar-regions.
Implications of rising sea levels
Undoubtedly, we are the victims of our own making. Continuous carbon dioxide emissions from fossil fuel burning could well cause tens of metres rise in sea levels. However, not all is doom and gloom for all areas of our planet. Where ice loss is increasing as in Greenland and Antarctica, the underlying mountains, released from the pressure of ice caps, will steadily rise upwards. This process is referred to as ‘isostatic readjustment to equilibrium’ and is already seen in the Baltic States and in Hudson Bay, Canada.
The areas of the world most affected by rising sea levels are those urban conglomerations built on river deltas where subsidence of land, principally caused by draining and the extraction of groundwater, and the creation of flood management systems occurs. There, the deltaic floodwaters are not allowed to overflow to add silt and height to the land surface. Higher sea levels will see increased, faster erosion of sedimentary rock shorelines, storm-surge flooding, coastal inundation and potential loss of human lives. It will impact agriculture, especially on relatively recently reclaimed land, the tourist industry and riverine and estuarine ecosystems and wildlife. The displacement of people is inevitable and especially in Africa, Asia, and small island states. It is already seen in the Maldives in the Indian Ocean and in Tuvalu in the Pacific. Tourist island destinations are here today but will be gone tomorrow!
Closer to home
Worldwide, most insurance companies produce ‘flood-risk maps’ for those urban areas built on reclaimed river deltas and for river flood plains or those areas susceptible to coastal erosion. Such demarcated zones will affect our annual house insurance premiums. Most of our world’s conurbations, cities, ports and agricultural regions are built on reclaimed river deltas and Kuching, Bintulu, Miri, Kota Kinabalu, Sandakan, and Tawau are no exceptions, for they are all affected by king tides.
The drainage of further wetlands to accommodate increasing population will, in the short term, place such areas in increasing jeopardy with ever rising sea levels. Present day beach resorts will be short-lived as they are only a few metres above present high tide levels. What has been happening to ice sheets and ice caps in our global extremities will gradually affect us wherever we may live. Sadly, my pessimistic view is to suggest that the process of global warming cannot be reversed but can be slowed down by cutting down on fossil fuel emissions. Even then the waters will still rise and affect over 600 million people who live in coastal and riverine environments. Indonesia has already made its mark by planning to relocate its capital’s administrative area to southern Kalimantan.