On thinning ice
.....
In the two hundred years since industrialisation ? a geological millisecond ? we?ve increased the concentration of carbon dioxide in the Earth?s atmosphere by 35 per cent; a third of that has appeared in the last four decades. Carbon dioxide and other greenhouse gases, such as methane, trap heat that would otherwise radiate into space. As greenhouse gas levels rise, the lower atmosphere heats up and the climate changes, sometimes in unexpected ways.
The global average temperature has increased by about 0.6°C over the last two centuries. Most greenhouse gases remain in the atmosphere for decades, and have an ongoing, cumulative warming effect. In 2001, the UN Intergovernmental Panel on Climate Change, a group of 2500 scientists, predicted an additional increase during the 21st century of between 1.4 and 5.8°C. In October, a body of nearly 300 scientists completed the Arctic Climate Impact Assessment, a report based not on worst-case scenarios but on observed changes to-date combined with projected temperature increases that are below the middle range of those anticipated by complex, increasingly accurate global climate models. Despite this methodological caution, the predictions made in the Assessment are terrifying. By the end of the century, annual average temperatures in the north will rise between 3 and 5°C on land and up to 7°C over the Arctic Ocean, with winter temperatures increasing even more. Sea-ice cover will decline by 50 per cent, and could disappear entirely in summer.
The Assessment expresses particular concern about ?feedback loops? exacerbating climate change. The first such loop is already operating, as rising temperatures melt snow and ice and expose more open water and bare ground each summer: these darker surfaces reflect 75 per cent less heat away from the planet?s surface and this means further warming, which melts more ice and snow, which reflects less heat, and so on. In addition, the atmosphere is thinner at the Earth?s poles, and rising greenhouse gas levels therefore have a more immediate impact on surface temperatures. In the Arctic the average annual temperature has already increased almost twice as much as it has globally: in Alaska and north-west Canada, average winter temperatures are up by more than 3°C. In summer, across the Arctic, the average extent of sea-ice cover is 15 per cent less than three decades ago. More than two million square kilometres of highly reflective sea ice has been lost, an area eight times the size of the UK.
The second feedback loop involves fresh water from melting Arctic and Greenland ice flowing south into the North Atlantic and disrupting the Gulf Stream, the ocean current from the Caribbean that moderates temperatures in Northern Europe. The Assessment reports a ?tentative indication from the North Atlantic of an initial slowing of the deep ocean circulation?. Were the circulation to slow significantly, or stop, the result would be a dramatic reduction in winter temperatures and rainfall levels in Ireland, Britain and Scandinavia, at least for a few decades. It is because of this possibility of localised cooling that the term ?climate change? is preferred to ?global warming?.
The third feedback loop involves melting permafrost releasing huge quantities of methane and carbon dioxide as the plant material in the soil decomposes. Methane is 23 times more effective than carbon dioxide at trapping heat in the atmosphere. As methane and carbon dioxide from the melting permafrost reach the atmosphere, they cause further temperature rises, which in turn cause more melting, and so on. According to the Assessment the southern limit of permafrost is liable to retreat several hundred kilometres northwards during this century. Melting permafrost has already forced the Alaskan state government to cut from 200 to 100 days the annual period during which oil and gas equipment is permitted to travel on the Arctic tundra. The impact of this third feedback loop may already be apparent: measurements from Hawaii?s Mauna Loa Observatory show that atmospheric carbon dioxide concentrations increased by 2.08 parts per million in 2002 and by 2.54 ppm in 2003, considerably higher than the 1.50 ppm average of recent decades.
Massive quantities of methane are also trapped on the frozen seabed of the Arctic Ocean in the form of solid hydrates. As the temperature of the seabed rises, these hydrates could decompose, releasing additional methane into the atmosphere. Although the Assessment describes this as ?a less certain outcome?, it warns that ?if such releases did occur . . . the climate impacts could be very large.?
A rise in the sea level is also a concern. Melting sea ice does not affect the water level any more than an ice cube melting in a glass. But there are about three million cubic kilometres of land-based ice in the Arctic, and in most places it is melting. The Assessment foresees a rise of 3°C in Greenland?s temperature in the course of this century and the eventual disappearance of the Greenland ice sheet. In August 2004, the Geological Survey of Greenland and Denmark reported that in the southernmost part of the island the ice is already thinning at a rate of ten metres per year. In several centuries? time, when the ice sheet has melted completely, it will have caused a global sea-level rise of about seven metres; the melting of the Antarctic icecap could push that even higher. During this century, we may see only a 50 centimetre rise, with much of that resulting not from melting ice but from the expansion of water as it warms. Yet even this rise will inundate several entire island-nations and large portions of the world?s best farmland, displace hundreds of millions of people, and impose potentially unbearable costs on low-lying cities such as Amsterdam, Calcutta, London, Manila and New Orleans. During high tides in November, 80 per cent of Venice was underwater. A new report by the Hadley Centre for Climate Prediction and Research ? part of the Met Office ? indicates that large parts of Britain, including London?s Docklands, will soon be under threat.
Climate change is distinct from ozone level depletion, which is linked to chlorofluorocarbons (CFCs) used in refrigeration units, fire extinguishers and some industrial processes. CFC emissions have dropped dramatically as a result of the 1987 Montreal Protocol and the consequent switch to alternative technologies. But the ozone layer, which protects living things from ultraviolet radiation, will still take decades to recover, and increasing levels of greenhouse gases could ? in a blurring of the distinction between climate change and ozone depletion ? cause further delay. For although greenhouse gases warm the lower atmosphere, by trapping the heat down low they cool the upper atmosphere, contributing to the formation of polar stratospheric clouds that support ozone-destroying chemical reactions. The Assessment projects elevated UV levels at northern latitudes for decades to come.
It?s difficult to overstate the perilousness of the situation. Climate change, instead of occurring slowly over millennia, will soon outpace the ability of many species to adapt and evolve, and not just in the Arctic. An article a year ago in Nature estimated that between 15 and 37 per cent of terrestrial species ? that is, more than a million discrete forms of life ? will be extinct by 2050. In any case, climate change is already disrupting the lives of millions of human beings. According to James Morris, the executive director of the World Food Programme, the number of people suffering food crises as a result of natural disasters has tripled in the last thirty years....
etc.
Interactive: Antarctic ice collapse
Facebook
Twitter