Pressures on Antarctica
`We are doing things that have not happened in 650,000 years’
Rajendra Pachauri, chair of the IPCC.
Nearly 2.5 times the size of continental USA, Antarctica is the world’s highest, coldest and windiest continent. Although its ice cap contains 75 per cent of the globe’s fresh water (and 90 per cent of its ice), very low precipitation means much of this remote, inhospitable continent is classed as desert. Massive icebergs are spawned every year from Antarctica’s floating ice shelves and each winter the surrounding oceans freeze, doubling the size of the continent. What effects would global warming have on Antarctica?
About 80% of Antarctica’s sea ice melts each summer, from a winter maximum of around 19 million square kilometres to a summer minimum of about 3 million square kilometres. This seasonal change is important to both Antarctica’s marine ecosystem and Earth’s global climate.
The Earth’s global surface temperature is regulated through the amount of radiation received from the sun, the amount reflected back into space and the ability of atmospheric gases to absorb heat (the greenhouse effect). Sea ice reflects from 50% to 95% of the solar radiation that reaches it, depending on the age and the snow cover on it. Open water only reflects about 8%.
Changes in the extent of sea ice can be positive:
more ice = more reflection = lower temperature = more ice formation
But on the other hand, less ice cover means more solar energy is absorbed by the ocean, leading it further melting and more open water. Water is very effective at storing heat, so massive melting in one season can add enough heat to the system to prevent ice formation the next season.
Sea ice controls local climate extremes because it releases heat when it freezes and absorbs heat when it melts. The effect is especially obvious at the edges of the ice. Sea ice also affects the regional climate when it drifts away from the area where it was formed, redistributing heat and fresh water.
Sea ice forms in the autumn, when there are considerable concentrations of micro-organisms in Antarctic surface waters. Some of these organisms become trapped within the ice and start growing, forming communities. The organisms are released to the water in the spring as the ice melts and provide an important food source for krill during winter and early spring.
Krill are a major food source, directly or indirectly, for birds, seals, whales, penguins, squid and fish and changes in sea ice thickness or extent could have a significant effect on krill distribution or populations that could, in turn, affect organisms higher on the food chain.
The extent of sea ice is known to influence penguin-breeding success; contracting of the sea ice will negatively affect penguin colonies as krill stocks decline.
Other pressures that Antarctica would face under global warming are:
Increased iceberg production and the rapid disintegration of large areas of ice shelves which would have implications for shipping and nature.
Ice sheet movement into the ocean which will cause sea-level rise. A rise of 30cm, for instance would spell the disappearance of entire South Pacific island-states and the loss of West Antarctica’s ice sheet, could contribute to a sea level rise of up to 6m.
Finally, oceans naturally absorb carbon dioxide and for the first time, the IPCC scientists address the acidification of the oceans. Much of the CO2 we are producing is absorbed by the sea. But more carbon dioxide will see it starting to react chemically with the water to produce carbonic acid and will pose a severe threat to many small marine organisms which need an alkaline environment, to build their calcium carbonate shells.
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Climate Change
Quick Facts
Introduction
What is Global Warming ?
The Evidence
How Much Hotter ?
Pressures on Antarctica <<
Arguments Against It
The Political Response
Conclusion
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