Global Warming
By Sarah Afzal

July 16, 2009

Defined as a sustained overall increase in world temperatures which is caused by additional heat being trapped by greenhouse gases, global warming has been subject to a serious debate and a great deal of political controversy in the recent years.

Arguments that support the possible incident of global warming include the fact that average temperatures have climbed 1.4 degrees Fahrenheit around the world since 1880, much of this in the recent decades, according to NASA’s Goddard Institute for Space Studies. The United Nations' Intergovernmental Panel on Climate Change (IPCC) reports that 11 of the past 12 years are among the dozen warmest since 1850. Average temperatures in Alaska, western Canada, and eastern Russia have risen at twice the global average, according to the multinational Arctic Climate Impact Assessment report compiled between 2000 and 2004. Arctic ice is rapidly disappearing, and the region may have its first completely ice-free summer by 2040 or earlier. Polar bears and indigenous cultures are already suffering from the sea-ice loss. Glaciers and mountain snows are rapidly melting—for example, Montana's Glacier National Park now has only 27 glaciers, versus 150 in 1910. Therefore, global warming is “very likely”, according to the IPCC report of February 2007. The report, based on the work of some 2,500 scientists in more than 130 countries, concluded that humans have caused all or most of the current planetary warming.

On the other hand, there are some scientists who oppose the possibility of global warming. Some experts, for example have questioned the theory that global warming will lead to shrinkage of Himalayan glaciers. V.K. Raina, a leading glaciologist, is among them. He maintains that the glaciers are undergoing natural changes witnessed periodically and that they have not shown any evidence of major retreat. These views are echoed by other eminent scientists. Some experts point out that natural cycles in Earth's orbit can alter the planet's exposure to sunlight, which may explain the current trend. Earth has indeed experienced warming and cooling cycles roughly every hundred thousand years due to these orbital shifts, but such changes have occurred over the span of several centuries. Today's changes, though, have taken place over the past hundred years or less. Similarly, more than 17000 scientists have signed a petition circulated by Oregon Institute of Science and Medicine, saying, in part, “there is no convincing scientific evidence that human release of carbon dioxide, methane, and other greenhouse gases is causing, or will, in the foreseeable future, cause catastrophic heating of the earth’s atmosphere and disruption of the Earth’s climate.” As far as the so-called consensus of scientists on global warming’s inevitability is concerned, University of London’s professor of biogeography Philip Stott has effectively illustrated how science does not progress by consensus, it progresses by falsification and by what we call paradigm shifts; in the in the early 20th century, 95% of scientists believed in eugenics and other theories that seem to us now as quack science.

However, as scientific knowledge has grown, this debate is moving away from whether humans are causing warming and toward questions of how best to respond. For this, knowledge of the sources of the problem is essential.

Carbon dioxide is being poured into the atmosphere by industries and vehicles much faster than plants and oceans can absorb it. This and other greenhouse gases, like methane, persist there for many years and trap heat near the earth’s surface. Other recent research has suggested that complicated solar mechanisms could possibly play a role in causing the problem.

A follow-up report by the IPCC released in April 2007 warned that global warming could lead to large-scale food and water shortages and have catastrophic effects on wildlife. Sea level could rise between 7 and 23 inches by century's end, the IPCC's February 2007 report projects. Rises of just 4 inches could flood many South Seas islands and swamp large parts of Southeast Asia. Some hundred million people live within 3 feet of mean sea level, and much of the world's population is concentrated in vulnerable coastal cities. Glaciers around the world could melt, causing sea levels to rise while creating water shortages in regions dependent on runoff for fresh water. Strong hurricanes, droughts, heat waves, wildfires, and other natural disasters may become commonplace in many parts of the world. The growth of deserts may also cause food shortages in many places. More than a million species face extinction from disappearing habitat, changing ecosystems, and acidifying oceans. At some point in the future, warming could become uncontrollable by creating a so-called positive feedback effect. Rising temperatures could release additional greenhouse gases by unlocking methane in permafrost and undersea deposits, freeing carbon trapped in sea ice, and causing increased evaporation of water.

Sources:
http://environment.nationalgeographic.com/environment/global-warming/
http://forecast.weather.gov/glossary.php
http://www.aproundtable.org/tps30info/globalwarmup.html

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