Global Warming: Understanding the Controversy and Its Potential Impacts, Resúmenes de Idioma Inglés

¡Descarga Global Warming: Understanding the Controversy and Its Potential Impacts y más Resúmenes en PDF de Idioma Inglés solo en Docsity! Global Warming has been described as the greatest threat facing humanity. What worries researchers, says the journal Science, “is the prospect that we've started a slow-moving but relentless avalanche of change.” Skeptics question this assertion. True, many agree that the earth is warming, but they are uncertain of both the causes and the consequences. Human activities may be a factor, they say, but not necessarily the primary one. Why the disagreement? For one thing, the physical processes that underlie global climate systems are complex and not fully understood. In addition, interest groups tend to put their own spin on the scientific data, such as that used to show why temperatures are rising. Temperature Rise—ls lt Real? According to a recent report of the UN-sponsored Intergovernmental Panel on Climate Change (IPCC), global warming is “unequivocal,” or a fact; and “very likely,” mankind is largely to blame. Some who differ with this conclusion, especially in regard to the human factor, concede that cities may be heating up because they are growing in size. Moreover, concrete and steel readily absorb the sun's heat and tend to cool down slowly at night. But urban readings, skeptics say, do not reflect the trend in rural areas and can distort global statistics. On the other hand, Clifford, a village elder who lives on an island off the coast of Alaska, says he has seen changes with his own eyes. The people of his village travel across sea ice to the mainland to hunt caribou and moose. Rising temperatures, though, are making the traditional lifestyle impossible. “The currents have changed, ice conditions have changed, and the freeze-up of the Chukchi Sea has... changed,” says Clifford. The sea used to freeze up at the end of October, he explains, but now it does not freeze until late December. In 2007, warming was also evident in the Northwest Passage, which was fully open for the first time in recorded history. “What we've seen this year fits the profile of lengthening melt seasons,” said a senior scientist for the National Snow and Ice Data Center in the United States. Areason given for such changes is an intensification of the greenhouse effect, natural pnenomena vital for life on earth. When energy from the sun reaches the earth, about 70 percent is absorbed, heating air, land, and sea. If it were not for this mechanism, the average surface temperature would be about zero degrees Fahrenheit (-18 degrees Celsius). Eventually, the absorbed heat is released back into space as infrared radiation, thus preventing the earth from overheating. But when pollutants change the composition of the atmosphere, less heat escapes. This can cause earth's temperatures to rise. Gases that contribute to the greenhouse effect include carbon dioxide, nitrous oxide, and methane, as well as water vapor. The atmospheric concentration of greenhouse gases has increased markedly over the past 250 years, since the start of the industrial revolution and the increased use of fossil fuels, such as coal and oil. Another greenhouse-enhancing factor seems to be the rising population of farm animals, whose digestive processes produce methane and nitrous oxide. Some researchers point to other causes of warming that they say occurred before humans could have influenced climate. Just Another Fluctuation? Skeptics of human-induced warming point out that earth's temperature has undergone substantial fluctuations in the past. They point to the so-called ice ages, when the earth was supposedly much cooler than it is now; and in support of natural warming, they cite evidence that cold regions, such as Greenland, at one time supported vegetation that prefers warm areas. Of course, scientists concede that the further back they go, the more their certainty about climate diminishes. What may have caused temperatures to vary significantly before human influence was a factor? Possible causes include sunspots and solar flares, which correlate with fluctuations in solar energy output. Additionally, earth's orbit moves in cycles that take many thousands of years and that affect our planet's distance from the sun. There is also the influence of volcanic dust and changes in oceanic currents. If earth's temperature is rising—no matter what the cause or causes—how will it affect us and the environment? Precise predictions are hard to make. Nowadays, though, scientists have access to powerful computers, which they use to create digital simulations of the climate system. Incorporated into their models are the laws of physics, climate data, and natural phenomena that influence climate. Simulations enable scientists to experiment with climate in ways that are otherwise impossible. For instance, they can “change” solar output to see how this affects polar ice, air and sea temperatures, evaporation rates, atmospheric pressure, cloud formation, wind, and rainfall. They can “create” volcanic eruptions and examine the effects of volcanic dust on weather. And they can examine the effects of human population growth, deforestation, land use, changes in the emission of greenhouse gases, and so on. Scientists hope that their models will progressively become more accurate and reliable. How precise are present models? Much, of course, depends on the accuracy of the data and the amount of it fed into the machines. Hence, climate projections vary from the mild to the catastrophic. Even so, says Science, “surprises could spring from the [natural] climate system.” And some already have, such as the unusually rapid rate of Arctic melting, which has amazed many