Реферат: El Nino Essay Research Paper There
El Nino Essay, Research Paper
There’s trouble in the air. Specifically, in the West Coast of the Americas, where the sea surface has been heated to abnormal extremes by an ominous, intermittent flood of hot water called El Nino. The term. “El-Nino,” which means “the child,” was originally in reference to a warm current arriving annually during the Christmas season off the coast of Peru and Ecuador. The term was later restricted to the particularly strong periodic warming that disrupt the local fish and bird populations, and extend westward across the equatorial Pacific Ocean to near the date line. What is an El Nino? El-Nino is the warming of the Pacific waters that is brought about from time to time by naturally occurring oscillations in atmospheric pressure and ocean movements in the equatorial Pacific. The warmer ocean pumps more energy and moisture into the atmosphere and this in turn alters wind and rainfall patterns around the world. The atmospheric circulation also changes when the sea-surface temperatures in the eastern tropical Pacific rise above normal. In normal, non-El Nino conditions, the trade winds blow towards the west across the tropical Pacific. These winds pile up warm water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador. The sea surface temperature is about 8 degrees C higher in the west, with cool temperatures off South America, dut to an upwelling of cold water from deeper levels. This cold water is nutrient-rich, supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries. Rainfall is found in rising air over the warmest water, and the east Pacific is relatively dry. Warming of the Pacific waters is not the only thing El-Nino is to be blames for. The current El-Nino warming has been so strong, is has added noticeable zip to atmospheric winds and slowed Earth’s spin, suggest scientists who track the planet’s rotation. El-Nino exert these profound effects by speeding up the eastward movement of the atmosphere, relative to the solid body of the planet. The change shows up in the analyses of the atmosphere’s angular momentum-a property comparable to the momentum of a spinning tire. “From mid-March through late November 1997, the angular momentum remaind significantly above average” (Monastersky 45-46). During non-El Nino years, winds in the tropics blow from east to west, whereas winds over the rest of the globe travel from west to east. Combined, they give the atmosphere a net eastward momentum. The atmosphere routinely trades some of this momentum back and forth with the solid Earth as winds drag across the surface of the planet and push against the mountain ranges. In the Northern Hemisphere’s winter, the atmosphere speeds up and Earth slows. In summer, the reverse happens. El-Nino also boosts the atmosphere’s angular momentum by slowing down the tropical easterlies and speeding the westerlies outside the tropics. As the atmosphere speeds up during El Nino, earth itself slows down to conserve the combined angular momentum. John M. Gipson of NASA’s Goddard Space Flight Center in Greenbelt, Md., has tracked the planet’s spin by monitoring changes in the length of the day. Over a typical year, the day shortens and lengthens by roughly 1 millisecond, mostly because of shifts in atmospheric angular momentum. During the current El Nino, the day has grown longer by four-tenths of a millisecond. Last year, Earth squeaked past the previous record high for globally averaged temperatures, continuing a balmy trend that has made this decade the hottest in more than a century of temperature data. “All of us are pretty happy with the agreement of the different methods,” says Thomas R. Karl of the National Climate Data Center (NCDC) in Asheville, NC. “There are differences [among the teams' findings], but they are small” (Karl 38). Earth’s land and ocean surface last year was 0.42 degrees C warmer than the long-term average of 16.5 degrees C for the reference period 1961 through 1990, says Karl. The NCDC team analyzed data from more than 5,000 land stations and from water temperature reading collected by satellite sensors, buoys, and ships. 1997 came in almost a tenth of a degree warmer than the previous record years, 1990 and 1995, which were virtually identical in the NCDC data. Researchers play down the differences among these three years because the uncertainties in the figures exceed the gaps between them. The important message is that 9 of the top 10 warmest years on record have occurred since 1987. Such evidence adds weight to arguments that humans are altering climate in noticeable ways. It is likely that greenhouse emissions are playing a role in the sustained upward trend in temperatures. El Nino helped push Earths temperature into a new territory last year by producing a vast pool of warm water in the equatorial Pacific Ocean. Even without El Nino, however, global temperatures would have remained high. During the first few months of 1997-before El Nino blossomed-the land surface was already quite warm. In contrast to the global pattern, eastern North America stayed cooler than normal last year, as did the eastern Mediterranean and northern India. In the analysis of global temperatures researchers at the United Kingdom Meteorological Office in Bracknell found 1997 to be 0.43 degrees C above average-the highest since they began keeping records, in 1860. Their calculations do not yet include December data, but value will not change appreciably. A third study of global temperatures, conducted at NASA’s Goddard Institute for Space Studies in New York, puts 1997 temperatures at 0.40 degrees C above for the base years 1951-1980 (Monastersky 45-46). Although consistent with each other, these surface measurements contrast with satellite readings of Earths lower atmosphere. The temperature between the ground and an altitude of 6,000 meters last year hovered slightly below the average value for the years 1982 through 1991. In the 19-year record of satellite date, 1997 ranked as the eighth coolest (Science News).
Satellite data also indicates that the lower atmosphere has cooled over the last 19 years. However when you correct for the strong cooling effects of volcanic eruptions and warming effects of El Nino, the satellite trend turns into a warming of 0.007 degrees C per decade. The surface has warmed at twice that rate. Climate scientists are investigating this discrepancy. The two data sets need not agree perfectly, because they measure different parts of the planet. Still, the size and duration of the difference has raised concerns. It is highly unlikely that the atmosphere and surface could behave independently for so long. Last year, a term of researchers reported finding evidence of problems that artificially lowered the satellite temperature measurements, but at the same time these satellite readings agree almost perfectly with balloon readings. The present El Nino is the strongest observed in the latter half of the 1900’s, during which the most sophisticated measurements have been taken. It may very well be the strongest of the century. This El Nino has also become strong earlier in the year than most others have. The last time conditions looked like this was when the strongest, most destructive El Nino on record struck in 1982-1983. By the time that event subsided, some 2,000 people died in flooding, mud slides, droughts, fires and sundry related calamities, hundred of thousands were forced out of their homes, and economic losses topped $8 billion in the United States. This year s version of El Nino lived up to its expectations that had been predicted. There are not any exact totals as of yet, but we have already seen the destruction it has caused the United States and the world as well. There were the mudslides in California, which stranded civilians and vacationers in their homes, which forced the National Guard to come and airlift them to safety, before they became a permanent part of the landscape. Here in Iowa, we recorded the second warmest winter on record, at an average temperature of 36 degrees C. In the southern states they recorded record amounts of snowfall. One winter storm dropped more snow in Kentucky and Tennessee than we saw here in Iowa throughout the whole winter. Towns and cities throughout the world have been ravished by El Nino’s wrath and the worst of it could still be to come. The bottom line is the potential for dangerous weather is still a major threat for our upcoming 1998 spring and summer season, just as we saw during the 1997-1998 winter effects of El Nino, and indeed people ought to be prepared. However, that the potential exists for any given location during any given season or year, whether during an El Nino or not, and people should educate themselves on an ongoing basis about ways to minimize weather-related threats to their life and property. We live on a planet where at any given time disaster can strike whether predicted or not, so be prepared for nature’s wrath!