|
TPO11 Lecture 3 Environmental scienceNarratorListen to part of a lecture in an environmental science class.
Professor:When land gets develop for human use, the landscape changes. We don’t seeas many types of vegetation, trees, grasses and so forth. This in turn leads toother losses: the loss of animal that once lived there. Err…but these are theobvious changes, but there are also less obvious changes like the climate.One interesting case of this…of…of changes in the local land use causingchanges in climate, specifically the temperature is in Florida. Now what comesto mind when you think of the state of Florida?
Student A:Sunshine, beaches.
Student B:Warm weather, oranges…
Professor:Yes, exactly. Florida has long had a great citric industry; large growth oforanges, lemons and the like. Florida’s winter is very mild; the temperaturedoesn’t often get below freezing. But there are some areas in Florida that dofreeze. So in the early 1900s, farmers moved even further south in Florida, toareas that were even less likely to freeze. Obviously, freezing temperaturesare danger to the crops. A bad barrier of cold weather, a long spell of frostscould ruin a farm and the entire crop, anyway, before these citric growersmoved south, much of the land in south Florida, was what we called wetlands.Wetlands are areas of marshy, swampy land, areas where water covers thesoil, or is present either at or near the surface of the soil for large part of theyear. Wetlands have their own unique ecosystem, with plants and animals withspecial an interesting adaptation. Very exciting, but it’s not what we are talkingabout today. Emm…where was I?
Student A:Farmers moved south?
Professor:Oh, yes. Farmers moved south. But the land was not suitable for farming. Youcan’t grow orange in wetland, so farmers had to transform the wetlands intolands suitable for farming. To do that, you have to drain the water from the land,move the water elsewhere, and divert to the water sources such as rivers. Hundreds of miles of drainage canals were built in the wetlands. Now theseareas, the new areas the farmers moved to, used to be warm and unlikely tofreeze, however, recently the area has become susceptible to freezes. And weare trying to understand why.
Student B:Is it some global temperature change or weather pattern like El Ni?o orsomething?
ProfessorWell, there are two theories. One idea is as you suggested that major weatherpatterns, something like El Ni?o, are responsible. But the other idea and this isthe one that I personally subscribe to, is of the changes in the temperaturepattern had been brought about by the loss of wetlands.
Student A:Well, how would the loss of wetlands make a difference?
Professor:Well, think about what we’ve been studying so far. We discussed the impact oflandscapes on temperature, right? What affects does the body of water haveon an area?
Student A:Oh, yeah. Bodies of water tend to absorb the heat during the day, and thenthey release the heat at night.
Professor:Yes, exactly. What you just said is what I want you all to understand. Bodies ofwater release heat and moisture back into the environment. So places nearlarge bodies of water are generally milder, err...slightly warmer than thosewithout water. And what I, another think is that the loss of the wetlands hascreated the situation where the local temperatures in the area are not slightlydifferent, slightly colder than they were 100 years ago, before the wetland weredrained.
Student B:Emm…do we know what the temperature was like back then?
Professor:Well, we were able to estimate this. We have data about South Florida’scurrent landscape, emm…the plant cover. And we were able to reconstructdata about the landscape prior to 1900. Then we enter those data, informationabout what the landscape look like before and after the wetlands were drained.We enter the data into a computer weather model. This model can predicttemperatures. And when all the data were entered, an overall cooling trendwas predicted by the model.
Student B:How much colder does it get now?
Professor:Well, actually the model shows a drop of only a few degrees Celsius. But this isenough to cause dramatic damage to crops. If temperatures over night arealready very close to the freezing point, then this drop of just a few degreescan take the temperature below freezing. And freezing causes frosts, which killcrops. These damaging frosts wouldn’t happen if the wetlands were still inexistence, just as the tiny temperature difference can have major.
相关资料
|
