Лекция: Sea level changes

The mechanisms influencing sea level over the globe are extremely complex. Present sea level is not easy to define, estimates of sea levels over the past 100 years are difficult to make, and predictions over the next 100 years are highly speculative. Sea level changes are influenced by the following mechanisms (those of short time scales — i.e. tens of years-italicized);

1 Changes in осеan water mass – e.g. exchanges with glaciers; changes in the atmosphere-earth-ocean-ice-water distribution.

2 Changes in ocean water volume – e.g. thermal expansion and contraction; salinity changes; changes in atmospheric pressure.

3 Changes in earth crustal levels.

(a) Tectonic – e.g. rise of ocean ridges; sea-floor subsidence; plate movements.

(b) Isostatic – e.g. tectonic loading; ice and water loading.

4 Changes in the global distribution of water

(a) Terrestrial rotation effects.

(c) Global axis changes.

(d) Terrestrial gravity variations.

(e) Changes in the attraction of sun and moon.

(f) Changes in the velocity of ocean currents.

Over the past 100 years, the general global sea level has risen by 10–25 cm or more, accelerating during the century. This rise has been attributed proportionately to the following causes:

1 Thermal expansion of ocean waters (2–7 cm; i.e. possibly 50 per cent or more). This is difficult to estimate due to lack of knowledge regarding oceanic circulations, such that estimates vary from 30 to 60 per cent.

2 Glacier and small ice cap melting (2-5 cm; i.e. possibly 30 per cent). Estimates of this contribution to sea level rise go as high as 48 percent.

3 Greenland ice cap melting (very indeterminate). This could be as great as 25 per cent and as little as 5 per cent.

4 Antarctic ice sheet melting. This is very uncertain; the Antarctic ice sheet is a large and complex system with its own internal mechanisms and a mass balance that changes slowly. Some workers believe the balance is positive, which would offset sea level rise. This source has probably not yet contributed greatly to the global sea level rise but may do so in the future.

Uncertainties regarding sea level rise are still considerable, mainly because of our lack of knowledge concerning the behavior of the large ice sheets, especially Antarctica. There is even the possibility that increased global warming may introduce a tendency for sea level to fallbecause of increased snow accu­mulation rates in high latitudes. Another outside possibility is that a rise in sea level might cause the West Antarctic ice sheet to be buoyed up and melt bodily (not just around the edges, as in the past) and cause a further catastrophic sea level rise but spread over several hundred years. Final considera­tions are the possible effects of extreme sea level events (such as tides, waves and storm surges), but these are extremely difficult to predict.


Упражнение 2.

Прочитайте следующие слова и определите их соответствия
в русском языке:

Mechanism, globe, complex, thermal, crustal, tectonic, effect, gravity, proportionately, circulation, contribution, sheet, system, balance, positive, tendency, accu­mulation, catastrophic, final, extreme, storm.



Упражнение 3.

Какие части речи обозначаются в словарях следующими сокращениями:

v., adv., n., adj., conj., num., part., prep., pron.?

Упражнение 4.

Определите, к каким частям речи относятся следующие слова; напишите соответствующие английские сокращения для каждого из них:

Global, first, distribution, of, behavior, that, to, and, greatly, are, contributed, hundred, vary.


Упражнение 5.

Найдите в тексте примеры этих частей речи.

v. n. adj. adv. num. prep. part.


Упражнение 6.

Образуйте причастия 1 и 2 рода из следующих глаголов. Найдите примеры таких причастий в тексте из упражнения 1.

Define, make, offset, introduce, fall, cause, spread, predict.


Упражнение 7.

В правой колонке найдите русские эквиваленты следующих английских словосочетаний:

1. sea level rise 2. thermal expansion 3. mass balance 4. global warming 5. atmospheric pressure 6. complex system 7. plate movement 8. global axis 9. sea-floor subsidence a. движение тектонических плит b. сложная система c. опускание морского дна d. подъем уровня моря e. баланс массы f.земная ось g. атмосферное давление h. тепловое расширение i. глобальное потепление


Упражнение 8.

Прочитайте текст и найдите в нем ответы на следующие вопросы:

1. Где находятся основные запасы углерода?

2. Какова роль океанов в глобальном углеродном цикле?

3. Почему рост концентрации углекислого газа в атмосфере не обязательно приведет к увеличению производительности океана?

(Контрольное время – 5 минут)

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