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Snow and Ice. The effects of the twentieth-century climate change on global snow and ice cover are apparent in many ways




The effects of the twentieth-century climate change on global snow and ice cover are apparent in many ways, but the responses differ widely as a result of the different factors and time scales involved. Snow cover is essentially seasonal, related to storm system precipitation and temperature levels. Sea ice is also seasonal around much of the Antarctic continent and the marginal seas of the Arctic Ocean, but the central Arctic has thick multi-year ice. Seasonal (or first-year) ice grows and decays in response to ocean surface temperature, radiation balance, snowfalland ice motion due to winds and currents. The loss of multi-year ice from the Arctic is mainly through ice export. Glacier ice builds up from the net balance of snow accumulation and summer melt (ablation), but glacier flow transports ice towards the terminus, where it may melt or calve into water. In small glaciers the ice may have a residence time of 1 Os-100s of years, but in ice caps and ice sheets this increases to 103 -106 years.

In the twentieth century there was a rapid retreat of most of the world's glaciers. Glaciers in the North Atlantic area retreated during the 1920s to the mid-1960s and since 1980s, due largely to temperature increases, which have the effect of lengthening the ablation season with the corresponding raising of the snowline. In the last 10-15 years the freezing level in the troposphere has risen in the inner tropics by 100-150m, contributing to rapid ice loss on equatorial glaciers in East Africa and the Northern Andes. Also in the last decade or so, some glaciers in maritime climates (western North America and Scandinavia) have shown advances, due to heavier snowfalls during warmer winters. Major alpine glaciers in many areas of the world have lost mass and shrunk since the late nineteenth century, whereas smaller ones show short-term fluctuations in response to climatic variability. Projections for AD 2050 suggest that one quarter of the present glacier mass may disappear.

Another tendency illustrating world warming is the retreat of Arctic sea ice. Ports in the Arctic remained free of ice for longer periods during the 1920s—50-s for example. This trend was reversed in the 1960-s~70-s, but since the late 1980-s the summer extent of Arctic ice has decreased, with large reductions, particularly in the Eurasian Arctic, in 1990, 1993 and 1995. There appears to be no general trend in Antarctic ice extent, although comprehensive records began only with all-weather satellite coverage in 1973. Sea ice in both polar regions is expected to shrink and thin with continued warming, but modelling of these processes remains rudimentary.

Major iceberg calving events have occurred along the Ross Ice Shelf and on the Larsen Ice Shelf of the Antarctic Peninsular, but the causes of such calving are more related to the long history of the ice shelves and ice dynamics than to recent climate trends.

Snow cover extent shows perhaps the clearest indication of a response to recent temperature trends. Northern hemisphere snow cover has been mapped by visible satellite images since 1966. Compared with the 1970s—mid- 1980s, annual snow cover since 1988 has shrunk by about 10 per cent. The decrease is most pronounced in spring and is well-correlated with springtime warming. Winter snow extent shows little or no change. Nevertheless, annual snowfall in North America north of 55° increased during 1950-90. Much work remains to be done to analyse station snowfall and snow depth records for other countries, particularly since these variables are difficult to measure and the design of gauges and wind shields has changed through time. Scenarios for AD 2050 suggest a shorter snow cover period in North America, with decrease of 70 per cent over the Great Plains. In alpine areas snow lines will rise by 100-400m, depending on precipitation.

 

Упражнение 2.

Ответьте на следующие вопросы

14. What does seasonal ice cover depend upon?

15. Have the world's glaciers moved forward or backward during the last two
centuries?

16. How much has the freezing level in the troposphere in the inner tropics risen
by?

17. How much of the present glacier mass might have disappeared by 2050?

18. How long were ports in the Arctic free of ice in different periods of the XX
century?

6. When did records of Antarctic ice extent begin?

9. What are the trends of sea ice in the polar regions like?

10. How long has northern hemisphere snow cover been mapped?

11. Did annual snowfall in North America north of 55° go up or down in the
middle of the XX century?

10. What are the prospects of snow cover in North America for 2050?

Упражнение 3.

Найдите в тексте термины, соответствующие следующим выражениям.

 

broadly go back quick going up and down
rainfall thanks to go up change direction to the
summer melt become longer ten years opposite
reduce carry mountain (adj.) every year
       
       

Упражнение 4.

Добавьте одно или более слов в каждую группу.

all-weather satellite multi-year XX century climate

snow cover snow depth iceberg calving

ocean surface storm system northern hemisphere snow

 

Упражнение 5.

 

Переведите следующие слова на русский язык.

also around since
as well as about over
which therefore such/so

through perhaps

although/though nevertheless
particularly whereas

Упражнение 6..

Из слов в правой и левой колонке образуйте цепочки существительных

ice images

snow surface

satellite range

temperature loss

summer cover

springtime flow

glacier melt
ocean advances

Упражнение 7.

Вставьте пропущенные буквы в приведенные ниже слова из текста.

- - nt- bu- e, r - co~s, -ncr--se, -aus-, c-r-e-t, r- - r- a t, -ar-t-me, -e-gt-en, s-r-nk, -cc—, -lu--ua--on, re--in, m-a-ur-.

Упражнение 8.

Прочитайте следующие выражения

1989, 40°S, 107, 1970s, 75%, lA, Va, 0. 25

 

Упражнение 9.

Вставьте в пропуски в тексте подходящие слова: contributes, although, those, frozen, a little, level, dissolved, reflecting.

Glaciers and ice sheets both affect and are affected by changes in Earth's climate.

They are ______ fresh-water reservoirs that change volume in response to changesin temperature and snowfall. Were the ice sheets in Greenland and Antarctica to melt entirely, global sea would rise about 75 meters.

________ great polar ice sheets also contribute to the formation of cold salty sea water that sinks to fill the deep ocean. When the ice forms, it uses only water; the salts are left behind, increasing the water salinity. Ice and snow play

a role in the global energy balance by from 60 to 90 per cent of the solar radiation they receive.

On a scale more relevant to peoples' daily lives, the seasonal melting of mountain

glaciers__________ to summertime river flow and to the ongoing sea level rise.

Today permanent ice covers _____ less than 10 per cent of Earth's land

surface, yet contains almost 87 per cent of its fresh water. _______ glaciers and

ice caps make up less than 1 per cent of Earth's terrestrial ice volume, their small size allows them to respond rapidly to climate change.

 

Упражнение 11.

Прочитайте текст за 10 минут и передайте его содержание максимально подробно.




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