Page 331 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 10 Global Climate Systems 295
tundra Climates
The term tundra refers to the characteristic vegetation of high latitudes and high elevations, where plant growth is restricted by cold temperatures and a short growing season. In tundra climates, land is under some snow cover for 8–10 months, with the warmest month above 0°C, yet never warming above 10°C. These climates occur only in the Northern Hemisphere, except for el- evated mountain locations in the Southern Hemisphere and a portion of the Antarctic Peninsula. Because of its elevation, the summit of Mount Washington in New Hampshire (1914 m) statistically qualifies as a highland tundra climate despite its limited areal extent. In con- trast, approximately 410 500 km2 of Greenland comprise an area of tundra and rock about the size of Newfound- land and Labrador.
In spring when the snow melts, numerous plants appear—stunted sedges, mosses, dwarf shrubs, flowering plants, and lichens—and persist through the short sum- mer (Figure 10.17). Some of the dwarf willows (7.5 cm) can exceed 300 years in age. Much of the area experi- ences permafrost and ground ice conditions; these are Earth’s periglacial regions, discussed in Chapter 17.
ice-Cap and ice-sheet Climates
An ice sheet is a continuous layer of ice covering an ex- tensive continental region. Earth’s two ice sheets cover the Antarctic continent and most of the island of Green- land (Figure 10.18). An ice cap is smaller in extent, roughly less than 50000 km2, but completely buries the landscape like an ice sheet. The Vatnajökull ice cap in southeastern Iceland is an example (see the NASA image in Figure 17.5).
Most of Antarctica and central Greenland fall within the ice-cap and ice-sheet climate category, as does the North Pole, with all months averaging below freezing (the area of the North Pole is actually a sea covered by ice, rather than a continental landmass). These regions are dominated by dry, frigid air masses, with vast expanses that never warm above freezing. In fact, winter minimum temperatures in central Ant- arctica (July) frequently drop below the temperature of solid carbon dioxide, or “dry ice” (–78°C). Antarctica is constantly snow-covered, but receives less than 8 cm of precipitation each year. However, Antarctic ice has
▲Figure 10.17 Greenland tundra. late September in east Greenland, with fall colours and musk oxen. [Bobbé Christopherson.]
accumulated to several kilometres deep and is the larg- est repository of freshwater on Earth.
Polar marine Climates
Polar marine climates are more moderate than other polar climates in winter, with no month below –7°C, yet overall they are not as warm as tundra climates. Because of marine influences, annual temperature ranges are low. This climate exists along the Bering Sea, on the southern tip of Greenland, and in northern Iceland and northern Norway; in the Southern Hemisphere, it generally occurs over oceans between 50° S and 60° S. Macquarie Island at 54° S in the Southern Ocean, south of New Zealand, is polar marine.
South Georgia Island, made famous as the place where Ernest Shackleton sought rescue help for himself and his men in 1916 after their failed Antarctic expedi- tion, exemplifies a polar marine climate (Figure 10.19, page 297). Although the island is in the Southern Ocean and part of Antarctica, the annual temperature range is only 8.5 C° between the seasons (the averages are 7°C in January and –1.5°C in July), with 7 months averag- ing slightly above freezing. Ocean temperatures, rang- ing between 0°C and 4°C, help to moderate the climate so that temperatures are warmer than expected at its 54°-S-latitude location. Average precipitation is 150 cm, and it can snow during any month.
Georeport 10.2 Boundary Considerations and shifting Climates
The boundary between mesothermal and microthermal climates is sometimes placed along the isotherm where the coldest month is −3°C or lower. That might be a suitable criterion for europe, but for conditions in North america, the 0°C isotherm is considered more appropriate. The distance between the 0°C and −3°C isotherms is about 350 km. In Figure 10.2, you see
the 0°C boundary used.
Scientists estimate that the poleward shift of climate regions will be 150 to 550 km in the midlatitudes during this century. as you
examine North america in Figure 10.2, use the graphic scale to get an idea of the magnitude of these potential shifts.