Page 332 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

296 part II The Water, Weather, and Climate Systems
(a) In the Antarctic Sound, between Bransfield Strait and the Weddell (b) Glaciers move toward the ocean in West Greenland, with the Sea, mountains rise from the mist behind a flank of tabular icebergs. ice sheet on the horizon.
▲Figure 10.18 Earth’s ice sheets—antarctica and Greenland. [Bobbé Christopherson.]
Dry Climates (permanent moisture deficits)
For understanding the dry climates, we consider moisture efficiency (both timing and quantity of moisture) along with temperature. These dry regions occupy more than 35% of Earth’s land area and are by far the most extensive climate over land. Sparse vegetation leaves the landscape bare; water demand exceeds the precipitation water supply throughout, creating permanent water deficits. The extent of these deficits distinguishes two types of dry climatic regions: arid deserts, where the precipitation supply is roughly less than one-half of the natural moisture demand; and semiarid steppes, where the precipitation supply is roughly more than one-half of natural moisture demand. (Review pressure systems in Chapter 6
and temperature controls, including the highest recorded temperatures, in Chapter 5. Desert environments are discussed in Chapter 20.)
Important causal elements in these dry lands include:
• The dominant presence of dry, subsiding air in subtropical high-pressure systems;
• location in the rain shadow (or leeward side) of mountains, where dry air subsides after moisture is intercepted on the windward slopes;
• location in continental interiors, particularly central asia, which are far from moisture-bearing air masses;
Lethbridge, Alberta
Albuquerque, NM
Arid deserts
Semey, Kazakstan
Riyadh, Saudi Arabia
Walgett, NSW Australia
• location along western continental margins with cool, stabi- lising ocean currents;
• Shifting subtropical high-pressure systems, which produce semiarid steppes around the periphery of arid deserts.
Dry climates fall into four distinct regimes, according to latitude and to the amount of moisture deficit: arid climates include tropical, subtropical hot desert, and midlatitude cold desert regimes; semiarid climates include tropical, subtropical hot steppe, and midlatitude cold steppe regimes.
Semiarid steppes
Georeport 10.3 tundra Climates respond to Warming
Global warming is bringing dramatic changes to the tundra climate regions, where temperatures in the arctic are warming at a rate twice that of the global average increase. In parts of Canada and alaska, near-record temperatures as much as 5
to 10 C° above average are a regular occurrence. as organic peat deposits in the tundra thaw, vast stores of carbon and methane are released to the atmosphere, further adding to the greenhouse gas problem (more discussion is in Chapters 11, 17, and 18).