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Climate and Ecosystems
Chapter 29, sections 1 and 2
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Climate Climate is not the same thing as weather!
Climate consists of the prevailing weather patterns in a region over longs periods of time. Climate is caused by many factors, including location on the globe, nearness to an ocean, wind direction, geography.
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Think about this… If it were true that seasons were caused by the earth being closer to or further away from the sun… …how would it be possible that the southern hemisphere is experiencing summer while the northern hemisphere is experiencing winter? Remember, we are 93 million miles from the sun. Small changes in distance aren’t going to have a big effect.
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The sun drives climate as well as the seasons.
Summer in the Northern Hemisphere North Pole 90° N 23.5° tilt 0° equator FIGURE 29-1 Earth's curvature and tilt produce seasons and climate Temperatures are highest and most uniform at the equator and lowest and most variable at the poles. Equatorial sunlight is more perpendicular and hits this band year-round, while polar sunlight is seasonal, and its angle spreads it over a much larger land surface. The tilt of Earth on its axis causes seasonal variations in the range and directness of sunlight. 0° 23.5° tilt Summer in the Southern Hemisphere South Pole 90° S June 21st : northern summer solstice; southern winter solstice December 21st : northern winter solstice; southern summer solstice
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Average temperature at any part of the globe is affected not by how close we are to the sun (a common misconception) but by the angle of incidence of the sun’s rays. Less direct rays = less solar energy = cooler region More direct rays = more solar energy = warmer region
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Global air circulation influences local climates.
Rising air cools and drops moisture. Descending air tends to be dry. cold, dry air falls cool, moist air rises (rain/snow) Polar Easterlies 90 N polar cap 60 N Westerlies warm, dry air falls 30 N desert N.E. Tradewinds hot, moist air rises (rain) rain forest rotation S.E. Tradewinds rain forest desert 30 S warm, dry air falls Westerlies 60 S Polar Easterlies polar cap 90 S cool, moist air rises (rain/snow) cold, dry air falls
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According to this diagram, where on the planet should we find:
Deserts? Tropical rain forests? Permanent snowfields? A. Cool, moist, rising air D A I L Y W O R K B. Warm, dry, falling air C. Warm, moist, rising air
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Ocean current also affects climate.
Water tends to absorb and retain heat, and lose it slowly. Ocean water near the equator tends to be warm, so currents from the equator are warm. Water near the poles is much cooler.
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The Gulf Stream carries warm water from the equator northward, warming the coast of Europe.
There is evidence that the Greenland ice is melting, due to Global Climate Change, and pouring cold water into the North Atlantic. If enough cold water is dumped into the Atlantic, it could divert the Gulf Stream.
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Climate Fluctuations Some natural processes can cause local climate to fluctuate from year to year. One example: El Niño/ La Niña weather cycles along the American Pacific coasts.
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More info at: http://www.sbg.ac.at/ipk/avstudio/pierofun/atmo/elnino.htm
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In an El Niño cycle, prevailing Trade Winds weaken
In an El Niño cycle, prevailing Trade Winds weaken. Warm water spreads back across the Pacific, disrupting upwellings along the South American coast.
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Local Climate Localized climate zones can be caused by:
Proximity to oceans or large lakes. Position of mountain ranges. Wind direction.
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Oregon Coast Peruvian Coast Oregon is on the west side of the North American continent. Peru is on the west side of the South American continent. Why do these two areas look so different?
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Water is released as air rises and cools. Dry air sinks, warms and absorbs water from the land. Water is carried from ocean by prevailing winds. dry climate in rain shadow moist climate The rain shadow effect can cause moist conditions on one side of a mountain range and dryer conditions on the opposite side of the mountains. On the Peruvian coast, prevailing winds blow from the mountains toward the ocean. What effect might that have on climate on the coast of Peru?
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high rock, snow, ice tundra coniferous forest deciduous forest altitude tropical forest low equator (0°) poles (90°) latitude Altitude and latitude also interact to create local climates that support different types of communities.
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Recap Climate begins with the sun’s heat.
Climate is influenced by ocean and atmospheric currents, which are driven by the sun’s heat. Geography influences local climate. Climate directly affects what organisms can live in an area.
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