Climate and Climate Change Chapter 21
Temperature and Precipitation • Climate is an area’s long-term pattern of weather • The two main characteristics of climate are Temperature and Precipitation • Other characteristics are the number of days and hours of sunlight; direction, speed and steadiness of the wind; and occurrence of severe weather
Annual Temperature range is the difference between the average temperature of the warmest month and the average temperature of the coldest month • Average Temperature can be misleading. • e.g. Average temperature for Beijing, China, and Valdivia, Chile are the same. However, Beijing goes to extremes from –4°C to 26°C while Valdivia ranges from 7°C to 16°C.
Average Precipitation can also be misleading, one place may get all its rain during a few months (Bombay, India) and another over the entire year (Mobile, Alabama)
Climate Controls • Latitude – generally colder toward poles with little precipitation • Elevation – higher the cooler and drier • Nearby Water – Temperature range small mild climate if downwind more moisture • Ocean Currents – warm currents warm nearby coasts • Topography – leeward side warmer than windward, windward side may be wetter, can act as a barrier to air masses.
Prevailing Winds – blow from a hot or cold region, blow from water or land • Vegetation – will effect insulation, releases water vapor • Some climate controls are more important than others depending on location. • e.g. London, England is pretty far north, however the warm ocean currents keep its climate mild.
Polar Climates • Very cold in winter with little or no daylight • The sun strikes at such a low angle in summer it provides little solar energy • Much of the light is reflected back to space by snow and ice • Tundra are located in Polar Climates, they are very cold with little precipitation • Ice caps are another sub climate in polar climates
Dry Climates – cover 30% of Earth • Occur in regions that lose more water due to evaporation than it receives from rain • Dry climates often exist on leeward sides of mountain ranges and where air sinks in the horse latitude • Semi-arid climates are not as dry as deserts and are often home to dense grasses. (Great Plains of the US)
Humid Tropical Climates • Hot year round – near the equator…ITCZ • Two sub climates…Tropical wet & Tropical wet and dry – wet summers, dry winters.
Most mid-latitude Climate – There are 2 of them, one with mild winters, the other with severe winters. • Mild winter – There are 3 types • Humid subtropical – SE U.S. – Hot muggy summer, mild winters • Marine west coast – west coast of Canada and NW U.S. – cool summers, mild winters • Mediterranean – west coast of SW U.S. & the Mediterranean Sea – dry summers – wet winters with mild temperatures
Severe winters – snow often covers ground in winter but summers are warm – subclimates humid continental and the subarctic • Humid continental – found in the interior of continents and on eastern coasts including the N U.S. east of the great plains – winters very cold and summers very warm • Subarctic – near poles – short summers • Highlands – mountainous regions in which multiple climates exist
Cause of Climate Change • Global mean temperature during the last Ice Age was only 5°C cooler than today’s global mean temperature • If an increase in cloud or ice cover causes more sunlight to be reflected out to space, Earth may cool
There is thought to be 4 basic causes for climate change • Earth’s Motion – shape of its orbit, tilt of its axis varies between 22.1° to 24.5° in a 41,000 year period • These changes affect sun intensity which may allow ice to grow on surface • Plate tectonics – moving of the continents • e.g. Greenland is thought to once have a warmer climate (close to equator) because of tropic fossils found in Greenland
Sunspots – the more sunspots the more energy given off by the sun • Volcanoes – increase dust, clouds and CO2 – may add to warming the atmosphere like what happened during the cretaceous period.
Human Effects on Climate • Due to deforestation and fossil fuel burning CO2 in the atmosphere has increased since the 1800’s • Computer models not accurate because of all the variables
Measuring Climate Change • Scientists use sea floor sediments, glacier samples and tree rings to study the past climates