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Climate Chapters 18 & 19


Climatic Controls The world's many climates are controlled by the same factors affecting weather intensity of sunshine and its variation with latitude distribution of land and water ocean currents This map shows sea-level temperatures (°F).


Regions of Rising & Sinking Air Global patterns of temperature and precipitation are affected by global cells of rising and sinking air, which run meridionally north to south.


Observed Precipitation vs Ideal North-to-south patterns of rising and sinking air help to predict precipitation, but zonal variation in land masses and ocean currents create deviations from these predictions.


Topographic Controls on Climate Westerly winds blowing moist air from the Pacific Ocean encounter several mountain ranges that create patterns of rising air and precipitation followed by sinking air and warm dry rain shadows.


Ancient Greeks classified 3 climate regions as tropical, polar, and temperate zones. The Koppen classification system is now widely used, based on temperature and precipitation, and distinguishes 5 major climatic types as tropical moist, dry, moist mid-latitude with mild winters, moist mid-latitude with severe winters, and polar climates. Thornthwaite's classification system considers precipitation to evaporation ratios. Climate Classification


Tropical Rain Forest Annual rains greater than 150 cm in this Peruvian tropical wet climate may leach most nutrients from the soil. Annual temperature variations are often within 3°C.


Monthly precipitation has greater variation than temperature in this tropical wet climate, a fact that is supported by the migrating pattern of the Intertropical Convergence Zone (ITCZ). A Steady Climograph


Tropical Wet-and-Dry Climate North of the equator annual precipitation may still exceed 100 cm, but there is greater monthly variation in precipitation, with 2 months receiving less than 6 cm. African acacia trees and savanna grass thrive in this climate with wet and dry seasons.


The climograph for Timbo, New Guinea at 11° North latitude shows the greater variation in temperature and precipitation than at the equator. Punctuated Dry & Wet Seasons


Arid Climate Approximately 12% of global lands are arid, including interior Australia and the U.S. Sonoran and Mojave deserts.


Xerophytes, such as cacti, are arid climate plants well suited for long droughts. Summer maximum temperatures reach well above 100°F, but humidity is often below 25%. Xerophytes & Water Stress


Semi-Arid Climate Regions of short bunch grass, scattered low bushes, and few trees are referred to as steppe, and in the U.S. it includes most of the Great Plains and south-central California.


Winter precipitation changes from liquid to frozen snow in more northern sections of this climatic region, with annual totals between 20 and 40 cm. Semi-Arid Climograph


In this climate, annual precipitation may range from 80 to 165 cm, and for interior regions the summer brings vast amounts of rain during thunderstorms. Humid Subtropical Climate


Low clouds, fog, and drizzle characterize coastal marine areas for much of the year. If mountains line the coast, the regions are often restricted to narrow belts. Marine Climate


Mediterranean Climate Temperature and precipitation differences for a coastal, left, and interior, right. Mediterranean climates of San Francisco and Sacramento.


Mediterranean Vegetation The wet winters and dry warm summers common to California lead to chaparral vegetation types of chamis, manzanita, and foothill pine.


Humid Continental Climate Temperature is used to further subdivide this climatic region as hot or cool summers. Vegetation in these wetter regions provides brilliant autumn color.


Humid Continental Differences Comparison of the hot summer interior of Des Moines with the cool summer of Winnipeg reveals the similar annual pattern but with different maximum temperatures.


Subpolar & Polar Climate Sub polar regions of southern Alaska, such as Fairbanks, have higher temperatures and greater precipitation than the cooler, drier, polar regions of northern Alaska, shown here with Barrow.


Taiga Forests & Boreal Climate Coniferous forests occur where winter temperatures are low and precipitation is abundant.


Tundra Vegetation Extremely short growing seasons keep woody vegetation short and scattered, with ground cover is comprised mostly of mosses and lichens.


Precipitation and temperature data reveal the severity of this climate type, which occupies the interior ice sheets of Greenland and Antarctica. Earth's coldest places are located in this climate. Polar Ice Cap Climate


Vertical Climate Change Ascending a mountain brings changes in temperature and precipitation, and so to will bring changes in vegetation types and micro-climates, as illustrated in this sketch that moves from grassland to tundra and icecap across a short distance of 180 km, and up a steep elevation of 4 km.


Climate Influences & Senstivity Climate is affected by changes in temperature and precipitation. Even urban development, such as warm lights, can trigger microclimate changes. In this image, the streetlight warmth keeps leaves on the tree well into fall.


Reason for Climate Concern Oceans might rise by 65 m if all of earth's glaciers, which cover 10% of the land surface, were to melt. Smaller predicted sea level change of 1 m might still devastate many areas.


Reconstructing Past Climates Sea surface isotherms for 18,000 years ago were estimated from analysis of ocean sediment cores that held temperature sensitive signatures such as sea shell content and oxygen-isotope ratios. These isotherms are compared with those of today, for the month of August.


Climate Through the Ages Data important for estimating past climate include: lake bottom sediment, pollen in ice caves, fossil evidence, written documents, coral isotopes, calcium carbonate layers in caves, borehole temperature, and dendrochronology or tree ring data. These data have helped identify the Younger-Dryas cold spell that broke a warming trend in this current interglacial period.


Climate Change Triggers Earth's climate is affected by feedback loops such as the water vapor-greenhouse feedback, where increases in air temperature increases water vapor, which is a greenhouse gas that increases temperature. Plate tectonics and drift concentrated continents at higher latitudes allowed for more ice cover, which reflected more sunlight and created a positive feedback to cause greater cooling.


Carbon Dioxide Fluctuations Tectonic processes associated with continental drift lead to increased periods of volcanic degassing of CO2, which causes warming. Higher temperatures leads to increased weathering, which will remove CO2 from the atmosphere and reverse warming in a negative feedback loop.


Milankovitch Theory of Climate Change Climate change may be driven by changes in earth's: orbit (eccentricity), from ellipse to circle at 100,000 year cycles, wobble (precession), from the north pole pointing toward or away from the sun in June at 23,000 year cycles, and tilt (obliquity), from 22° to 24.5° at 41,000 year cycles. Figure 19.9


Tropospheric & Stratospheric Aerosols Auto emissions and wild land fires are 2 sources that emit aerosols into the troposphere that reduce incoming radiation and have a net cooling effect on earth's surface. Volcanic eruptions push aerosols into the stratosphere. Large eruptions, such as Mt. Pinatubo, have been linked to significant cooling episodes.


Mt. Pinatubo Eruption & Impact Three months after the June 1991 eruption of this Philippine volcano, much of the 20 million tons of ejected sulfur dioxide had been directed by zonal stratospheric winds and girdled the equator. Recorded changes in air temperature indicates the volcanic impact on climate.


Climate Model Simulation & Uncertainty Climate models often test their skill by hind casting observed climate from 1860 to the present. As the model sophistication increases to include greenhouse gasses, aerosols, and changes in solar radiation the model has improved prediction.


Consequences of Climate Change Climate models predict that land areas will warm more rapidly than oceans, particularly at northern high latitudes.This results from dark boreal trees absorbing 3 times more solar energy than the snow-covered tundra, which creates warmer weather, and the positive feedback of boreal forests to expanding their range.

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