how does heat transfer affect climate? –the horse latitudes and the intertropical convergence zone...

How Does Heat Transfer Affect Climate?– The Horse Latitudes and The Intertropical Convergence Zone

• Dry air sinks at about 30⁰N and 30 S latitudes ⁰ locations of deserts; great evaporation from ocean; often lack winds “Horse Latitudes”

• The Intertropical Convergence Zone: ~ equator; trade winds converge, warm air rises; often lack winds “Doldrums”

– Ocean Currents Affect Regional Climates• Example: San Francisco cooled by California Current, while Washington D.C.

warmed by Gulf Stream (both cities at same latitude)

– Monsoons and Cyclones• Monsoons: seasonal wind patterns caused by heating and cooling of continents;

in summer, warm air rises over land, draws in moist warm air from ocean, which rises and cools heavy rainfall; common in India, Southeast Asia

• Cyclones: rotating storm systems around low-pressure center (eye of storm); tropical cyclones (typhoons in Pacific, hurricanes in Atlantic) fueled by warm water, draw in moist tropical air; extratropical cyclones form where polar winds meet the westerlies (lead to unstable air, thunderstorms); cyclones rotate counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere

– Clouds and the Hydrologic Cycle• The Water (Hydrologic) Cycle: includes evaporation, condensation, precipitation• Clouds (condensed water vapor) trap heat but also reflect energy (white)

Figure 8-20

Figure 7-9

Figures 8-21 and 8-22

Figure 7-16

Figure 8-4

Figure 8-5

Is the Ozone Layer Still Threatened?

• Stratospheric Ozone Depletion– Ozone a component of smog in lower atmosphere; in

upper atmosphere, shields Earth from UVB radiation– Chlorofluorocarbons (CFC’s) lighter than air, rise to

upper atmosphere, where they stick to ice crystals; each molecule able to destroy many ozone molecules

(most during summer); Antarctic ozone hole detected in 1985, Arctic ozone hole detected in early 1990’s; global ozone declining (ex. Toronto, UV increased 5.3% per year from 1989-1993)

– Effects of UV: skin cancers, stress immune systems, coral bleaching, reduces productivity of phytoplankton

– International Response: Montreal Protocol (1987) phased out production of CFC’s, but existing CFC’s stable (long-lived; ex. freon)

Figure 8-2

Figure 8-3

What Evidence Supports the Theory of Global Warming?

• A theory, supported by multiple lines of evidence (that current observed warming trend is due largely to human-caused influences)

– Greenhouse Effect: greenhouse gases trap warm air in lower atmosphere (esp. carbon dioxide, methane, and carbon monoxide)

– Combustion of fossil fuels adds CO2 to atmosphere; deforestation is often via burning (combustion) and loss of trees reduces uptake of carbon dioxide; more cattle more methane (proposal for effort to measure this effect laughed out of

U.S. Congress as “cow-fart study”)– Observed: rise in atmospheric CO2; global atmospheric and

oceanic warming; rising sea levels (Tuvalu, Kiribati, other Pacific islands flooding); retreat of mountain glaciers,

Arctic ice thinned, Antarctic ice shelves apparently breaking up; tropical diseases and insects spreading; regional climates

shifting, affecting species ranges and causing extinctions; widespread coral bleaching; lower heating costs on the “bright side”

Figures 16-2 and 16-3

What are the Predicted Effects of Global Warming and the International Response?

– Predicted: approx. 6°C rise by 2100; warming of tundra releases more CO2, melting of polar ice reduces reflection of energy by white

ice and accelerates melting (vicious cycles); melting of West Antarctic ice sheet would raise sea level by 20 feet, flooding London, New York, Florida, New Orleans (among others); cooling of Northern Europe due to likely disruption of Gulf Stream current by melting Arctic (more icebergs will also endanger ships); rise in intensity of tropical cyclones due to warmer water temperature

– Debate among specialists is mainly regarding the ocean’s role in the absorption of CO2 (but note that levels steadily rising in

atmosphere, corresponding to steady rise in combustion/emissions)– Public debate mainly regarding Earth’s natural cycles of warming/cooling

and lack of “definite proof”; also regarding economic costs of reducing carbon emissions

– International Response: Rio Earth Summit (1992) – agreed that Global Warming is serious problem and response needed by year 2000 (George Bush Sr. signed); Kyoto Accord (1998) – signed by

nearly all nations; Copenhagen (Dec. 2009); Adapt (?): sea walls planned in Thailand and Bangladesh