Transcript Document
Climate is the state factor that most strongly governs the global pattern of ecosystem structure and function Climate is a key mechanism by which ecosystems interact with the total Earth System Major goals in this lecture • Understand how the climate system works • Enable you to predict the climate any place on Earth Energy in = energy out Half of solar radiation reaches Earth The atmosphere is transparent to shortwave but absorbs longwave radiation (greenhouse effect) The atmosphere is heated from the bottom by longwave radiation and convection The temperature of a body determines wavelengths of energy emitted Solar radiation has high energy (shortwave) that readily penetrates the atmosphere Earth emits low-energy (longwave) radiation that is absorbed by the atmosphere The atmosphere is heated from the bottom Therefore it is warmest near the and gets colder with increasing elevation Uneven heating of Earth’s surface causes atmospheric circulation Greater heating at equator than poles 1. sun’s rays hit more directly 2. less atmosphere to penetrate Therefore 1. Net gain of energy at equator 2. Net loss of energy at poles Air rises at equator and subsides at poles (vertical circulation) Circulation cells explain global distribution of rainfall Earth’s rotation determines wind direction (horizontal circulation) (Coriolis force) tropical easterlies temperate westerlies At 30º N & S, air descends more strongly over cold ocean than over land At 60 º N & S, air descends over cold land (high pressure) and rises over warm ocean (low pressure) Pressure gradients create geographic variation in prevailing winds In summer at 60 º N & S, air descends over cold ocean (high pressure) and rises over warm land (low pressure) 1. Cool equator-ward flow of air on W coast of continents 2. Warm poleward flow of air on E coasts of continents Creates planetary waves Ocean currents are similar to wind patterns: 1. Driven by Coriolis forces 2. Driven by winds Climate of any region is predictable from topography, wind and ocean currents Alaska’s July temperature Warming leads to thawing of permafrost in Alaska Uneven heating of Earth’s surface causes atmospheric circulation 60% of heat transport is carried by atmosphere through storms that Move along pressure gradients 40% is carried by ocean currents (conveyor belt) surface (warm) currents move poleward deep (cold) currents move equatorward Ocean currents move 40% of “excess heat” from equator to poles Driven by circulation of deep ocean waters Deepwater formation occurs near Greenland and in Antarctic Landform effects on climate • Land-water interactions – Monsoons – Land-sea breezes • Mountain effects – Rain shadow – Effects of aspect – Air drainage (inversion) Climate effects on vegetation Vegetation effects on climate How can the atmosphere warm? 1. More solar radiation variation in Earth’s orbit 2. Less reflected shortwave less sulfate aerosols darker surface of Earth (land-cover change) 3. More absorbed longwave more “greenhouse gases” Earth’s climate is now warmer than at any time in the last 1000 years 1. increased solar input (small warming effect) 2. Increased sulfate aerosols reflects radiation (small cooling effect) 3. Increased greenhouse gas concentrations (large warming effect) 4. Land-cover change creates a darker surface (large warming effect) Changes in solar orbit causes long-term variations in solar input to Earth Most major greenhouse gases are increasing in atmospheric concentrations Climate is warming most rapidly at high latitudes This warming is most pronounced in Siberia and western North America The Pacific Ocean strongly influences the climate system because It is the largest ocean basin Normal ocean current and wind direction in central Pacific is easterly Interannual climate variation ENSO events Teleconnections carry these climate effects throughout the globe (e.g., El Niño creates warm winters in AK and Calif) Seasonal variation in climate results from tilt in Earth’s axis Changes sun angle and day length Functioning of ecosystems varies predictably with climate Climate gives rise to predictable types of ecosystems Ecosystem distribution of ecosystems is predictable from global patterns of wind and ocean circulation