Climate System Sophie Zechmeister-Boltenstern Reference: Chapin F. St., Matson P., Mooney Harold A. 2002 Principles of Terrestrial Ecosystem Ecology. Springer, Berlin, 490 p.
Structure of this lecture The Atmospheric System The Oceans Landform effects on Climate Vegetation Influences on Climate Climate Variability Climate and Ecosystems
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
Energy Budget 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
Energy Budget 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
Atmospheric Structure The atmosphere is heated from the bottom Therefore it is warmest near the and gets colder with increasing elevation
Atmospheric Circulation 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
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 Circulation Ocean currents are similar to wind patterns: 1. Driven by Coriolis forces 2. Driven by winds
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)
Vegetation effects on climate Amazonasgebiet
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
Temporal Variability in Climate 1. Long-Term Changes
Changes in solar orbit causes long-term variations in solar input to Earth
Climate effects on vegetation
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)
Inerannual Climate Variability The Pacific Ocean strongly influences the climate system becauseit 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)
Weltweite Folgen von El Niňo
Seasonal and Daily Variations Seasonal variation in climate results from tilt in Earth s axis Changes sun angle and day length
Climate and Ecosystem Distribution and Structure Climate gives rise to predictable types of ecosystems
Summary Climate is a complex system determined by radiation in- and output, atmospheric circulations and oceans Milankowich cycles induce ice ages Landforms and landcover affect climate Interannual variability include ENSO (El Nino) and NAO events Vegetation depends on climate but it also affects climate