Climate Chap 2 Introduction I Forces that drive climate and their global patterns A Solar Input Earth s energy budget B Seasonal cycles C Atmospheric circulation D Oceanic circulation E Landform effects F Vegetation feedbacks II Variability in climate A Seasonally see I B B Yearly El Ni o Southern Oscillation ENSO C Millenial D Human impacts Powerpoint modified from Harte Hungate http www2 for nau edu courses hart for479 notes htm and Chapin http www faculty uaf edu fffsc Climate is the state factor that most strongly governs the global pattern of ecosystem structure and processes 1 3 Climate gives rise to predictable types of ecosystems 2 21 Climate is a key mechanism by which ecosystems interact with the total Earth System 1 2 Observation predictable patterns of ecosystem distribution across Earth Why are there rainforests in the tropics Why are there bands of desert at 30o N S Observation predictable patterns of ecosystem distribution across Earth Plate 1 Major goals in this lecture Answer these questions I What are the forces that drive climate Are there predictable patterns of climate across the globe II Why and how does climate vary through time Seasonally Annually Millenial scales Human effects I What are the forces that drive climate What are the global patterns A Solar radiation Earth s energy budget Question What is the greenhouse effect Is this a recent phenomenon Enhanced Greenhouse Effect Starr and Taggart 1997 Atmosphere is more transparent to incoming shortwave radiation than to outgoing long wave radiation 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 different gases in the atmosphere 2 1 Energy in energy out Half of solar radiation reaches Earth latent sensible heat The atmosphere is transparent to shortwave but absorbs longwave radiation greenhouse effect The atmosphere is heated from the bottom by longwave radiation and 2 2 convection The atmosphere is heated from the bottom Therefore it is warmest near the bottom and gets colder with increasing elevation Except the stratosphere is heated from the top ozone absorption of incoming UV Mesosphere and Thermosphere have little impact on the biosphere 2 3 Uneven heating of Earth s surface causes predictable latitudinal variation in climate 1 Greater heating at equator than poles 2 Why a sun s rays hit more directly b less atmosphere to penetrate 2 5 B Seasonality What causes seasons Earth s distance from the sun varies throughout the year 2 20 Tilt Because of the tilt of Earth s axis the amount of radiation received by Northern and Southern Hemispheres varies through the year angle of incidence and day length 2 20 Look at this light projected onto the globe Earth s Seasons of the Earth s axis towards or away from the sun creates the seasons When the north pole tilts toward the SUMMER Northern Hemisphere e l sun it gets more radiation more warmth o P h during the summer t r No o t a Equ r rth Ea When the north pole tilts toward the sun the south pole tilts away So when it s summer in the north it s winter in the south ole P h t u So WINTER Southern Hemisphere Earth s Seasons of the Earth s axis towards or away from the sun creates the seasons WINTER Northern Hemisphere ole P th r o N When the north pole tilts away from the sun it gets less radiation So it s colder during the winter th r a E to r a u q E ole P h t u So When the north pole tilts away from the sun the south pole tilts toward it When it s winter in the north SUMMER Southern Hemisphere it s summer in the south Common geographic boundaries relate directly to Earth s tilt Tropics Capricorn S Cancer N Arctic Antarctic circles 2 20 C Atmospheric circulation Questions 1 Why are there rainforests in the tropics and deserts at 30oN and S 2 What drives the major wind patterns e g Doldrums Tradewinds Westerlies C Atmospheric circulation Uneven heating of Earth s surface causes atmospheric circulation Greater heating at equator than poles Therefore 1 Net transfer of energy from Equator to poles 2 Transfer occurs through circulation of atmosphere and oceans Here s how it works 2 5 Intense radiation at the equator warms the air Air cools as it rises moisture condenses and falls as rain Warm air rises collecting moisture Lots of rain in the tropics Rising air is now dry some of the rising air flows north Dry air descends at around 30 N Deserts some of the rising air flows south and at around 30 S The descending air flows N and S Deserts These are called circulation cells the basic units of Vertical atmospheric circulation Circulation patterns repeat at 30 60 and 60 90 Dry Wet Hadley cells Wet Dry Ferrell cells 30 60 Wet Polar cells 60 90 Dry Dry Air rises and falls in Hadley Ferrel and Polar cells vertical circulation Circulation cells explain global distribution of rainfall Earth s rotation determines wind direction horizontal circulation Coriolis force ITCZ and cell locations shift seasonally depending on location of maximal heating of Earth s surface 2 6 These general circulation patterns are modified by the distribution of oceans and continents High heat capacity of water and ocean currents buffer ocean temperatures Land temperatures fluctuate more especially in higher latitudes These differences in surface energy balance influence air movements and create prevailing winds In summer at 60 N S air descends over cold ocean high pressure and rises over warm land low pressure 2 7b Cool equator ward flow of air on W coast of continents Warm poleward flow of air on E coasts of continents Observation predictable patterns of ecosystem distribution across Earth Plate 1 D Ocean currents Questions 1 Why is San Francisco so cold 2 Why is London so warm D Surface ocean currents are similar to wind patterns 1 Driven by Coriolis forces 2 Driven by winds 2 9 Warm currents solid Cold currents dashed Deep ocean currents are driven by cooling freezing of pole bound water thermohaline circulation Deepwater formation occurs at high latitudes near Greenland and Antarctic Upwelling at lower latitudes western continental margins due to Coriolis effect 2 10 Ocean currents move 40 of excess heat from equator to poles 60 of heat transport is carried by atmosphere through storms that move along pressure gradients Oceans affect terrestrial climate by 1 High heat capacity of water 2 Currents 3 Upwelling 2 9 E Landform effects on