2.1 environmental science


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  • Climate is the state factor which is most important in explaining global patterns of ecosystem distribution and function. That’s why we have tundra near the poles or mountain tops and rainforest near the equator.
  • Let’s start by trying to understand the average energy budget of Earth. Over a year, on average the amount of incoming energy must be balanced by the same amount of energy leaving Earth.
  • Now let’s look at regional variations in Earth’s energy budget
  • Now let’s look at regional variations in Earth’s energy budget
  • Now let’s look at regional variations in Earth’s energy budget
  • Let’s start by trying to understand the average energy budget of Earth. Over a year, on average the amount of incoming energy must be balanced by the same amount of energy leaving Earth.
  • 2.1 environmental science

    1. 1. Environmental Science
    2. 2. Climate is the state factor that most stronglygoverns the global pattern of ecosystem structureand processes
    3. 3. Climate gives rise to predictable types of ecosystems
    4. 4. Climate is a key mechanism by which ecosystems interact with the total Earth System1.2
    5. 5. Observation: predictable patterns of ecosystemdistribution across EarthWhy are there rainforests in the tropics?Why are there bands of desert at ~30o N & S?
    6. 6. Observation: predictable patterns ofecosystem distribution across Earth
    7. 7. 1. What are the forces that drive climate? Are there predictable patterns of climate across the globe?2. Why and how does climate vary through time? – Seasonally – Annually – Millenial scales – Human effects
    8. 8. Atmosphere is more transparent toincoming short-wave radiation than tooutgoing long-wave radiationThe 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
    9. 9. Energy in = energy out Half of solar radiation reaches Earth(latent & sensible heat) The atmosphere is transparent toshortwave but absorbs longwave radiation (greenhouse effect) The atmosphere is heated from the bottom by longwaveradiation and convection 2.2
    10. 10. The atmosphere is heated from the bottom Therefore it is warmest near the bottom, and gets colder with increasing elevation Except the stratosphere isheated from the top – ozone absorption of incoming UV Mesosphere and Thermosphere have little impact on the biosphere. 2.3
    11. 11. Uneven heating of Earth’s surface causespredictable latitudinal variation in climate.1. Greater heating at equator than poles, Why? a. sun’s rays hit more directly b. less atmosphere to penetrate
    12. 12. SeasonalityWhat causes seasons?Earth’s distance from the sun varies throughout the year
    13. 13. Tilt!Because of the tilt of Earth’s axis, the amount ofradiation received by Northern and SouthernHemispheres varies through the year- angle of incidence and day length
    14. 14. Earth’s Seasons Tilt of the Earth’s axis towards or away from the sun creates the seasons SUMMER (Northern Hemisphere) e P olWhen the north pole tilts toward the h ortsun, it gets more radiation – more warmthduring the summer N r qu ato E Eart h e h P ol SoutWhen the north pole tilts toward the sun, the south pole tilts away So when it’s summer in the north, WINTER (Southern Hemisphere) it’s winter in the south
    15. 15. Earth’s SeasonsTilt of the Earth’s axis towards or away from the suncreates the seasons Pole When the north pole tilts away th from the sun, it gets less radiation –Nor WINTER (Northern Hemisphere) So it’s colder during the winter rt h Ea or t Equ a h Pole out When the north pole tilts away from the S sun, the south pole tilts toward it… When it’s winter in the north, SUMMER (Southern Hemisphere) it’s summer in the south
    16. 16. Common geographic boundaries relate directlyto Earth’s tilt Tropics: Capricorn (S) & Cancer(N) Arctic, Antarctic circles
    17. 17. Atmospheric circulationQuestions1. 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)
    18. 18. Atmospheric circulation - Uneven heating ofEarth’s surface causes atmospheric circulationGreater heating at equator than polesTherefore1. Net transfer of energy from Equator to poles.2. Transfer occurs through circulation ofatmosphere and oceans.Here’s how it works…
    19. 19. Intense radiation at the Air cools as it equator warms the airrises, moisturecondenses and falls as rain Warm air rises, collecting moisture Lots of rain in the tropics!
    20. 20. Rising air is now dry… some of the rising some of the rising air flows north air flows south Dry air descends …and at around at around 30º N 30º SDeserts Deserts The descending air flows N and S
    21. 21. These are called circulation cells – the basic units of Circulation patterns Vertical atmospheric circulationrepeat at 30-60º and 60-90º… Hadley cells Wet Dry Dry Ferrell cells (30 - 60º) Wet Wet Polar cells (60-90º) Dry Dry
    22. 22. Air rises and fallsin Hadley, Ferrel, andPolar cells(vertical circulation)Circulation cellsexplain globaldistribution ofrainfallEarth’s rotationdetermineswind direction(horizontal circulation,Coriolis force)ITCZ and cell locationsshift seasonally dependingon location of maximalheating of Earth’s surface 2.6
    23. 23. These general circulation patterns are modifiedby the distribution of oceans and continents.High heat capacity of water and ocean currentsbuffer ocean temperaturesLand temperatures fluctuate more, especially inhigher latitudesThese differences in surface energy balanceinfluence air movements, and create prevailingwinds
    24. 24. In summer at 60 º N & S, air descends over cold ocean (high pressure) and rises over warm land (low pressure) Cool equator-ward flow of air on W coast of continents Warm poleward flow of air on E coasts of continents
    25. 25. Observation: predictable patterns of ecosystem distribution across Earth
    26. 26. Ocean currentsQuestions:1. Why is San Francisco so cold?2. Why is London so warm?
    27. 27. Surface ocean currents are similar to wind patterns: 1. Driven by Coriolis forces 2. Driven by winds2.9 Warm currents – solid, Cold currents - dashed
    28. 28. Deep ocean currents are driven by cooling, freezing of pole-bound water (thermohaline circulation).- Deepwater formation occurs at high latitudes (nearGreenland and Antarctic)- Upwelling at lower latitudes, western continental marginsdue to Coriolis effect. 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).
    29. 29. Oceans affect terrestrial climate by1. High heat capacity of water2. Currents3. Upwelling
    30. 30. Landform effects on climateMountain effects – Orographic precipitation – Rain shadow – Effects of aspect – Air drainage (inversion, arising due to topography, where cold air settles in valleys, for example)
    31. 31. Climate of any regionis predictable fromtopography, wind andocean currents http://www.ocs.orst.edu/pub/maps/Precipitation/Total/States/WA/wa.gif
    32. 32. Changes in climate A. Seasonal (see I.B.) B. Yearly (interannual) C. Millenial scales D. Human impacts- Is global warming for real?- How do we know that it isn’t just a natural fluctuation intemperature?- What are some of the forces that lead to natural climatevariability?
    33. 33. Interannual Variation – El Niño Southern Oscillation- The Pacific Ocean strongly influences the globalclimate system because it is the largest ocean basin- Normal ocean current and wind direction in centralPacific is easterly
    34. 34. ENSO events result fromweakening of tropicalPacific atmospheric andoceanic circulationClimatic connectionscarry these climateeffects throughoutthe globe (e.g., El Niño createswarm winters in AK andlots of rain in Calif)
    35. 35. II. C. Millenial scale variation
    36. 36. Changes in orbit cause long-term variations in solar input to Earth Shape of orbit (100,000 yrs) Wobble of tilt (23,000 yrs) Angle of tilt (41,000 yrs)2.14
    37. 37. Eccentricity: The Earths orbit around the sun is anellipse. The shape of the elliptical orbit, which is measured by itseccentricity, varies through time.The eccentricity affects the difference in the amounts of radiationthe Earths surface receives at aphelion and at perihelion.When the orbit is highly elliptical, one hemisphere will have hotsummers and cold winters; the other hemisphere will have warmsummers and cool winters. When the orbit is nearly circular (now), both hemispheres will have similar seasonal contrasts in temperature.
    38. 38. Rotation axis executes a slow precession with a period of 23,000 years (see following figure) Pole Stars are TransientWobble in the tilt
    39. 39. Precession: Present and past orbital locations of the Earth during the N Hemisphere winter
    40. 40. Milankovitch cycles • The interactive effects of Earth’s orbital variation on timing and distribution of total solar input. • Strong effect on glacial/interglacial cycleshttp://en.wikipedia.org/wiki/Image:Vostok_420ky_4curves_insolation.jpg
    41. 41. D. Human effects• Global warming
    42. 42. Earth’s climate is now warmer than at any time in the last 1000 years2.16
    43. 43. How can the atmosphere warm? 1. Increased solar input 2. Less reflected shortwave, less sulfate aerosols, darker surface of Earth (land-cover change) 3. More absorbed longwave more “greenhouse gases”2.2
    44. 44. Most major greenhouse gases are increasingin atmospheric concentrations 15.3
    45. 45. 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)2.16
    46. 46. Climate is warming most rapidly at high latitudesThis warming is most pronounced in Siberia and western North America
    47. 47. Summary: Functioning of ecosystems varies predictably with climate
    48. 48. Combination of temperature and precipitation END
    49. 49. In January… At 30º N & S, air descends more strongly over cold ocean than over land At 60 º N & S, air descends more strongly over cold land than over oceanThese pressure gradients create geographic variation in prevailing winds