Atmospheres & Global Warming Earth and the Other Terrestrial Worlds

1. Atmospheres &Global WarmingEarth and the Other Terrestrial Worlds

2. Weather and Climate Weather – short-term changes in wind, clouds, temperature, and pressure in an atmosphere at a given location • These are Earth’s global wind patterns or circulation • local weather systems move along with them • weather moves from W to E at mid-latitudes in N hemisphere • Two factors cause these patterns • atmospheric heating • planetary rotation Climate– long-term average of the weather at a given location

3. Air heated more at equator Warm air rises at equator; Pressure pushes to poles Cold air moves from poles to equator along the surface Two circulation cells are created in each hemisphere Cells of air do not go directly from pole to equator; air circulation is diverted by… Coriolis effect moving objects veer right on a surface rotating counterclockwise moving objects veer left on a surface rotating clockwise Global Wind Patterns

4. Global Wind Patterns • On Earth, the Coriolis effect breaks each circulation cell into three separate cells • winds move either W to E or E to W • Coriolis effect not strong on Mars & Venus • Mars is too small • Venus rotates too slowly • In thick Venusian atmosphere, the pole-to-equator circulation cells distribute heat efficiently • surface temperature is uniform all over the planet

5. Earth’s Atmosphere

6. Pressure & density of decrease with altitude Temperature both increases and decreases with altitude Temperature domains define the major atmospheric layers exosphere low density; fades into space thermosphere temp begins to rise at the top stratosphere rise and fall of temp troposphere layer closest to surface temp drops with altitude Structure of Earth’s Atmosphere (mesosphere) Stratosphere Ozone Layer (absorbs UV) Troposphere

7. Reasons for Atmospheric Structure • Absorption of sunlight energy causes layering structure. • Troposphere • Air absorbs IR photons from the surface • Hot air rises and high gas density causes storms (convection) • Temperature drops with altitude • Stratosphere • Lies above the greenhouse gases (no IR absorption) • Absorbs heat via Solar UV photons which dissociate ozone (O3) • UV penetrates only top layer; hotter air is above colder air • Thermosphere • Absorbs heat via Solar X-rays which ionizes all gases • Contains ionosphere, which reflects back human radio signals • Exosphere • Hottest layer; gas extremely rarified; provides noticeable drag on satellites

8. Structure of Terrestrial Planet Atmospheres • Mars, Venus, Earth all • have warm tropospheres (and greenhouse gases) • have warm thermospheres which absorb Solar X rays • Only Earth has • a warm stratosphere • an UV-absorbing gas (O3) • All three planets have warmer surface temps due to greenhouse effect

9. Climate History of Venus • Venus should have outgassed as much H2O as Earth. • Early on, when the Sun was dimmer, Venus may have had oceans of water • Venus’ proximity to the Sun caused all H2O to evaporate. • H2O caused runaway greenhouse effect • surface heated to extreme temperature • CO2 released from rocks: Adds to greenhouse effect • UV photons from Sun dissociate H2O; H2 escapes, O is stripped If Earth moved to Venus’ Orbit

10. Venusian Weather Today • Venus has no seasons to speak of. • rotation axis is nearly 90º to the ecliptic plane • Venus has little wind at its surface • rotates very slowly, so there is no Coriolis effect • The surface temperature stays constant all over Venus. • thick atmosphere distributes heat via two large circulation cells • There is no rain on the surface. • it is too hot and Venus has almost no H2O • Venusian clouds contain sulfuric acid! • implies recent volcanic outgassing?

11. Mars’ Thin Atmosphere • Martian sunset illustrates just how thin the Martian atmosphere is.

12. Martian Weather: N Polar Ice Cap & Dust Storm

13. Martian Weather Today • Seasons on Mars are more extreme than on Earth • Mars’ orbit is more elliptical • CO2 condenses & vaporizes at opposite poles • changes in atmospheric pressure drive pole-to-pole winds • sometimes cause huge dust storms

14. The last decade of the 20th Century was the warmest in the entire global instrumental temperature record, starting in the mid-1800’s. • All 10 years rank among the 15 warmest, and include the 6 warmest years on record. • Through the reconstruction of past climate we can evaluate the rarity and magnitude of this warming.

15. Venus Earth Mars 0.7 AU 1 AU 1.5 AU 4.6 Billion Years Ago ... SUN (150 million km from Sun)

16. 500 300 Temperature (Celsius) 100 0 -100 Temperature: Top of Atmosphere decreases with distance from Sun Earth -18oC (0oF) Venus Mars 0 0 AU 1 AU Distance From Sun -100 5500 oC

17. EARTH: Surface 15oC (60oF) Top of Atm: -18oC (0oF) 500 300  All three phases of water 100 Temperature (Celsius) 0 -100 Surface No Greenhouse Surface warmer than top of atm Greenhouse Effect Clue: atm composition

18. n1symmetric O O C C n2 bending 15 mm O O n2asymmetric 4.3 mm O C O Vibrational Modes for CO2 Greenhouse effect:Radiation at specific wavelengths excite CO2 into higher energy states. Light energy is absorbed by the CO2 molecules

19. O O O H O H H H C H N O N H nitrous oxide methane Other Greenhouse Gases ozone water

20. Absorption Transmission Peak terrestrial emission at ~300K Absorption by different molecules l = 0-15 µm CO2 Bending Mode

21. How Greenhouse Gases Warm the Troposphere CO2

22. Energy Balance

23. Carbon Dioxide:in our atmosphere isIncreasing rapidly Burning coal Worldwide CO2 Emission By fuel type: 1970 - 2020 gasoline CO2 Causes Global Warming: Stay tuned . . . Natural gas

24. Increase in Temperature tracks Increase in Greenhouse Gases Since 1850: Atmospheric CO2 has increased by 30% Temperture vs Time Year 1850 2000

26. CO2 Since the Year 1000 AD CO2 in atmosphere, measured in thick arctic ice.

27. Heat Content:Increase in Atmosphere and Ocean since 1945.

28. Retreat of Glaciers 2006 1948 2002 Trift Glacier, Gadmental, Berner, Oberland Switzerland

29. 1939 1951 • Franz Josef Glacier In Retreat 1964 1960

30. Receding Glaciers Glacier Length (km) South Cascade Glacier in Washington. The yellow line indicates the location of the terminus in 1958. The red line shows the position of the terminus in 1998. 1500 2000

31. Is the Sun to Blame ? No. Luminosity has been constant. W / m2 Year • Sunlight hitting Earth: • 11 year Sunspot cycle • Offsets among instruments • No trend

32. Global Warming • Made a political issue by certain people. Three Facts are Absolute: • Earth has warmed by 0.5 C in past 50 years. Temperature rise greatest in past 10 years. • Humans are increasing by 30-50% the CO2 in the atmosphere. • Rising CO2 will cause rising temperatures Only Question: Not Whether, but by how much are humans contributing to Global Warming ?

33. Feedback Proceses:Positive and Negative Suppose Temp rises ==> Evaporation of ocean water. Feedback: • H2O is a greenhouse gas ==> Earth gets even Warmer ! • But clouds may form, increasing albedo. ==> Earth cools.

34. The Arctic:Positive Feedback Process • Temp rise causes polar cap ice to melt. • Artic ground exposed: dirt absorbs more sunlight (lower albedo). • Ground warms up more: Earth gets hotter. • More polar cap ice melts. Earth gets even hotter.

35. Consequences ofGlobal Warming • More evaporation of oceans: More storms, and more severe storms. • Water in oceans exand with rising Temp. Sea level has already risen 20 cm in past 100 years. Coastal regions and islands flood. • Polar caps and Glaciers melt: Causes rising ocean levels. • Change in ocean current patterns. Desserts may get rain; Farmland may get none.

36. Predictions of temperatures next 100 years DEPENDS ON MAGNITUDE OF FEEDBACK AND RATE OF INCREASE OF GHG. IN 100 YEARS, FORCED CLIMATE CHANGE WILL MOST LIKELY EXCEED NATURAL VARIABILITY

37. The Kyoto Agreement The Kyoto Protocol, negotiated by more than 160 nations in 1997, will reduce emissions of certain greenhouse gases (primarily CO2). Each of the participating developed countries must decide how to meet its respective reduction goal. Signed by every country in the European Union, by Japan, and by Russia.

38. Kyoto Agreement:The United States Won’t Sign • In March 2001, President Bush announced that the United States would not sign the Kyoto Protocol on Global Climate Change. • The Protocol requires signatories to cut carbon dioxide emissions an average of 5 percent below 1990 levels between 2008 and 2012. Developing nations are exempt from emission reductions. • “President Bush strongly opposes any treaty or policy that would cause the loss of a single American job, let alone the nearly 5 million jobs Kyoto would have cost.” - James Connaughton, chairman of the White House council on Environmental Quality.

39. Show the movie:An Inconvenient Truth

40. Three Perspectives onGlobal Warming • Kyoto Protocol: unfccc.int/resource/convkp.html • White House Council on Environmental Quality: www.whitehouse.gov/ceq • Pew Center on Global Climate Change: www.pewclimate.org

41. http://www.eia.doe.gov/oiaf/1605/vrrpt/summary/longform.html

43. United States Policy on CO2“Voluntary Reductions”

44. Three Perspectives onGlobal Warming • Kyoto Protocol: unfccc.int/resource/convkp.html • White House Council on Environmental Quality: www.whitehouse.gov/ceq • Pew Center on Global Climate Change: www.pewclimate.org