Chapter 20

1. Chapter 20 The Atmosphere: Climate, Climate Change, and Ozone Depletion

2. Warm Up • When did hurricane Katrina happen? • What category was Katrina when it touched down on land? • How much damage was caused? • How many deaths? • What trend are some scientists researching that is considered a controversy? • Why have the oceans been absorbing more heat?

3. Section 20.1 Atmosphere and Weather

4. Atmosphere Structure • The atmosphere is a collection of gases that gravity holds in a thin envelope around the Earth • Nitrogen – 78% • Oxygen – 21 % • Other gases include argon, carbon dioxide, and helium to make up the other 1% • In addition, water vapor and trace amounts of air pollutants are present in the air

5. Layers of the Atmosphere • Troposphere • Lowest level (closest to earth’s surface) • Extends 10 miles from the surface of the earth • All weather occurs in this layer • Temperature decreases as altitude increases • Much vertical mixing of air masses • Capping the troposphere is the tropopause

6. Layers of the Atmosphere • Stratosphere • Above the tropopause • Up to about 40 miles above surface of the earth • Temperature increases as altitude increases • Due to OZONE LAYER that absorbs UV radiation emitted by the sun • Little vertical mixing of air masses • Therefore substances that enter can linger for a very long time

7. Layers of the Atmosphere • Mesosphere • Directly above the stratosphere • Extends from 45 – 80 km above earth’s surface • Coldest layer • Temperatures drop as low as -138oC

8. Layers of the Atmosphere • Thermosphere • Extends from 80-500 km above Earth’s surface • Characterized by steadily rising temperatures • Gases absorb x-rays and UV radiation • Causes this layer to be the hottest – reaching temps of 1,000oC or more • Aurora borealis occurs in this layer as a result of charged particles from the sun hitting oxygen or nitrogen molecules in the thermosphere

9. Layers of the Atmosphere • Exosphere • Begins about 500 km above earth’s surface and continues to thin until it converges with interplanetary space

11. Weather • Weather • The day-to-day variations in temperature, air pressure, wind, humidity, and precipitation – all mediated by the atmosphere • Climate • Result of long-term weather patterns in a region

12. Solar Radiation • The majority of the sun’s radiation is absorbed by the atmosphere, oceans, and land • What gets reflected back the atmosphere depends upon a surface’s albedo • Solar radiation runs the hydrologic cycle, drives winds and ocean currents, powers photosynthesis, and warms the planet

13. Albedo • Proportional reflectance of Earth's surface • Glaciers and ice sheets have high albedos • Reflect 80-90% of the sunlight hitting their surfaces • Asphalt pavement and buildings have low albedos • Reflect 10 – 15% • (forests and ocean only reflect about 5%)

14. Solar Energy Balance Much of the incoming radiation from the Sun is reflected back to space (30%), but the remainder is absorbed by the oceans, land and atmosphere (70%), where it creates our weather and fuels photosynthesis. Eventually, this absorbed energy is radiated back to space as infrared energy (heat)

15. Flowing Air • Some of the heat that is radiated back from the earth is transferred to the atmosphere • Therefore air masses will grow warmer at the surface of the earth and will expand, becoming lighter • The lighter air will rise creating vertical air currents – or convection currents

16. Flowing air • Air must flow in to replace the rising warm air, and inflow leads to horizontal air flows, or wind • The ultimate source of horizontal flow is cooler air that is sinking, and the combination produces a Hadley Cell

17. Hadley Cell • A system of vertical and horizontal air circulation predominating in tropical and subtropical regions and creating major weather patterns • These major flows of air create regions of high rainfall (equatorial), deserts, (25o to 35o N and S of the equator) and horizontal winds (trade winds)

19. Convection • On a smaller scale, convection currents bring us the day-to-day changes in our weather as they move from east to west • Weather reports inform us of regions of high and low pressure

20. High/Low Pressure • Rising air (due to solar heating) creates high pressure in the atmosphere • This leaves behind a region of lower pressure close to earth • Moist, high pressure air will cool by radiation of heat into space and also looses heat through condensation

21. High/Low Pressure • Once the air mass precipitates, the air then flows horizontally towards regions of sinking cool, dry air (where the pressure is lower) • The air is warmed and the convection current will start over again • The differences in pressure results in air flows, which are the winds we experience

23. Coriolis Effect • Earth’s rotation influences the direction of wind. • Earth rotates from west to east, which causes moving air to be deflected from its path and swerve to the right of the direction in which it is traveling in the Northern Hemisphere and to the left of the direction in which it is traveling in the Southern Hemisphere

25. Global Air Circulation: Global trade wind patterns formed as a result of the Earth’s rotation

26. Trade Winds • Tropical winds that blow from the northeast in the Northern Hemisphere or from the southeast in the Southern Hemisphere • Produced by the upward movements of air called convection currents

27. Jet Streams • The larger scale air movements of Hadley Cells are influenced by the Earth’s rotation from west to east • Creates trade winds over the oceans and the general flow of weather from west to east • Jet streams flow eastward at speeds of more than 300 mph due to Earth’s rotation and air pressure gradients

28. Fronts • Air masses of different temperatures and pressures meet at boundaries we call fronts • Regions of rapid weather change • Other movements of air masses due to differences in pressure and temperature include • Hurricanes • Typhoons • tornadoes

29. BRAIN POP • Wind

30. 20.2 Climate

31. Climate • Average temperature and precipitation expected throughout a typical year in a given region • Humans can adapt to mostly any type of climate, whereas other types or organisms become well suited, or specialized to its specific climate.

32. Climates in the Past • Weather records have been kept for a little more than 100 years • Since 1880, global average temperature has shown periods of cooling and warming • However has generally increased 0.8oC (1.4oF)

33. Annual mean global surface temperature anomalies. The baseline, or zero point, is the 1961-1990 average temperature. The warming trend since 1975 is conspicuous.

34. Climates in the Past • To estimate climate further back than 1880, scientists use proxies • Measureable records that can provide data on factors such as temperature, ice cover, and precipitation, tree rings, pollen deposits, changes in landscapes, and ice cores

35. Ice Core Proxies • In Greenland and the Antarctic, ice cores have been analyzed for thickness in gas contents and isotopes • Isotopes – alternative chemical configurations of a given compound due to different nuclear components • Isotopes of O and H behave differently at different temperatures when condensed in clouds and incorporated in ice

36. Ice Core Proxies • Earth’s climate has oscillated between ice ages and warm periods • Most likely explanation for oscillations is variations in Earth’s orbit • The distribution of solar radiation of different continents and latitudes varies substantially • This will change the temperature and precipitation of regions • Oscillations take place according to several periodic time intervals, called Milankovitch cycles

37. Younger Dryas Event • A rapid climatic fluctuation • Warm periods and periods of glaciations • Occurred towards the end of the last ice age • Earth warmed for 6,000 years, plunged into 1,500 years of cold weather • At the end of the event, 10,700 years ago, arctic temperatures rose 7oC in 50 years • Scientist think the fluctuation was due to the link between the ocean and the atmosphere, not a change in Earth’s orbital path

38. Past Climates Determined by Ice Cores Carbon dioxide, methane, and estimated global temperature from Antarctic ice cores, covering the past 450,000 years, compared with changes of the past century. (source Hansen, James, Climactic Change 58: 269-279)

39. Temperature Patterns of the last 160,000 years demonstrating temperature oscillations Higher resolution of the “Younger Dryas” cold spell occurred at the start of this record. Note how rapidly the cold spell dissipated, at around 10,700 years before the present. (Source: Christopherson, Robert W., Geosystems: An Introduction to Physical Geography, 5th ed., Upper Saddle River NJ: Pearson Prentice Hall, 2005.

40. Ocean and Atmosphere • Oceans are the major source of water for the hydrologic cycle and the main source of heat entering the atmosphere • Ocean has a high heat capacity • Ability to absorb energy when water is heated • Through movement of currents, the oceans convey heat throughout the globe

41. El Nino • Examples of how the ocean and the atmosphere are strongly linked • El Niño – a periodic warming of surface waters of the tropical East Pacific • Alters ocean and atmospheric circulation patterns and results in unusual weather patterns far from the tropical Pacific

42. What Causes El Niño • Normally, westward blowing trade winds restrict the warmest waters to the western Pacific near Australia • Every 3 – 7 years, the trade winds weaken and the warm water expands eastward to South America • This increases surface temperatures in the Eastern Pacific • Ocean currents that usually flow westward will slow or stop all together

43. Effects of El Niño • Effects fisheries off of South America due to the warm water • Alters global air currents • 1997-1998 worst on record • 20,000 deaths, $33 billion in property damage • Heavy snows in western U.S., ice storms in Canada, floods in Peru, Ecuador, California, Arizona, and Western Europe, droughts in Texas, Australia, Indonesia

44. La Niña • Opposite of El Niño • Easterly trade winds are reestablished with greater intensity • An upwelling of colder ocean water in the eastern Pacific from the depths replaces the surface water blown westward • Jet streams are weakened • Weather patterns are affected over much of the planet

45. Effects of La Niña • Effects are more difficult to predict • Causes wetter than usual winters in Pacific Northwest, warmer weather in the Southeast, and drought conditions in the Southwest • Atlantic hurricanes are stronger and more numerous during La Niña events

46. Thermohaline Circulation • Thermohaline refers to the effects that temperature and salinity have on the density of seawater • This conveyor system acts as a giant, complex conveyor belt moving water masses from the surface to the deep oceans and back again • According to the density of the mass

47. Thermohaline Circulation • Key Area – High-latitude North Atlantic • Salty water from the Gulf Stream moves northward on the surface and is cooled by Arctic air currents • Cooling increases the density of the water, which causes it to sink • Deep water spreads southward through the Atlantic to the southern tip of Africa where it is joined by cold Antarctic waters • Together the two streams spread northward into the Indian and Pacific oceans as deep currents • Gradually, the currents slow and become warmer and less dense • Less dense water wells up to the surface, where it is further warmed and begins to move surface waters back again toward the North Atlantic

49. Abrupt Change • Evidence indicates that the conveyor system has been interrupted in the past, changing climate abruptly. • One mechanism that could account for this happening is the appearance of unusually large amounts of fresh water in the North Atlantic • This lowers the density of the water and therefore prevents much of the massive sinking that normally occurs there • Blocks the northward movement of the warmer, saltier water

50. Brain Pop! • Ocean Currents