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Chapter 19

Chapter 19. Climate Change and Ozone Depletion. (we can get along!). Mount Pinatubo erupts!. …the Phillipines…. 1991…. Figure 20-1.

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Chapter 19

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  1. Chapter 19 Climate Change and Ozone Depletion (we can get along!)

  2. Mount Pinatubo erupts! …the Phillipines… 1991… Figure 20-1

  3. “The effects of the eruption were felt worldwide. It ejected roughly 10 billion metric tonnes (10 cubic kilometres) of magma, and 20 million tons of SO2, bringing vast quantities of minerals and metals to the surface environment. It injected large amounts of aerosols into the stratosphere—more than any eruption since that of Krakatoa in 1883. Over the following months, the aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F), and ozone depletion temporarily increased substantially.” -Wikipedia

  4. Core Case Study: Studying a Volcano to Understand Climate Change • A NASA scientist correctly predicted that the 1991 Philippines explosion would cool the average temperature of the earth by 0.5Co over a 15 month period and then return to normal by 1995. Figure 20-1

  5. Core Case Study: Studying a Volcano to Understand Climate Change • The NASA climate change model was correct. • The Mt. Pinatubo modelprediction success convince scientists and policy makers that climate model projections should be taken seriously. • Other climate models have shown that global temperatures are likely to rise several degrees during this century.

  6. Chapter Overview Questions • How have the earth’s temperature and climate changed in the past? • How might the earth’s temperature and climate change in the future? • What factors influence the earth’s average temperature? • What are some possible beneficial and harmful effects of a warmer earth?

  7. Chapter Overview Questions (cont’d) • How can we slow projected increases in the earth’s temperature or adapt to such changes? • How have human activities depleted ozone in the stratosphere, and why should we care?

  8. PAST CLIMATE AND THE GREENHOUSE EFFECT • Over the past 900,000 years, the troposphere has experienced prolonged periods of global cooling and global warming. • For the past 1,000 years, temperatures have remained fairly stable but began to rise during the last century.

  9. PAST CLIMATE AND THE GREENHOUSE EFFECT Figure 20-2

  10. Average temperature over past 900,000 years Average surface temperature (°C) Thousands of years ago Fig. 20-2a, p. 465

  11. Average temperature over past 130 years Average surface temperature (°C) Year Fig. 20-2b, p. 465

  12. Temperature change over past 22,000 years Agriculture established Temperature change (C°) End of last ice age Average temperature over past 10,000 years = 15°C (59°F) Years ago Fig. 20-2c, p. 465

  13. Temperature change over past 1,000 years Temperature change (C°) Year Fig. 20-2d, p. 465

  14. From website “Logicalscience. com”

  15. How Do We Know What Temperatures Were in the Past? • Scientists analyze tiny air bubbles trapped in ice cores learn about past: • troposphere composition. • temperature trends. • greenhouse gas concentrations. • solar,snowfall, and forest fire activity. Figure 20-3

  16. Ice Core Analysis

  17. Ice Core Analysis

  18. National Ice Core Laboratory

  19. Ice Core Analysis A “thin cut” slice of an ice core.

  20. How Do We Know What Temperatures Were in the Past? • In 2005, an ice core showed that CO2 levels in the troposphere are the highest they have been in 650,000 years. Figure 20-4

  21. 384 ppm in 2007 Concentration of carbon dioxide in the atmosphere (ppm) Carbon dioxide Variation of temperature (C°) from current level 280 ppm in 1725 Temperature change End of last ice age Thousands of years before present Fig. 20-4, p. 466

  22. The Natural Greenhouse Effect • Four major factors shape the earth’s climate: • The sun. • Greenhouse effect warms the earth’s lower troposphere and surface because of the presence of greenhouse gases. • Oceansstore CO2 and heat, evaporate and receive water, move stored heat to other parts of the world. • Natural cooling process through water vapor in the troposphere (heat rises). • Evaporation cools the Earth’s surface • Condensation in clouds releases heat in upper troposphere

  23. Major Greenhouse Gases • The major greenhouse gases in the lower atmosphere are, IN ORDER: • water vapor- most important greenhouse gas • carbon dioxide- greatest effect from human activities • Methane- CH4 -more powerful greenhouse gas per molecule than CO2, but less of it than CO2 • nitrous oxide- N2O -comes from fertilizers and planting rice

  24. Major Greenhouse Gases • The major greenhouse gases in the lower atmosphere are: • water vapor carbon dioxide Methane nitrous oxide. • These gases have always been present in the earth’s troposphere in varying concentrations. • Fluctuations in these gases, plus changes in solar output and Earth’s Mankelovich cycles are the major factors causing the changes in tropospheric temperature over the past 400,000 years.

  25. Major Greenhouse Gases Increases in average concentrations of three greenhouse gases in the troposphere between 1860 and 2004, mostly due to • Fossil fuel burning(CO2 & CH4) • Deforestation (CO2 & N2O) • Agriculture(N2O) Figure 20-5

  26. 384 ppm in 2007 280 ppm in 1725 Fig. 20-5a, p. 467

  27. Fig. 20-5b, p. 467

  28. Fig. 20-5c, p. 467

  29. CLIMATE CHANGE AND HUMAN ACTIVITIES • Evidence that the earth’s troposphere is warming: • The 20th century was the hottest century in the past 1000 years. • The 10 hottest years since 1861 have been since 1990

  30. CLIMATE CHANGE AND HUMAN ACTIVITIES • Since 1900, the earth’s average tropospheric temperature has risen 0.6 C°. • Over the past 50 years, Arctic temperatures have risen almost twice as fast as those in the rest of the world. • Glaciers and floating sea ice are melting and shrinking at increasing rates.

  31. CLIMATE CHANGE AND HUMAN ACTIVITIES • Warmer temperatures in Alaska, Russia, and the Arctic are melting permafrost, releasing more CO2 and CH4 into the troposphere (feedback loop) • During the last century, the world’s sea level rose by 10-20 cm, mostly due to runoff from melting of land-based ice and the expansion of ocean water as temperatures rise.

  32. The Scientific Consensus about Future Climate Change • There is strong evidence that human activities will play an important role in changing the earth’s climate during this century. • Coupled General Circulation Models (CGCMs) couple, or combine, the effects of the atmosphere and the oceans on climate.

  33. Coupled General Circulation Modelof the Earth’s Climate • Simplified model of major processes that interact to determine the average temperature and greenhouse gas content of the troposphere. Figure 20-6

  34. Factors that cool Sun CO2 removal by plants and soil organisms Greenhouse gases Cooling from increase Heat and CO2 removal CO2 emissions from land cleaning, fires, and decay Warming from decrease Aerosols Heat and CO2 emissions Long-term storage Factors that warm Troposphere Ice and snow cover Shallow ocean Land and soil biota Natural and human emissions Deep ocean Stepped Art Fig. 20-6, p. 469

  35. Measured and projected changes in the average temperature of the atmosphere (2005). • ↑ 0.6 °C since 1900 • Consensus projection is 5 °C by 2100 if we “do nothing” • Consensus is 4 °C could threaten civilization as we know it Figure 20-7

  36. Most recent data suggests that temperatures are increasing even faster than the worst-case 2007 IPCC estimates Fig. 20-7, p. 470

  37. Why Should We Be Concerned about a Warmer Earth? • A rapid increase (non-linear response pattern) in the temperature of the troposphere during this century would give us little time to deal with its harmful effects. • As a prevention strategy scientists urge to cut global CO2 emissions 50% over the next 50 years…. “50/50” • This could prevent changes in the earth’s climate system that might last for tens of thousands of years (due to many positive feedback loops)

  38. FACTORS AFFECTING THE EARTH’S TEMPERATURE • Some factors can amplify (positive feedback) and some can dampen (negative feedback) projected global warming. • There is uncertainty about how much CO2 and heat the oceans can remove from the troposphere and how long the heat and CO2 might remain there (feedback?) • Warmer temperatures create more clouds that could warm or cool the troposphere (feedback?).

  39. Human Effects on the Carbon Cycle • Burning fossil fuels for energy • Residential • Commercial • Industrial • Transportation • Clearing forests for agriculture & forest products • Covering land with pavement • Exponential population growth

  40. Effects of Higher CO2 Levels on Photosynthesis • Increased CO2 in the troposphere can increase plant photosynthesis (PS) but: • The increase in PS would slow as the plants reach maturity. • Carbon stored by the plants would be returned to the atmosphere as CO2 when the plants die & decay • Increased PS decreases the amount of carbon stored in the soil.

  41. FACTORS AFFECTING THE EARTH’S TEMPERATURE • Aerosol and soot pollutants produced by human activities can warm (SO4 aerosols) or cool (soot particulates) the atmosphere, but such effects will decrease with any decline in outdoor air pollution. • Warmer air can release methane gas stored in bogs, wetlands, and melting tundra soils and accelerate global warming (feedback?).

  42. EFFECTS OF GLOBAL WARMING • A warmer climate would have beneficial and harmful effects but poor nations in the tropics would suffer the most. • Some of the world’s floating ice and land-based glaciers are slowly melting and are helping warm the troposphere by reflecting less sunlight (“albedo”) back into space (feedback?).

  43. Fig. 19-5a, p. 501

  44. Fig. 19-5b, p. 501

  45. Sept. 1979 Sept. 2007 Russia Russia North pole North pole Greenland Greenland Alaska (U.S.) Alaska (U.S.) Canada Canada Fig. 19-6, p. 501

  46. Rising Sea Levels • During this century rising seas levels are projected to flood low-lying urban areas, coastal estuaries, wetlands, coral reefs, and barrier islands and beaches (effects?) Next

  47. High Projection New Orleans, Shanghai, and other low-lying cities largely underwater 35 inches Mean Sea-Level Rises (centimeters) Medium Projection More than a third of U.S. wetlands underwater 4 inches Low Projection Year IPCC (2000) Projections “very likely” (90-99% confidence level) Fig. 20-10, p. 475

  48. Rising Sea Levels • Changes in average sea level over the past 250,000 years based on data from ocean cores. Figure 20-9

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