MET 10 Global Climate Change-Chapter 14

1. MET 10 Global Climate Change-Chapter 14 Global Climate Change Dr. Craig Clements San José State University

2. Review: Why is CO2 So Important? • Carbon Dioxide is a greenhouse gas. • Greenhouse gases are those gases that cause the greenhouse effect. • The greenhouse effect makes a planet’s surface temperature warmer than it would otherwise be. • The stronger the greenhouse effect, the warmer the surface (other factors being equal). • Consider the blanket analogy

3. Earth’s Energy Balance • Energy entering top of atmosphere • Energy entering the Earth’s surface = Energy leaving top of atmosphere = Energy leaving Earth’s surface Conservation of Energy

4. Absorption of Radiation in the Earth’s Atmosphere

5. Incoming solar radiation • Each ‘beam’ of incoming sunlight can be either: • Reflected back to space: • Clouds • Atmosphere • Surface • Or absorbed; either by atmosphere (e.g. clouds or ozone) or Earth’s surface. Albedo

8. Some atmospheric radiation escapes to space Some surface radiation escapes to space Greenhouse gases emit longwave upward and downward Most outgoing longwave is absorbed in atmosphere (by greenhouse gases) Some atmospheric radiation is absorbed at the surface Longwave radiation is emitted from surface.

9. Greenhouse Effect Sequence of steps: • Solar radiation absorbed by earth’s surface. • Earth gives off infrared radiation. • Greenhouse gases absorb some of the Earth’s infrared radiation. • Greenhouse gases (water and CO2) give off infrared radiation in all directions. • Earth absorbs downward directed infrared radiation Result: warmer surface temperature

10. Energy Balance • Assume that the Earth’s surface is in thermodynamic equilibrium: • Thermodynamic Equilibrium: • The flow of energy away the surface equals the flow of energy toward the surface Surface Average surface temperature = 15°C

11. Sudden Removal of all Greenhouse Gases Removal of greenhouse gases would decrease downward flow of energy; now energy away from surface is greater than energy toward surface.

12. Sudden Removal of all Greenhouse Gases Removal of greenhouse gases would decrease downward flow of energy; now energy away from surface is greater than energy toward surface. Thus, average surface temperature starts to decrease.

13. Sudden Removal of all Greenhouse Gases As surface cools, emission of radiation decreases until balance is restored. At this point, cooling stops

14. Result: A Very Cold Planet! As surface cools, emission of radiation decreases until balance is restored. At this point, cooling stops and equilibrium is restored. Average surface temperature = -18°C

15. Earth’s Greenhouse Effect • Without the greenhouse effect, the surface temperature of Earth would be • Way Cold (-18°C) • Greenhouse gases play an important role in shaping climate. • More GHGs – warmer climate • Less GHGs – cooler climate

17. Recent Climate Change

18. Modeled temperature changes

19. IPCC (2007)

20. (b) Additionally, the year by year (blue curve) and 50 year average (black curve) variations of the average surface temperature of the Northern Hemisphere for the past 1000 years have been reconstructed from “proxy” data calibrated against thermometer data (see list of the main proxy data in the diagram). The 95% confidence range in the annual data is represented by the grey region. These uncertainties increase in more distant times and are always much larger than in the instrumental record due to the use of relatively sparse proxy data. Nevertheless the rate and duration of warming of the 20th century has been much greater than in any of the previous nine centuries. Similarly, it is likely7 that the 1990s have been the warmest decade and 1998 the warmest year of the millennium.

21. Latest global temperatures

22. …“Over the last 140 years, the best estimate is that the global average surface temperature has increased by 0.6 ± 0.2°C” (IPCC 2001) • So the temperature trend is: 0.6°C ± 0.2°C • What does this mean? • Temperature trend is between 0.8°C and 0.4°C • The Uncertainty (± 0.2°C ) is critical component to the observed trend

23. CO2 Concentration in Atmosphere

24. Short Term Carbon Cycle • One example of the short term carbon cycle involves plants • Photosynthesis: is the conversion of carbon dioxide and water into a sugar called glucose (carbohydrate) using sunlight energy. Oxygen is produced as a waste product. • Plants require • Sunlight, water and carbon, (from CO2 in atmosphere or ocean) to produce carbohydrates (food) to grow. • When plants decay, carbon is mostly returned to the atmosphere (respiration) • During spring: (more photosynthesis) • atmospheric CO2 levels go down (slightly) • During fall: (more respiration) • atmospheric CO2 levels go up (slightly)

25. Current CO2: ~387 ppm

26. What Changed Around 1800? • Industrial Revolution • Increased burning of fossil fuels • Also, extensive changes in land use began • the clearing and removal of forests

28. Burning of Fossil Fuels • Fossil Fuels: Fuels obtained from the earth are part of the buried organic carbon “reservoir” • Examples: Coal, petroleum products, natural gas • The burning of fossil fuels is essentially • A large acceleration of the oxidation of buried organic carbon

29. Land-Use Changes • Deforestation: • The intentional clearing of forests for farmland and habitation • This process is essentially an acceleration of one part of the short-term carbon cycle: • the decay of dead vegetation • Also causes change in surface albedo (generally cooling)

31. Climate Feedbacks

32. Earth’s Climate • The Earth’s climate is fairly stable in terms of temperature • This can be visualized using in the following system diagram. • The idea is that even though the system may change away from it’s initial point, it will have the tendency to go back to ‘normal’ eventually. 2 3 1 Stable Stable

33. Stability versus instability • Stable: • Given a perturbation, the system tends to return to original state • Instability: • Given a perturbation, the system moves to another state. Stable equilibrium Unstable equilibrium

34. States of equilibrium • The system may have multiple states of equilibrium 2 3 1 Stable to small perturbations, until a big force perturbs the system into a new equilibrium

35. The Earth’s climate changes as a result of internal/external forcing: Changes in solar radiation Changes in the earth’s orbit Plate tectonics Volcanoes Human pollution etc. These forcings can be thought of as a perturbation (or push) to climate stability. These changes can be enhanced or diminished by positive or negative feedbacks Climate Stability

36. Internal Forcing mechanisms - processes that are internal to the climate system that involve the various elements: ice, water vapor, CO2 External Forcing mechanisms - some forcing that can alter the system without itself being altered. - solar variability, axis wobble, etc. Climate Stability

37. Positive feedback: initial change reinforced by another process. Trends towards instability Negative feedback: initial change counteracted by another process. Trends towards stability Climate Feedbacks

38. Positive Feedbacks • Processes that accelerate a change • Note: Feedbacks cannot initiate change; they can only alter the pace of change • Important climate examples: • Ice-albedo feedback • Water-vapor feedback • Cloud feedback

39. Ice-Albedo Feedback (Cooling) Initiating Mechanism Earth Cools Somehow this happens Ice Coverage Increases Positive Feedback Albedo Increases Absorption of Sunlight Decreases

40. Fill in the blanks Initiating Mechanism • increases, decreases, decreases • Decreases, decreases, increases • Increases, increases, increases • Decreases, decreases, decreases Earth Warms Ice Coverage ___________ Albedo _____________ Absorption of Sunlight _______

41. Ice-Albedo Feedback (Warming) Initiating Mechanism Earth Warms Ice Coverage Decreases Positive Feedback Albedo Decreases Absorption of Sunlight Increases

42. 0 of 70 Fill in the blanks • Increases, increases, increases • Increases, decreases, decreases • Decreases, increases, increases • Decreases, decreases, decreases

43. Water Vapor Feedback (Warming) Initiating Mechanism Earth Warms Evaporation Increases Positive Feedback Atmospheric Water Vapor Content Increases Greenhouse Effect Strengthens

44. Water Vapor Feedback (Cooling) Initiating Mechanism Earth Cools Evaporation Decreases Positive Feedback Atmospheric Water Vapor Content Decreases Greenhouse Effect Weakens

45. Negative Feedbacks • Processes that reduces an imposed change - Trends towards stability • Important examples: • Cloud feedback • Chemical weathering • Note: Positive/negative feedbacks have no relation to ‘good versus bad’, but are about how a system responds to a change.

46. Possible Role of Cloud in Warming or Cooling the Atmosphere

47. 43 of 70 Which feedback is positive? • Left • Right