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Chapter 14: Climate Change

Chapter 14: Climate Change. The earth’s changing climate Possible causes of climatic change Global warming. The Earth’s Changing Climate. 18,000 years ago. The earth’s climate is always changing 18,000 years ago the sea level was so low that the English

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Chapter 14: Climate Change

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  1. Chapter 14: Climate Change • The earth’s changing climate • Possible causes of climatic change • Global warming

  2. The Earth’s Changing Climate 18,000 years ago • The earth’s climate is • always changing • 18,000 years ago the • sea level was so low • that the English • Channel didn’t • even exist, and Bering land bridge did exist

  3. Determining Past Climates 1) fossil evidence Q1: if fossil pollen of a tundra plant is collected in a layer of sediments in New England and dated to be 12,000 years old, it would suggest that compared with today, the climate then is a) much colder, b) much warmer, c) similar, d) unknown 2) Ocean floor sediment oxygen isotope ratio (of oxygen 18 over oxygen 16) • Isotopes are atoms whose nuclei have the same number of protons but different numbers of neutrons. • This ratio is higher during a colder climate 3) dendrochronology- tree ring growth depends on temperature and precipitation over certain regions Q2: Which university established the dendrochronology field first? a) U. of Arizona; b) Harvard; c) Stanford; d) Yale

  4. Determining Past Climates • sediment cores: ocean, lake • ice cores: Antarctic, Greenland • borehole temperature profiles • Dating calcium carbonate layers of stalactites in caves • As the global warming debate has intensified in recent years, many methods of reconstructing past climates have undergone close scrutiny Q3: What is the main uncertainty of these proxy data in representing temperature? a) relation is not linear b) non-temperature effects are not easy to separate c) correlation is not causality d) all of them

  5. Climate During Past 1000 Years and since 1860 “Hockey Stick” graph The global warming of the past 100 years has notbeen constant Q4: is the temperature decrease from 1940-1970 contradictory with global warming? a) yes; b) no

  6. Climate Change and Feedback Mechanisms • Feedbacks cause climate changes to be either amplified (positive feedback) or reduced (negative feedback). Q5: The water vapor-greenhouse feedback is? a) positive feedback; b) negative feedback c) unknown Q6: Why is the snow-albedo feedback positive? A: increasing T decreases snow cover; this decreases surface albedo and hence increases surface solar absorption; leading to further increasing T Q7: why is cloud feedback overall negative? A: low clouds are negative by reflecting solar radiation; high clouds are positive just like greenhouse gases; overall low clouds are more dominant, leading to overall negative feedback

  7. Possible Causes of Climate Change • external: changes in incoming solar radiation • external (e.g., volcano) or human (e.g., CO2): changes in the composition of the atmosphere • external (e.g., mountain uplifting) or human (e.g., land use in urban and agricultural areas): changes in the earth’s surface • Emissions of CO2 and other greenhouse gases are by no means the only way to change the climate.

  8. Climate Change and Atmospheric Particles (decadal-century) Q8: why does volcano eruptions, rich in sulfur, cool the atmosphere in general? A: sulfur aerosols reflect solar radiation; they also modify clouds by increasing the cloud’s reflectivity • Sulfate aerosols cool the climate and therefore counteract global warming to some extent.

  9. Climate Change and Variations in Solar Output (decadal-century) • Sunspots: are huge magnetic storms on the sun that show up as cooler (darker) regions on the sun’s surface Q9: why does solar radiation increases with the increase of sunspot numbers? A: sunspots are cooler; but the surrounding margins of sunspots are brighter (i.e., hotter); overall effect is to increase solar radiation

  10. Climate Change and Variations in the Earth’s Orbit (10K-100K years) • Milankovitch theory:- eccentricity: geometry of orbit (100K yr)- obliquity: tilt angle of axis (41K yr) - precession: direction of axis (23K yr) Min: 22o Max: 24.5o

  11. Climate Change, Plate Tectonics, and Mountain-Building (100M yr) • theory of plate tectonics Landmasses 150M years ago Today Earth’s land mass in 650 million years: http://boingboing.net/2009/07/16/time-lapse-sim-of-ea.html

  12. Q10: what are the external causes of climate change? • a) solar radiation change; b) air composition change; • c) earth’s land mass change; d) all of them • Q11: with the change of earth’s axis in 11K years (due to precession), current July in northern hemisphere would be • a) spring; b) summer; c) fall; d) winter • Q12: How do major volcanoes change surface temperature? • decrease; b) no change; c) increase • Q13: Since the sunspot number is below average in 1986, the solar radiation that year is • a) below average; b) normal; c) above average

  13. Rising atmospheric temperature Rising sea level Reductions in NH snow cover And oceans.. And upper atmosphere…. Warming is Unequivocal

  14. Human and Natural Drivers of Climate Change CO2 is causing the bulk of the forcing On average, it lives > 100 years in the atmosphere and therefore affects climate over long time scales. without air, the earth surface temperature would be much colder

  15. Human and Natural Drivers of Climate Change Q14: Since the radiative forcing due to CO2 is nearly the same as the total forcing in the figure, can we claim that only CO2 is important? a) yes; b) no

  16. Natural versus human-caused temperature increase • Climate models are needed: aerosols; cloud; precipitation; land processes; ….

  17. Observed Expected for all forcings Natural forcing only Understanding and Attributing Climate Change Anthropogenic warming is likely discernible on all inhabited continents

  18. Q15: Does the figure prove that the global warming is man-made? a) yes; b) no

  19. What’s in the pipeline and what could come Warming will increase if GHG increase. If GHG were kept fixed at current levels, a committed 0.6°C of further warming would be expected by 2100. More warming would accompany more emission. CO2 Eq 3.4oC = 6.1oF 850 2.8oC = 5.0oF 600 1.8oC = 3.2oF 0.6oC = 1.0oF 400

  20. A1B is a typical “business as usual” (2090-2099) scenario: Global mean warming 2.8oC;Much of land area warms by ~3.5oCArctic warms by ~7oC; would be less for less emission

  21. Q16: will the world actually warm this much? a) yes; b) no Q17: What is a possible reason? a) volcano, b) earthquake, c) orbital change, d) axis change

  22. What else happens in a hotter world? Future changes just from these processes could be up to 1.5 feet (0.5 m) by 2100, and up to 3 feet (1 meter) within about 2-3 centuries, depending on how much GHGs are emitted. Observations of sea level rise from satellites, 1993-2003. Q18: what are the reasons for the sea level rise? a) expansion of warmer ocean, b) glacier melt; c) both

  23. Other related issues • Drought • Tropical forest dieoff • Hurricane activities • Kyoto Protocol

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