1. I. I.Climate Change – Greenhouse Gases A. A.Background Greenhouse Effect Gases absorb heat (not light) Natural Greenhouse Effect Mean planetary temperature = 15 o C vs. -6 o C Enhanced Greenhouse Effect Due to GHGs emitted from human activity

3. I. I.Climate Change – Greenhouse Gases B. B.Greenhouse Gases Most important GHG is water vapor Accounts for ~50% of natural GHE

4. Greenhouse Gases GasSourcesResidence Time (y) Radiative Forcing Relative Influence Carbon Dioxide FF Combustion Deforestation Biomass Burning 50-200163% Methane Rice Paddies Cattle/TermitesLandfills FF Production 102118% Nitrous Oxide FertilizersDeforestation Biomass Burning 150-1702066% HCs (incl. CFCs) Aerosol Sprays FoamsRefrigerants15-650 10,700 – 15,800 10,700 – 15,800 +13%

6. After Petit et al. 1999

8. I. I.Climate Change – Greenhouse Gases B. B.Greenhouse Gases Long residence times indicate atmospheric concentrations will remain high even if emissions stop Other factors besides GHGs may influence global climate

9. II. II.Climate Change – Other Factors A. A.Cloud Cover Reflects incoming radiation Difficult to estimate in climate models Effects vary in relation to altitude, thickness, composition B. B.Atmospheric Dust & Aerosols Important factor in cool period from 1930s to 1960s Overwhelmed effects of rising CO 2 during this period Dust from volcanic eruptions, drought areas Cool period following eruption of Mt. Pinatubo in 1991 Anthropogenic aerosols from sulfate, nitrate, black carbon, etc. (mostly from combustion) Also may influence cloud lifetime, precipitation

11. II. II.Climate Change – Other Factors C. C.Sunspots May affect amount of incoming radiation Solar output varies – sunspots, solar flares Sunspots are magnetic storms that appear as dark patches on sun’s surface Number and size are maximal every 11 years Solar output ca. 0.1% higher than normal during maxima

12. http://calspace.ucsd.edu/virtualmuseum/climatechange2/06_3.shtml

13. II. II.Climate Change – Other Factors C. C.Sunspots May affect amount of incoming radiation Solar output varies – sunspots, solar flares Researchers have correlated minima with “Little Ice Age” in Europe during 17 th and early 18 th centuries when sun was 0.25% dimmer than normal 20 th century dominated by sunspot maxima Some predictions that 21 st century will see minima Estimated that sunspot variability may have contributed to half of 0.55 o C warming since 1860 and one third of warming since 1970 (Lean et al.)

14. http://calspace.ucsd.edu/virtualmuseum/climatechange2/06_3.shtml

15. II. II.Climate Change – Other Factors D. D.Volcanism Affects water vapor, particles, sulfides, nitrates Generally leads to planetary cooling Theory about extinctions at P/T & K/T boundaries Mt. St. Helens and Mt. Pinatubo eruptions caused planetary cooling, and those were small eruptions E. E.Photosynthesis & Transpiration Affect CO 2, water vapor As [CO 2 ] rises, some plants Photosynthesize more rapidly Grow faster Incorporate more CO 2 into biomass Keep their stomata open less Transpiration releases water vapor into atmosphere Less transpiration when [CO 2 ] is higher (stomata)

17. II. II.Climate Change – Other Factors D. D.Volcanism Affects water vapor, particles, sulfides, nitrates Generally leads to planetary cooling Theory about extinctions at P/T & K/T boundaries Mt. St. Helens and Mt. Pinatubo eruptions caused planetary cooling, and those were small eruptions E. E.Photosynthesis & Transpiration Affect CO 2, water vapor As [CO 2 ] rises, some plants Photosynthesize more rapidly Grow faster Incorporate more CO 2 into biomass Keep their stomata open less Transpiration releases water vapor into atmosphere Less transpiration when [CO 2 ] is higher (stomata)

18. II. II.Climate Change – Other Factors F. F.Soil Characteristics Affect heat capacity and retention More hydrated soil leads to Darker color (less reflective) More heat capacity (high heat capacity of water) G. G.Albedo (Reflectivity) Earth’s surface varies considerably (mean = 0.30-0.36) Ice/Snow highly reflective (0.9) Clouds vary in reflectivity Land generally less reflective Changes in land use affect albedo Desertification increases albedo Forest – 0.12 Grassland – 0.19 Desert – 0.30

19. II. II.Climate Change – Other Factors H. H.Astronomical Factors Earth’s axis precesses on a ~23,000 year cycle Axial tilt (obliquity) varies on a 41,000 year cycle Orbital eccentricity has a 100,000 year cycle Correlated with glacial periods over past 1,000,000 years

22. II. II.Climate Change – Other Factors Many factors affect global climate in multiple ways Ex – Clouds absorb re-radiated long- wavelength radiation but also may reflect incoming short-wavelength radiation Net effect is cooling Ex – Particles in the atmosphere reduce the re- radiation of long-wavelength radiation but also reflect incoming short-wavelength radiation Net effect is probably warming at low levels but cooling at high levels (e.g. following a large volcanic eruption) Uncertainty about impact of many factors