Climate Change – Greenhouse Gases Background Greenhouse Effect Gases absorb heat (not light)

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

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

4. Greenhouse Gases

6. After Petit et al. 1999

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

9. Climate Change – Other Factors • Cloud Cover • Reflects incoming radiation • Difficult to estimate in climate models • Effects vary in relation to altitude, thickness, composition • Atmospheric Dust & Aerosols • Important factor in cool period from 1930s to 1960s • Overwhelmed effects of rising CO2 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. Climate Change – Other Factors • 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.shtmlhttp://calspace.ucsd.edu/virtualmuseum/climatechange2/06_3.shtml

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

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

15. Climate Change – Other Factors • 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 • Photosynthesis & Transpiration • Affect CO2, water vapor • As [CO2] rises, some plants • Photosynthesize more rapidly • Grow faster • Incorporate more CO2 into biomass • Keep their stomata open less • Transpiration releases water vapor into atmosphere • Less transpiration when [CO2] is higher (stomata)

17. Climate Change – Other Factors • 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 • Photosynthesis & Transpiration • Affect CO2, water vapor • As [CO2] rises, some plants • Photosynthesize more rapidly • Grow faster • Incorporate more CO2 into biomass • Keep their stomata open less • Transpiration releases water vapor into atmosphere • Less transpiration when [CO2] is higher (stomata)

18. Climate Change – Other Factors • Soil Characteristics • Affect heat capacity and retention • More hydrated soil leads to • Darker color (less reflective) • More heat capacity (high heat capacity of water) • 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. Climate Change – Other Factors • 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. 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