Lecture 12: Climate Change and Life in the Greenhouse

1. Climate Change - Life in the Greenhouse
- Natural Climate Change
- What is the Greenhouse Effect?
- Climate Change and the Future
Reading:
4th Ed., Ch 18, Sec 21
5th Ed., Ch 18, Sec 22
Graphic: Garrison, 4th Ed., Fig. 18.22, pg 483, 5th Ed., Fig. 18.26, pg 455.

2. What Causes Climate?
Many changes in climate are driven by energy from the sun
Climate depends on:
- the amount of energy received
- what happens to this energy once it reaches Earth's atmosphere
Graphic: Earth's orbit, adapted from Pisias and Imbrie (1986/1987). Courtesy of NOAA.

3. Climate Forcing
External forcing:
- due to changes in Earth’s orbit about the sun
- occurs on time scales of 20,000-100,000 years
Internal forcing:
- due to variations of atmospheric and oceanic circulation
- occurs on time scales from tens to thousands of years
Graphics: (top panels) Changes in orbit circularity ("eccentricity"), images by R.Simmon, courtesy of NASA GSFC. (bottom) Sea level signatures of El Niño and La Niña measured by the TOPEX/-POSEIDON satellite altimeter. Image courtesy of NASA JPL.

4. Heat Exchange and Climate
Solar energy is unevenly distributed:
- excess heat in the tropics
- deficit of heat at the poles
Different climates can be produced with the same amount of solar energy as energy is redistributed by oceanic and atmospheric circulation
Graphics: Garrison, 4th Ed., Fig. 8.4, pg 189, 5th Ed., Fig. 8.5, pg 181.

5. Measuring Climate Change
Scientists can monitor past climate using natural climate recorders
Examples
- chemical composition of coral skeletons
- air bubbles trapped in polar ice caps
Graphics: (above) Diver drills for coral samples, courtesy of NOAA, (right) Banding in coral skeletons NOAA Coral Paleoclimate slide set.

6. The Greenhouse Effect
"Greenhouse gases" in the atmosphere trap heat, resulting in higher surface temperatures
Graphic: See Garrison, 4th Ed., Fig. 8.2, pg 188, 5th Ed., Fig. 8.3, pg 180.

7. Life in the Greenhouse
The greenhouse effect is a natural part of how the atmosphere works
Natural sources of greenhouse gases:
- volcanoes
- burning and decay of organic matter
- respiration and other biological processes
Graphic: Oldoinyo Lengai, erupts explosively in 1966. Photography by G.Davies, courtesy of C.Nyamweru, St. Lawrence University, Canton NY.

8. A Planetary Comparison
Venus, Earth and Mars are all warmed by greenhouse gases in their atmospheres
Without the greenhouse effect average Earth surface temperatures would be -18 degC (0 degF)
Actual average surface temperatures were 16 degC (61 degF) prior to industrialization

9. Anthropogenic Inputs of Greenhouse Gases
Carbon dioxide - fossil fuels, deforestation
Water vapor - changes in land use, ocean warming
Methane - rice farming, ranching
CFCs - cleaning agents, refrigerants
Graphic: Garrison, 4th Ed., Fig. 18.19, pg 482, 5th Ed., Fig. 18.23, pg 454.

10. The Fossil Fuel Connection
Burning fossil fuels produces CO2
Example: burning 1 gallon of gasoline produce 19.6 lbs of CO2
The impact of a population on atmospheric CO2 depends on:
- size of population
- affluence per capita
- technology choices
2001 CO2 emissions (metric tons/person/yr)*
North America: ~5
Western Europe ~2
Africa ~0.3
Graphic: Carbon Dioxide Information Analysis Center (CDIAC), USDOE.
*Data from the CDIAC, USDOE.

11. Atmospheric CO2, 1950-Present
Atmospheric CO2 can be measured directly from air samples
Measurements at Mauna Loa, Hawaii show an increase in atmospheric CO2 of 85 parts per million (ppm) over the past 50 years
Data source: Keeling, D.C., and T.P. Whorf, 1998: Atmospheric CO2 records from sites in the SIO air sampling network. In "Trends: A Compendium of Data on Global Change", Carbon Dioxide Information Analysis Center, US Dept. of Energy. Lower picture: CO2 monitoring station on Mauna Loa, courtesy of NOAA.

12. Atmospheric CO2, 1740-1990's
Air bubbles within polar and glacial ice are analyzed to determine CO2 levels in the past (yellow squares)
Atmospheric CO2 has increased nearly exponentially from 280 ppm in the 1740's to about 380 ppm today
Other greenhouse gases have also increased
Graphic: Garrison, 4th Ed., Fig. 18.20, pg 482, 5th Ed., Fig. 18.24, pg 455.

13. Just How Unusual is the Today’s CO2 Level?
Data shows that today's CO2 levels were last reached 125,000 years ago
Some climatologists believe that a doubling of today's CO2 level last occurred 20-40 million years ago

14. Industrialization in the Greenhouse
Global temperature has increased about 0.6 oC over the past 100 years and about 0.5 oC over the past 25 years
This is coincident with increases in atmospheric greenhouse gas concentrations
Graphics: (top) Average global temperature, 1850-2005, courtesy of University of East Anglia Climate Research Unit, (bottom) CO2 emissions. Graphics courtesy of US Global Change Research Information Office.

15. The Missing Carbon?
Based on data from the 1980-1990’s
   CO2 emission rate: ~5 GT C yr-1
   Atmospheric increase ~ 3 GT C yr-1
Fate of Remaining ~2 GT C yr-1?
   Terrestrial Biosphere (Forrest, soils)
   Dissolved as carbon compounds in the Deep Ocean (HCO3-, CO3=, CO2)
Graphics: (top) Coastal forest, courtesy of NOAA, (bottom) North Pacific storm waves as seen from the M/V NOBLE STAR. Photo courtesy of NOAA photo library.

16. The Missing Heat?
The increase in atmospheric CO2 should have warmed the Earth by about 1 deg. C (rather than 0.6 deg C) over the past few decades
Analysis of measurements from over 12 million oceanographic stations indicates ocean warming to 3000 m depth¹
The heat is being stored in the ocean and melting ice and snow²
Graphic: From Levitus et al., 2000.
¹ At a rate of ~0.3 W/m2 averaged over the Earth’s surface (Levitus et al., 2000).
² (e.g. Levitus et al., 2001).

17. 20th Century Changes in Glaciers

18. Historic Air Temperatures and Future Predictions
Measurable polar warming in last 50 yrs:
Red = warming trend
Blue = cooling trend
White = No change
Climate models predict continued warming as greenhouse forcing increases
Graphics: (top) Annual atmospheric temperatures 1951-1997, (From “The Greenhouse Debate” J. Hansen, NASA GISS www.giss.nasa.gov/edu/gwdebate/). (bottom) Predicted Surface air temperature change following CO2 doubling (colors) predicted by an ensemble of climate models with CO2 increasing 1% per year, IPCC

19. National Academy of Sciences Surface Temperature Reconstructions for the Last 2,000 years
This report, completed in 2006 assessed the state-of-the- art science for understanding changes in Earth’s surface temperature over the last 2000 years

20. Principle Conclusions of the 2006 National Academy of Science Report
“It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries. This statement is justified by the consistency of the evidence from a wide variety of geographically diverse proxies.”

“Surface temperature reconstructions for periods prior to the industrial era are only one of multiple lines of evidence supporting the conclusion that climatic warming is occurring in response to human activities, and they are not the primary evidence.”

21. Annual Global Mean Temperature - Actual and Predicted

22. Potential Climate Changes
Primary effects:
- Warmer temperatures
- Sea level rise
- Water cycle impacts (reduced N.hemisphere snow)
- Reduced sea ice extent (Arctic)
- Changes in frequency, intensity of storms (notably hurricanes)
Types of changes:
- changes in average conditions
- changes in variability
- rapid changes
- "surprises"
Graphic: Hurricane Floyd, Sept. 14, 1999. Courtesy of NASA.

23.Global Impacts of Sea Level Rise
- Damage to housing and high-value infrastructure
- Altered patterns of damage by storm waves
- Potential refugee issues involving low-lying coastal nations
Graphics: (left) Impact of a 1 meter rise in sea level on Florida. In relatively flat coastal areas, a small rise in sea level can flood large areas (right). Graphics from “Impacts of a Warming Arctic: Arctic Climate Impact Assessment, Cambridge University Press, 2004.

24. Sea Level Rise
Arctic warming can raise global sea level
- melting adds water to the ocean
- warmer temperatures due to the ice-albedo feedback can cause sea water to expand globally, increasing sea level
Graphics: (top left) TOPEX/POSEIDON data, (bottom left) sea level rise predicted by a suite of climate models for different emissions scenarios, (c) seasonal meltwater zone around Greenland, as measured by satellite. Courtesy of “Impacts of a Warming Arctic: Arctic Climate Impact Assessment”, Cambridge University Press, 2004.

25. Sea Ice Coverage
Satellite-measured sea ice cover:
- is decreasing throughout the year, with most dramatic declines observed in summer
- cools climate by reflecting solar energy back to space
- is an important habitat for many marine animals
Graphic: Sea ice coverage, 1979 and 2003 based on satellite data, courtesy of “Impacts of a Warming Arctic: Arctic Climate Impact Assessment”, Cambridge University Press, 2004.

26. Ice in the News – The 2005 Minimum
Data source: September (minimum) sea ice extent. National Snow and Ice Data Center (NSIDC). Additional information available at http://news.bbc.co.uk/2/hi/science/nature/4290340.stm

27. Potential Impacts of Climate Change on Society
Many sectors of society may be affected...
- Agriculture and fisheries
- Infrastructure
- Water resource management
- Human health
- Ecosystems/biodiversity
Climatologists, economists, sociologists, politicians and others are studying the potential impacts of climate change on these sectors and on individual countries
Graphic: (top) Sunrise, courtesy of NOAA, (bottom) wheat harvest, at ARS Central Great Plains Research Station, Akron, Colorado. Photo by S.Bauer, courtesy of US Dept. of Agriculture.

28. Predicting Future Climate
Uncertainties:
- Interactions between different elements of the climate system (e.g., global warming and clouds)
- Future CO2 emissions are unknown
- Potential impacts of mitigation technologies
- Unforeseen surprises
Graphic: Climate change feedbacks, courtesy of United Nations Environmental Program, World Meteorology Office.

29. What Does the Future Hold?
Options being studied include:
Mitigation to reduce emissions:
- using fewer fossil fuels
- energy efficiency
- substitution of technologies
- removing CO2 once it's produced ("sequestration")
Adaptation to a new climate
- may require sweeping changes in key sectors of society (e.g., farming, the insurance industry)
- success depends on available capital and other resources
Graphics: (top) A wind farm, photo courtesy of US DOE, (bottom) Cool change logo, courtesy of US EPA.

30. Preview of Next Lecture
- Tsunami
- Review for Exam 2
Reading: 4th Ed., Ch 11 Secs 5-10 or 5th Ed., Ch 10 Secs 24-29
Graphic: Fishing boat beached near a damaged fire truck. Photo by D.J. Sigrist International Tsunami Info. Center, Honolulu. Courtesy of NOAA.