Pollution Politics Permit, Prevent, or Prohibit?
I. Global Warming Theory (GWT) as a Research Program • Hypothesized in early 20th century: Relationship between CO2 and temperature understood in 1920s • Largely ignored until 1970s. Why? • Research largely retrospective – focused on climate reconstruction rather than prediction • Research emphasized natural rhythms – changes in earth’s orbit, solar radiation, etc – and expected cooling • Anthropogenic effects assumed to be trivial until environmental movement of 1970s
C. Setting Forth the Problem • Question: How do anthropogenic emissions affect climate? • Competing Hypotheses: • They don’t (null hypothesis) • Pollution causes cooling: Aerosols • Pollution causes warming: CO2 and other “warming gases” • Research Activity: Develop long time-series of warming gases, aerosol levels, temperature
5. Measuring Past CO2 • Recent measurements: Direct atmospheric sampling, esp. from Mauna Loa (high) • 19th century measurements: Selected measurements (control for seasonal “breathing,” urban environments, sea breezes vs. urban winds, etc) since switched to Law Dome core • Long-term measurements: Ice cores. Note that bubbles aren’t trapped in deep cores until many years pass (4000 to 6000) but new ice (Law Dome site) has gas from as recent as 1978
D. Early Predictions • Invention of GCMs (computerized climate models) allows predictions BUT depends on many unknown parameters • Early models ignore ocean circulation, focus entirely on atmosphere (usually without clouds) usually predict massive warming, but fail to “postdict” past temperature changes • Problem of Feedback Loops: The environment is interconnected, not strictly linear
E. Climate Feedbacks • Three of the most important direct climatic feedbacks to greenhouse forcing are: • water vapor feedback, • cloud cover feedback and the • ice-albedo feedback.
1. Water Vapor Feedback • The concentration of water vapor in the atmosphere increases rapidly with rising temperature (about 6%/°C). • This is the basis for the strong positive water vapor feedback in current climate models • increases in temperature produce increases in atmospheric water vapor which in turn enhance the greenhouse forcing leading to further warming).
2. Ice-Albedo Feedback • A warmer Earth will have less snow and ice cover, resulting in a lower global albedo and consequent absorption of more solar radiation. This, in turn causes a further warming of the climate. • Most GCMs have simulated this positive surface albedo feedback, but • significant uncertainties exist over the size of the effect, particularly for sea-ice
3. Cloud Feedbacks • The effects of changes in cloud on a change of climate have been identified as a major source of uncertainty in climate models • clouds contribute to the greenhouse warming of the climate system by absorbing more outgoing infrared radiation (positive feedback), • they also produce a cooling through the reflection and reduction in absorption of solar radiation (negative feedback) generally thought to be stronger
4. Why feedbacks matter: The SO2 Surprise • Environmentalism says that belching out clouds of black smoke is probably a bad idea • One component of “dirty” exhaust (coal, diesel, etc.) is sulfur dioxide (SO2) – and associates sulfates • SO2 is a warming gas BUT • Sulfate aerosols cool AND SO2 helps form clouds, generating a negative feedback loop that reduces warming • Aerosols are removed form the atmosphere much more quickly than gases • Result: Limiting some types of emissions may accelerate warming (by removing a cooling loop) rather than slowing it
F. Findings • Warming Gases (GHGs) • Most of Earth’s atmosphere is climatically neutral: GHGs present in trace amounts only • Implication: Relatively small releases (on a global scale) may significantly increase concentrations
c. Trends in GHGs • Since the mid-1800s, • atmospheric levels of carbon dioxide have increased 30 percent (from 280 parts per million to 360 parts per million), • the concentration of methane has more than doubled (to about 1.72 parts per million), and • nitrous oxide levels have increased by a more modest 10-15%. • CFCs have appeared in the atmosphere
2. The “Carbon Cycle” – Nature vs. Human Contributions a. The Cycle: The earth's natural processes continually exchange massive quantities of carbon. • Oceans release about 90 billion tonnes of CO2 into the atmosphere each year. • Decaying vegetation adds another 30 billion tonnes annually, while • another 30 billion tonnes each year is released from the natural respiration of living creatures and plants.
b. Human Sources of CO2 • Human activities add an extra 3% to this natural cycle, or about 7 billion tons per year. Why worry about a 3% increase? The majority of human CO2 comes from the burning of fossil fuels. The residence time of CO2 in the atmosphere is ~100 to 200 years
Cumulative carbon emissions, 1950-1996 Data Source: Marland et al, 1999. Carbon Dioxide Information Analysis Center.
c. Carbon Sinks • Absorption by the oceans and plants removes the natural -- and much of the human -- CO2 from the atmosphere. • BUT: The net result of this "carbon cycle" is a net increase of about 3.1 to 3.5 billion tonnes of CO2 annually to the atmosphere. • Implication: Natural cycle dwarfs human contributions in any one year, but many years of cumulative “extra” emissions that just slightly overload the cycle start to add up
Atmospheric carbon dioxide (CO2):1750 to present Data Source: C.D. Keeling and T.P. Whorf, Atmospheric CO2 Concentrations (ppmv) derived from in situ air samples collected at Mauna Loa Observatory, Hawaii, Scripps Institute of Oceanography, August 1998. A. Neftel et al, Historical CO2 Record from the Siple Station Ice Core, Physics Institute, University of Bern, Switzerland, September 1994. See http://cdiac.esd.ornl.gov/trends/co2/contents.htm
Alternate view of same data… Data Source: C.D. Keeling and T.P. Whorf, Atmospheric CO2 Concentrations (ppmv) derived from in situ air samples collected at Mauna Loa Observatory, Hawaii, Scripps Institute of Oceanography, August 1998. A. Neftel et al, Historical CO2 Record from the Siple Station Ice Core, Physics Institute, University of Bern, Switzerland, September 1994. See http://cdiac.esd.ornl.gov/trends/co2/contents.htm
3. Methane • A. The good news: Unlike carbon dioxide, methane is destroyed by reactions with other chemicals in the atmosphere. • Its approximate lifetime is about 10 years.
b. The bad news • On the other hand, on a molecule-for-molecule basis, methane is a much greater absorber of energy than carbon dioxide. • As a greenhouse gas, a methane molecule is more than 20-times more potent than than a carbon dioxide molecule.
4. Nitrous Oxide • As a greenhouse gas, its major source is the bacterial breakdown of nitrogen compounds in soils. • When land is deforested and then cultivated, nitrous oxide emissions can increase, particularly if nitrogen-containing fertilizers are used. • Nitrous oxide is even more potent than methane as a greenhouse gas. • A nitrous oxide molecule may be as much as 300 times more potent than a molecule of carbon dioxide in absorbing Earth radiation.
5. Ozone (O3) a. Good (stratospheric) ozone: protects against UV radiation b. Bad (tropospheric) ozone: causes smog, acts as a warming gas (but breaks down very quickly – so emission reductions take only weeks to work)
6. CFCs • Molecule for molecule, chlorofluorocarbons are the most potent of greenhouse gases. • CFC-12 or "Freon-12" as it is known by its trade name, is 17,700 times more potent than carbon dioxide. • Although they exist in only minute quantities in the atmosphere, CFCs are thought to be responsible for about 20% of the enhanced greenhouse effect. • CFCs phased out in most countries due to destruction of stratospheric ozone (not concern about warming)
II. Is GWT a Progressive Research Program? • Remember: Every theory fails. Key is how theory is modified: • Degenerative = explain failure but nothing else (no new knowledge or predictions). • Progressive = explain failure AND makes new testable predictions • Let’s see how GWT responded to failures….
A. Temperature Anomalies • Satellite data – • Challenge: Shows cooling in atmosphere over time • Response: Must correct for decay in satellite orbits over time • New Prediction? “New” satellites ought to show warmer temps than “old” satellites, since their orbits haven’t decayed as much
2. Weather balloons • Challenge: Weather balloons show cooling in upper atmosphere during daytime, but warming at night • Response: Balloon instruments have been better shielded against sunlight over time – explaining apparent decrease in day temps and increase in night temps • New prediction? Relaunching vintage instruments during daytime should show warmer temps than modern instruments
B. CO2-Warming Anomalies • The 1940-1975 dip • Challenge: Records of atmospheric carbon dioxide (CO2) levels since 1940 show a continual increase, but during this period global temperature decreased until 1975 (and has increased since then).
B. CO2-Warming Anomalies • The 1940-1975 dip • Challenge: Records of atmospheric carbon dioxide (CO2) levels since 1940 show a continual increase, but during this period global temperature decreased until 1975 (and has increased since then). • Response: industrialization poured SO2 and aerosols into the atmosphere, leading to cooling • New prediction? Reduction in aerosols should lead to increases in temperature
2. Reverse causality • Challenge: Ice cores from Antarctica show that CO2 levels lagged behind temperature increases during glacial terminations. • Response: Glacial terminations correspond to changes in the Earth’s orbit (Milankovitch cycles – more on these in a bit), which triggered warming. As ice sheets retreated, thawing permafrost and warming oceans released CO2 and methane, leading to still further warming • New prediction? Vague: “permafrost and oceans” isn’t very specific. GWT researcher acknowledge that “exact mechanism is unknown” (i.e. anomaly remains)
3. Medieval Records • Challenge: Temperature reconstructions from tree rings fail to show the Little Ice Age or Medieval Warm Period • Response: These were regional rather than global changes, caused by changes in the Gulf Stream and other ocean currents • New prediction? Tree rings from Western US should show no change when compared to tree rings from Northern Europe. Also, newly discovered North Atlantic corals should show increased temps vs. Pacific ones (not yet tested)
Regional Differences in Annual Temperature Trends: 1901 - 1990 Source: Watson 2000
U.S. Temperature Trends: 1901 to 1998 Red circles = warming; Blue circles = cooling All stations/trends displayed regardless of statistical significance. Source: National Climatic Data Center/NESDIS/NOAA
C. Unanswered questions • Cloud formation: Existing GCMs fail to model changes in water vapor, which is tied to both water temperatures and cloud formation • Ocean currents: While Gore implies that we know that the “Global Conveyor Belt” is driven by temperature and salinity, we have been unable to identify its natural range of variation absent temperature changes (no long-term records)
III. Comparing GWT to the “Natural Causes” Research Program • Precedes GWT: Early climate models focused on the role of cycles in the Earth’s orbit and tectonic changes (movement of land masses) • Evolution of the Research Program: While GWT added anthropogenic to natural causes, the “Natural Causes” research program remains convinced that anthropogenic factors are minor
C. Orbital forcing • The theory that large scale climate changes (glacials/interglacials) are due to the variations in precession, eccentricity and obliquity of the Earth’s solar orbit that affects the amount of solar radiation received at the surface of the Earth. • Attributed to Milankovitch
1. Orbital attributes • The Earth has three fundamental orbital attributes: • Changes in the tilt of the axis of rotation (termed the obliquity) • Changes in the shape of the elliptical orbit around the sun (termed eccentricity) • Changes in the date of the Earth’s closest approach to the Sun (termed precession of the equinox)
2. Periods of variation • The tilt of the Earth’s axis varies over a period of about 41,000 years • The cycle of orbital eccentricity is 90,000 to 100,000 years • The precession cycle of the equinox is about 23,000 years