The Greenhouse Effect 1. What is the greenhouse effect? 2. Are humans causing GHGs to rise? 3. Is the earth warming? 4. Are humans causing the earth to warm? 5. Have ecological effects occurred yet? 6. What about me? 1. WHAT IS THE GREENHOUSE EFFECT? If the earth were the diameter of an apple, then the earth plus its atmosphere would be the diameter of a) A grapefruit b) A basketball c) An apple The Atmosphere • Nitrogen • Oxygen (N2) (O2) 78% 21% • • • • (CO2) (CH4) (O3) (N2O) .035% 0.00017% 0.000001% 0.000003% Carbon dioxide Methane Ozone Nitrous oxide “Greenhouse” gases constitute a tiny portion of the atmosphere. Gases that are triatomic or larger have greenhouse properties. • Nitrogen • Oxygen (N2) (O2) 78% 21% • • • • (CO2) (CH4) (O3) (N2O) .035% 0.00017% 0.000001% 0.000003% Carbon dioxide Methane Ozone Nitrous oxide From Philander, G. Is the Temperature Rising? Princeton Univ Press 1998 Greenhouse gases let heat in but not out. UV radiated from sun IR refected from earth Energy radiated from earth can be measured using satellites in space. Greenhouse gases reduce the amount of energy escaping the atmosphere. (Without the greenhouse effect, life on earth as we know it would not be possible.) • The Greenhouse Effect is a factual physical phenomenon. • How to downplay it: – Greenhouse gases (GHGs) are not rising – GHGs rising, but the earth is not getting warmer – Earth is warming, but • • • • Humans didn’t do it Feedback effects will save us It is natural Some scientists say we are OK 2. ARE HUMANS CAUSING ghgs TO RISE? Climate Forcing – A change in energy flux between earth and space. – Positive forcing – warms earth – Negative forcing – cools earth Humans may affect climate forcing by putting greenhouse gases into the atmosphere. Humans have affected concentrations of greenhouse gases Fossil fuel burning Deforestation Natural gas escape in extraction Cattle belching Rice cultivation Landfills Industrial fertilizers Propellants Refrigerants Hansen, J. E., M. Sato, A. Lacis, R. Ruedy, I. Gegen, and E. Matthews, Climate forcings in the industrial era, Proceedings of the National Academy of Sciences, 95: 12753-12758 (1998) “Atmospheric CO2 (379 ppm) in 2005 exceeded by far the natural range over the last 650,000 years.” – Also true for methane (1,774 ppb) IPCC 2007 Earliest fossils of Homo sapiens: ≈200,000 years (IPCC—Intergovernmental Panel on Climate Change) – Established by World Meteorological Organization & United Nations Environment Program – Scientists involved are generally primary researchers in climaterelevant fields – Base assessments primarily on peer reviewed scientific literature – Release updated assessments every 6 years (1995, 2001, 2007) Estimated changes in GHG forcings, 1850 – 2000 Hansen et al. (2000) PNAS 97:9875 (Concentration Change x Greenhouse Properties = Forcing Change) GHG & temperature levels have fluctuated a lot over long time scales. However, we are currently headed off the charts. Brook, E. Nature 453:291 3. IS THE EARTH’S TEMPERATURE RISING? “Warming of the climate system is unequivocal.” IPCC 2007 • Detection questions: – Greenhouse gases are rising? (yes) – The earth’s temperature is rising? (yes) • Attribution question: – Are anthropogenic ghgs causing the earth to warm? 4. ARE HUMANS CHANGING THE CLIMATE? Reasons not to worry: a. b. c. d. Net effects of humans are negative? Warming is natural, not man-made? Feedback effects will save us? Some scientists say the evidence for anthropogenic climate change is weak? e. Things we can’t predict will make it better? a. Anthropogenic Negative Forcings from Fossil Fuels Hansen et al. (2000) PNAS 97:9875-9880 However, net anthropogenic forcing is positive IPCC 2007 b. Human v. Natural Warming: IPCC 1995: “The balance of evidence suggests a discernible human influence on global climate.” (Civil, not criminal, standard of proof) 2001: “There is new & stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.” 2007: “Most of the observed increase in temperatures since the mid20th century is very likely due to anthropogenic greenhouse gas concentrations.” (very likely = 90% certainty) More time, better models, continued warming c. Feedback effects – negative or positive? – Some effects may dampen warming (negative) • More warmth means more NPP • More water in atmosphere: clouds shade planet – Most feedback effects promote warming (positive) • Permafrost melts: methane & CO2 released • Loss of reflectivity from ice caps • Biomass die-off due to rapid climate change d. Some scientists say the evidence is weak • Climate scientists compared for attitudes about Anthropogenic Climate Change (ACC): 1. Convinced of ACC • Scientists on the 4th IPCC • Scientists who signed any of four statements endorsing the 4th IPCC 2. Unconvinced of ACC • Signed any of 12 statements criticizing 4th IPCC CE = convinced by evidence of ACC UE = unconvinced by evidence Timeline for Scientific Detection = size of human signal 1995: “Balance of evidence…” 2001: “New & stronger evidence…” 2007: “Most…very likely…” Ability to solve the problem: > > > Size of human signal: > > > Conundrum Countdown - e. Things we can’t predict will make it better unexpected effects Heat storage by oceans: Climate change irreversible for 1000 years under 450 ppm scenario • Solomon et al. (2009) PNAS 106:1704-1709 Skyrocketing CO2 emissions, better models: We may need to reduce atmospheric CO2 below current levels • Hansen et al. (2008) Open Atmos. Sci. J. 2: 217-231 “Because of the very long lifetime of CO2 emitted in burning fossil fuels, sky-rocketing CO2 has brought us to an emergency situation -- we need to cut off the CO2 source soon…I had hoped that a CO2 amount as large as about 450 ppm might be safe. It has become very clear that was wrong -- the safe level is no higher than 350 ppm, and it is probably less than that…” » J. Hansen, email to M. Orr, Feb. 3 2009 » Current CO2 is 380 ppm Are Humans Changing the Climate? Not to Worry Recap a. b. c. d. e. Net anthropogenic forcings positive Feedback effects mostly positive Human vs. natural warming mostly human Scientist who say we’re okay are the minority “Unexpected” effects making it worse 6. HAVE ECOLOGICAL EFFECTS BEEN DOCUMENTED? Some high elevation species at risk Arenaria tetraquetr (Europe) The Pika (USA) Krajick Science 303:1602 (2004) Note different reflectance of different forest types Beckage et al. 2008 PNAS 105(11):4197 159 species of butterflies surveyed every two weeks at 10 sites over 35 years Avg. shift up = 95 m Optimal elevation for 171 European plant species Circles = 1905-1985 Triangles = 1985-2005 How far up has distribution shifted? Lenoir et al. Science 320:1768 Timing of flowering in Arctic plant species Timing of an event = phenology Post et al. Parmesan & Yohe Nature 421:37-42 A globally coherent fingerprint of climate change impacts across natural systems Trait No. Species No Change / No Pattern Warming - Warming + Phenology 677 27% 9% 62% Distribution 893 27% / 24% 11% 39% Phenology = timing of an event (e.g. flowering in the spring) Climate + means it reproduces earlier (consistent with warming) Climate - means it reproduces later (not consistent with warming) Distribution = organisms’ geographic range Climate + means it has shifted into historically colder habitat (e.g. upslope) Climate - means it has shifted away from historically colder habitat 6. WHAT ABOUT ME? H. sapiens on “Hedonic Treadmill” (Brickman & Campbell 1971) Figure courtesy Chris Wolsko 7/9 7/9 Snowpack/precip = SWE/P JFM Tmin = minimum temperatures River flow 1/3 Stern Report: Economics of Climate Change • Cost of stemming climate change: 1% GDP/yr • Cost of doing nothing: 5% GDP/yr • Cost of cutting 1 ton of CO2 emissions: $25 • 1 ton of CO2 has $85 in future costs • Benefits of low-carbon future: $2.5 trillion/yr See http://en.wikipedia.org/wiki/Stern_Review