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Anthropogenic Climate Change: What Science Tells Us About Global Warming Dan Herms Department of Entomology The Ohio State University Ohio Agricultural Research and Development Center Wooster, OH [email protected] The 10 warmest years since 1000 AD: 1. 2010, 2005 Source: NASA Goddard 2. 2009 Institute for Space Studies 3. 1998 4. 2007 5. 2002 6. 2006 7. 2003 8. 2004 9. 2011 (warmest La Niña year on record) 10. 2001 Key questions to address: 1. Is global warming real and is it caused by humans? scientific 2. If so, what will be the impacts? health, agriculture, environment 3. What can be done: mitigation and / or adaptation? policy: technological, economic, cost / benefit Key scientific questions: 1. Is Earth warming? 2. If so, what is the cause(s)? 3. What are / will be the impacts? 4. Future climate projections? Consilience: convergence of evidence 4 independent surface temperature records: NASA, NOAA, Hadley Climate Research Unit, Berkeley Earth Surface Temp Corroborated by: • 2 satellite records of upper and lower troposphere • Weather balloons • Proxy reconstructions (e.g. tree rings, boreholes, ice cores, glaciers, coral, etc.) • Phenology, species distributions, physical evidence 4 independent surface temperature records converge on the same pattern Satellite and surface measurements agree: Earth is warming R.A. Rohde, www.globalwarmingart.com Is the Earth warming? 30 year trends: 1. Increasing air temperature in lower atmosphere. 2. Increasing temperature over land. 3. Increasing temperature over oceans. 4. Increasing sea-surface temperature. 5. Increasing ocean heat content. 6. Increasing humidity. 7. Increasing sea level. 8. Decreasing glacier cover. 9. Decreasing sea ice cover. 10. Decreasing snow cover. NOAA National Climatic Data Center, 2010 Record high temps far exceed record low temps (if Earth was not warming the ratio would be 1:1) Meehl et al. (2009) Relative increase of record high maximum temperatures compared to record low minimum temperatures in the U.S., Geophys. Res. Lett., 36, L23701, doi:10.1029/2009GL040736. Warming did not stop in 1998 www.realclimate.org/wp-content/uploads/GISStrends.jpg Earth has warmed almost 2ºF since 1860 compare to about 10°F difference between coolest point of ice age and warmest inter-glacial maxima At request of Congress in 2006, National Academy of Sciences investigates and validates “hockey stick” surface temperature reconstruction. SURFACE TEMPERATURE RECONSTRUCTIONS FOR THE LAST 2,000 YEARS NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES THE NATIONAL ACADEMIES PRESS (2006) www.nap.edu Ocean temperatures show same pattern of warming (source: NOAA) http://www1.ncdc.noaa.gov/pub/data/oisst/ann.ocean.60s.60n.png Climate Warming Inertia: Most excess heat is trapped in the ocean where it will be released slowly Physical signs of warming are everywhere Glaciers are melting world-wide 2000 Toboggan Glacier Oerlemans, J. 2005. Extracting a climate signal from 169 glacier records. Science 308:675-677. http://www.coasttocoastam.com/timages/page/glacier_bay012905.jpg 1909 Glacier Bay Glacier National Park: Number of glaciers in 1910 when park formed: 150 Number today: 25 http://www.globalwarmingart.com The (Vanishing) Snows of Kilimanjaro Unprecedented ice loss within past 11,700 yrs: 85% of ice present in 1912 has vanished. 26% of ice present in 2006 has vanished. www.commondreams.org/ Thompson et al. 2009. Glacier loss on Kilimanjaro continues unabated. PNAS 106:19770-19775 The fabled Northwest Passage opened for first time in 2007, and Northeast Passage opened in 2011 NASA, http://earthobservatory.nasa.gov Trends in average Arctic sea ice since 1900 Steig et al. 2009. Warming of the Antarctic ice-sheet surface since 1957. Nature 457:459-463. http://www.nature.com/ Antarctic ice mass loss is accelerating: 2002-2005: 139 gigatons / yr 2006: 200 gigatons / yr (contributing >0.5 mm to sea level rise) Rignot et al. 2008. Nature Geoscience Climate change at Thoreau’s Walden Pond “We determined that plants bloomed seven days earlier on average than they did in Thoreau’s times.” Miller-Rushing & Primack. 2008. Global warming and flowering times in Thoreau’s Concord: a community perspective. Ecology 89:332-341. Climate change and phenology at Sand County, WI “The mean of regressions for the 55 phenophases studied was -0.12 day / yr, an overall increase in phenological earliness…” Bradley et al. 1999. Phenological changes reflect climate change in Wisconsin. Proc. Natl. Acad. Sci. 96:9701-9704 Change in growing season from satellite imagery (days / decade) Observation Geographic range period Earlier leafout Longer growing season Reference 1981 – 1991 45 N 70 N, Eurasia 8 12 Myneni et al. (1997a) 1981 – 1999 40 N 70 N, Eurasia 3.5 9.4 Zhou et al. (2001) 1981 – 1999 40 N 70 N, North America 4.3 6.3 Zhou et al. (2001) 1982 – 2001 25 W 60E; 27 N 72 N, Europe 5.4 9.6 Stöckli & Vidale (2004) Badeck et al. 2004. Responses of spring phenology to climate change. New Phytologist 162:295-309 New USDA Plant Hardiness Zone Map: much of Ohio updated to warmer zone PNAS (2006) 103:11217-11222 Bird phenology Between 1971 and 1995 the laying date for many species of British birds has shifted earlier by an average of 9 days. (Nature 388: 526) Breeding date of North American common murre advanced by 24 days / decade Toad phenology Bufo bufo in southern England, 1980-2001. Adult arrival at pond advanced by 11 d per 1°C of warming. Reading, C. J. 2003. The effects of variation in climatic temperature (1980-2001) on breeding activity and tadpole stage duration in the common toad, Bufo bufo. Sci. Tot. Environ. 310, 231-236. OARDC is part of the National Phenology Network that has documented earlier springs in NA Lilac bloom as a phenological indicator of continental-scale climate change. Six undisputed facts: 1. The amount of heat trapped by CO 2 increases with its concentration. 2. After remaining stable for thousands of years, CO 2 has risen rapidly to record levels, and is now rising even faster. 3. After being relatively cool over the last millennium, Earth has warmed sharply over the last 30 years. 4. Over 650,000 years, Earth’s temperature has been tightly linked with atmospheric CO2. 5. Earth is absorbing more heat than it dissipates. 6. Ice is melting world-wide and sea level is rising. Scientific “consensus” is based on a survey of peer-reviewed literature, rather than polls of opinions held by scientists. 1. Global warming is already apparent. 2. Anthropogenic greenhouse gasses are responsible for the vast majority of the warming. Oreskes, N. 2004. The scientific consensus on climate change. Science 306:1686 At request of President Bush, National Academy of Sciences reviewed Third IPCC Report, and affirmed its conclusions. “Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise.” National Academy of Sciences, National Research Council 2001 assessment of IPCC report: http://www.nap.edu/openbook.php?record_id=10139 Official policy of Bush Administration as outlined by Secretary of Energy Spencer Abraham: • Global warming is real and caused, in part, by humans. • Stabilize greenhouse gasses at safe level. • Reduce greenhouse gas intensity 18% by 2012 via financial incentives and voluntary programs. Abraham, S. 2004. The Bush Administration’s approach to climate change. Science 305:616-618. Earth’s energy balance: • • • • Solar radiation emitted by Sun Solar radiation intercepted by Earth Energy radiated back to space Energy absorbed, stored, redistributed as heat Earth’s energy balance: Kiehl, J. T. and Trenberth, K. E. 1997. Earth's annual global mean energy budget. Bull. Am. Meteorol. Assoc. 78: 197-208. Earth’s Energy Imbalance Earth is absorbing 0.85 W / m2 more than it is dissipating Hansen et al. 2005. Science 308:1431-1435 Greenhouse effect keep Earth’s average temperature (59°F) much warmer than the moon’s (-1°F), and greatly dampen day-night temperature fluctuations. • Water vapor: 50% of greenhouse effect • Clouds: 25% • CO2: 19% • Other (methane, ozone): 7% Schmidt et al. 2010. The attribution of the present-day total greenhouse effect. J. Geophys. Res. 115: D20106. “CO2 and other noncondensing greenhouse gasses, which account for 25% of the greenhouse effect, serve to provide the stable temperature structure that sustains the current levels of atmospheric water vapor and clouds via feedback processes that account for 75% of the greenhouse effect.” “Without the radiative forcing supplied by CO2 and other noncondensing greenhouse gasses, the terrestrial greenhouse would collapse, plunging the global climate into an icebound Earth state.” Lacis, et al. 2010. Atmospheric CO2: principal control knob governing Earth’s temperature. Science 330:356-359. Carbon emissions have increased exponentially since dawn of industrial revolution… http://upload.wikimedia.org/wikipedia/commons/5/56/Global_Carbon_Emission_by_Type.png ...increasing atmospheric CO2 from 280 ppm in 1800 to 386 ppm today http://www.bom.gov.au/info/climate/change/gallery/images/25.jpg Geological Carbon vs. Ecological Carbon Geological carbon: as fossilized carbon that has been locked in the Earth for millions of years (e.g. coal, oil) is extracted and burned, concentration of atmospheric CO2 increases. Ecological carbon: carbon that is continually recycled between the atmosphere and living organisms (e.g. photosynthesis, respiration, firewood, biofuels) remains in equilibrium and has no effect on atmospheric CO2 concentration (exception: wide scale deforestation). http://www.apartmenttherapy.com vs. http://img.alibaba.com http://www.globalwarmingart.com Recent advances in paleoclimate: Glaciers, bore holes, tree rings, stalactites, coral, and fossils hold ancient records of: • Temperature • CO2 • Glacial cycles • Solar radiation • Volcanic activity • Precipitation • Wind and ocean currents http://www.aad.gov.au/asset/images/525_ul-core.jpg Leading to greatly increased understanding of long- and short-term climate drivers: • • • • • • Continental drift Earth’s orbit / rotation Solar radiation / sunspots Volcanic activity Greenhouse gasses Air pollution Earth’s temperature over 10 million years http://www.bom.gov.au/info/climate/change/gallery/images/51.jpg http://www.emporia.edu/earthsci/student/tinsley1/drilling.jpg Nature 429, 623-628 (10 June 2004). CO2 is at highest level in 650,000 years, and rising R.A. Rhohde, www.globalwarmingart.com Temperature and CO2 have been tightly linked across eight ice ages http://p6.hostingprod.com/@treks.org/arctic_800px-co2-temperature-plot.gif Why do ice ages occur every 100,000 years? http://members.aol.com/scipioiv/globice.jpg Predictable variation in Earth’s orbit, wobble, and tilt (Milankovic Cycles) change the amount of solar radiation intercepted by Earth (solar forcing). Eccentricity: 100K yrs Obliquity: 41K years Precession: 20K years Milankovic Cycles generate ice ages every 100,000 years that last 80,000 years http://math.ucr.edu/home/baez/Milankovitch_Variations.png Bintanja and van de Wal. 2008. North American ice-sheet dynamics and the onset of 100,000-year glacial cycles. Nature 454:869-872 Earth should now be cooling gradually… http://images.allposters.com/images/102/039_ice_age_2sided.jpg …and it was for 1000 years, until very recently. http://math.ucr.edu/home/baez/temperature/1000.gif But solar forcing due to Milankovic Cycles is not strong enough to fully drive glacial cycles. There must be feedbacks that amplify or dampen solar forcing and accelerate climate change. • CO2 • Water vapor • Albedo (reflectance) • Clouds http://sitemaker.umich.edu/section2_group1/files/secondfeedback.jpg Feedbacks as solar forcing warms Earth: Decomposition releases greenhouse gasses: melting permafrost releases huge amounts of CO2 and methane. Oceans absorb less CO2: oceans saturate and more CO2 remains in the atmosphere. Humidity increases: water vapor is the most powerful greenhouse gas. Ice melts and white becomes dark: radiation that was reflected to space is now absorbed as heat. Positive Feedback: Temperature and CO2 http://p6.hostingprod.com/@treks.org/arctic_800px-co2-temperature-plot.gif Feedbacks as solar forcing warms Earth: Humidity increases: water vapor is the most powerful greenhouse gas. Decomposition releases greenhouse gasses: melting permafrost releases huge amounts of CO2 and methane. Oceans absorb less CO2: oceans saturate and more CO2 remains in the atmosphere. Ice melts and white becomes dark: radiation that was reflected to space is now absorbed as heat. Recent paradigm shift: paleoclimate studies reveals sudden, not gradual, climate change. L.G. Thompson et al. 2006. Evidence of abrupt tropical climate change: past and present. Proc. Natl. Acad. Sci. USA 103:10536-10543. Is there a “tipping point” beyond which feedbacks generate unstoppable warming even if CO2 emissions stabilize? www.motherjones.com/ As the number of studies on climate have increased exponentially, so has the level of understanding: Temperature and sea level forecasts have been continually revised upward. Previous projections of increased warming (2-6 ºF) and sea level rise (3 feet) by the end of this century are now considered too conservative. Global warming is altering ecosystems Fish move north http://news.nationalgeographic.com Plant and animal life cycles change Corals bleach Hoegh-Guldberg, O. 1999. Climate change, coral bleaching and the future of the world's coral reefs. Marine and Freshwater Research 50:839–866. “Global warming is the main cause of a significant intensification in the North Atlantic Subtropical High (NASH) that in recent decades has more than doubled the frequency of abnormally wet or dry summer weather in the southeastern United States.” Li et al. (2011) J Climate 24:1499-1506. Fire: more frequent and more intense Since 2000: 6 worst wildfire years on record. Since 2002: Acreage burned is 211% higher than 48 year average. San Diego Montana John McColgan, BLM Alaska Fire Service © 2004 San Diego State University Foundation Westerling et al. 2006. Warming and earlier spring increase western US forest wildfire activity. Science 313:940-943 The largest recorded bark beetle outbreak in human history in northern British Columbia where winters used to be too cold for the beetles to survive. http://www.for.gov.bc.ca/hfp Dezene Huber, UNBC http://www.garna.org/ Kurz et al. 2008. Mountain pine beetle and carbon feedback to climate change. Nature 452:987-990. Sea level is rising: 20 cm in the last century R.A. Rhohde, www.globalwarmingart.com Recent sea-level contributions of the Antarctic and Greenland ice sheets. 2007. Science 315:15291532. Antarctica 2002-2005: Lost 31 cubic miles of ice. Greenland 2003-2005: Lost 27 cubic miles of ice. Contribution to sea level rise: 0.35 mm / yr NASA / German Aerospace Center Gravity Recovery and Climate Experiment (GRACE) Greenland ice mass losses continue to accelerate. ADAPTED FROM ISABELLA VELICOGNA, GEOPHYSICAL RESEARCH LETTERS Similar patterns in Antarctica are accelerating the rate of sea level rise 5% per year. Science (2009) 326:217 http://www.globalwarmingart.com Extreme events: Increased frequency of heavy precipitation and heat waves. Number of strong (class 4-5) hurricanes has doubled. Webster, et al. 2005. Changes in tropical cyclone number, duration, and intensity in a warming environment. Science 309:1844-1846. Hurricane Katrina was a Category 1 storm before entering record warm Gulf waters A Class 5 Hurricane Long-term correlation between cyclone frequency and tropical Atlantic warmth. Mann et al. (2009) Atlantic hurricanes and climate over the past 1,500 years. Nature 460:880-883. NASA, http://visibleearth.nasa.gov/ Is the sun is responsible for recent warming? There is no relationship between solar activity and recent warming. “Variations measured from satellites since 1978 are too small to have contributed appreciably to accelerated warming over the past 30 years.” http://data.giss.nasa.gov/ Foukal et al. 2006. Variations in solar luminosity and their effect on the Earth’s climate. Nature 443:161-166 Since satellite measurements began in 1979, no relationship between solar irradiance and warming http://www.realclimate.org/images//T_vs_solar.png Since 1970, no relationship between solar activity and warming Max Planck Institute for Solar System Research www.mps.mpg.de/en/projekte/sun-climate/ No artifacts from urban heat islands (urban and rural areas warming at same rate) Peterson, TC. 2003. Assessment of urban versus surface temperatures in the US: no difference found. J. of Climate 16: 2941-2959. Alternative hypotheses considered and rejected by IPCC and NAS: • Earth’s orbit / rotation: slight cooling effect. • Solar activity: atmosphere is warming from bottom up, not top down. • Ocean vents: ocean is warming from surface down, not bottom up. • Volcanic activity: Pinatubo eruption had short-term cooling effect. • Air pollution: global dimming caused by sulfate aerosols has cooling effect (but is relaxing); however black soot is having significant warming effect. No volcanic signature on atmospheric CO2 concentration Internal climate variability: cooling effects of volcanic eruptions and La Niña; warming effects of El Niño http://data.giss.nasa.gov/gistemp/2011 Predicting future climate: General Circulation Models www.usgcrp.gov Compare to reality Develop Model Generate predictions Revise model Models accurately reconstruct past climate only when they incorporate both natural and human influences Modeled Global Mean Surface Temperature natural forcing human forcing natural & human http://www.grida.no/climate/ipcc_tar/wg1/007.htm#figspm4 Successful predictions of climate models (observations predicted to occur by models before the data were collected and/or inspected) 1. Surface warming but stratosphere cooling. 2. Energy imbalance between incoming sunlight and outgoing infrared radiation. 3. Cooler nights after planes (and their contrails) were grounded following 9/11. 4. Two years of global cooling caused by Pinatubo eruption. 5. Pattern of CO2 record in EPICA ice core (“The EPICA Challenge”). Climate sensitivity: amount of warming expected with doubling of atmospheric CO2: 3°C with likely range of 2.0 – 4.5°C (3.6 – 8.1 °F) Knutti, R. & G.C. Hegerl. 2008. The equilibrium sensitivity of the Earth’s temperature to radiation changes. Nature Geoscience 1:735-743. Climate models have underestimated recent increase in rate of warming and sea level rise. Rahmstorf et al. 2007. Recent climate observations compared to projections. Science 316:709. Largest uncertainty in models: • climate feedbacks, especially clouds • human behavior (how will CO2 emissions change?) Patterns of Regional Warming in the US NOAA National Climatic Data Center Projected Climate Change Scenario for Ohio Projected Impacts of Climate Change Knuttie & Hegerl (2008) Nature Geoscience 1:735-743 Projected Impacts of Climate Change (IPCC TAR) Business as usual Best case scenario http://www.globalwarmingart.com Each “wedge” reduces CO2 emissions 1 billion tons over 50 yrs. 7 “wedges” to stabilize emissions: 525 ppm CO2, +5.4°F (status quo = 850 ppm, +9°F) • • • • • • • • • • • • • Efficient vehicles: increase mpg from 30 to 60 (2 billion cars) Drive less: from 10,000 to 5,000 miles / yr (for 30 mpg car) Increase efficiency of buildings and appliances by 25% Double efficiency of coal plants Replace 1400 coal plants with natural gas (4X increase) Capture CO2 at power plants (800 coal or 1600 gas) Increase nuclear 2X to replace coal Increase wind 50X to replace coal Increase solar 700X to replace coal Increase wind 100X to produce H2 for cars Increase biofuels 150X (using 1/6 of Earth’s cropland) Stop all deforestation, 2X tree planting Conservation tillage on all crop land (10X current) Pacala & Socolow. 2004. Stabilization wedges: solving the climate problem for the next 50 years with current technologies. Science 305:968-972. CO2 mitigation scenarios for next 50 years: 1. Maintain current rate of emissions increase: 800 ppm, +9°F 2. • • • • • Hold emissions at today’s rate: 525 ppm, +5.4°F Double fuel economy; halve number of miles driven. 25% more efficient heating, cooling, lighting, appliances. 50% more efficient coal-fired plants. Capture and store CO2 generated by power plants. Replace 1400 coal plants with natural gas. 3. Reduce emissions by 50%: 450 ppm, +3.6°F • All of the above but with complete elimination of coal. • Increase nuclear 3X, biofuels 50X, solar 700X. • Increase wind 50X to generate hydrogen for fuel-cell cars. • Stop all deforestation. Adapted from Pacala & Socolow. 2004. Science 305:968-972. Since 2004, the number of wedges needed to stabilize climate has increased from 7 to 9 R Socolow (2011) Wedges reaffirmed. Bull Atom Sci http://www.thebulletin.org/web-edition/features/wedges-reaffirmed Key scientific questions: 1. Is Earth warming? yes 2. If so, what is the cause? primarily, anthropogenic greenhouse gasses Inescapable conclusion: Convergence of thousands of independent studies from many disciplines provides overwhelming evidence that: • global warming is underway. • it is caused by humans. • future warming and sea level rise is inevitable. Rejecting anthropogenic global warming represents support for the hypothesis that CO2 can increase dramatically without warming Earth, and that the ancient link between CO2 and temperature can somehow be uncoupled. No evidence has emerged to support this hypothesis. Acknowledgements: Dr. Lonnie Thompson, Byrd Polar Research Center, The Ohio State University Dr. Matt Ayres, Dartmouth College Dr. Lyn Loveless, College of Wooster Climate Science Websites Intergovernmental Panel on Climate Change www.ipcc.ch US Global Change Research Program: http://www.usgcrp.gov/usgcrp/ National Academy of Sciences Review of IPCC: http://www.nap.edu/openbook.php?record_id=10139 Real Climate: climate science blog by climate scientists www.realclimate.org Ethical implications: statement of US Catholic Bishops “Global Climate Change: A Plea for Dialogue, Prudence, and the Common Good” http://www.usccb.org/sdwp/international/globalclimate.shtml