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Science of Human-Induced Climate Change Joseph P. Straley Paul Vincelli University of Kentucky [email protected] [email protected] 3-5 PM Friday, November 1 Session 58 Patterson D The Physics of Global Warming Joseph P. Straley Department of Physics & Astronomy University of Kentucky [email protected] Why climate change is interesting *It’s going to happen to you. *It’s part of the new science standards. Why climate change belongs in the new science curriculum *It’s an example of how science works. Exactly because it’s controversial, we can experience science as a process, rather than a compilation of facts. *Understanding the climate change theory involves many science concepts. The Method of Science • Collect facts • Look for patterns and explanations that unite the facts. The best explanation is called The Theory • The Theory usually implies effects that haven’t been noticed. Look for these effects. • If they are found, add them to the list of facts • Repeat from step 1! Fact: it gets cold at night. The temperature steadily decreases at night. Why? Bertie says, “Because X X XtheXsunXis not X shining.” X X Carla objects, “But it isn’t cold in a closet!” The leaky bucket model The water corresponds to the energy coming from the sun. Energy (and water) are “conserved.” The water level corresponds to the temperature It goes up during the day. It goes down at night. The temperature goes up during the day, and decreases at night The leaky bucket model What are the leaks? Where does the energy go? Physics news: All objects emit light • • • • Sufficiently hot objects glow – Red hot == 500 C Yellow hot == 1000 C White hot (like the sun) == 6000 C • Near room temperature the emission is not visible (infrared light), and low power Stefan-Boltzmann Law The power radiated per square meter at Kelvin temperature T is At T = 300 K (room temperature), J = 460 Watt/m2 The temperature of the earth Energy comes from the sun in the form of visible light All of this energy is reemitted, so that the energy of the earth stays the same from day to day. Both input and output are nearly constant in time. This determines the average temperature of the earth The temperature of the earth Energy comes from the sun in the form of visible light, and leaves in the form of infrared light.. This determines the average temperature of the earth Any questions? The temperature of the earth There’s a problem with the theory: The power from the sun averages to 235 W/m2, but the power radiated should be 460 W/m2. The theory predicts that the earth should be much colder than it is (0 F instead of 55 F). This means that something is a blocking some of the leaks. What is plugging the leaks? • The atmosphere is transparent in the visible, but not in the infrared. This is due to the presence of “greenhouse gases”: Greenhouse effect Greenhouse gases • Water vapor -- 2/3 of the effect • Carbon dioxide (CO2) -- 1/4 • Methane and other gases -- 1/10 http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png Any questions? Where does our energy come from? … from burning fossil fuels. What happens to the CO2? Theory: It gets stored in various reservoirs: • • • • • The atmosphere Ocean surface water Plants Deep ocean 500 year time scale Mineralization Really slow Reservoirs for CO2 • The atmosphere • Ocean surface water • Plants The atmosphere and the ocean surface water are closely coupled: CO2 freely moves among them, and is shared in a fixed proportion. Plants are not a long-term storage. Implication of the theory The CO2 content of the atmosphere is cumulative of all burning of fossil fuels. It is a permanent change (on a 500-year time scale). The amount of CO2 in the atmosphere should be steadily rising, and this will continue as long as we continue to burn fossil fuels. Increasing carbon dioxide Did humans cause the increase? It seems likely. We know how much coal and oil we burn in a year (the equivalent of 10 billion tons of coal) and we know how much CO2 there is in the atmosphere. The CO2 concentration would be increasing by 3.3 parts per million per year if it all stayed in the atmosphere. Did humans cause the increase? It seems likely. We know how much coal and oil we burn in a year. Any questions? Greenhouse gases, again • Water evaporates from the ocean, and comes down as rain. The concentration in the atmosphere doesn’t change. • Methane doesn’t last very long. • Carbon dioxide keeps the earth warm. • CO2 is accumulating in the environment. This should cause the earth to get warmer (another theory!). Is the temperature increasing? Can we calculate the effect of CO2 on the temperature of the earth? This is hard, because of feedback effects. • Increasing temperature more water vapor • Increasing water vapor more clouds • Increasing temperature less snow and ice • Increasing temperature more CO2 The temperature rise is small, because CO2 is only a small part of the atmosphere, and the CO2 concentration hasn’t increased much … yet. Overlaying two graphs Apparently, the earth is getting warmer It amounts to about 2 Fahrenheit degrees over the last century. However, the theory says that increasing CO2 concentration in the atmosphere is inevitable and permanent, and that this should lead to a permanent temperature rise. It is a distant but unstoppable problem for our descendants. History of the earth’s temperature Summary • The earth has definitely gotten warmer in the last century • The increase in carbon dioxide in the atmosphere is the likely cause; this theory implies that the temperature will continue to go up in the future. • We need to agree that there might be a problem, discuss the implications, and develop a plan. Any questions? • The earth has definitely gotten warmer in the last century • The increase in carbon dioxide in the atmosphere is the likely cause; this theory implies that the temperature will continue to go up in the future. • We need discuss the implications and develop a plan At The Half… Paul Vincelli Extension Professor and Provost’s Distinguished Service Professor Draft US National Climate Assessment, 2013 Dessler and Parson, 2010 Dessler and Parson, 2010 Climate change from perspective of geological time End of last glaciation Today=CO2 is off the chart Temperature Red=Antarctic temp Blue=global temp Yellow dots=CO2 Shakun et al, 2012. Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation. Nature 484:49-55. Present-day impacts Ocean CO2 NASA Observed global mean sea level (from tide gauges) In geologic past, sea level changed 10-20 m for every 1°C. (Archer, 2012, Global Warming. J. Wiley. Cazenave and Llovel. 2010. Contemporary Sea Level Rise. Annu. Rev. Mar. Sci. 2:145–73 Cryosphere: Sea ice vs. ice sheets vs. glaciers Glacier Continental ice sheet (http://www.solcomhouse.com/icecap.htm) Sea ice (at right) (http://fac-staff.seattleu.edu/gualtieri/web/images/sea_ice.jpg) (http://www.usgs.gov/images/topical/glac iers/dsc00035.jpg Glaciers Muir Glacier, photographed by W. O. Field in August 1941 and B. F. Molnia in August 2004. — Image Credit: NSIDC Glacier Photo Collection. Arctic sea ice A NASA image shows how the record-low Arctic sea ice extent compares with the average minimum extent over the past 30 years, in yellow. Ian Joughin, University of Washington Acceleration on both land masses confirmed: http://bit.ly/TvxEZl Melting permafrost http://soils.cals.uidaho.edu/soilorders/gelisols_09.htm Global atmospheric moisture http://ngm.nationalgeographic.com/2012/09/extreme-weather/data-charts Heat waves in USA http://ngm.nationalgeographic.com/2012/09/extreme-weather/data-charts Extreme rainfalls http://ngm.nationalgeographic.com/2012/09/extreme-weather/data-charts Departure from average (days) Length of growing season Climate Change Indicators in the USA, EPA Report, 2012 Changes in USDA Plant Hardiness Zones Impact of climate trends on corn yield, 1980-2008 Climate Trends and Global Crop Production Since 1980, Science 333:616, 2011 Southern diseases moving northward Bacteria streaming from vascular tissue of root Example of outbreak of southern bacterial wilt http://www.cals.ncsu.edu/course/pp728/Ralstonia/Tomato_bacterial_wilt_symptoms.html Snowpack Climate Change Indicators in the USA, EPA Report, 2012 Projections All models show increasing temp Models show increasing uncertainty IPCC 2007 Atmospheric CO2 responds slowly Soloman et al, 2009. Irreversible climate change due to carbon dioxide emissions. PNAS 106:1704 Global cooling responds even more slowly than CO2 Soloman et al, 2009. Irreversible climate change due to carbon dioxide emissions. PNAS 106:1704 Sea level continues to rise well after cessation of CO2 emissions Soloman et al, 2009. Irreversible climate change due to carbon dioxide emissions. PNAS 106:1704 How fast will warming happen? Some key uncertainties How much GHGs will human emit? Cloud feedbacks Clouds and global warming High clouds trap heat Image at left: NASA Image at right: weather.ou.edu Low clouds reflect sunlight Modeling cloud behavior is difficult. How fast will warming happen? Some key uncertainties How much GHGs will human emit? Cloud feedbacks Equilibrium climate sensitivity (1.5-4.5°C) https://twitter.com/skepticscience/status/358062079959265280/photo/1 How fast will warming happen? Some key uncertainties How much GHGs will human emit? Cloud feedbacks Equilibrium climate sensitivity (1.5-4.5°C) Aerosols Can the oceans buffer the warming fast enough? CO2 www.pa.uky.edu/sciworks/climatechange