CEE 3510 Environmental Quality Engineering

Transcription

1 CEE 3510 Environmental Quality Engineering

2 What Is Global Warming? An increasing trend in global temperature over the past century Presumably because of an increase of greenhouse gases in the atmosphere

3 How Does It Work? Greenhouse effect (a natural phenomenon) Solar radiation 30% is reflected by earth and atmosphere back into space The rest absorbed by earth s surface, warming it Infrared radiation is released from earth s surface Some escapes into space Some absorbed and scattered by certain gases in atmosphere, further warming earth s surface and lower atmosphere Earth s temperature would be much lower without it (i.e., -19 o C vs, 15 o C)

4 Greenhouse Gases Able to absorb infrared energy emitted by the earth s surface. Naturally occurring Water vapor, CO 2, CH 4, N 2 O, and O 3 Unnatural Chloroflourocarbons (CFC) [Ex. CF12(CF 2 Cl 2 ) and CF11(CFCl 3 )] Hydroflourocarbons (HFC) [Ex. tetraflouroethane (C 2 H 2 F 4 )] Perflourocarbons (PFC) [Ex. tetraflouromethane (CF 4 ) or hexaflouroethane (C 2 F 6 )] Hydrochloroflourocarbons (HCFC) [Ex. chlorodiflouromethane (CHClF 2 )] Sulfur hexaflouride (SF 6 )

5 Greenhouse Gases Water vapor - most abundant greenhouse gas 98% of emissions are natural (only 2% from human activities) Water vapor at high altitude (i.e., contrails from jets) can have a significant warming effect.

6 Carbon Dioxide (CO 2 ) Accounts for 50-60% of global warming since preindustrial times Preindustrial concentration ~280 ppm Current concentration ~390 ppm Sources Combustion of fossil fuels (coal, oil, gas, wood) Plant and animal respiration 10X greater than emissions from human activities Sinks Absorbed by oceans Utilized in plant photosynthesis

7 Methane (CH 4 ) Sources 2/3 from human activities (cattle farming, rice paddies, landfills, oil & gas production, coal mining) 1/3 from natural processes (wetlands & termites) Reflects 21x more radiation than CO 2 per molecule Present in concentrations 2 orders of magnitude less than CO 2

8 Nitrous Oxide (N 2 O) Sources Primarily human activities (burning wood, use of nitrogen fertilizers, some industrial processes) Traps 270X more radiation than CO 2 per molecule Present in concentrations 3 orders of magnitude less than CO 2

9 Synthetic Gases Emitted from various industrial processes Aluminum smelting Semiconductor manufacture SF 6 used in electrical transmission systems HFCs and PFCs used as substitutes for CFCs, which deplete the ozone layer Industrial applications Refrigeration, air conditioning, coatings, paints, and aerosols Most potent greenhouse gases Ex. CFCs trap ~2000X as much heat per molecule as CO 2

10 Dip attributed to recession + switch to from coal to natural gas for power.

11 The U.S. was the world s largest green-house gas emitter until 2006 when China took the lead. Source: US EPA

12 Soot is also warming the atmosphere 8 million tons/ yr. produced by burning coal, oil, etc. Soot adsorbs sunlight, shrinks cloud droplets (brightening clouds) and darkens ice and snow. One study puts soot 2 nd behind CO 2 as a warming agent [see Science (2013) V 339, p 382] Not all soot is created equal Coal burning releases soot but also releases sulfur that reflects sunlight back to space. Forest and brush fires produce soot but also produce microscopic bits of unburned organic carbon that can brighten clouds. Soot from diesel engines is at the top of the list for a preventable source of global warming.

13 What Are the Possible Effects? Increase in global temperature Rising sea level Ocean expansion due to increased temperature Melting of mountain glaciers and polar ice sheets Increased evaporation and precipitation Increased frequency and severity of storms Long term impact on human health, agriculture, water resources, forests, wildlife, and costal areas

14 Evidence? Concentration of greenhouse gases have increased since the industrial revolution. CO 2 : 30% CH 4 : 100% N 2 O: 15% Scientists generally agree that the cause of this increase is human activity.

15 More Evidence Over the last century Global temperature: ºF Global sea level: 4-10 inches Global precipitation: 1% Reported in Nature Aug, 2004 The timing of the seasonal abundance of plankton in the northeastern Pacific has shifted over the past 45 years. Each species has an annual cycle with herbivore growth preceding a bloom in carnivores but the cycle peaks have shifted out of synch. In places where water has warmed phytoplankton (plants) peak occurs 3 weeks earlier but zooplankton (predators) peak only 10 days earlier. Result: predators may go hungry and provide less prey for fish larvae, changing the whole North Atlantic ecology.

16 SHRINKING ICE Decades of airborne laser measurements, orbiting radar, and satellites that measure ice mass by its gravitational pull all show that both Greenland and Antarctica have been rapidly losing ice over the past 5 to 10 years. Sea ice could disappear by Arctic sea ice has shrunk 7.4%/10 yr. since Current sea level rise 0.1 m/100 yr. but the rate could increase by 10x. Inundation of low-lying coasts (ex. New Orleans) could occur within 200 yr. vs. the 1000 s previously projected. Loss of ice = loss of habitat for polar bears The U.S. Fish and Wildlife service is considering protection of polar bears under the endangered species act.

17 Arctic sea ice appears to have reached a record low wintertime maximum extent on March 7, 2017 according to scientists at NASA.

18 Algae detritus and melt water darken Greenland s ice, accelerating surface melt. This has doubled Greenland s contribution to global sea level rise since If all the ice covering Antarctica, Greenland, and in mountain glaciers around the world were to melt, sea level would rise about 70 meters (230 feet). The ocean would then cover all coastal cities. Source: Science 24 Feb. 2017

19 UN Panel conclusions (Feb. 2, 2007) Global warming is unequivocal (90% certainty) and human activities are the major factor responsible.. Global temperature anomalies averaged from 2008 through Source: Chemical and Engineering News Jan. 21, 2013

20 Predictions for 2100 Temperature: 2007 UN Panel report est. 1.8 to 4 o C Sea level: 2-feet CO 2 emissions: 2 to 7 times more than the increase over the past century

21 What Are the Uncertainties? Natural climatic variations Our ability to quantify the human influence on global climate is currently limited because the expected signal is still emerging from the noise of natural variability (Intergovernmental Panel on Climate Change) Amount and intensity of sun s energy Cooling effects of pollutant aerosols (e.g. sulfates) Cloud response to changes in temperature and precipitation

22 More Uncertainties Ocean heat transport mechanisms Effect of intense weather events (e.g. hurricanes) on climate and vice versa Lack of a good crystal ball demographics/population growth economics technological advances industrial production policy

23 What Can We Do? Decrease energy usage Develop alternative sources of energy Burning of fossil fuels contributes 98% of the CO 2, 24% CH 4, and 18% of the N 2 O emitted to the atmosphere by human activities Decrease deforestation Depletes a major sink for CO 2 Often land is utilized for agriculture Reduce, Reuse, Recycle Change policy Kyoto Summit Required industrialized countries to reduce greenhouse emissions by ~5% below 1990 levels by 2012 Russia signed on in U.S. did not sign Copenhagen Summit U.S. and People's Republic of China, the world's top two carbon dioxide emitters, joined forces to stymie every attempt made in the summit to reach an agreement.

24 Finally the US acts to prevent climate change, but then reverses course. The Paris agreement on climate change was negotiated by representatives of 195 countries in In 2015 President Obama and President Xi Jinping of China formally committed to the Paris climate agreement. President Obama issued an Executive Order in March 2015 to cut the Federal Government s greenhouse gas emissions 40 percent over the next decade, relative to 2008 levels. President Trump signed an Energy Independence executive order March 2017 eliminating many of former President Barack Obama s key climate change policies.

25 Decreasing emissions is not enough! Decreasing CO 2 emissions only slows the rate of warming. If we want to limit the atmosphere to a doubling of the pre-industrial CO 2 then there is a fixed amount of fossil carbon we can burn ( 720 gigatons). If we divide this fixed amount of carbon combustion by the world s population, then the rich nations share is 150 gigatons. At the 2007 rich nation consumption rate (6 gigatons/yr.), we will have burnt our share in 25 years. (ref. Science vol. 315, p. 1371, 2007). Ultimately we are going to need to find a way to remove as much carbon as we release to keep CO 2 constant.

26 Wedging our way to a solution In 2004 stabilization wedges were proposed as a solution to global warming. A wedge was defined as an intensive campaign to prevent 25 billion tons of CO 2 emissions by focusing on a topic such as building a fleet of nuclear reactors or stopping tropical deforestation. 7 wedges were needed in wedges needed in 2010 because of increased emissions 12 more wedges needed if we don t cut emissions as forecast 10 more wedges needed to phase out emissions

27 Global warming is changing the oceans. The ocean has absorbed an estimated 118 billion metric tons of carbon dioxide since the onset of the Industrial Revolution. 20 to 25 tons of CO 2 are being added to the atmosphere daily, and increasing levels of dissolved CO 2 are changing the ph balance of the oceans. Shells, and coral dissolve within 48 hours when exposed to the oceanic acidity expected by Measurements indicate circulation of warm ocean into northern Europe slowed by 1/3 between 1957 and 2004 causing fear of a shutdown and cataclysmic climate change.

28 It can happen! Carbon isotope data from protozoa in ocean sediments indicate that ocean circulation stopped or abruptly slowed 100,000 years ago when the world was only a bit warmer than today*. If this happed today, the loss of the southward bottom flow in the North Atlantic could increase sea level rise by an additional meter. Isotopically distinctive North Atlantic Deep Water (orange) hugs the bottom of the North Atlantic as it moves to the Southern Hemisphere. *Science (2014) 343, p 831

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