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Ch 4. The three modern global change problems. 1 Earth has been changing and will continue to do so. It is changing faster today than it ever has. The major reason is human activity. 1. Ozone depletion; Ozone hole in South 2. 3. Pole deforestation; Greenhouse gases and global warming 2 • Ozone source: O and O2 makes it through chemical process. Location: in middle-layer atmosphere (stratosphere). roles: absorb ultraviolet radiation from Sun. 3 Vertical Structure of the Atmosphere 4 distinct layers determined by the change of temperature with height 4 • Ozone depletion describes two distinct, but related observations: (1) a slow, steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere (ozone layer) since the late 1970s, (2) a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. 5 • Ozone ( O ) is a form of oxygen, and protects the earth’s surface from Sun’s harmful ultraviolet radiation. Ozone depletion is the result of a complex set of circumstances and chemistry . 3 • • Antarctic Ozone Levels in Fall 2003 The ozone hole is represented by the purple, red, burgundy, and gray areas that appeared over Antarctica in the fall of 2003. The ozone hole is defined as the area having less than 220 Dobson units (DU) of ozone in the overhead column (i.e., between the ground and space). 6 Image of the largest Antarctic ozone hole ever recorded (September 2006). 7 Ozone over Antarctic during Oct. 8 • Mean total ozone over Antarctica during the month of October 9 It shows a sharp drop beginning in the early 1970s. The graph to the left shows longterm ozone levels over Arosa, Switzerland. Although ozone levels rise and fall in natural cycles, the average level remained constant from 1926 until 1973. Beginning in 1973, however, and continuing through 2001, ozone levels have dropped at a rate of 2.3 percent / decade. 10 Too much ultra-violet light can result in: • • • • Skin cancer Eye damage such as cataracts Immune system damage Reduction in phytoplankton in the oceans that forms the basis of all marine food chains including those in Antarctica. • Damage to the DNA in various life-forms. So far this has been as observed in Antarctic ice-fish that lack pigments to shield them from the ultraviolet light (they've never needed them before) • Probably other things too that we don't know about at the moment. 11 12 Global warming is the serious problem because: • It affects the greatest number of people • Migration of marine animals could result • Rising sea level could result • Cold climate species might die • Ozone depletion and deforestation are both confined to particular areas whereas global warming is truly global 13 Global warming is the serious problem because: • It affects the greatest number of people • Migration of marine animals could result • Rising sea level could result • Cold climate species might die • Ozone depletion and deforestation are both confined to particular areas whereas global warming is truly global 14 Why does a ozone hole form over Antarctica? The ozone hole is caused by the effect of pollutants in the atmosphere destroying stratospheric ozone. During the Antarctic winter something special happens to the Antarctic weather. • • Firstly, strong winds blowing around the continent form, this is known as the "polar vortex" - this isolates the air over Antarctica from the rest of the world. Secondly, clouds form called Polar Stratospheric Clouds. Clouds turn out to have the effect of concentrating the pollutants that break down the ozone, so speeding the process up. 15 Deforestation 16 Deforestation affects Carbon balance Hydrological cycle Radiative energy balance Biodiversity 17 Statistics It has been estimated that about half of the earth's mature tropical forests — between 7.5 million and 8 million km2 of the original 15 million to 16 million km2 , have now been cleared since 1947. North America and Europe – already done 85% of old growth forests in US destroyed by settlers – most replanted Parts of Pacific NW and Alaska – deforesting now as fast as Brazil Canada: One case of deforestation in Canada is happening in Ontario's boreal forests, near Thunder Bay, where 28.9% of a 19,000 km² of forest area had been lost in the last 5 years and is threatening woodland caribou. This is happening mostly to supply pulp for the facial tissue industry. In Canada, less than 8% of the boreal forest is protected from development and more than 50% has been allocated to logging companies for cutting. 18 Tropical Rainforest Earth's most complex biome in terms of both structure and species diversity; abundant precipitation and year round warmth. Climate: Mean monthly temperatures are above 64°F; precipitation is often in excess of 100 inches a year. Vegetation: 100 to 120 feet tall canopy. Soil: infertile, deeply weathered and severely leached. Red color because of high iron and aluminum oxides. Fauna: Animal life is highly diverse Distribution of biome: 10°N and 10°S latitude. Neotropical (Amazonia into Central America), African (Zaire Basin with an outlier in West Africa; also eastern Madagascar), Indo-Malaysian (west coast of India, southeast Asia) 19 Tropics Rainforests 50 years ago covered 14% of the world's land surface and have been reduced to 6%, and that all tropical forests will be gone by the year 2090 Brazil – slash and burn; Amazon – 200% increase in deforested area from 1979 - 1988 Some scientists have predicted that unless significant measures (such as seeking out and protecting old growth forests that have not been disturbed) are taken on a worldwide basis, by 2030 there will only be ten percent remaining. 20 The problem Disappearing at a rate of tens of thousands of square miles per year Land clearing in developing countries for farming and ranching (e.g., Brazil) Wood as a fuel (e.g., 90% of Africans use wood as primary fuel) Ballooning populations in developing countries Loss of fauna associated with the forests Current extinction rate of 50,000 species per year Rate reflects fact that most fauna and flora in tropics are disappearing Loss of soil value for farming (formation of laterites) 21 Effects Lowered oxygen production levels Increased CO2 Changed climate (radiation, temperature) and hydrologic cycle Loss of flora and fauna Increased soil erosion (i.e., global erosion rate of 25.4 billion tons of top soil per year) Increased effects of floods, especially coastal (e.g., 10x increase in catastrophic floods in Bangladesh) Landslides Cycle (vicious circle): deforestation soil erosion and loss of wood materials lowered productivity of soil and loss of wood source increased human needs enhanced deforestation e.g., 40-50 million trees removed in Haiti each year – correlates with 7x increase in food aid over last 20 years 22 Global warming 23 24 25 `The balance of evidence suggests that there is a discernible human influence on global climate ' Intergovernmental Panel on Climate Change (United Nations), Second Assessment Report, 1996 26 `There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activity' Intergovernmental Panel on Climate Change (United Nations), Third Assessment Report, 2001 27 `Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations’ Intergovernmental Panel on Climate Change (United Nations), Fourth Assessment Report, 2007 28 Discovery of the Greenhouse Effect Joseph Fourier (1827) Recognized that gases in the atmosphere might trap the heat received from the Sun. James Tyndall (1859) Careful laboratory experiments demonstrated that several gases could trap infrared radiation. The most important was simple water vapor. Also effective was carbon dioxide, although in the atmosphere the gas is only a few parts in ten thousand. Svante Arrhenius (1896) Performed numerical calculations that suggested that doubling the amount of carbon dioxide in the atmosphere could raise global mean surface temperatures by 5-6°C. Guy Callender (1939) Argued that rising levels of carbon dioxide were responsible for measurable increases in Earth surface temperatures. Estimated that doubling the amount of CO2 in the atmosphere could raise global mean surface temperatures by 2°C. 29 30 31 32 33 GREENHOUSE EFFECT? Glass allows visible radiation to pass through the glass which absorbs thermal radiation and re-emits some of it back into the greenhouse --- like a radiation blanket. 34 Heat Transfer --- Convection • Less dense warm air moves upward and more dense cold air moves downward. Convection is the dominant process for transferring heat in the troposphere. 35 The distribution of temperature in a convective atmos.(red line). The green line shows how the temperature increases when the amount of CO2 present in atmos. is increased (in the diagram the difference between the lines is exaggerated). Also shown for the two cases are the average levels from which thermal radiation leaving the atmosphere originates (about 6km for the unperturbed atmosphere). 36 Radiation is emitted out to space by these gases from level somewhere near the top of the atmos. – typically from between 5 and 10km high. Here, temperature is much colder -30 – 50C or so colder than at the surface. => emitting less radiation to space. So: absorb radiation emitted from the earth surface but then to emit much less radiation out to space. 37 Component of the radiation (in watts per square meter) which on average enter and leave the earth’s atmos. and make up the radiation budget for the atmosphere. 38 The enhanced greenhouse effect F = T4 = 5.67 x 10-8 W/m2/K4 average levels from which thermal radiation leaving the atmosphere originates 39 Blackbody rad. curves for Sun & Earth max = const./T Temp. T in K const. = 2898 m 40 41 42 43 44 45 Planetary energy balance • Earth is at steady state: Energy emitted by Earth = Energy absorbed • E emitted = (area of Earth) Te4 = 4 Re2 Te4 ..(1) (Te= Earth’s effective rad. temp., Re= Earth’s radius) • E absorbed = E intercepted - E reflected • Solar E intercepted = S Re2 (solar flux S) • Solar E reflected = AS Re2 (albedo A) • E absorbed = (1-A) S Re2 • (1) => 4 Re2 Te4 = (1-A) S Re2 46 Magnitude of greenhouse effect • Te4 = (1-A) S/4 • Te = [(1-A) S/(4 )]1/4 (i.e. fourth root) • Te = 255K = -18°C, very cold! • Observ. mean surf. temp. Ts = 288K = 15°C • Earth’s atm. acts as greenhouse, trapping outgoing rad. • Ts - Te = Tg, the greenhouse effect • Tg = 33°C 47 Greenhouse effect of a 1-layer atm. •Energy balance at Earth’s surface: Ts4 = (1-A)S/4 + Te4 ..(1) •Energy balance for atm.: Ts4 = 2 Te4 .. (2) S/4 Te AS/4 Te4 Atm. (1-A)S/4 Ts Ts4 Te4 Earth 48 Subst. (2) into (1): Te4 = (1-A)S/4 ..(3) (same eq. as in last lec.) Divide (2) by ; take 4th root: Ts = 21/4 Te = 1.19 Te For Te = 255K, Ts = 303K. (Observ. Ts = 288K) Tg = Ts - Te = 48K, 15K higher than actual value. • Overestimation: atm. is not perfectly absorbing all IR rad. from Earth’s surface. 49 • Weather forecasting also uses atm. GCMs. Assimilate observ. data into model. Advance model into future => forecasts. • Simpler: 1-D (vertical direction) radiativeconvective model (RCM): Doubling atm. CO2 => +1.2°C in ave.sfc.T • Need to incorporate climate feedbacks: • water vapour feedback • snow & ice albedo feedback • IR flux/Temp. feedback • cloud feedback 50 Water vapour feedback • If Ts incr., more evap. => more water vapour => more greenhouse gas => Ts incr. • If Ts decr., water vap. condenses out => less greenhouse gas => Ts decr. • Feedback factor f = 2. • From RCM: T0 = 1.2°C (without feedback) => Teq = f T0 = 2.4°C. Ts (+) Atm. H2O Greenhouse effect 51 Snow & ice albedo feedback • If Ts incr. => less snow & ice => decr. planetary albedo => Ts incr. snow & ice cover Ts (+) planetary albedo 52 IR flux/Temp. feedback • So far only +ve feedbacks => unstable. • Neg. feedback: If Ts incr. => more IR rad. from Earth’s sfc. => decr. Ts Ts (-) Outgoing IR flux •But this feedback loop can be overwhelmed if Ts is high & lots of water vap. around => water vap. blocks outgoing IR => runaway greenhouse (e.g. Venus) 53 Climatic effects of clouds • Without clouds, Earths’ albedo drops from 0.3 to 0.1. By reflecting solar rad., clouds cool Earth. • But clouds absorb IR radiation from Earth’s surface (greenhouse effect) => warms Earth. • Cirrus clouds: ice crystals let solar rad. thru, but absorbs IR rad. from Earth’s sfc. => warm Earth • Low level clouds (e.g. stratus): reflects solar rad. & absorbs IR => net cooling of Earth 54 • IR rad. from clouds at T4 • High clouds has much lower T than low clouds => high clouds radiate much less to space than low clouds. => high clouds much stronger greenhouse effect. 55 Uncertainties in cloud feedback • Incr. Ts => more evap. => more clouds • But clouds occur when air is ascending, not when air is descending. If area of ascending/descending air stays const. => area of cloud cover const. • High clouds or low clouds? High clouds warm while low clouds cool the Earth. • GCM’s resolution too coarse to resolve clouds => need to “parameterize” (ie. approx.) clouds. • GCM => incr. Ts => more cirrus clouds => warming => positive feedback. => Teq = 2 -5°C for CO2 doubling 56 Greenhouse Gases Water Vapor: Carbon Dioxide (CO2) CH4 methane, N2O = nitrous oxide... NATURAL GREENHOUSE EFFECT 58 ENHANCED GREENHOUSE EFFECT 59 • Water Vapor: source: evaporation from Earth’s surface location: the lowest 5 km of the atmosphere residence time: 10 days variation range: 0.1% - 4% roles in atmosphere: source of moisture for cloud; absorber of energy emitted by Earth’s surface: greenhouse gas. 60 Water Vapor • Naturally occurring greenhouse gas, generally unaffected by humans. Importance: The Clausius-Clapeyron relationship (shown below) suggests that warmer air can hold more water vapor. As the planet warms due to the greenhouse effect, more water vapor will change global climate conditions. By solving for water vapor (e), we can see that temperature (T) increases the amount of water vapor. • Carbon Dioxide (CO2) source: plant and animal respiration, the decay of organic materials, and natural and anthropogenic (human-produced). Current concentration: 380ppm (parts per million, i.e., 0.04%); a global increase in recent decades. The increase in carbon dioxide (CO2) has contributed about 72% of the enhanced greenhouse effect to date, methane (CH4) about 21% and nitrous oxide (N2O) about 7%. 62 The “Carbon Cycle” There is a natural process by which carbon dioxide is cycled through the Earth's ecosystems and atmosphere. The blue arrows represent the natural processes by which living organisms emit and absorb carbon throughout their life and death (e.g. Respiration, photosynthesis, decomposition) The red arrows represent the “anthropogenic flux” which is a scientific term for the human effect on the carbon cycle, including industrialization and fossil fuel burning. • carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere of the Earth. • Four reservoirs of CO2: atmosphere, ocean, biosphere and sediments. • Carbon cycle modeling. Models of the carbon cycle can be incorporated into global climate models, so that the interactive response of the oceans and biosphere on future CO2 levels can be modeled. Such models typically show that there is a positive feedback between temperature and CO2. 64 • The land and ocean are large reservoirs to stock carbon than atmos. For example, the release of just 2% of the carbon stored in the oceans would double the amount of atmos. CO2. • At the time scales which we concern, CO2 is not destroyed but redistributed among the various carbon reservoirs. E.g., about 50% of an increase in atmos. CO2 will be removed within 30 years, a further 30% within a few centuries, and the remaining 20% may remain in the atmos. for many thousands of years. 65 The Human Footprint • 5% of the world's population resides in the United States, creating ¼ of the total greenhouse gas emissions. • For most people, their car is the main source of emissions. 22Lbs of CO2 is produced from every gallon of gas. Do the math: • Number of miles traveled by car each year __ , divide by average miles per gallon = __ gallons of gas, multiplied by 22 lbs CO2/gallon of gas = __ pounds of CO2 • The 1997 Kyoto protocol called for all people to limit their carbon emissions to 5.4 tons, or about 11,000 lbs, per year. • Some scientists believe that in order to reverse the damage caused by greenhouse gas emissions, we would need to reduce our individual emissions down to 5,000 lbs per year. Solving the Carbon Dilemma: What are some things that you can do to reduce your carbon emissions? It's the act of consuming difference. less that will ultimately make a Energy-efficient, energy-conserving electronics, lightbulbs, hardware and other devices are available for almost anything. You can expect that energy-efficient products are meant to last longer and will save you money. Reduce your dependency on cars! Greenhouse gases • Greenhouse gases (CH4 = methane, N2O = nitrous oxide): trap outgoing radiation from Earth’s surface • Coal burning Sulfur dioxide (SO2) acid rain. • SO2 Sulfate aerosol, reflects sunlight => cooling. • 1940-1970 cooling may be due to coal burning. • Coal burning incr. CO2 (long-term warming) and incr. sulfate aerosol (short-term cooling) [aerosol washed out by precip.] 68 Seasonal cycle of atmospheric CO2 (Mauna Loa record) Atmospheric CO2 concentrations--recent. 69 Short-term variability 70 • Some facts of global changes: (1) Global warming: Global mean surface temperatures have increased 0.5-1.0 F since the late 19th century; The 20th century's 10 warmest years all occurred in the last 15 years of the century. Of these, 1998 was the warmest year on record. The snow cover in the Northern Hemisphere and floating ice in the Arctic Ocean have decreased, sea level has risen 4-8 inches over the past century. 71 Atmospheric CO2 concentrations--past 1000 years. 72 Short term climate change Short term climat e Earth’s chang surface temp. e: 0.8 -0.8 1860 0.8 incr. by 0.7 °C/cent -0.8 ury 10 2000 2000 00 73 Holland in 1565 (Little Ice Age) (Pieter Bruegel) 74 •Cooling in 1940s-1960s => fear of coming ice age! •Volcanic eruptions => drop in temp. for 3 years (e.g., Agung 1963) •Viking colony on Greenland lost by early 1400s. •Little Ice Age in late 1500s. 75 76 El Chicon Mexico, 1982 Mount Pinatubo, Philippines, 1991 Emitted millions of tons of sulfur dioxide and ash particles. Agung, Indonesia, 1963 77 London smog in 1952 78 79 Red cross: simulated global mean Tem. (62 simulations); black line: mean of all simulations; blue round: observed global mean Tem. 80 Anthropogenic greenhouse warming Atm. CO2: • Keeling started measuring atm.CO2 in 1958 on Mauna Loa, Hawaii • Seasonal cycle (forests absorb CO2 in summer & release CO2 in winter) + rising trend 81 82 CO2 (ppm) CO2 (ppm) CO2 (ppm) 1000 1000 1000 N2O (ppb) N2O (ppb) N2O (ppb) 2000 2000 2000 CH4 (ppb) CH4 (ppb) CH4 (ppb) 83 84 85 86 87 An increasing body of observations gives a collective picture of a warming world and other changes in the climate system • Global mean surface temperature increase (NH, SH, land, ocean) • Melting of glaciers, sea ice retreat and thinning • Rise of sea levels • Decrease in snow cover • Decrease in duration of lake and river ice • Increased water vapor, precipitation and intensity of precipitation over the NH • Less extreme low temperatures, more extreme high temperatures 88 Recent Range Shifts due to Warming Species Affected Location Observed Changes Alaska Expansion into shrub-free areas 39 butterfly spp. NA, Europe Northward shift up to 200 km in 27 yrs. Lowland birds Costa Rica Advancing to higher elevations 12 bird species Britain 19 km northward average range extension Red & Arctic Fox Canada Red fox replacing Arctic fox Treeline Europe, NZ Advancing to higher altitude Plants & invertebrates Antarctica Distribution changes Zooplankton, fish & invertebrates California, N. Atlantic Increasing abundance of warm water spp. Arctic shrubs Walther et al., Ecological responses to recent climate change, Nature 416:389 (2002) 89 Red & Arctic Fox 90 91 Modes of Climate Variation Periodicvariation variation Periodic Abrupt shift in climate state Warming or cooling to new climate state Changes in amplitude or frequency of climate oscillations 92 The three serious problems The three modern global change problems discussed in this chapter-- global warming, ozone depletion, or loss of biodiversity 93 The ozone depletion is the serious problem because: • It causes the most immediate damage to our planet and its inhabitants • It can cause skin cancer • It occurs faster than global warming, because global temperatures only rise 1 degree in 100 years so this is an insignificant amount compared to the decline in the total amount of ozone 94 The loss of biodiversity is the serious problem because: • There is potential for recovery for the other problems: the ozone layer could recover within a few generations and greenhouse gas concentrations should return to “normal” within a few million years. • The recovery rate for species following extinction is tens of millions of years. • Once a species is gone, it is gone for good. • It could cause an imbalance in the Earth’s ecosystem and economy. • Deforestation also contributes to global warming. 95 Global warming is the serious problem because: • It affects the greatest number of people • Migration of marine animals could result • Rising sea level could result • Cold climate species might die • Ozone depletion and deforestation are both confined to particular areas whereas global warming is truly global 96