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Global warming and climate change This lecture will help you understand: • Earth’s climate • Human influences on the atmosphere and climate • Current and potential impacts of climate change • Scientific, economic, and political debate on climate change • Potential responses Climate and climate change • Climate: a region’s long-term pattern of atmospheric conditions, results from all the combined elements of – General atmospheric circulation patterns and precipitation – Wind and weather systems – Rotation and tilt of Earth, which creates seasons • Global climate change: changes in Earth’s climate, including temperature, precipitation, and other variables • Global warming: an increase in Earth’s average surface temperature • Climate changes naturally, but the recent rapid warming of the planet and its change in atmospheric composition are widely thought to be due to human activities. How do we know what temperatures were in the past? • Scientists analyze tiny air bubbles trapped in ice cores learn about past: – Troposphere composition – temperature trends – Greenhouse gas concentrations – solar, snowfall, forest fire activity Ice cores • Analyzing ice cores from Greenland and the Antarctic shows global climate can change within decades. – Uses CO2 and CH4 (methane) and isotopes of O and H • Climate oscillates between ice ages and warm periods. – Ice ages tie up water in glaciers, lowering sea levels – 8 glacial periods occurred over the past 800,000 years • Ice ages have lower green house gases temperatures. – CO2 levels ranged between 150 and 280 ppm and • Milanovitch cycles: climate oscillations due to Earth’s orbit – Periodic intervals of 100,000, 41,000, and 23,000 years Changes in Earth’s temperature during the past million years Milankovitch cycles • Over thousands of years, changes in Earth's orbit cause changes in the amount of the Sun's energy that gets to the planet. Over the past several million years these changes have caused cycles of global warming and cooling. • There are three ways that Earth's orbit changes over time. – Eccentricity: The shape of Earth's orbit around the Sun becomes slightly more and then less oval every 100,000 years. – Precession: Earth wobbles on it axis as it spins, completing a full wobble every 23,000 years. – Tilt: The angle of the Earth's axis relative to the plane of its orbit changes about three degrees every 41,000 years. • Once the Sun's energy reaches the Earth, several things can happen. The energy can be absorbed by the planet, reflected back into space, or become trapped in the atmosphere. Milankovitch cycles These 3 types of cycles also affect climate in the long term. Variation of Earth’s orbit → a cycle of about 100,000 years Wobble of Earth’s axis → a periodicity of 23,000 years. Variation of Earth’s tilt → a periodicity of 41,000 years Fluctuation in natural climate Milankovitch theory of climate change Glacial Ice Growth Configuration: High eccentricity High Tilt Small Earth-Sun Distance in Summer Net Effect: More seasonal contrast Interglacial Ice Growth Configuration: Low eccentricity Low Tilt Large Earth-Sun Distance in Summer Net Effect: Less seasonal contrast Factors that influence climate Three factors influence Earth’s climate more than all others combined: • The sun, which provides most of Earth’s energy • The atmosphere, which both absorbs energy from the sun and reflects it back into space • The oceans, which stores and transports heat and moisture The Earth as a greenhouse • Factors that influence climate – Internal components: oceans, atmosphere, snow, ice – External factors: solar radiation, Earth’s rotation and orbit, gaseous makeup of the atmosphere • Radiative forcing: unit used to compare the relative contribution to the IR absorption per molecule added to the atmosphere Positive and negative forcing: leads to warming or cooling • Forcing is measured in Watts/m2 – Solar radiation entering the atmosphere = 340 W/m2 – Radiation is acted on by forcing factors Radiative forcing Greenhouse effect: warming process • Greenhouse gases (GHGs): water vapor, CO2, other gases (NOx, CH4, CFC) • Light energy goes through the atmosphere to Earth. – Earth absorbs and converts energy to heat – Infrared heat energy radiates back to space • GHGs (but not N2 and O2) in the troposphere absorb some infrared radiation. – Direct it back to Earth’s surface • The greenhouse effect was first recognized in 1827. – It is now firmly established. Properties of anthropologic greenhouse gases GHGs insulate Earth • GHGs delay the loss of infrared heat (energy) – Without insulation, Earth would be -19°C instead of +15°C. – Life would be impossible. • Earth’s global climate depends on the concentration of GHGs. – Changing amounts of GHGs change positive forcing agents, which would change the climate. • Tropospheric ozone has a positive forcing effect. – Varying with time and location Cooling processes • Planetary albedo: sunlight reflected by clouds – Contributes to overall cooling by preventing warming – Low-flying clouds have a negative forcing effect • High-flying, wispy clouds have a positive forcing effect – Absorb solar radiation and emit infrared radiation. • Snow and ice contribute to albedo by reflecting sunlight – Black carbon soot darkens snow and ice – Dark snow/ice absorbs radiant energy instead of reflecting it and reduces albedo Global warming and cooling Net effect of forcing reagents on atmosphere • Global atmospheric temperatures are a balance between positive and negative forcing from natural causes (volcanoes, clouds, natural GHGs, solar irradiance) and forcing from anthropogenic causes (sulfate aerosols, soot, ozone, increased GHGs) • Forcing agents result in climate fluctuations – It is hard to say any one event or extreme season is due to humans – But climate has shifted enough to generate international attention Major greenhouse gases • Increases in average concentrations of three greenhouse gases in the troposphere between 1860 and 2004, mostly due to fossil fuel burning, deforestation, and agriculture. Global warming potential • Carbon dioxide: primary greenhouse gas • • • methane traps 23 times the heat of CO2 nitrous oxide traps 296 times the heat of CO2 HFC-23 traps 12,000 times the heat of CO2 Rising greenhouse gases • The Intergovernmental Panel on Climate Change (IPCC) AR4 report states that global GHG emissions from humans have grown 70% between 1970 and 2004 – The most important GHG is carbon dioxide (CO2) • Carbon dioxide: – Over 100 years ago, Swedish scientist Arrhenius suggested that burning fossil fuels may increase CO2 – But he was not concerned about the impacts • Carbon dioxide monitoring: CO2 levels have been monitored on Mauna Loa, Hawaii since 1958 – Atmospheric CO2 levels have increased 1.5–2 ppm/yr Average concentration of atmospheric carbon dioxide, 1500-2000 In 2005, an ice core showed that CO2 levels in the troposphere are the highest they have been in 650,000 years. Carbon dioxide levels • CO2 concentration has increased 33% in the past 200 years. • It is now at its highest level in 400,000 years, and probably 20 million years. • CO2 levels oscillate 5–7 ppm, reflecting seasonal changes in photosynthesis and respiration. – Fall through spring: respiration increases CO2 levels – Spring through fall: photosynthesis decreases CO2 • By 2011, atmospheric CO2 levels = 390.5 ppm – 40% higher than before the Industrial Revolution – Higher than in the past 800,000 years • Fossil fuels increase CO2 levels. – 1 kg of fossil fuel burned releases 3 kg CO2 – Eight billion tons (gigatons, Gt) of fossil fuel carbon/year Sources of carbon dioxide • Half of fossil fuel carbon comes from industrialized nations – Burning forests adds 1.6 GtC/year – Over the past 50 years, release of carbon has tripled – Half of the carbon is removed by sinks • Sinks: burning fossil fuels should add 8 GtC/year to the air – But only 3.3 GtC/year are actually added – Carbon sinks (the ocean, biota, CaCO3 formation) absorb CO2 • Oceans take up CO2 by phytoplankton or undersaturation – But there are limitations to uptake • Forests are valuable for their ability to sequester carbon Global carbon cycle Other GHGs • Water vapor: the most abundant GHG – Its tropospheric concentration varies, but is rising. – Higher temperatures increase evaporation and water vapor (humidity). – Higher humidity traps more heat, causing more warming (positive feedback). • Methane: 20 times more effective than CO2 in heating – From microbial fermentation (in wetlands), green plants – Two-thirds of emissions are from human sources: animal digestion, wet lands, landfills, coal mines, natural gas, rice cultivation, manure – Rising at 0.8 ppb/year, it is more abundant than in the past 800,000 years • Nitrous oxide: has increased 18% over the last 200 years – From agriculture, oceans, biomass burning, fossil fuel burning, industry, anaerobic denitrification (fertilizers) – Warms the troposphere and destroys stratospheric ozone • Ozone: a short-lived but potent GHG in the troposphere – From sunlight acting on pollutants – Has increased 36% since 1750 – From traffic, forest fires, agricultural wastes • CFC and other halocarbons are entirely anthropogenic. – Long-lived GHGs causing warming and ozone destruction – From refrigerants, solvents, fire retardants – They absorb 10,000 times more infrared energy than CO2 – Levels are slowly declining but will remain for decades. Thermohaline circulation • High-latitude North Atlantic ocean flows from the Gulf Stream north on the surface and is cooled by Arctic air. • North Atlantic Deep Water (NADW): the cool water increases in density, so it sinks (up to 4,000 m) – The current spreads to Africa’s southern tip – It is joined by cold Antarctic waters – The two streams spread north into the Indian and Pacific Oceans as deep current • The currents slow and warm and rise to the surface – Move back to the North Atlantic Polar (ice) Warm temperate Highland Subarctic (snow) Dry Major upwelling zones Cool temperate Tropical Warm ocean current Cold ocean current River Heinrich events • Heinrich events: fresh water from melting icebergs from the polar ice cap dilutes salt water – Six times in the past 75,000 years – Diluted water doesn’t sink – The conveyor system is shifted southward to Bermuda (instead of Greenland) – The climate cools in a few decades • Return of the normal pattern abruptly warms the climate • The Younger Dryas event involved dammed-up water from glacial Lake Agassiz entering the St. Lawrence • Extended global warming will – Increase precipitation over the North Atlantic – Melt sea ice and ice caps • The conveyor will decrease over the 21st century • The Achilles’ heel of our climate system: weakening of the conveyor and a changed climate – Especially in the northern latitudes Ocean-atmosphere oscillations These processes produce globally erratic climates. • The North Atlantic Oscillation (NAO): atmospheric pressure centers switch back and forth across the Atlantic – Switching wind and storms • El Niño/La Niña Southern Oscillation (ENSO): shifts in atmospheric pressure over central equatorial Pacific Ocean – Dominates global climate for over a year at a time – 1997–2000 ENSO cost $36 billion and killed thousands • Interdecadal Pacific Oscillation (IPO): a warm-cool cycle that swings over the Pacific over several decades El Nino and La Nina In normal conditions, winds push warm waters (red) to the western Pacific Ocean. This allows cold water to well up from the deep in the eastern Pacific. In an El Niño event, winds weaken, warm water sloshes to the east, and prevents the cold upwelling. La Niña is the opposite: Cold water spreads west. History of El Niño • El Niño, as a oceanic phenomenon along the coasts of northern Peru and Ecuador, has been documented since the 1500s. • Originally, the term El Niño was used to describe the annual appearance of warm waters along the coast of northern Peru around Christmastime. • In some years the warm waters appeared earlier and lasted longer. Eventually, the term El Niño was applied to the periods of anomalous warming. • The stronger events disrupted local fish and bird populations. History of the Southern Oscillation • Beginning in the late 1800s scientists began to describe large-scale pressure fluctuations. • Dr. Gilbert Walker and colleagues extended the early studies and determined that a global-scale pressure fluctuation (the Southern Oscillation, SO) is related to rainfall anomalies in many areas of the Tropics (e.g., India and South America). • The SO was used as the basis for seasonal rainfall predictions (ca 1930s). Discovery of the “El NiñoSouthern Oscillation (ENSO)” • El Niño and the Southern Oscillation were studied as separate phenomena until the 1950s-1960s. • Important works by Berlage (1956) and J. Bjerknes (late 1960s) demonstrated a link between the two phenomena. • Studies at that time also showed that the anomalous warming of the waters during El Niño extended over a large portion of the equatorial Pacific. The ENSO cycle • Naturally occurring phenomenon • Equatorial Pacific fluctuates between warmer-thanaverage (El Niño) and colder-than-average (La Niña) conditions • The changes in SST (Sea surface temperatures) affect the distribution of tropical rainfall and atmospheric circulation features (Southern Oscillation) • Changes in intensity and position of jet streams and storm activity occur at higher latitudes Properties of El Niño/ La Nina Signals in Tropical Pacific: • • • • • Sea surface temperatures (SSTs) Precipitation Sea Level Pressure The Southern Oscillation (High vs. Low Phases) Low-level Winds and Thermocline Depth Sea Surface Temperatures(SST) • Equatorial cold tongue is weaker than average or absent during El Niño, resulting in positive SST anomalies. • Equatorial cold tongue is stronger than average during La Niña, resulting in negative SST anomalies. Precipitation Enhanced rainfall occurs over warmerthan-average waters during El Niño. Reduced rainfall occurs over colderthan-average waters during La Niña. Sea Level Pressure(SLP) • El Niño: Positive SLP anomalies over the western tropical Pacific, Indonesia and Australia. Negative SLP anomalies over eastern tropical Pacific, middle and high latitudes of the North Pacific, and over U.S. • Opposite pattern for La Niña. The pressure see-saw between the eastern and western tropical Pacific is known as the Southern Oscillation. Low-Level Winds & Thermocline Depth El Niño: weaker-thanaverage easterlies lead to a deeper (shallower)-thanaverage thermocline in the eastern (western) eq. Pacific. La Niña: strongerthan-average easterlies lead to a deeper (shallower)than-average thermocline in the western (eastern) eq. Pacific. ENSO: A Coupled Ocean-Atmosphere Cycle ENSO is a “coupled” phenomenon: atmosphere drives the ocean and the ocean drives the atmosphere. “Positive Feedback” between ocean and atmosphere. Example: Weaker equatorial trade winds cold water upwelling in the east will decrease surface warming of the ocean reduced east-west temperature gradient Weaker equatorial trade winds Normal(Average) condition Winds and Sea Surface Temperature are COUPLED. The SSTs influence the winds and vice versa. Warm Warm Cold Cold (1) Easterly trade-winds help push warm water to the western Pacific and upwell cold water along the equator in the eastern Pacific Ocean. (2) Warm water heats the atmosphere, the air rises, and low-level trade winds converge toward the warm water. Subsiding air occurs in the eastern Pacific basin. “El Niño” Warm Warm Cold NOTE: Location of the warmest SSTs (>~28°C) determines where tropical convection will be located. • Convection shifts eastward over the central and/or eastern Pacific Ocean. Convection becomes suppressed over the far western Pacific/ Indonesia. • Easterly weaken trade winds • Thermocline deepens and the cold water upwelling decreases in the eastern Pacific. Warm Cold Global El Niño Impacts Impacts are generally more extensive during the northern winter. “La Niña” Enhanced More Convection Stronger Stronger Upwelling Warm ColdCold becomes more shallow • Convection becomes stronger over the far western Pacific Ocean/ Indonesia and more suppressed in the central Pacific. • Easterly trade winds strengthen • Thermocline becomes more shallow and the cold water upwelling increases in the eastern Pacific. Warm Cold Global La Niña impacts Mid-latitude impacts generally occur during the winter season (NH–DJF;SH- JJA). Typical evolution of the ENSO cycle • Irregular cycle with alternating periods of warm (El Niño) and cold (La Niña) conditions • El Niño tends to occur every 3-4 years and generally lasts 12-18 months • Strongest El Niño episodes occur every 10-15 years • La Niña episodes may last from 1 to 3 years • Transitions from El Niño to La Niña are more rapid than transitions from La Niña to El Niño. Evidence of climate change • Weather varies naturally year to year – Local temperatures may not follow global averages • But the 10 warmest years on record were 1997–2008. – 2005 set a record high—the warmest since the late 1800s – The average global temperature has risen 0.6°C since the mid-1970s (0.2°C/decade) • Warming is happening everywhere. – Most rapidly at high latitudes of the Northern Hemisphere • The warming is a consequence of an “enhanced greenhouse effect”. Intergovernmental panel on climate change (IPCC) • Founded in 1988 by the UN Environmental Program and the World Meteorological Society to provide accurate and relevant information leading to understanding human-induced climate change • Working Group I: assesses scientific issues of climate change • Working Group II: evaluates impacts and adaptation to it • Working Group III: investigates ways to mitigate its effects • The AR4 report had over 2,000 experts from 154 countries – Risk assessment: is the climate changing? – Risk management: how do we adapt and mitigate effects? Synopsis of global climate change • In 2007, scientists from the IPCC sifted through thousands of studies and published the Fourth Assessment Report (AR4). • The report concluded that warming of the climate is unequivocal – The atmosphere and oceans are warmer. – Sea levels are rising and glaciers are melting. – There are more extreme weather events. The IPCC’s report • The report concluded that it is very likely (90% probability) that warming is caused by human factors – Increased greenhouse gases (GHGs) trap infrared radiation • GHGs come from burning fossil fuels – Along with deforestation – The major GHG: CO2 • Responses to climate change – Mitigation: reducing GHG emissions – Adaptation: adjusting to climate change Ocean warming • Recently, the upper 3,000 meters of the ocean have warmed. – Dwarfing warming of the atmosphere – 90% of the heat increase of Earth’s systems • Over the last decade, oceans have absorbed most of the nonatmospheric heat. • A long-term consequence: the impact of this stored heat as it comes into equilibrium with the atmosphere. – It will increase atmospheric and land heat even more. • A short-term consequence: unprecedented rising sea levels – Thermal expansion and melting glaciers and ice caps Shrinkage of the Muir glacier Decline of Arctic sea ice 1979 2003 Ice cover decreased by 9% during this period and then 20% at 2005 Arctic sea ice thinned 10–40% in recent decades. Changes in average sea level Today’s sea level 0 –130 250,000 200,000 150,000 100,000 50,000 Years before present 0 –426 0 Present Height above or below present sea level (feet) Height above or below present sea level (meters) Average sea level increased 10–20 centimeters (4–8 inches) during 20th century. World sea level will rise 15-90 cm. Mean Sea-Level Rises (centimeters) Estimated global sea level 100 90 80 70 60 50 40 30 20 10 High Projection Shanghai, New Orleans, and other low-lying cities largely underwater Medium Projection More than a third of U.S. wetlands underwater Low Projection 0 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 Year Potential global temperature and precipitation change by 2050 Global warming impacts on biological systems Causes and consequences of climate change Achieving stabilization of global warming • The Framework Convention on Climate Change (FCCC) – We must stabilize GHG levels on a time scale that prevents interfering with climate. – 3°C rise: rising sea levels of 80 feet – 2°C rise: irreversible melting of the Greenland Ice Sheet • We have a target of 1–1.5°C more warming. – CO2 = 400–500 ppm – Al Gore’s inconvenient truth: carbon emissions must fall from 8 GtC/year to 2 GtC/year What has been done? • The Framework Convention on Climate Change (FCCC) agreed to stabilize GHG emissions to 1990 levels by 2000 in all industrialized nations. • This voluntary approach failed – All developed countries (except the EU) increased GHG emissions by 7%–9%. – Developing countries increased theirs by 25%! • Kyoto Protocol: the third Conference of Parties to the FCCC met in 1997 in Japan to craft a binding agreement on reducing emissions International climate negotiations The Kyoto protocol • 38 industrial nations agreed to reduce GHG emissions 5% below 1990 levels by 2012. – Annex I parties: signatories to this agreement – Non-Annex I parties: developing countries • Developing nations refused any reductions – They said they have the right to develop using fossil fuels, just as developed nations had • FCCC principle of “common but responsibilities” – Each nation must address climate change – But its priorities and efforts could differ different Ratifying the Kyoto protocol • Treaty on global warming which first phase went into effect January, 2005 with 189 countries participating. – The U.S. is the only Annex I party that has not. • Signers of the protocol have flexibility in how they will achieve their GHG reductions – Renewable fuels, nuclear, conservation, planting trees – Emissions trading, helping other nations • There are penalties for failing to meet commitments • Many Annex I countries are on target – But not the U.S., Australia, Canada, Japan Weaknesses of the Kyoto protocol • The protocol’s targeted reductions will not stabilize GHGs – It would take immediate reductions of 60% globally – There is no chance of this happening, so emissions will continue to rise • The world’s largest GHG emitters are not participating – India, China, the U.S. • A 2007 UN-sponsored climate conference occurred in Bali – The U.S. and some developing countries opposed emission cuts and targets – Negotiations on emissions occurred in Copenhagen (2009) Mitigation tools • Reducing GHG emissions (several are already in place) • Cap-and-trade, renewable energy, carbon capture and storage, nuclear power, reforestation, efficiency • Mileage standards, subsidies, carbon tax • Stabilization triangle: carbon savings by reducing GHGs – It is broken into seven wedges (mitigation strategies) – Each wedge reduces 1 billion tons of carbon emissions • 15 wedge strategies in four categories: efficiency/ conservation, fossil fuels, nuclear, renewables – Only seven are needed to bring about the desired future Stabilization wedges Preparation for global warming Carbon capture and storage (CCS) Several problems approach with this • Power plants using CCS More expensive to build None exist • Unproven technology • Large inputs of energy to work • Increasing CO2 emissions • Promotes the continued use of coal (world’s dirtiest fuel) • Effect of government subsidies and tax breaks • Stored CO2 would have to remain sealed forever: no leaking Carbon capture and storage (CCS) We can capture at least 90% of emissions from fixed emitters We have been transporting CO2 for decades CO2 can be stored safely and permanently using natural trapping mechanisms CO2 Capture There are 3 technologies to capture CO2 : • Pre-combustion: Where CO2 is captured before fuel is burned • Oxy-fuel: Where CO2 is captured during fuel combustion • Post-combustion: Where CO2 is captured after fuel has been burned (This technology can also be retrofitted to existing power and industrial plants) Pre-combustion CO2 is captured before fuel is burned Oxy-fuel CO2 is captured during fuel combustion Post-combustion CO2 is captured after fuel has been burned 73 CO2Transport • Once captured, the CO2 is compressed into a liquid state and dehydrated for transport and storage. • CO2 is preferably transported by pipeline. • …or by ships when a storage site is too far from the CCS capture plant Safely storing CO2 • We use a natural mechanism that has trapped CO2, gas and oil for millions of years. • Liquid CO2 is pumped deep underground into one of two types of reservoirs: – deep saline aquifers (700m-3,000m) – depleted gas and oil fields (up to 5,000m) • Both types of reservoirs have a layer of porous rock to absorb the CO2 and an impermeable layer of cap rock to seal the porous layer Safely Storing CO2 The liquid CO2 is pumped deep underground into one of two types of CO2 storage reservoir (porous rock) Cap rock Deep saline aquifer 700m - 3,000m Cap rock up to 5,000m Depleted oil and gas fields 76 The safety of stored CO2 increases over time ... due to 3 natural mechanisms 1 2 3 Residual trapping CO2 is trapped in tiny rock pores and cannot move Dissolution trapping CO2 dissolves into surrounding salt water Mineral trapping CO2-rich water sinks to the bottom of the reservoir and reacts to form minerals Monitoring CO2 storage sites • To ensure that a CO2 storage site functions as it should, a rigorous monitoring process begins at the reservoir selection stage and continues for as long as required. • Monitoring continues even after a CO2 injection well is closed and EU legislation requires that stored CO2 is kept safely and permanently underground ouldGeoengineering? • Paul Crutzen (Nobel Prize in Chemistry) and Tom Wigley (NCAR) suggested that we consider temporary geoengineering as an emergency response. • Some Proposed Geoengineering Schemes: A. Space Modifier of solar radiation B. Stratospheric Stratospheric aerosols (sulfate, soot, dust) Stratospheric balloons or mirrors C. Tropospheric Modifying total reflection from marine stratus clouds D. Surface Making deserts more reflective Modifying ocean albedo Reforestation (CO2 effect, but albedo effect causes warming) Direct absorption of CO2 Ocean fertilization Keith, David, 2001: Geoengineering, Nature, 409, 420. Geoengineering • Futuristic schemes to fight climate change may not work – Fertilizing oceans with iron to stimulate photosynthesis – Scrubbers to remove and store CO2 – Sulfate particles or satellites to block solar radiation • These schemes consequences. have huge costs and unintended • We are conducting an enormous global experiment in geoengineering – Our children and their descendants will have to live with the consequences. Conclusions • Much if not all recent increases in global temperatures are due to anthropogenic sources. • Global temperatures and CO2 concentrations in ice cores are strongly correlated. • Only certain vibrations of molecules will absorb infrared radiation and be effective greenhouse gases. • The relative importance of various greenhouse gases is given by their relative abundance and global warming potential. • Controlling population growth and economic development, energy conservation, alternate energy sources, and CO2 sequestration are key elements in mitigating climate change.