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Chapter 23: The Atmosphere, Climate and Global Warming The Origins of the Global Warming Issue • Concern arises from two kinds of evidence: – Increase in average surface temperature of the Earth from 1860 to the present – Increase in carbon dioxide concentrations in the atmosphere. • Measured on Mauna Loa in Hawaii by Charles Keeling The Origins of the Global Warming Issue • Relationship between chemistry of planet’s atmosphere and planet’s surface temperature. – Certain gases trap heat energy and warm the plant – Since this idea was first introduce has stirred controversy The Atmosphere • Thin layer of gases that envelops Earth. – Held near the surface by gravitation and pushed upward by thermal energy. – Primarily nitrogen (78%), oxygen (21%), argon (0.9%), carbon dioxide (0.03%) and water vapor. – Trace amounts of other gases/pollutants – Dynamic system Structure of the Atmosphere • Made up of several vertical layers – Troposphere- bottom layer • Where weather occurs • Temperature decrease w/ elevation • At the top is tropopause- acts as a lid – Stratosphere- above the troposphere • Stratospheric ozone layer just above the tropopause • Protects again UV radiation Atmospheric Processes • Two important qualities of the atmosphere are pressure and temperature. • Pressure is force per unit area. – Caused by the weight of overlying atmospheric gases on those below – Decreases w/ altitude – Low pressure systems usually bring clouds – High pressure systems usually bring clear skies Atmospheric Processes • Temperature is the relative hotness or coldness of materials – Measure of thermal energy • Water vapor content another important characteristic – Varies from 1% to 4% Atmospheric Processes • Atmosphere moves because of the Earth’s rotation and differential heating. – Produce global patterns of prevailing winds and latitudinal belts of high and low pressure What Makes the Earth Warm • Almost all the energy from the sun. • Sunlight comes in a wide range of electromagnetic radiation. – Long to short wavelengths – Most of the radiation that reaches the Earth is in the infrared and visible wavelengths What Makes the Earth Warm • Under typical conditions Earth’s atmosphere – Reflects about 30% of the electromagnetic energy that comes in from the sun – The atmosphere absorbs about 25% – The remaining 45% gets to the surface • Radiates back to the atmosphere or into outer space Weather and Climate • Weather is what’s happening now w/ the atmosphere near the ground. – Its temperature, pressure, cloudiness, precipitation, winds • Climate is the average weather – Usually refers to long periods of time – Classified mainly by latitude and wet/dry The Climate is Always Changing • Climate has warmed and cooled may times in Earth’s history – Times of high temp involve relatively ice free periods – Times of low temp involve glacial events Causes of Climate Change • It wasn’t until the 19th century that scientists began to understand that climate changed greatly over long periods and included times of continental glaciations. – Evidence was debris at the edges of existing glaciers which is the same kind found deposited at lower elevations. Causes of Climate Change • Why does climate change? – Explanation might have to do w/ the way the Earth revolves on its axis and rotates around the sun. • Earth is like a wobbling top following an elliptical orbit around the sun. • Three kinds of changes occur. – (1) Earth is unable to keep its poles at a constant angle in relation to the sun. The wobble makes a complete cycle in 26,000 years. Causes of Climate Change – (2) The tilt of wobble also varies over a period of 41,000 years – (3) The elliptical orbit around the sun also changes. Sometimes it is a more extreme ellipse; other times it is closer to a circle and this occurs over 100,000 years. Causes of Climate Change • The combination of these lead to periodic changes in the amount of sunlight reaching the Earth. – Milankovitch showed that these variations correlated w/ the major glacial and interglacial periods. – Called Milankovitch cycles – Don’t account for all climate variations Solar Cycles • The Sun Goes Through Cycles Too – Sometimes hotter, sometimes cooler – Documented by differing amounts of isotopes trapped in glacial ice • Appears that variability of solar input of energy explains some of the climatic variability too. Atmospheric Transparency Affects Climate and Weather • How transparent the atmosphere is to radiation coming into it affects the temp of the Earth – From the sun and from the Earth’s surface • Dust and aerosols absorb light – Volcanoes, forest fires and farming put dust into the atmosphere – Chemical and physical comp of atmosphere can make it warmer or cooler The Green House Effect • Each gas in the atmosphere has its own absorption spectrum – Certain gases are especially strong absorbers in the infrared – They absorb radiation emitted by the warmed surfaces of the Earth – They then re-emit this radiation – Making the Earth’s surface warmer The Green House Effect • Effect called the greenhouse effect – Natural phenomenon • Major green house gases are – – – – – Water vapor Carbon dioxide Methane Some oxides of nitrogen CFCs The Roles of Major Greenhouse Gases In Affecting Climate • Nobody doubts that the greenhouse effect exists and affects planets. • The puzzle arises on the Earth about relative importance of greenhouse gases in affecting climate. • Evidence indicates that carbon dioxide, methane, and temperature rise and fall together. – From this most scientists conclude that greenhouse gases are causing climate change. Positive and Negative Feedbacks • The atmosphere and its interactions w/ the ocean and land surfaces experience positive and negative feedbacks. • Negative feedback – Warms temps warm air and lead to increased evaporation – Evaporation leads to more cloud formation which reflects more sunlight which could cool the surface. Positive and Negative Feedbacks • Positive feedback – Warms temps warm air and lead to increased evaporation but instead of clouds forming remain as water vapor. – Water vapor is a greenhouse gas. The warmer it gets the more water vapor, and the process continues. The Ocean’s Effect on Climate Change • Water has the highest heat capacity of any compound. – Large amount of heat energy can be stored in oceans • Ocean can absorb CO2 – As CO2 increases in atmosphere it also increases in the oceans The Ocean’s Effect on Climate Change • Part of what drives the climate system is the ocean conveyor belt. – A global circulation of ocean waters – If the conveyor was shut down, major changes in climate would occur. El Niño and Climate • El Niño refers to a certain kind of periodic variation of currents in the Pacific Ocean. • Under non-El Niño conditions – Trade-winds blow west across the tropical Pacific – Warm surface water pile up in W. Pacific El Niño and Climate • During El Niño years – Trade winds weaken – Western moving current weakens or reverses – As a result eastern equatorial ocean unusually warm – High rates of precipitation and flooding in Peru • Changes global atmospheric circulation – Causes changes in weather in regions that are far removed from tropical Pacific El Niño and Climate • Rise in temp of sea surface waters off the SA coast inhibits the upwelling of nutrientrich cold water from deeper levels. – Upwelling releases carbon dioxide – El Niño events reduce the amount of oceanic carbon outgassing Predicting the Future of the Climate • For climate and its effects on living things , there are two ways to forecast the future: – Empirical and theoretical • Empirical approach is to go back to the geological idea of uniformitarianism – Has led to the extensive research on climates and atmospheric conditions of the past Predicting the Future of the Climate • Empirical problem we face is temperature records recent and not widespread. – Expects have to find ways to extrapolate, interpolate and estimate – Places like Hadley Meteorological Center in Great Britain • Reconstructing temp records Predicting the Future of the Climate • Computer simulation – The second method to forecast climate changes is to develop computer models of the world climate. – All based around the atmosphere being divided into rectangular solids • Each a few km high and several km N or S • For each the flux of energy and matter is calculated to each adjacent cell Predicting the Future of the Climate • These global climate models are called “general circulation models” (GMCs) by the climatologist that develop them. – Crude compared to real world – And determining how well they work is a major challenge What a Global Warming World Might be Like • Global surface temp has increased 0.2°C/ decade in the past 30 years. – Since 1998, the eight warmest years have occurred. – Continued warming of 0.2°C /decade is projected. What a Global Warming World Might be Like • By 2030 the concentration of CO2 in the atmosphere will have doubled from pre– Industrial Revolution concentrations. – The average global temperature will have risen approximately 1° to 2°C – W/ greater temperature increases toward the poles. • Polar amplification Potential Environmental, Ecological, and Human Effects of Global Warming • Changes in River Flow – Melting of glacial ice and reductions in snow cover are anticipated to accelerate throughout the twenty-first century. – Rainfall will likely increase, but runoff will be more rapid than if snow slowly melts. • Reservoirs will fill sooner and more water will escape to the ocean. Potential Effects of Global Warming • Rise in Sea Level – A major warming could increase sea levels because of • 1. Expansion of liquid water as water warms • 2. Melting of ice sheets on land whose waters then flow into the ocean. – About half the people on Earth live in the coastal zone. – Sea level and population rising, the number of people vulnerable to coastal flooding increases. Potential Effects of Global Warming • Rise in sea level could: – Threatens island nations – Increase coastal erosion on open beaches and cause property loss. – Cause landward progression of estuaries and salt marshes – Lead to lost of coastal wetlands – Threaten ground water supply in coastal communities Potential Effects of Global Warming • Glaciers and Antarctic Ice Cap – Many more glaciers in the world are retreating than advancing. – Not all due to global warming • E.g. Mt. Kilimanjaro – Northern Hemisphere sea ice coverage has declined an average of 10.7% / decade since 1970s Potential Effects of Global Warming • The central ice cap on Antarctica is growing – This is consistent w/ prediction of global climate change models. – As Earth warms, more snow falls on Antarctica. • The rate of melting of the Greenland ice sheet has doubled since about 1998. Potential Effects of Global Warming • Changes in Biological Diversity – The Intergovernmental Panel on Climate Change (IPCC) report states that • “approximately 2–20% of species assessed so far are likely to be at increased risk of extinction as global mean temperatures exceed a warming of 2 to 3°C above preindustrial levels.” Potential Effects of Global Warming • Black guillemots – Birds that nest on Cooper Island, Alaska, • The abundance of this species has decreased. – Recession of sea ice occurred before chicks were mature enough to survive on their own. – Parent birds feed on Arctic cod found under the sea ice. • Distance from feeding grounds to nest must be <30 km • In recent years, been s much as 250 km from the island • As a result, lost an important source of food. Potential Effects of Global Warming • Agricultural Productivity – Globally, agriculture production is likely to increase in some regions and decline in others. – A climate shift could have serious negative effects on mid-latitude food production. – In addition, lands in the southern part of the Northern Hemisphere may become more arid. • soil moisture relationships will change. Potential Effects of Global Warming • Human Health Effects – Health status of millions of people could potentially be affected through • Increases in malnutrition • Increased deaths, diseases, and injury due to extreme weather events • Increased burden of diarrhoeal diseases • Increased frequency of cardio-respiratory diseases Adjusting to Potential Global Warming • There are two kinds of adjustments people can make to the threat of global warming: – Adapt: Learn to live with future global climatic change. – Mitigate: Work to reduce emissions of greenhouse gases. Adjusting to Potential Global Warming • How can carbon dioxide emissions be reduced? – Energy planning that relies heavily on energy conservation and efficiency – Use of alternative energy sources, use of natural gas – Use of mass transit – Greater economic incentives to energy-efficient technology, higher fuel-economy Adjusting to Potential Global Warming • Burning forests to convert land to agricultural – Accounts for about 20% of anthropogenic emissions of carbon dioxide into the atmosphere. – Minimizing burning and protecting the world’s forests would help reduce the threat of global warming. • Reforestation – Planting more trees – Increase biospheric sinks for carbon dioxide. Adjusting to Potential Global Warming • Geologic sequestration of carbon is another possible mitigation measure. – The idea is to capture carbon dioxide from power plants and industrial smokestacks. – Compressing the gas and changing it to a mixture of both liquid and gas and then injecting it deep underground. – Have the potential to sequester as much as 1,000 gigatons of carbon. International Agreements to Mitigate Global Warming • Two major approaches are: – international agreements in which each nation agrees to some specific limit on emissions – Carbon trading International Agreements to Mitigate Global Warming • In carbon trading, a nation or nation agrees to a cap of carbon emissions. – Then corporations and other entities are issued emission permits, allowing a certain quantity of emissions. – These can be traded. International Agreements to Mitigate Global Warming • First international meeting to discuss limiting greenhouse gases held in Toronto, Canada in 1988. • In 1992, Earth Summit in Rio de Janeiro, Brazil. – General blueprint for reduction of global emissions suggested – US thought it would be to costly and no legally binding limits set. International Agreements to Mitigate Global Warming • In 1997, legally binding limits discussed in Kyoto, Japan. – US eventually agreed to cut emissions to 7% below 1990 levels (leading scientists recommend cuts 60-80% below) – Became a formal treaty in 2006