Food and the Future Environment

Introduction

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Introduction 

Understanding the Science of Climate Change: The Basics

Module 9 focuses on how agriculture contributes to global climate and how climate change will affect global agriculture. In addition, we'll explore agricultural strategies for adapting to a changing climate. But, before we explore the connections between global climate change and food production, we want to make sure that everyone understands some of the basic science underpinning global climate change.

Have you ever thought about the difference between weather and climate? If you don't like the weather right now, what do you do? In many places, you just need to "wait five minutes"! If you don't like the climate where you live, what do you do? Move! Weather is the day-to-day fluctuation in meteorological variables including temperature, precipitation, wind, and relative humidity, whereas climate is the long-term average of those variables. If someone asked you what the climate of your hometown is like, your response might be "hot and dry" or "cold and damp". Often we describe climate by the consistent expected temperature and precipitation pattern for the geographic region. So, when we talk about climate change, we're not talking about the day-to-day weather, which can at times be quite extreme. Instead, we're talking about changes in those long-term temperature and precipitation patterns that are quite predictable. A warming climate means that the average temperature over the long term is increasing, but there can still be cold snowy days, and blizzards even!

The two videos below are excellent introductions to the science of climate change. We'll use these videos as your introduction to the basic science behind our understanding of climate change that we'll build on as we explore the connections between climate change and food production in the rest of this module. Follow instructions from your instructor for this introductory section of Module 9.

Optional Video Climate Change: Lines of Evidence

The National Academies of Sciences Engineering and Medicine have prepared an excellent 20-minute sequence of videos, Climate Change: Lines of Evidence, that explains how scientists have arrived at the state of knowledge about current climate change and its causes. Use the worksheet linked below to summarize the story that the video tells about anthropogenic greenhouse gas emissions and the resulting changes in Earth's climate. The narrator speaks pretty quickly, so you'll want to pause the video and rewind when you need to make sure you understand what he's explaining. It's important to take the time to understand and answer the questions in the worksheet because you'll use this information in a future assignment.

If instructed by your instructor, download detailed questions about the Climate Change: Lines of Evidence videos:

Video: What is Climate? Climate Change, Lines of Evidence: Chapter 1 (25:59)

Click for a transcript of What is Climate? Climate Change, Lines of Evidence.
Seven consecutive videos. Video #1 What is Climate? Climate Change, Lines of Evidence: Chapter 1. The National Academy of Sciences has produced this video to help summarize what is known about climate change. What is climate? Climate is commonly thought of as the average weather conditions at a given location or region over time. People understand climate in many familiar ways. For example, we know that winter will generally be cooler than summer. We also know the climate in the Mojave Desert will be much different than the climate in Greenland. Climate is measured by statistics such as average temperatures and rainfall and frequency of droughts. Climate change refers to changes in these statistics over seasons and year-to-year changes, as well as decades - over centuries and even over thousands of years, as with how Earth moves in and out of ice ages and warm periods. This video is intended to help people understand what has been learned about climate change. Enormous inroads have been made in increasing our understanding of climate change and its causes. And a clearer picture of current and future impacts is emerging. Research is also shedding light on actions that might be taken to limit the magnitude of climate change or adapt to its impacts. We lay out the evidence that human activities, especially the burning of fossil fuels, are responsible for much of the warming and related changes being observed on earth. The information is based on a number of national research council reports, each of which represents the consensus of experts who have reviewed hundreds of studies, describing many years of accumulating evidence. The overwhelming majority of climate scientists agree that human activities, especially the burning of fossil fuels, are responsible for most of the global warming being observed. But how is this conclusion reached? Climate science, like all science, is a process of collective learning that relies on the careful gathering and analysis of data, the formulation of hypotheses, and the development of computer models to help understand past and present change. It is the combined use of observations and models that help test scientific understanding, in order to help predict future change. Scientific knowledge builds over time, as new observations and data become available. Confidence in our understanding grows when independent global analysis, by scientific groups in different countries, show the same warming pattern, or if other explanations can be ruled out. In the case of climate change, scientists have understood for more than a century that emissions from the burning of fossil fuels should lead to an increase in the Earth's average surface temperature. Decades of observations and research have confirmed and extended this understanding. Video #2 Is Earth Warming? Climate Change, Lines of Evidence: Chapter 2 How do we know that earth is warmed? Scientists have been taking widespread global measurements of Earth's surface temperature for centuries. By the 1880s, there was enough data to produce reliable estimates of global average temperature. These data have steadily improved and today temperatures are recorded by thermometers at many thousands of locations, both on land and over the oceans. Different research groups, including NASA's Goddard Institute for Space Studies, Great Britain's Hadley Center, and the Japanese Meteorological Agency, have used these raw measurements to produce records of long-term surface temperature change. Research groups work carefully to make sure the data aren't skewed by such things as changes in the instruments taking the measurements, or by other factors that affect local temperature, such as additional heat that has come from the gradual growth of cities. These analyses all show that Earth's average surface temperature has increased by more than 1.4 degrees Fahrenheit over the past 100 years, with much of this increase taking place over the past 35 years. A temperature change of one point four degrees Fahrenheit may not seem like much if you're thinking about a daily or seasonal fluctuation. However, it is a significant change when you think about a permanent increase averaged across the entire planet. For example, one point four degrees is more than the average annual temperature difference between Washington, DC and Charleston, South Carolina, which is more than 450 miles south of Washington. Think about this. On any given day, a difference of nine degrees Fahrenheit might be the difference between wearing a sweater or not. But a change of nine degrees in the global average temperature is the estimated difference between the climate of today and an ice age. In addition to surface temperature, other parts of the climate system are also being monitored carefully. For example, a variety of instruments are used to measure temperature, salinity, and currents beneath the ocean surface. Weather balloons are used to probe the temperature, humidity, and winds in the atmosphere. A key breakthrough in the ability to track global environmental changes began in the 1970s, with the dawn of the era of satellite remote sensing. Many different types of sensors, carried on many dozens of satellites, have allowed us to build a truly global picture of changes in the temperature of the atmosphere, and of the ocean and land surfaces. Satellite data are also used to study shifts in precipitation and changes in land cover. Even though satellites do not measure temperature in the same way as instruments on the surface of Earth, and any errors would be of a completely different nature, the two records agree. A number of other indicators of global warming have also been observed. For example, heat waves are becoming more frequent. Cold snaps are now shorter and milder. Snow and ice cover are decreasing in the northern hemisphere. Glaciers and ice caps around the world are melting and many plants and animal species are moving to different latitudes or higher altitudes due to changes in temperature. The picture that emerges from all of these datasets is clear and consistent. Earth is warming. Video #3 Greenhouse Gases: Climate Change, Lines of Evident: Chapter 3 How do we know that greenhouse gases lead to warming? As early as the 1820s scientists began to appreciate the importance of certain gases in regulating the temperature of Earth. Greenhouse gases, which include water vapor, carbon dioxide, methane, and nitrous oxide, act like a blanket covering the earth, trapping heat in the lower atmosphere, known as the troposphere. Although greenhouse gases are only a tiny fraction of Earth's atmosphere, they are critical for keeping the planet warm enough to support life as we know it. Here's how the greenhouse effect works. As the sun's energy hits earth, some of it is reflected back to space, but most of it is absorbed by land and oceans. This absorbed energy is then radiated upward from the surface of Earth in the form of heat. In the absence of greenhouse gases, this heat would simply escape to space and the planet's average surface temperature would be well below freezing. But greenhouse gases absorb and redirect some of this energy downward, keeping heat near the surface of Earth. As concentrations of heat trapping greenhouse gases increase in the atmosphere, Earth's natural greenhouse effect is amplified, like having a thicker blanket, and surface temperatures slowly rise. Reducing the levels of greenhouse gases in the atmosphere would cause a decrease in surface temperature. Video #4 Increased Emissions: Climate Change, Lines of Evidence: Chapter 4 How do we know humans are causing greenhouse gas concentrations to increase? Determining the human influence of greenhouse gas concentrations was challenging, because many greenhouse gases occur naturally in Earth's atmosphere. Carbon dioxide is produced and consumed in many natural processes that are part of the carbon cycle. Once humans began digging up long buried forms of carbon, such as coal and oil, and burning them for energy, additional CO2 was released into the atmosphere, much more rapidly than in the natural carbon cycle. Other human activities, such as cement production and cutting down forests, have also added CO2 to the atmosphere. Until the 1950s, many scientists thought the oceans would absorb most of the excess CO2 released by human activities. Then a series of scientific papers were published that examined the dynamics of carbon dioxide exchange between the ocean and atmosphere, including a paper by oceanographers Roger Revelle and Han Soos in 1957, and another by Bert Bolin and Erik Erikson in 1959. This work led scientists to the hypothesis that the oceans could not absorb all of the CO2 being emitted. To test this hypothesis, Ravel's colleague Charles David Keeling began collecting air samples at the Mauna Loa Observatory in Hawaii, to track changes in CO2 concentrations. Today such measurements are made at many sites around the world. The data reveal a steady increase in atmospheric CO2. To determine how CO2 concentration varied prior to modern measurements, scientists have studied the composition of air bubbles trapped in ice cores extracted from Greenland and Antarctica. These data show that for at least two thousand years before the Industrial Revolution, atmospheric CO2 concentration was steady and then began to rise sharply beginning in the late 19th century. Today atmospheric CO2 concentration exceeds 390 parts per million, around 40 percent higher than pre-industrial levels. And according to ice core data, higher than any point in the past 800,000 years. Human activities have increased the atmospheric concentrations of other important greenhouse gases as well. Methane, which is produced by the burning of fossil fuels, the raising of livestock, the decay of landfill wastes, the production and transport of natural gas, and other activities, increased sharply throughout the industrial age, before starting to level off at about two and a half times its pre-industrial level. Nitrous oxide has increased by roughly fifteen percent since 1750, mainly as a result of agricultural fertilizer use, but also from fossil fuel burning and certain industrial processes. Some industrial chemicals, such as chlorofluorocarbons used in refrigerants and spray cans, act as potent greenhouse gases and are long-lived in the atmosphere. However, the concentration of CFCs are decreasing due to the success of the 1989 Montreal Protocol, which banned their use. Because CFCs do not have natural sources, their increases can easily be attributed to human activities. In addition to direct measurements of atmospheric CO2 concentrations, there are detailed records of how much coal, oil, and natural gas is burned each year. Through science, estimates are made of how much CO2 is being absorbed on average, by the oceans and plant life on land. These analyses show that almost half of the excess CO2 emitted from human activity remains in the atmosphere for many centuries. Just as a sink will fill up if water enters faster than it can drain, human production of CO2 is outstripping Earth's natural ability to remove it from the air. As a result, atmospheric CO2 levels are increasing. A forensic style analysis of the CO2 in the atmosphere reveals the chemical fingerprints of natural and fossil fuel carbon. These lines of evidence prove conclusively that the increase in atmospheric CO2 is the result of human activities. Video #5 How Much Warming? Climate Change, Lines of Evidence: Chapter 5 How much are human activities heating earth? Greenhouse gases are referred to as forcing agents because of their ability to change the planets energy balance. A forcing agent can push Earth's temperature up or down. Greenhouse gases differ in their forcing power. For example, a single methane molecule has about 25 times the warming power of a single CO2 molecule. However, methane has a shorter lifetime in the atmosphere and is less abundant, while CO2 has a larger warming effect because it is much more abundant and stays in the atmosphere for much longer periods of time. Scientists can calculate the forcing power of greenhouse gases based on the changes in their concentrations over time, and on physically based calculations of how they transfer energy through the atmosphere. Some forcing agents push Earth's energy balance toward cooling, offsetting some of the heating associated with greenhouse gases. For example, some aerosols, which are tiny liquid or solid particles such as sea spray, or visible air pollution suspended in the atmosphere, have a cooling effect because they scatter a portion of incoming sunlight back into space. Human activities, especially the burning of fossil fuels, have increased the number of aerosol particles in the atmosphere, particularly over and around major urban and industrial areas. Changes in land use and land cover are another way that human activities are influencing Earth's climate, and deforestation is responsible for 10 to 20 percent of the excess CO2 emitted to the atmosphere. As mentioned previously, agriculture contributes nitrous oxide and methane. Changes in land use and land cover also modify the reflectivity of Earth's surface. The more reflective a surface, the more sunlight is sent back to space. Cropland is generally more reflective than undisturbed forest, while urban areas often reflect less energy than undisturbed land. Globally, human land-use changes have had a slight cooling effect. When all human agents are considered together, scientists have calculated that the net change in climate forcing, between 1750 in 2005, is pushing earth toward warming. The extra energy is about 1.6 watts per square meter on the surface of Earth. When multiplied by the total surface area of Earth, this represents more than 800 trillion watts of energy. This energy is being added to Earth's climate system every second of every day. That means each year we add to the climate system more than 50 times the amount of power produced annually, by all the power plants of the world combined. The total amount of warming that will occur in response to a climate forcing is determined by a variety of feedbacks, which either amplify or dampen the initial change. For example, as Earth warms, polar snow and ice melt away, allowing the darker colored land and oceans to absorb more heat, causing Earth to become even warmer, which leads to more snow and ice melt and so on. Another important feedback involves water vapor. The amount of water vapor in the atmosphere increases as the ocean surface and the lower atmosphere warm up. Warming of 1 degree Celsius or 1.8 degrees Fahrenheit increases water vapor by about 7%. Because water vapor is also a greenhouse gas, this increase causes additional warming. Feedbacks that reinforce the initial climate forcing are referred to in the scientific community as positive or amplifying feedbacks. There is an inherent lag time in the warming caused by a given forcing. This lag occurs because it takes time for parts of the Earth's climate system, especially the massive oceans, to warm or cool. Even if by magic we could hold all human produced forcing agents at present-day values, Earth would continue to warm well beyond the 1.4 degrees Fahrenheit already observed because of human emissions to date. Video #6 Solar Influence: Climate Change, Lines of Evidence: Chapter 6 How do we know the current warming trend isn't caused by the Sun? Another way to test the scientific theory is to investigate alternative explanations. Because the sun's output has a strong influence on Earth's temperature, scientists have examined records of solar activity to determine if changes in solar output might be responsible for the observed global warming trend. The most direct measurements of solar output are satellite readings, which have been available since 1979. These satellite records show that the sun's output has not shown a net increase during the past 30 years and thus cannot be responsible for the global warming during that period. Before satellites solar energy had to be estimated by more indirect methods, such as records of the number of sunspots observed each year, which is an indicator of solar activity. These indirect methods suggest that there was a slight increase in solar energy during the first half of the 20th century, and a decrease in the latter half. The increase may have contributed to warming in the first half of the century, but that does not explain warming in the latter part of the century. Further evidence that current warming is not a result of solar changes can be found in the temperature trends in the different layers of the atmosphere. These data come from two sources, weather balloons which have been launched twice daily from hundreds of sites around the world since the late 1950s, and satellites, which have monitored the temperature of different layers of the atmosphere since the late 1970s. Both of these datasets have been heavily scrutinized and both show a warming trend in the lower layer of the atmosphere, the troposphere, and a cooling trend in the upper layer, the stratosphere. This is exactly the vertical pattern of temperature change expected from increased greenhouse gases, which trap energy closer to the Earth's surface. If an increase in solar output were responsible for the recent warming trend, the vertical pattern of warming would be more uniform through the layers of the atmosphere. Video #7 Natural Cycles: Climate Change, Lines of Evidence: Chapter 7 How do we know that the current warming trend is not caused by natural cycles? Detecting human influence on climate is complicated by the fact that there are many natural variations in temperature, precipitation and other climate variables. These natural variations are caused by many different processes that can occur across a wide range of timescales, from a particularly warm summer or snowy winter, to changes over many millions of years. Among the most well-known short-term climate fluctuations are El Nino and La Nina, which are periods of natural warming and cooling in the tropical Pacific Ocean. Strong El Nino and La Nina are associated with significant year-to-year changes in temperature and rainfall patterns across many parts of the planet, including the United States. These events have been linked as causes of some extreme conditions, such as flooding in some regions and severe droughts in other areas. Globally, temperatures tend to be higher during El Nino periods such as 1998, and lower during La Nina periods such as 2008. But it is clear that these natural variations are notably smaller than the 20th century warming trend. Major eruptions like that of Mount Pinatubo in 1991, expel massive amounts of particles into the stratosphere that cooled the earth. However, surface temperatures typically rebound in two to five years, as the particles settle out of the atmosphere. The short-term cooling effects of large volcanic eruptions can be seen in the 20th century temperature record, as can the global temperature variations associated with strong El Nino and La Nina events. But an overall warming trend is evident. Natural climate variations can also be forced by slow orbital changes, affecting how solar energy impacts the earth climate system, as is the case with the ice age cycles. For the past 800,000 years, these longer-term natural cycles between ice ages and warm periods saw carbon dioxide fluctuating between around 180 parts per million, at the coldest points, up to about 300 parts per million at the warmest point. Today with carbon dioxide concentrations rising above 390 parts per million, we are overriding the natural cycle and forcing Earth's climate system into a warmer state. Attributing climate change to human activities relies on the combined assessment from observations, as well as information from climate models to help test scientific understanding. Scientists have used these models to simulate what would have happened if humans had not modified Earth's climate during the 20th century. In other words, how global temperatures would have evolved if only natural factors were influencing the climate system, such as volcanoes, the sun, or ocean cycles. These undisturbed earth simulations predict that in the absence of human activities there would have been negligible warming, or even a slight cooling, over the 20th century. When human greenhouse gas emissions and other activities are included in the models, the resulting surface temperatures more closely resemble the observed changes in temperature. Based on a rigorous assessment of available temperature records, climate forcing estimates, and sources of natural climate variability, scientists have concluded that there is more than a 90 percent chance that most of the observed global warming trend over the past 50 to 60 years can be attributed to emissions from the burning of fossil fuels and other human activities. Understanding the causes of climate change provides valuable information to help us manage our future, to find smarter more economical and better ways to produce the food, energy and technologies we need to live and thrive.

If the video does not show up, please watch on the NAS website.

Another resource you can use to help answer the questions is the booklet that goes with this video: Climate Change: Evidence, Impacts, Choices. It is 40 pages, so you might not want to print it. Use it as an online reference.

Penn State geology professor, Richard Alley's, 45-minute video uses earth science to tell the story of Earth's climate history and our relationship with fossil fuels. There is no worksheet associated with this video.

Optional Video: Earth: The Operators' Manual (53:42)

Click for a transcript of Earth: The Operators' Manual video.

RICHARD ALLEY: All across the planet, nations and cities are working to reduce their dependence on fossil fuels and promote sustainable energy options.

ANNISE PARKER: Because it's the smart thing, because it makes business sense, and it's the right thing. NARRATOR: In China, Europe, and Brazil, energy innovations are changing how we live. And in the US, every branch of the military is mobilizing to cut its carbon bootprint.

DAVID TITLEY: We really believe that the climate is changing.

RICHARD ALLEY: In this program, we'll share how we know Earth is warming and why and discover what Earth science tells us about clean, green energy opportunities. I'm Richard Alley. I'm a geologist at Penn State University. But my research has taken me around the planet, from Greenland to Antarctica. I'm fascinated by how our climate has changed dramatically and often, from times with ice everywhere to no ice anywhere on the planet. Records of past climate help us learn how our Earth operates. What has happened can happen again. And I know that sometimes, things change really fast. I'm a registered Republican, play soccer on Saturdays, and go to church on Sundays. I'm a parent and a professor. I worry about jobs for my students and my daughter's future. I've been a proud member of the UN Panel on Climate Change. And I know the risks. And I've worked for an oil company and know how much we all need energy. And the best science shows we'll be better off if we address the twin stories of climate change and energy, and that the sooner we move forward, the better. Our use of fossil fuels for energy is pushing us towards a climate unlike any seen in the history of civilization. But a growing population needs more and more clean energy. But I believe science offers us an operator's manual with answers to both of these huge challenges.

[MUSIC PLAYING] NARRATOR: "Earth-- The Operator's Manual" is made possible by NSF, the National Science Foundation, where discoveries begin.

RICHARD ALLEY: Humans need energy. We always have and always will. But how we use energy is now critical for our survival. It all began with fire. Today, it's mostly fossil fuels. Now we're closing in on 7 billion of us, and the planet's population is headed toward 10 billion. Our cities and our civilization depend on vast amounts of energy. Fossil fuels-- coal, oil, and natural gas-- provide almost 80% of the energy used worldwide. Nuclear is a little less than 5%, hydropower a little under 6%, and the other renewables-- solar, wind, and geothermal-- about 1%, but growing fast. Wood and dung make up the rest. Using energy is helping many of us live better than ever before. Yet well over 1.5 billion are lagging behind, without access to electricity or clean fuels. In recent years, Brazil has brought electricity to 10 million. But in rural Ceara, some still live off the grid-- no electricity, no running water, and no refrigerators to keep food safe. Life's essentials come from their own hard labor. Education is compulsory, but studying is a challenge when evening arrives. The only light is from kerosene lamps. They're smoky, dim, and dangerous. Someday, this mother prays, the electric grid will reach her home.

TRANSLATOR: The first thing I'll do when the electricity arrives in my house will be to say a rosary and give praise to God.

RICHARD ALLEY: More than half of China's 1.3 billion citizens live in the countryside. Many rural residents still use wood or coal for cooking and heating, although most of China is already on the grid. China has used energy to fuel the development that has brought more than 500 million out of poverty. In village homes, there are flat-screen TVs and air conditioners. By 2030, it's projected that 350 million Chinese-- more than the population of the entire United States-- will move from the countryside to cities, a trend that's echoed worldwide. Development in Asia, Africa, and South America will mean 3 billion people will start using more and more energy as they escape from poverty. Suppose we make the familiar, if old-fashioned, 100-watt light bulb our unit for comparing energy use. If you're off the grid, your share of your nation's energy will be just a few hundred watts, a few light bulbs. South Americans average about 13 bulbs. For fast-developing China, it's more like 22 bulbs. Europe and Russia, 5,000 watts, 50 bulbs, and North Americans, over 10,000 watts, more than 100 bulbs. Now let's replace those light bulbs with the actual numbers. Population is shown across the bottom and energy use displayed vertically-- off the grid to the left, North America to the right. If everyone everywhere started using energy at the rate North Americans do, the world's energy consumption would more than quadruple. And using fossil fuels, that's clearly unsustainable. No doubt about it-- coal, gas, and oil have brought huge benefits. But we're burning through them approximately a million times faster than nature saved them for us, and they will run out. What's even worse-- the carbon dioxide from our energy system threatens to change the planet in ways that will make our lives much harder. So why are fossil fuels such a powerful, but ultimately problematic, source of energy? Conditions on the waterways of today's Louisiana help us understand how fossil fuels are made and why they're ultimately unsustainable. Oil, coal, and natural gas are made from things-- mostly plants-- that lived and died long ago. It's taken hundreds and millions of years for nature to create enough of the special conditions that saved the carbon and energy and plants to form the fossil fuels that we use. Here's how it works. Plants, like these tiny diatoms encased in silica shells, grow in the upper layers of lakes and oceans, using the sun's energy to turn carbon dioxide and water into more plants. When they die, if they're buried where there's little oxygen to break them down, their chemical bonds retain the energy that began as sunlight. If enough carbon-rich matter is buried deeply enough for long enough, the Earth's heat and pressure turn it into fossil fuel, concentrating the energy that once fed the growing plants. Vary what goes into Earth's pressure cooker and the temperature, and you end up with the different kinds of fossil fuel. Woody plants make coal. Slimy plants, algae, will give you oil, and both of them give rise to natural gas. The fossil fuels formed over a few hundred million years, and we're burning them over a few hundred years. And if we keep doing that, sooner or later, they must run out. But there's a bigger problem with fossil fuels. As we've seen, they're made of carbon, primarily. And when you burn them, you add oxygen, and that makes CO2 that goes in the air. We're reversing the process by which they formed. And if we keep doing this, it must change the composition of Earth's atmosphere. What CO2 does was confirmed by basic research that had absolutely nothing to do with climate change.

REPORTER: A continuance of the Upper Air Program will provide scientific data concerning the physics of the upper atmosphere.

RICHARD ALLEY: World War II was over, but the Cold War had begun. The US Air Force needed to understand the atmosphere for communications and to design heat-seeking missiles. At certain wavelengths, carbon dioxide and water vapor block radiation, so the new missiles couldn't see very far if they used a wavelength that CO2 absorbs. Research at the Air Force Geophysics Laboratory in Hanscom, Massachusetts produced an immense database with careful measurements of atmospheric gases. Further research by others applied and extended those discoveries, clearly showing the heat-trapping influence of CO2. The Air Force hadn't set out to study global warming. They just wanted their missiles to work. But physics is physics. The atmosphere doesn't care if you're studying it for warring or warming. Adding CO2 turns up the planet's thermostat. It works the other way as well. Remove CO2, and things cool down. These are the Southern Alps of New Zealand, and their climate history shows that the physicists really got it right. These deep, thick piles of frozen water are glaciers-- slow-moving rivers of ice sitting on land. But once, when temperatures were warmer, they were liquid water stored in the sea. We're going to follow this one, the Franz Josef, from summit to ocean to see the real world impact of changing levels of CO2. It's beautiful up here on the highest snow field, but dangers lurk beneath the surface. I've spent a lot of time on the ice. It's standard practice up here to travel in pairs, roped up for safety. The glacier is fed by something like six meters of water a year-- maybe 20 meters, 60 feet of snowfall, so really seriously high snowfall. The snow and ice spread under their own weight, and it's headed downhill at something like a kilometer a year. When ice is speeding up a lot as it flows towards the coast, it can crack and open great crevasses that give you a view into the guts of the glacier. Man, this is a big one. 10, 20, 30, meters more, 100 feet or more heading down in here. And we can see a whole lot of the structure of the glacier right here.

MAN: So what we're going to do is just sit on the edge and then walk backwards, and then I'll lower you.

RICHARD ALLEY: Tell me when. OK. Roll her around, and down we go. Snowfall arrives in layers, each storm putting one down. Summer sun heats the snow and makes it look a little bit different than the winter snow. And so you build up a history. In these layers, there's indications of climate-- how much it snowed, what the temperature was. And all of this is being buried by more snow. And the weight of that snow squeezes what's beneath it and turns it to ice. And in doing that, it can trap bubbles. And in those bubbles are samples of old air-- a record of the composition of the Earth's atmosphere, including how much CO2 was in it, a record of the temperature on the ice sheets and how much it snowed. As we'll see, we can open those icy bottles of ancient air and study the history of Earth's atmosphere. This landscape also tells the story of the Ice Ages and the forces that have shaped Earth's climate. Over the last millions of years, the brightness of the sun doesn't seem to have changed much. But the Earth's orbit, and the tilt of its axis, have shifted in regular patterns over tens and hundreds of thousands of years. The orbit changes shape, varying how close and far the Earth gets as it orbits the sun each year. Over 41,000 years, the tilt of Earth's axis gets larger and smaller, shifting some of the sunshine from the Equator to the poles and back. And our planet has a slight wobble, like a child's top, altering which hemisphere is most directly pointed towards the sun when Earth is closest to it. Over tens of thousands of years, these natural variations shift sunlight around on the planet, and that influences climate. More than 20,000 years ago, decreasing amounts of sunshine in the Arctic allowed great ice sheets to grow across North America and Eurasia, reaching the modern sites of New York and Chicago. Sea level fell as water was locked up on land. Changing currents let the oceans absorb CO2 from the air. That cooled the Southern Hemisphere and unleashed the immense power of glaciers, such as the Franz Josef, which advanced down this wide valley, filling it with deep, thick ice. Now we're flying over today's coastline, where giant boulders are leftovers from that last ice age. A glacier is a great earth-moving machine. It's a dump truck that carries rocks that fall on top of it. It's a bulldozer that pushes rocks in front of it, and it outlines itself with those rocks, making a deposit that we call a moraine that tells us where the glacier has been. We're 20 kilometers, 12 miles, from the front of the Franz Josef glacier today. But about 20,000 years ago, the ice was depositing these rocks as it flowed past us and out to sea. The rocks we can still see today confirm where the glacier once was. Now, in a computer-generated time lapse condensing thousands of years of Earth's history, we're seeing what happened. Lower CO2, colder temperatures, more snow and ice, and the Franz Josef advanced. 20,000 years ago, 30% of today's land area was covered by great ice sheets which locked up so much water that the global sea level was almost 400 feet lower than today. And then, as Earth's orbit changed, temperatures and CO2 rose, and the glacier melted back. The orbits set the stage. But by themselves, there weren't enough. We need the warming and cooling effects of rising and falling CO2 to explain the changes we know happened. Today, atmospheric CO2 is increasing still more, temperatures are rising, and glaciers and ice sheets are melting. You can see this clearly on the lake formed by the shrinking Tasman Glacier across the range from the Franz Josef. This is what the end of an ice age looks like-- glaciers falling apart, new lakes, new land, icebergs coming off the front of the ice. In the early 1980s, we would have been inside New Zealand's Tasman Glacier right here. Now we're passing icebergs in a new lake from a glacier that has mostly fallen apart and ends over six kilometers, four miles away. One glacier doesn't tell us what the world is doing. But while the Tasman has been retreating, the great majority of glaciers on the planet have gotten smaller. This is the Columbia Glacier in Alaska. It's a type of glacier that makes the effects of warming easy to see. It's been retreating so fast that the Extreme Ice Survey had to reposition their time-lapse cameras to follow its motion. In Iceland, warming air temperatures have made this glacier simply melt away, leaving streams and small lakes behind. Thermometers in the air show warming. Thermometers in the air far from cities show warming. Put your thermometer in the ground, in the ocean, look down from satellites-- they show warming. The evidence is clear. The Earth's climate is warming. This frozen library, the National Ice Core Lab in Denver, Colorado, has ice from all over, kept at minus 35 degrees. The oldest core here goes back some 400,000 years. Here, really ancient ice from Greenland in the north and Antarctica in the south reveals Earth's climate history. Let's see what cores like this can tell us. First are those layers I mentioned in the New Zealand snow. They've turned to ice, and we can count them-- summer, winter, summer, winter. Like tree rings, we can date the core. Other cores tell other stories. Look at this. It's the ash of an Icelandic volcano that blew up to Greenland 50,000 years ago. Cores hold other, and even more important, secrets. Look at these bubbles. They formed as the snow turned to ice and trapped old air that's still in there. Scientists now are working with cores from Antarctica that go back even further. They tell us, with a very high degree of accuracy, how much carbon dioxide was in the air that far back. Researchers break chunks of ice in vacuum chambers and carefully analyze the gases that come off. They're able to measure, very precisely, levels of carbon dioxide in that ancient air. Looking at the cores, we see a pattern that repeats-- 280 parts per million of CO2, then 180, 280, 180, 280. By analyzing the chemistry of the oxygen atoms in the ice, you can also see the pattern of rising and falling temperature over time-- colder during the ice ages, warmer during the interglacial periods. Now put the two lines together, and you can see how closely temperature and carbon dioxide track each other. They're not exactly alike. At times, the orbits caused a little temperature change before the feedback effects of CO2 joined in. But just as we saw in New Zealand, we can't explain the large size of the changes in temperature without the effects of CO2. This is the signature of natural variation, the cycle of the ice ages driven by changes in Earth's orbit with no human involvement. But here's where we are today. In just 250 years since the Industrial Revolution, we've blown past 380 with no sign of slowing down. It's a level not seen in more than 400,000 years, 40 times longer than the oldest human civilization. So physics and chemistry tell us that adding carbon dioxide to the atmosphere warms things up, and Earth's climate history shows us there will be impacts, from melting ice sheets to rising sea level. But how do we know, with equal certainty, that it's not just more natural variation, that humans are the source of the increasing CO2? When we look at a landscape like this one, we know immediately that volcanoes put out all sorts of interesting things, and that includes CO2. So how do we know that the rise of CO2 in the atmosphere that we see comes from our burning of fossil fuels and not from something that the volcanoes have done? Well, the first step in the problem is just bookkeeping. We measure how much CO2 comes out of the volcanoes. We measure how much CO2 comes out of our smokestacks and tailpipes. The natural source is small. Humans are putting out 50 to 100 times more CO2 than the natural volcanic source. We can then ask the air whether our bookkeeping is right, and the air says that it is. Volcanoes make CO2 by melting rocks to release the CO2. They don't burn, and they don't use oxygen. But burning fossil fuels does use oxygen when it makes CO2. We see that the rise in CO2 goes with the fall of oxygen, which says that the rising CO2 comes from burning something. We can then ask the carbon in the rising CO2 where it came from. Carbon comes in three flavors-- the lightweight, carbon-12, which is especially common in plants, the medium weight, carbon-13, which is a little more common in the gases coming out of volcanoes, and the heavyweight, carbon-14. It's radioactive and decays almost entirely after about 50,000 years, which is why you won't find it in very old things, like dinosaur bones or fossil fuels. We see a rise in carbon-12 which comes from plants. We don't see a rise of carbon-13, so the CO2 isn't coming from the volcanoes. And we don't see a rise in carbon-14, so the CO2 can't be coming from recently living plants. And so the atmosphere says that the rising CO2 comes from burning of plants that have been dead a long time. That is fossil fuels. The CO2 is coming from our fossil fuels. It's us. So physics and chemistry show us carbon dioxide is at levels never seen in human history. And the evidence says it's all of us burning fossil fuels that's driving the increase. But what about climate change and global warming? Are they for real? Here's what those who have looked at all the data say about the future.

MAN: Climate change, energy security, and economic stability are inextricably linked. Climate change will contribute to food and water scarcity, will increase the spread of disease, and may spur or exacerbate mass migration.

RICHARD ALLEY: Who do you suppose said that? Not a pundit, not a politician. The Pentagon. These war games at Fort Irwin, California provide realistic training to keep our soldiers safe. The purpose of the Pentagon's Quadrennial Defense Review, the QDR, is to keep the nation safe. The review covers military strategies for an uncertain world. The Pentagon has to think long-term and be ready for all contingencies. The 2010 QDR was the first time that those contingencies included climate change. Rear Admiral David Titley is oceanographer of the Navy and contributed to the Defense Review.

DAVID TITLEY: Well, I think the QDR really talks about climate change in terms that really isn't for debate. And you take a look at the global temperatures. You take a look at sea level rise. You take a look at what the glaciers are doing-- not just one or two glaciers, but really glaciers worldwide. And you add all of those up together, and that's one of the reasons we really believe that the climate is changing. So the observations tell us that. Physics tells us this as well.

RICHARD ALLEY: What climate change means for key global hotspots is less clear.

DAVID TITLEY: We understand the Earth is getting warmer. We understand the oceans are getting warmer. What we do not understand is exactly how that will affect things like strong storms, rainfall rates, rainfall distribution. So yes, climate change is a certainty, but what is it going to be like in specific regions of the world, and when?

RICHARD ALLEY: One area of particular concern to the Navy is sea level rise.

DAVID TITLEY: Sea level rise is going to be a long-term and very, very significant issue for the 21st century.

RICHARD ALLEY: The QDR included an infrastructure vulnerability assessment that found that 153 Naval installations are at significant risk from climatic stresses. From Pearl Harbor, Hawaii to Norfolk, Virginia, the bases and their nearby communities will have to adapt.

DAVID TITLEY: Even with one to two meters of sea level rise, which is very, very substantial, we have time. This is not a crisis, but it is certainly going to be a strategic challenge.

RICHARD ALLEY: Globally, climate change is expected to mean more fires, floods, and famine. Nations may be destabilized. For the Pentagon, climate change is a threat multiplier. But with sound climate science, Titley believes forewarned is forearmed.

DAVID TITLEY: The good thing is the science is advanced enough in oceanography, glaciology, meteorology that we have some skill at some frames of predicting this. And if we choose to use those projections, we can, in fact, by our behavior, alter the future in our favor. RICHARD ALLEY: Titley and the Pentagon think the facts are in.

DAVID TITLEY: Climate change is happening, and there is very, very strong evidence that a large part of this is, in fact, man-made.

RICHARD ALLEY: The military is America's single largest user of energy, and it recognizes that its use of fossil fuels has to change. The Pentagon uses 300,000 barrels of oil each day. That's more than 12 million gallons. An armored Humvee gets four miles to the gallon. At full speed, an Abrams battle tank uses four gallons to the mile. And it can cost as much as $400 a gallon to get gas to some remote bases in Afghanistan. Fort Irwin is a test bed to see if the Army can operate just as effectively while using less fossil fuel and more renewables. And it's not just Fort Irwin in the Army. At Camp Pendleton, Marines were trained on an energy-saving experimental forward operating base that deployed with them to Afghanistan.

ROBERT HEDELUND: Before any equipment goes into theater, we want Marines to get trained on it. So what are some of the things that we can take hold of right away and make sure that we can make a difference for the warfighter down range? RICHARD ALLEY: They test out different kinds of portable solar power units. They also practice how to purify stagnant water and make it drinkable. The Army and Marines both want to minimize the number of convoys trucking in fuel and water. A report for the Army found that in five years, more than 3,000 service members had been killed or wounded in supply convoys.

ROBERT HEDELUND: And if you've got Marines guarding that convoy, and God forbid, it get hit by an IED, then what are the wounded, what are the deaths involved in that? And are we really utilizing those Marines and that capability the way we should?

RICHARD ALLEY: Generators used to keep accommodations livable and computers running are also major gas guzzlers.

ADORJAN FERENCZY: Right now, what we're doing is putting up a power shade. It has flexible solar panels on the top and gives us enough power to run small electronics, such as lighting systems and laptop computers. It also provides shade over the tent structure. Experimenting with this equipment in Africa proved that it could reduce the internal temperature of the tent seven to 10 degrees.

RICHARD ALLEY: All the LED lights in the entire tent use just 91 watts, less than one single old-fashioned incandescent bulb.

ADORJAN FERENCZY: It's a no-brainer when it comes to efficiency.

RICHARD ALLEY: Light-emitting diodes don't weigh much, but they're still rugged enough to survive a typical Marine's gentle touch.

ZACH LYMAN: When we put something into a military application and they beat it up, it's ruggedized. It's ready for the worst that the world can take. And so one thing that people say is if the military has used this thing and they trust it, then maybe it's OK for my backyard.

RICHARD ALLEY: Renewable energy will also play an important role at sea and in the air. The Navy's Makin Island is an amphibious assault ship with jump jets, helicopters, and landing craft. It's the first vessel to have both gas turbines and a hybrid electric drive, which it can use for 75% of its time at sea. This Prius of the ocean cut fuel costs by $2 million on its maiden voyage. By 2016, the Navy plans to have what it calls a Great Green Fleet, a complete carrier group running on renewable fuels with nuclear ships, hybrid electric surface vessels, and aircraft flying only biofuels. By 2020, the goal is to cut usage of fossil fuels by 50%. Once deployed in Afghanistan, the XFOB cut down on gas used in generators by over 80%. In the past, the Pentagon's innovations in computers, GPS, and radar have spun off into civilian life. In the future, the military's use of renewable energy can reduce dependence on foreign oil, increase operational security, and save lives and money.

JIM CHEVALLIER: A lot of the times, it is a culture change more than anything else. And the Department of Defense, over the years, has proved, time and time again, that they can lead the way in that culture change.

RICHARD ALLEY: If the US military is the largest user of energy in America, China is now the largest consumer on the planet. At 1.3 billion, China has a population about four times larger than the US, so average per-person use in CO2 emissions remain about 1/4 those of Americans. But like the US Military, China is moving ahead at full speed on multiple different sustainable energy options. And it pretty much has to. Cities are congested. The air is polluted. Continued rapid growth using old technologies seems unsustainable. This meeting in Beijing brought together mayors from all over China, executives from state-owned enterprises, and international representatives. The organizer was a US-Chinese NGO headed by Peggy Liu.

PEGGY LIU: Over 20 years, we're going to have 350 million people moving into cities in China. And we're going to be building 50,000 new skyscrapers, the equivalent of 10 Manhattans, 170 new mass transit systems. It's just incredible, incredible scale.

RICHARD ALLEY: This massive, rapid growth comes with a high environmental cost.

MARTIN SCHOENBAUER: They recognize that they're spending as much as 6% of their gross domestic product on environmental issues.

RICHARD ALLEY: In 2009, China committed $35 billion, almost twice as much as the US, TO energy research and incentives for wind, solar, and other clean energy technologies. It's attracted an American company to set up the world's most advanced solar power research plant. China now makes more solar panels than any other nation. But it's also promoting low-tech, low-cost solutions. Solar water heaters are seen on modest village homes. Some cities have them on almost every roof.

PEGGY LIU: China is throwing spaghetti on the wall right now in terms of over 27 different cities doing LED street lighting, or over 20, 30 different cities doing electric vehicles.

RICHARD ALLEY: But visit any city, and you can see that the coal used to generate more than 70% of China's electricity has serious consequences with visible pollution and adverse health effects. China uses more coal than any other nation on Earth, but it's also trying to find ways to burn coal more cleanly.

PEGGY LIU: In three years, 2006 to 2009, while China was building one new coal-fired power plant a week, it also shut down inefficient coal plants. So it's out with the old and in with the new. And they're really trying hard to invent new models.

RICHARD ALLEY: This pilot plant, designed for carbon capture and sequestration, was rushed to completion in time for Shanghai's 2010 World Expo. It absorbs and sells carbon dioxide and will soon scale up to capture 3 million tons a year that could be pumped back into the ground, keeping it out of the air.

MARTIN SCHOENBAUER: Here in China, they are bringing many plants online in a much shorter time span it takes us in the US. PEGGY LIU: China is right now the factory of the world. What we'd like to do is turn it into the clean tech laboratory of the world. RICHARD ALLEY: If nations choose to pay the price, burning coal with carbon capture can offer the world a temporary bridge until renewables come to scale. PEGGY LIU: China is going to come up with the clean energy solutions that are cost-effective and can be deployed at large scale-- in other words, solutions that everybody around the world wants.

RICHARD ALLEY: Can low-carbon solutions really give us enough energy to power the planet and a growing population? Let's put some numbers on how much energy we can get from non-fossil fuel renewables. Today, all humans everywhere on Earth use about 15.7 terawatts of energy. That's a big number. In watts, that's 157 followed by 11 0's, or 157 billion of those 100-watt light bulbs we used as a reference. To show what's possible, let's see if we can get to 15.7 terawatts using only renewable energy. I'm here in the Algodones Dunes near Yuma, Arizona. The Guinness Book of Records says it's the sunniest place in the world. There's barely a cloud in the daytime sky for roughly 90% of the year. 0.01%, 1/100 of 1%-- if we could collect that much of the sun's energy reaching the Earth, it would be more than all human use today. Today's technologies have made a start. This was the world's first commercial power station to use a tower to harvest concentrated solar energy. Near Seville, Spain, 624 mirrors stretch over an area of more than 135 acres, beaming back sunlight to a tower nearly 400 feet high. Intense heat produces steam that drives the turbine, which generates electricity. When completed, this one facility will be able to power 200,000 homes, enough to supply the entire nearby city of Seville. Remember our target of 15.7 terawatts? Well, the sun delivers 173,000 terawatts to the top of Earth's atmosphere, 11,000 times current human use. No way we can capture all of that potential energy at Earth's surface. But the deserts of America's Southwest, with today's technology, have enough suitable land to supply 80% of the entire planet's current use. Of course, there's one big problem with solar power-- night. But with more efficient transmission lines, and as part of a balanced renewable energy portfolio that includes storage, the sun's potential is vast. In tropical nations like Brazil, the sun heats water, makes clouds, and unleashes rainfall that feeds some of the planet's largest rivers. Iguazu Falls is a tourist attraction, one of the most spectacular waterfalls on Earth, where you can feel the immense power of falling water. The nearby Itaipu Dam on the border of Brazil in Paraguay produces the most hydroelectric power of any generating station in the world. This one dam supplies most of the electricity used in Sao Paulo, a city of more than 11 million. Sao Paulo is 600 miles away, but Brazil made the decision to build innovative, high-voltage direct current transmission lines to minimize energy loss. The Itaipu to Sao Paulo electrical grid has been in operation since 1984 and shows that renewable energy can go the distance. Dams can't be the answer for every nation. They flood landscapes, disrupt ecosystems, and displace people. But hydropower gives Brazil, a nation larger than the continental United States, 80% of its electricity. And worldwide, hydropower could contribute 12% of human energy use, ready at a moment's notice in case the sun goes behind a cloud. Brazil is also using its unique natural environment in another way. Its tropical climate provides ideal conditions for sugarcane, one of the Earth's most efficient plants in its ability to collect the energy of sunlight. Plantations like this one harvest the cane for the production of sugar and the biofuel called ethanol. The US is actually the number one producer of ethanol in the world, mostly using corn instead of cane. But ethanol made from sugar cane is several times more efficient at replacing fossil fuel than corn-based ethanol. Modern facilities like this one pipe back wet waste to fertilize the fields and burn the dry waste, called the gas, to generate electricity to run the factory. For Brazil, at least, ethanol works. Today, almost all cars sold in Brazil can use flex fuels. Drivers choose gasoline blended with 25% ethanol or pure ethanol, depending on price and how far they plan to drive. Local researchers say that if all the gasoline in the world suddenly disappeared, Brazil is the only nation that could go it alone and keep its cars running. Using food for fuel raises big questions in a hungry world. As of now, sugarcane ethanol hasn't affected food prices much. But there are concerns with corn. So here in the US, government labs like NREL, the National Renewable Energy Lab, have launched programs to see if biofuels can be made from agricultural waste. It does work, and researchers are trying to bring the cost down. So with plants capturing roughly 11 times human energy use, they're a growing opportunity. New Zealand takes advantage of another kind of energy. These are the geysers and hot springs at Rotorua on the North Island. Once, they were used by the native Maori people for cooking and bathing. Now geothermal power plants harvest heat and turn it into as much as 10% of all New Zealand's electricity. Many power projects are partnerships with the Maori, benefiting the local people and avoiding the "not in my backyard" problems that often complicate energy developments. Globally, geothermal energy offers three times our current use. But we can mine geothermal, extracting the energy faster than nature supplies it, cooling the rocks deep beneath us to make power for people. This energy exists even where you don't see geysers and mud pots, so it can be extracted without harming these natural wonders. A study by MIT showed that the accessible hot rocks beneath the United States contain enough energy to run the country for 130,000 years. And like hydroelectric, geothermal can provide peaking power, ready to go at a moment's notice if the sun doesn't shine and the wind doesn't blow. Mining energy from deep, hot rocks is a relatively new technology, but people have been using windmills for centuries, and the wind blows everywhere. Here's where the United States is very lucky. Let's take a trip up the nation's wind corridor, from Texas in the South to the Canadian border. Bright purple indicates the strongest winds. All along this nearly 2,000 miles, there's the potential to turn a free, non-CO2-emitting resource into electricity. But that takes choices and actions by individuals and governments. Here's what's been happening in West Texas. It's a land of ranches and farms and, of course, oil rigs and pump jacks. But in the early '90s, this was one of the most financially depressed areas in the state. Communities like Nolan Divide fell on hard times. Schools closed. People moved away. But since 1999, the new structures towering above the flat fields aren't oil derricks, but wind turbines. The largest number-- more than 1,600-- is in Nolan County. Greg Wortham is Mayor of Sweetwater, the county seat.

GREG WORTHAM: It wasn't a philosophical or political decision. It was ranchers and farmers and truck drivers and welders and railroads. and wind workers.

RICHARD ALLEY: Steve Oatman's family has been ranching the Double Heart for three generations. Steve may have doubts about the causes of climate change, but not about wind energy.

STEVE OATMAN: But it's been a blessing. It helps pay taxes. It helps pay the feed bill. Rosco, 30 May.

GREG WORTHAM: We talk about this being green energy because it pays money. The ranchers and the farmers call it mailbox money. They have to get up, and sweat, and work hard all day long. Things are pretty stressful. And if you can just walk to the mailbox and pick up some money because you've got turbines above the ground, that makes life a lot easier. RICHARD ALLEY: Each windmill can generate between $5,000 and $15,000 per year. So a ranch with an average of 10 to 20 turbines can provide financial stability for people who have always lived with uncertainty.

STEVE OATMAN: I don't just believe in it because I make a living from it. It's something that's going to have to happen for the country.

RICHARD ALLEY: So now, local schools have growing enrollments and funds to pay for programs.

GREG WORTHAM: We had about $500 million in tax based in the whole county in 2000. And by the late part of that decade, in less than 10 years, it went up to $2.5 billion in tax value.

RICHARD ALLEY: By the end of 2009, the capacity of wind turbines in West Texas totaled close to 10,000 megawatts. If Texas were a country, it would rank sixth in the world in wind power. The US Department of Energy estimates that wind could supply 20% of America's electricity by 2030. New offshore wind farms would generate more than 43,000 new jobs. That translates into a $200-billion boost to the US economy. Worldwide, wind could provide almost 80 times current human usage. No form of energy is totally free of environmental concerns or hefty startup costs. Some early wind farms gave little consideration to birds and other flying critters, like migrating bats. But recent reports by Greenpeace and the Audubon Society have found that properly sighted and operated turbines can minimize problems. Mayor Wortham, for one, welcomes wind turbines into his backyard.

GREG WORTHAM: We like them. Some people don't. But we're more than happy to export our energy to those states who want to buy green, but don't want to see green.

STEVE OATMAN: In the long run, I hope we have wind turbines everywhere they can produce energy. We need them. That's what America is going to have to do. That's the next stepping stone to save ourselves.

RICHARD ALLEY: The state of Texas has invested $5 billion to connect West Texas wind to big cities like Dallas and Fort Worth. Farther south is Houston, one of the most energy-hungry cities in the country. Its port is America's largest by foreign tonnage, and its refineries and chemical plants supply a good portion of the nation. But already, perhaps surprisingly, Houston is the largest municipal purchaser of renewable energy in the nation. 30% of the power city government uses comes from wind, with a target of 50%. And its mayor wants to cut energy costs and increase energy efficiency.

ANNISE PARKER: I want to go from the oil and gas capital of the world to the green and renewable energy capital of the world.

RICHARD ALLEY: Supported by federal stimulus dollars, the local utility is ahead of schedule to install smart meters. These will help consumers economize on energy use. The city has already installed 2,500 LED traffic lights using 85% less energy than traditional incandescent bulbs. That translates into savings of $3.6 million per year. City Hall thinks it can also improve air quality by changing the kinds of cars Houstonians drive.

ANNISE PARKER: If

RICHARD ALLEY: The city already operates a fleet of plug-in hybrids. Now it's encouraging the development of an infrastructure to make driving electric vehicles easy and practical. And in Houston's hot and humid environment, it helps to have an increasing number of energy-efficient, LEED-certified buildings. ANNISE PARKER: We're going to do it because it's the smart thing, because it makes business sense, and it's the right thing.

RICHARD ALLEY: Some estimates are that the US could save as much as 23% of projected demand from a more efficient use of energy.

ANNISE PARKER: Well, if you're going to tackle energy efficiency, you might as well do it in a place that is a profligate user of energy. And when you make a difference there, you can make a difference that's significant.

RICHARD ALLEY: Globally, efficiency could cut the demand for energy by 1/3 by 2030. Bottom line-- there are many ways forward, and we can hit that renewable energy target. And if next-generation nuclear is also included, one plan has the possible 2030 energy mix transformed from one relying on fossil fuels to one that looks like this, with renewables-- sun, wind, geothermal, biomass, and hydropower-- totaling 61%, fossil fuels down to 13%, and existing and new nuclear making up the balance. Another plan meets world energy needs with only wind, water, and solar. And in fact, there are many feasible paths to a sustainable energy future. Today's technologies can get us started, and a commitment to research and innovation will bring even more possibilities. We've traveled the world to see some of the sources the planet offers to meet our growing need for clean energy. There's too many options to cover all of them here. And besides, each nation, each state, each person must make their own choices as to what works best for them. But the central idea is clear. If we approach Earth as if we have an operator's manual that tells us how to keep the planet humming along at peak performance, we can do this. We can avoid climate catastrophes, improve energy security, and make millions of good jobs. For "Earth-- The Operator's Manual," I'm Richard Alley.

NARRATOR: "Earth-- The Operator's Manual" is made possible by NSF, the National Science Foundation, where discoveries begin.

[MUSIC PLAYING] For the annotated, illustrated script with links to information on climate change and sustainable energy, web-exclusive videos, educator resources, and much more, visit pbs.org. "Earth-- The Operator's Manual" is available on DVD. The companion book is also available. To order, visit shoppbs.org, or call us at 1-800-PLAY-PBS.

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