81. Sources - Human Activities Sources of greenhouse gases. The Problem Four Major greenhouse gases The atmospherehas always contained carbon dioxide, methane and nitrous oxide. http://globalwarming.enviroweb.org/ishappening/sources/

Sources of Greenhouse Gases The Problem: Four Major Greenhouse Gases The atmosphere has always contained carbon dioxide, methane and nitrous oxide. These gasestogether with water vaporcreate the natural greenhouse effect. They trap some of the sun's energy and keep the Earth warm enough to sustain life. By increasing some of these heat-trapping gasesand adding new oneswe intensify the natural greenhouse effect and further warm the atmosphere. This chart shows how much warming could be caused by each of the gases that human activities release. Carbon dioxide accounts for three fourths of the predicted increase in the greenhouse effect. Previous The Ozone Hole Next Section Carbon Dioxide Sources of Greenhouse Gases: Carbon dioxide Methane ... Nitrous oxide Design and construction by Knauer Communications

82. BBC - Climate Change - From The BBC Weather Centre - Greenhouse Gases The greenhouse gases. Almost all of the Earth’s atmosphere (99%)is made up of nitrogen (about 78%) and oxygen (about 21%). While http://www.bbc.co.uk/climate/evidence/greenhouse_gases.shtml

CATEGORIES TV RADIO COMMUNICATE ... INDEX SEARCH SUNDAY 23rd March 2003 Text only BBC Homepage Climate Change Evidence ... Help Like this page? Send it to a friend! The Greenhouse Gases Carbon dioxide Methane Nitrous oxide Ozone ... Halocarbons Although the proportion of the trace gases in the atmosphere appears relatively small, they can still have a big impact on climate change - and they are mainly caused by human activities. Privacy

83. BBC - Hot Topics - Climate Change - Key Points Should we reduce greenhouse gases? greenhouse gases made by humans (such asCFCs and carbon dioxide) may be responsible for these temperature rises. http://www.bbc.co.uk/science/hottopics/climatechange/index.shtml

CATEGORIES TV RADIO COMMUNICATE ... INDEX SEARCH SUNDAY 23rd March 2003 Text only BBC Homepage Science Beasts ... Help Like this page? Send it to a friend! HOT TOPICS Updated August : 22 : 2002 Climate Change Contents Key points Video : melting polar ice-caps Is the climate changing? Should we reduce greenhouse gases? Quiz : are you an environmental angel? The greenhouse effect Animation: how the greenhouse effect works The Kyoto Treaty Vote : is the climate changing? Timeline of events Key points By 2070, temperature increases could cause: - flooding as polar ice caps melt, raising sea levels - extreme weather events due to shifting ocean currents - deserts to spread across Europe as land dries up Greenhouse gases made by humans (such as CFCs and carbon dioxide) may be responsible for these temperature rises Scientists dispute whether or not these manufactured greenhouse gases significantly affect climate change The Kyoto Treaty was set up in 1997 to reduce greenhouse gas emissions. In 2001 the US pulled out of the agreement Is the climate changing?

84. USGS Carbon Cycle Research-Greenhouse Gases USGSScience for a Changing World USGS Global Change Research Program. Exchangesof greenhouse gases, Water Vapor, and Heat at the Earth's Surface. http://geochange.er.usgs.gov/pub/carbon/ghg/

Exchanges of Greenhouse Gases, Water Vapor, and Heat at the Earth's Surface Atmospheric turbulence transports greenhouse gases (notably: carbon dioxide (CO ), methane, and nitrous oxide), water vapor, and heat between Earth's land and water surfaces and the overlying atmosphere. These exchanges influence climate, viability of ecosystems, distribution of biomes, and the quantity of both surface- and ground-water. Using the eddy covariance method (explained later, below) derived from fundamental micrometeorological theory, the exchanges of greenhouse gases, water vapor, and heat may be directly measured to better understand interactions between Earth's surface and atmosphere. Lake-atmosphere CO exchange Wind, temperature, humidity, and CO concentration sensing instruments on tower in Williams Lake. Raft contains data logging and logistical support equipment. Researcher adjusting micrometeorological instruments on tower in Williams Lake. Although lakes occupy only a small fraction of Earth's surface area, study of the CO exchange between them and the atmosphere is needed to better define the carbon cycle and to improve our understanding of air-water gas transfer over much larger water bodies such as oceans. Williams Lake (part of the USGS's

85. C&EN: Climate Change CLEANER FUTURE FOR FOSSIL FUELS C EN, October 7, 2002. greenhouse gases C EN,September 16, 2002. HOW TO REDUCE greenhouse gases C EN, May 27, 2002. http://pubs.acs.org/cen/climate/climatearchive.html

Home Contact Us This page last revised November 4, 2002 CLIMATE NEGOTIATIONS PROGRESS TOWARD MEETING KYOTO GOALS CLEANER FUTURE FOR FOSSIL FUELS GREENHOUSE GASES ... CASE GROWS FOR CLIMATE CHANGE Industry Reactions TEXAS COMMISSION RECONSIDERS NOx ACCOUNTING FOR GREENHOUSE GASES FORD SETS CO2 REDUCTIONS OIL FIRMS ACT TO CURB CLIMATE CHANGE ... Companies agree on climate-change actions Go To Industry Reactions Home Contact Us

86. C&EN: TODAY'S HEADLINES - GREENHOUSE GASES 2347. ENVIRONMENT greenhouse gases. Firms affairs. AEP itself says it isthe biggest emitter of greenhouse gases in the Western Hemisphere. On http://pubs.acs.org/cen/topstory/8104/8104notw2.html

Table of Contents Today's Headlines Editor's Page Business ... What's That Stuff? Back Issues Safety Letters Chemcyclopedia ACS Members can Join ACS January 27, Volume 81, Number 4 CENEAR 81 4 p. 12 ISSN 0009-2347 ENVIRONMENT GREENHOUSE GASES Firms set up emissions exchange; President Bush pushes voluntary cuts BETTE HILEMAN Photo by Harry Walker L eading u.s. and interna tional companies and the city of Chicago are setting up a program called the Chicago Climate Exchange The 13 company members include American Electric Power (AEP), Baxter International, DuPont, Ford Motor Co., Motorola, and Manitoba Hydro. "These companies have demonstrated tremendous leadership. They really believe that a proactive approach to climate change advances everyone's long-term interests," CCX Chairman Richard L. Sandor says. CCX will enable its members to buy and sell emissions credits in order to find the most cost-effective way of achieving reductions. Trading will begin in the spring of 2003. "Through CCX, we hope to demonstrate the viability of a multisector greenhouse gas trading program," says Dale E. Heydlauff, AEP's senior vice president of governmental and environmental affairs. AEP itself says it is the biggest emitter of greenhouse gases in the Western Hemisphere. On a related front, White House officials are touring the country asking industries from all sectors to promise to reduce their greenhouse gas emissions to help reach the Administration's goal of an 18% reduction in the amount of greenhouse gases emitted per unit of gross domestic product from 2002 to 2012. Industry achieved roughly the same reduction in greenhouse gas intensity from 1990 to 2000, but at the same time total emissions rose by about 12%.

87. NOVA Online/Cracking The Ice Age/Greenhouse - Green Planet But greenhouse gases counteract that heat loss, trapping heat, andreflecting it back towards the Earth. The more greenhouse gases http://www.pbs.org/wgbh/nova/ice/greenhouse.html

Greenhouse - Green Planet Of all the planets in our solar system, the Earth is the only one that as far as we know supports life. So why is our planet alone so hospitable? In part, we owe our existence to a process called the greenhouse effect. Inside an artificial greenhouse filled with plants, the surrounding glass traps the sun's energy, making it warm inside, even while outside the temperature may be much colder. This same effect happens every day on the Earth. Gases within the atmosphere act like glass, trapping the sun's heat. These gases include water vapor, carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons (CFCs). Just like any other planet, the Earth absorbs the sun's heat and radiates it back towards space. But greenhouse gases counteract that heat loss, trapping heat, and reflecting it back towards the Earth. The more greenhouse gases in the atmosphere, the more heat that is trapped. The less the amount of greenhouse gases, the less heat that is trapped. Earth has just the right amount to help life flourish. Too many of these gases, as is the case on Venus, would create a runaway greenhouse and a sizzling hot surface. On the other hand, without any greenhouse gases, much of the sun's heat would be lost, and the Earth would become a frozen wasteland with an average temperature of degrees fahrenheit (-18 degrees celsius). Each greenhouse gas has its own important role in trapping the sun's heat, the most significant of which is water vapor. On a clear day, water vapor can comprise 60 to 70 percent of the greenhouse effect. Next in line, carbon dioxide contributes an additional 25 percent. Some gases trap solar radiation from the sun better than others. For example, while man-made CFCs are one of the least plentiful gases, they actually have a greater relative impact than many others.

88. Understanding Greenhouse Gases Understanding greenhouse gases greenhouse gasess are those in the airthat absorb some of the infrared radiation the Earth gives off. http://www.usatoday.com/weather/climate/wco2.htm

U.S. states Alabama Alaska Arizona Arkansas California Colorado Connecticut Delaware Wash., DC Florida Georgia Hawaii Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Mass. Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hamp. New Jersey N. Mexico New York N. Carolina N. Dakota Ohio Oklahoma Oregon Penn. R. Island S. Carolina S. Dakota Tennessee Texas Utah Vermont Virginia Washington W. Virginia Wisconsin Wyoming World Africa Asia Australia Caribbean Canada C. America Europe Mexico Middle East S. America S. Pacific USA Inside Weather World cities Almanac Highways Satellite ... City Guides 11/07/00- Updated 02:06 PM ET Understanding greenhouse gases Greenhouse gasess are those in the air that absorb some of the infrared radiation the Earth gives off. This warms the gases and the surrounding air. The gases also radiate infrared energy back to the Earth. The greenhouse gases help control the Earth's temperature. USATODAY.com graphic explains the greenhouse effect The air near the surface of the earth is a mixture of gases with nitrogen being the most common and oxygen the second most common. Nitrogen accounts for 78.08% of the volume of the gas in the air and oxygen for 20.95%. The remaining 0.97% is accounted for by several other gases including carbon dioxide and water vapor, the two most important greenhouse gases. Carbon dioxide The amount of carbon dioxide in the air has grown from around 290 parts per mission by volume (ppmv)around 1900 to about 366 ppmv at the end of 1998. In other words, at the end of 1998, for every million molecules of gasses in the air, 366 of them were carbon dioxide. This is the same as 0.0366% carbon dioxide by volume.

89. NASA GISS: Are Increasing Greenhouse Gases Creating An Arctic Ozone Hole? Skip to page content. Are Increasing greenhouse gases Creating anArctic Ozone Hole? By Drew Shindell. Figure 1 Past and projected http://www.giss.nasa.gov/research/intro/shindell_02/

Are Increasing Greenhouse Gases Creating an Arctic Ozone Hole? By Drew Shindell Figure 1: Past and projected abundances for carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), chlorofluorocarbons (CFCs), and chlorine (Cly) used in the model simulation. Ozone holes are caused by chemical reactions that take place primarily on the surface of polar stratospheric clouds, ice particles, or liquid droplets, which form at high altitudes in the extreme cold of the polar regions. The number of particles that form, and therefore the amount of chemical ozone destruction, is extremely sensitive to small changes in stratospheric temperature. Hence, even small amounts of stratospheric cooling can greatly increase ozone depletion. In fact, it is because stratospheric temperatures in the Northern Hemisphere winter/spring are generally slightly warmer than those in the Southern Hemisphere that ozone losses over the Arctic have been much smaller than over the Antarctic during the 1980s and early 1990s. However, the Arctic stratosphere has gradually cooled over the past few decades. Very large ozone losses have been observed there recently, especially in 1997. Why might this be happening, and what is likely to happen in the future? The well-known increase in greenhouse gas emissions is one possible cause of the observed trends. We have investigated the coupled chemistry-climate response to projected emissions of

90. NASA GISS: Greenhouse Gases: Refining The Role Of Carbon Dioxide Skip to page content. greenhouse gases Refining the Role of Carbon Dioxide. By QianchengMa. There has been growing interest in the global temperature of Earth. http://www.giss.nasa.gov/research/intro/ma_01/

Greenhouse Gases: Refining the Role of Carbon Dioxide By Qiancheng Ma The concentration of greenhouse gases, especially carbon dioxide and methane, has fluctuated naturally over geological time scales. While the mechanisms responsible for these fluctuations are unclear, the temperature of Earth has responded to them by switching between ice age and interglacial conditions, i.e., periods of reduced and increased greenhouse warming. In addition to these slow natural variations, the atmospheric concentrations of these gases are being changed rapidly (on a geological time scale) by human activity as we burn fossil fuels, clear forests, and use gasoline-dependent transportation. In particular, the amount of carbon dioxide (CO ) has increased by 30% since pre-industrial times (from about 270 molecules of CO per million molecules of air in 1850 to the present 360 parts per million), and continues to rise over time, due primarily to the burning of fossil fuel. Because carbon dioxide can drive climate change, it is important to be able to accurately determine its heat absorption characteristics. The spectrum of heat absorption by Earth's atmosphere contains hundreds of thousands of absorption "lines". For carbon dioxide alone there are over sixty thousand lines. In order to model the absorption spectrum of CO , we need to know the spectral location (wavelength), the strength, and also the shape of each line. If we visualize the absorption line as an inverted bell-shaped curve, the depth

91. Argonne Transportation - GREET Model The greenhouse gases, Regulated Emissions, and EnergyUse in Transportation (GREET) Model. Last Update. http://www.transportation.anl.gov/ttrdc/greet/

The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) Model Last Update How Does GREET Work? Uses of GREET Download V1.5/V1.6 Beta Publications How Does GREET Work? To fully evaluate energy and emission impacts of vehicle technologies, the fuel cycle from wells to wheels and the vehicle cycle through material recovery and vehicle disposal need to be considered. Sponsored by the U.S. Department of Energy's Office of Transportation Technologies, Argonne has developed a fuel-cycle model called GREET (Greenhouse gases, Regulated Emissions, and Energy use in Transportation). It allows researchers to evaluate various engine and fuel combinations on a consistent fuel-cycle basis. GREET was developed as a multidimensional spreadsheet model in Microsoft Excel. This public domain model is available free of charge for anyone to use ( download information ). The first version of GREET was released in 1996. Since then, Argonne has continued to update and expand the model. For a given engine and fuel system, GREET separately calculates the following:

92. Global Carbon Cycle And Greenhouse Gases The Global Carbon Cycle and greenhouse gases. Ocean / Atm Sci / ESS588 (A Program on Climate Change class). Meeting times and place http://www.ocean.washington.edu/courses/oc588/

The Global Carbon Cycle and Greenhouse Gases Ocean / Atm Sci / ESS 588 (A Program on Climate Change class) Meeting times and place: Mondays 4:00-5:30pm, Thursdays 2:30-4:00pm : 425 OSB On weeks where Monday is a holiday we will meet on Tuesday 4:00-5:30pm Faculty: Steven Emerson , Oceanography, 419 OSB, 543-0428, emerson@u.washington.edu Office hours: Wednesdays 1:00-3:00pm Ginger Armbrust , Oceanography, 175 MAR, 616-1738, armbrust@ocean.washington.edu Office hours: by appointment , Atmospheric Sciences, 306 ATG, 685-2679, jaegle@atmos.washington.edu Office hours: by appointment TA: Roberta Hamme , Oceanography, 420 OSB, 221-6740, rhamme@ocean.washington.edu Office hours: drop in or by appointment Syllabus: Assignments: Reading Assignments Problem Sets Final Project OSB = Ocean Sciences Building , MAR = Marine Studies Building , ATG = Atmospheric Sciences / Geophysics Building

93. Global Warming greenhouse gases trap heat, and thus warm the earth because they prevent asignificant proportion of infrared radiation from escaping into space. http://www.fueleconomy.gov/feg/climate.shtml

Site Map Links More Info Search ... Protect the Environment Global Warming Oil Spills Air Pollution Conserve Resources Reduce Oil Imports ... Save Money America is truly blessed with a vibrant and flourishing environment. But with blessings, come responsibility. There is much more to do. I encourage Americans to join me in renewing our commitment to protecting the environment and leaving our children and grandchildren with a legacy of clean water, clean air, and natural beauty. President George W. Bush Earth Day, April 21, 2001 The earth's well-being is an issue important to America. And it's an issue that should be important to every nation in every part of our world. As President Bush has emphasized, the issue of climate change respects no border. Its effects cannot be reined in by an army nor advanced by any ideology. Climate change, with its potential to impact every corner of the world, is an issue that must be addressed by the world.

94. Air Products And Chemicals, Inc. -- Environmental, Health, And Safety Climate Change/greenhouse gases. In 1998, Air Products joined the Pew Center onGlobal Climate Change in its effort to combat the problem of climate change. http://www.airproducts.com/ehs/change.asp

Gases Equipment Delivery Systems Your Business ... Medical Surveillance Climate Change/Greenhouse Gases In 1998, Air Products joined the Pew Center on Global Climate Change in its effort to combat the problem of climate change. Launched in May of that year, the Pew Center on Global Climate Change was established with $5 million in support from one of the nation's largest philanthropies, The Pew Charitable Trusts. The Pew Center is conducting studies, launching public education efforts, promoting climate change solutions globally, and working with businesses to develop marketplace solutions to reduce greenhouse gases. At Air Products, we have developed a global climate change policy that states: We are concerned about the potential effects of global climate change on world economies and the quality of life for world populations Even though the science of climate change is still evolving, we are committed to monitoring and responsibly managing energy consumption on a global basis as our primary focus for minimizing greenhouse gas emissions We will continue to invest in new, more energy-efficient products, practices, and technologies which enable us to cost-effectively manage energy resources

95. Bush Praises Industry Commitment To Reduce Greenhouse Gases Climate Change. 12 February 2003. Bush Praises Industry Commitment to Reduce GreenhouseGases. Statement coincides with rollout of business challenge initiative. http://usinfo.state.gov/topical/global/climate/03021201.htm

Climate Change 12 February 2003 Bush Praises Industry Commitment to Reduce Greenhouse Gases Statement coincides with rollout of business challenge initiative President Bush says the nation's major industrial sectors have announced ambitious commitments to reduce their heat-trapping greenhouse gas emissions – a major step toward the goal of reducing U.S. greenhouse gases by 18 percent in the next decade. In a White House statement released February 12, the president said the United States is taking "prudent steps" to address the challenge of global climate change by reducing projected greenhouse gas emissions in the near-term, while devoting greater resources to improving climate change science and developing advanced energy technologies over the long-term. The statement was released to coincide with the rollout of the president's business challenge climate change initiative called "Climate VISION," which stands for "Climate, Voluntary Innovative Sector Initiatives: Opportunities Now." "A year ago, I challenged American businesses to develop new, voluntary initiatives to reduce greenhouse gas emissions," Bush said in his statement. "I am pleased to announce today that 12 major industrial sectors ... and many of America's leading corporations have committed to actions that will prevent millions of tons of greenhouse gas emissions in the coming decade." The president's Climate VISION initiative, formally announced by Energy Secretary Spencer Abraham at a ceremony February 12, calls on American businesses and industries to undertake broader efforts to reduce greenhouse gases in the future, and recognizes the significant initiatives that energy-intensive sectors of the U.S. economy are already undertaking.

96. USGS Glossary global warming An increase in the average temperature of the Earth'ssurface, which occurs following an increase in greenhouse gases. http://interactive2.usgs.gov/glossary/index.asp?ini=d:\asp_ini\m3_dictionary.ini

97. Stormy Weather - Greenhouse Gases The Main greenhouse gases THE MAIN greenhouse gases. n/a = not applicable n/k= not known. PreIndustrial. Concentration. (1860). Concentration in 2000 (1). http://www.earthfuture.com/stormyweather/greenhouse/

by Guy Dauncey with Patrick Mazza The Main Greenhouse Gases THE MAIN GREENHOUSE GASES n/a = not applicable n/k = not known Pre-Industrial Concentration Concentration in 2000 ( Average atmospheric lifetime( Growth Rate % per yr. Anthropogenic Sources (from human activities) Global Warming Potential (GWP) over 100 years( Current Radiative Forcing Watts per sq. meter( Current Share of Overall Climate Change( Water Vapor Variable 1-3 parts per 100 Variable 1-3 parts per 100 Few days All of the below( n/a( n/a n/a Carbon Dioxide CO2 288 ppm 370 ppm Rising by 1.5 ppm per year 50 - 200 years Fossil fuel combustion (75%) Poor forest management (n/a) Deforestation (24%) Cement production (0.6%) Poor soil management (n/a) Methane CH4( 750 ppb 1750 ppb 12 years Fossil fuel extraction (20%) Dams, reservoirs (20%)

98. Planet Ark : Greenhouse Gases Rise To Exchange-traded Status greenhouse gases rise to exchangetraded status. http://www.planetark.org/dailynewsstory.cfm/newsid/19479/story.htm

Subscribe to daily environment news Recycling Near You A Current Affair -"Gunns" story Select a topic from this pull-down menu Read the latest Reuters World Environment News Look at the latest Reuters Environment News Pictures Receive free daily news headlines via email Search the Planet Ark News Archive Find out about National Tree Day Visit the Planet Ark Media Centre Download our free environmental software Who are Planet Ark? Find out how YOU can help the planet Find out about the local recycling services available in your area Greenhouse gases rise to exchange-traded status Mail this story to a friend Printer friendly version USA: January 20, 2003 CHICAGO - The greenhouse gases that companies pump into the atmosphere will soon go the way of soybeans and pork bellies - the right to pollute the air is about to become a tradeable commodity. Officials from the Chicago Climate Exchange announced last week its Internet-based market for greenhouse gases, such as methane and carbon dioxide, will begin trading in the spring of this year. The four-year pilot program aims to reduce greenhouse gas emissions by 50 million to 60 million tons by 2006. CCX currently has 14 members, ranging from the City of Chicago to Ohio-based American Electric Power (AEP.N), the largest carbon dioxide emitter in the United States. Exchange officials are hopeful they will attract more members and will be able to extend the pilot program beyond 2006.

99. INEEL Feature Story - Linking Energy Use And Greenhouse Gases Featured Research Linking Energy Use greenhouse gases Taking stock of gassy goods INEEL creates a method to link energy use, greenhouse gases Related links http://www.inel.gov/featurestories/00-09ghginventory.shtml

Security/Privacy HOME A-Z Index Staff Directory ... Jobs Saturday March 22, 2003 Feature Stories Featured Research Taking stock of gassy goods - INEEL creates a method to link energy use, greenhouse gases Related links: Carbon Sequestration Research By Mary Beckman, for INEEL Research Communications September 2000 It's an engineering problem. The scientists will be debating the effects for a long time, but the engineers can do something about it now. In a first step to understanding how to mitigate the effects of greenhouse gases on our environment, engineers have created a method to convert the numbers on an energy bill to the production of greenhouse gases. Systems engineer David Shropshire's research into more accurately assessing the different, complex scenarios for reducing greenhouse gas production was presented at this year's Third Annual Dixy Lee Ray Memorial Symposium in Washington, D.C. on the morning of August 30, 2000. The symposium is an international conference to discuss technologies to manage the carbon that human activities disperse to the environment. A COMMON CUR "Greenhouse gas" refers to carbon dioxide, methane, nitrous oxide and other gases that are thought to trap solar energy and cause changes to the world's environment. The gases are created through common industrial processes and also by using fossil fuel-based energy. Some energy production methods, such as hydroelectric and nuclear power, are "cleaner" than others and produce less or no greenhouse gases.

100. ESA Portal - Protecting The Environment - A Warmer World Awaits: Fact Or Fiction that have been associated with changes in global climate caused by human activity particularly the pumping of so-called greenhouse gases into the atmosphere. http://www.esa.int/export/esaCP/ESA19NZ84UC_Protecting_0.html

ESA Life in Space Expanding Frontiers Improving Daily Life ... Benefits for Europe 23-Mar-2003 03:41:05 UT Services Subscribe Contact Us Search All ESA Home Advanced Search Planet Earth as seen by the Apollo 17 astronauts A warmer world awaits: Fact or fiction? 10 December 2001 ESA Info 14-2001. Record global temperatures, melting polar ice caps and glaciers, shorter winters, reduced snow cover, rising sea level, increased coastal flooding, more frequent hurricanes, dramatic shifts in the distribution of wildlife, vegetation and diseases, and changes in ocean currents. These are just some of the consequences that have been associated with changes in global climate caused by human activity - particularly the pumping of so-called greenhouse gases into the atmosphere. No one disputes that, with a population exceeding 6 billion today and likely to become 9 billion in 50 years, the potential of humanity to alter our planet is now far greater than at any time during the previous 3,000 years of human history. However, the key questions remain. Is human interference with Nature really causing long-term changes to our climate? Just how realistic are the apocalyptic predictions? Greenhouse Earth Our Earth is a fertile oasis in space. The blue planet so admired by astronauts lies approximately 150 million km from the Sun. At this distance, our water-covered world should be frozen, a globe covered in a sheet of ice. On an airless Earth, the average surface temperature would be 33 degrees lower: -18°C instead of the present average temperature of +15°C. Only the atmosphere prevents Earth from freezing. In particular, the presence of certain heat-trapping gases - the "greenhouse" gases - provides our Earth with the mild, stable temperature that makes it so hospitable for life.

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