Earth's surface has undergone unprecedented warming over the last century, particularly over the last two decades. Astonishingly, every single year since 1992 is in the current list of the 20 warmest years on record.[1,2] The natural patterns of climate have been altered. Like detectives, science sleuths seek the answer to "Whodunnit?" — are humans part of the cause? To answer this question, patterns observed by meteorologists and oceanographers are compared with patterns developed using sophisticated models of Earth's atmosphere and ocean. By matching the observed and modeled patterns, scientists can now positively identify the "human fingerprints" associated with the changes. The fingerprints that humans have left on Earth's climate are turning up in a diverse range of records and can be seen in the ocean, in the atmosphere, and at the surface.
Because most global warming emissions remain in the atmosphere for decades or centuries, the energy choices we make today greatly influence the climate our children and grandchildren inherit. We have the technology to increase energy efficiency, significantly reduce these emissions from our energy and land use, and secure a high quality of life for future generations. We must act now to reduce dangerous consequences.
In its 2001 report, the Intergovernmental Panel on Climate Change stated, "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities." [3] Carbon dioxide from fossil fuel burning and land clearing has been accumulating in the atmosphere, where it acts like a blanket keeping Earth warm and heating up the surface, ocean, and atmosphere. As a result, current levels of carbon dioxide in the atmosphere are higher than at any time during the last 650,000 years. [4,5,6]
Background: Driving the Climate ("Forcing")
Climate is influenced by many factors, both natural and human. [7] Things that increase temperature, such as increases in heat-trapping emissions from cars and power plants or an increase in the amount of radiation the sun emits, are examples of "positive" forcings or drivers. Volcanic events and some types of human-made pollution, both of which inject sunlight-reflecting aerosols into the atmosphere, lower temperature and are examples of "negative" forcings or drivers. Natural climate drivers include the sun's energy output, aerosols from volcanic activity, and changes in snow and ice cover. Human climate drivers include heat-trapping emissions from cars and power plants, aerosols from pollution, and soot particles.
Much as the Air Force develops computer programs to simulate aircraft flight under different conditions, climate scientists develop computer programs to simulate global climate changes under different conditions. These programs use our knowledge of physical, chemical, and biological processes that occur within Earth's atmosphere and oceans and on its land surfaces. Mathematical models allow scientists to simulate the behavior of complex systems such as climate and explore how these systems respond to natural and human factors.
Fingerprint 1: The Ocean Layers Warm
The world's oceans have absorbed about 20 times as much heat as the atmosphere over the past half-century, leading to higher temperatures not only in surface waters but also in water 1,500 feet below the surface. [8,9] The measured increases in water temperature lie well outside the bounds of natural climate variation.
Fingerprint 2: The Atmosphere Shifts
Recent research shows that human activities have lifted the boundary of Earth's lower atmosphere. Known as the troposphere (from the Greek tropos, which means "turning"), this lowest layer of the atmosphere contains Earth's weather. The stable layer above is called the stratosphere. The boundary that separates the two layers, the tropopause, is as high as nine miles above the equator and as low as five miles above the poles. In an astounding development, a 2003 study showed that this tropopause has shifted upward over the last two decades by more than 900 feet. [10] The rising tropopause marks another human fingerprint on Earth's climate.
In their search for clues, scientists compared two natural drivers of climate (solar changes and volcanic aerosols) and three human drivers of climate (heat-trapping emissions, aerosol pollution, and ozone depletion), altering these one at a time in their sophisticated models. Changes in the sun during the twentieth century have warmed both the troposphere and stratosphere. But human activities have increased heat-trapping emissions and decreased stratospheric ozone. This has led to the troposphere warming more because the increase in heat-trapping emissions is trapping more of Earth's outgoing heat. The stratosphere has cooled more because there is less ozone to absorb incoming sunlight to heat up the stratosphere. Both these effects combine to shift the boundary upward. Over the period 1979-1999, a study shows that human-induced changes in heat-trapping emissions and ozone account for more than 80 percent of the rise in tropopause height. [10] This is yet another example of how science detectives are quantifying the impact of human activities on climate.
Fingerprint 3: The Surface Heats Up
Measurements show that global average temperature has risen by 1.4 degrees Fahrenheit in the last 100 years, with most of that happening in the last three decades. [1,2] By comparing Earth's temperature over that last century with models comparing climate drivers, a study showed that, from 1950 to the present, most of the warming was caused by heat-trapping emissions from human activities [3]. In fact, heat-trapping emissions are driving the climate about three times more strongly now than they were in 1950. The spatial pattern of where this warming is occurring around the globe indicates human-induced causes. Even accounting for the occasional short-lived cooling from volcanic events and moderate levels of cooling from aerosol pollution as well as minor fluctuations in the sun's output in the last 30 years, heat-trapping emissions far outweigh any other current climate driver. Once again, our scientific fingerprinting identifies human activities as the main driver of our warming climate.
Human Causes, Human Solutions
The identification of humans as the main driver of global warming helps us understand how and why our climate is changing, and it clearly defines the problem as one that is within our power to address. Because of past emissions, we cannot avoid some level of warming from the heat-trapping emissions already present in the atmosphere, some of which (such as carbon dioxide and nitrous oxide) last for 100 years or more. However, with aggressive emission reductions as well as flexibility in adapting to those changes we cannot avoid, we have a small window in which to avoid truly dangerous warming and provide future generations with a sustainable world. This will require immediate and sustained action to reduce our heat-trapping emissions through increased energy efficiency, expanding our use of renewable energy, and slowing deforestation (among other solutions).
Melanie Fitzpatrick (Earth and Space Sciences and Atmospheric Sciences at the University of Washington and UCS consultant) prepared this summary with input from Brenda Ekwurzel (Union of Concerned Scientists) and reviews by Philip Mote (Climate Impacts Group at the University of Washington and Washington's state climatologist), Richard Gammon (Chemistry, Oceanography, and Atmospheric Sciences at the University of Washington) and Peter Frumhoff (Union of Concerned Scientists). (c)2006 Union of Concerned Scientists
References
1. U.S. National Aeronautics and Space Administration (NASA) Goddard Institute for Space Studies. 2006. Global temperature trends: 2005 summation. New York, NY. Online at http://data.giss.nasa.gov/gistemp/2005.
2. U.S. National Oceanic and Atmospheric Administration (NOAA) National Climate Data Center. 2006. Climate of 2005 - annual report. Asheville, NC. Online at http://www.ncdc.noaa.gov/oa/climate/research/2005/ann/global.html.
3. Intergovernmental Panel on Climate Change. 2001. Climate change 2001: The scientific basis. Cambridge, UK: Cambridge University Press.
4. EPICA. 2004. Eight glacial cycles from an Antarctic ice core. Nature 429:623-628.
5. Petit, J.R., J. Jouzel, D. Raynaud, N.I. Barkov, J.-M. Barnola, I. Basile, M. Bender, J. Chappellaz, M. Davis, G. Delaygue, M. Delmotte, V.M. Kotlyakov, M. Legrand, V.Y. Lipenkov, C. Lorius, L. Pépin, C. Ritz, E. Saltzman, and M. Stievenard. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399:429-436.
6. Siegenthaler, U., T.F. Stocker, E. Monnin, D. Lüthi, J. Schwander, B. Stauffer, D. Raynaud, J.-M. Barnola, H. Fischer, V. Masson-Delmotte, and J. Jouzel. 2005. Stable carbon cycle-climate relationship during the late Pleistocene. Science 310:1313-1316.
7. Hansen, J., L. Nazarenko, R. Ruedy, M. Sato, J. Willis, A. Del Genio, D. Koch, A. Lacis, K. Lo, S. Menon, T. Novakov, J. Perlwitz, G. Russell, G.A. Schmidt, and N. Tausnev. 2005. Earth's energy imbalance: Confirmation and implications. Science 308:1431-1435.
8. Barnett, T.P., D.W. Pierce, K.M. AchutaRao, P.J. Gleckler, B.D. Santer, J.M. Gregory, and W.M. Washington. 2005. Penetration of human-induced warming into the world's oceans. Science 309:284-287.
9. Levitus, S., J. Antonov, and T. Boyer. 2005. Warming of the world ocean, 1955-2003. Geophysical Research Letters 32. Online at http://www.agu.org (doi:10.1029/2004GL021592).
10. Santer, B.D., M.F. Wehner, T.M.L. Wigley, R. Sausen, G.A. Meehl, K.E. Taylor, C. Ammann, J. Arblaster, W.M. Washington, J.S. Boyle, and W. Bruggemann. 2003. Contribution of anthropogenic and natural forcing to recent
20 Ekim 2011 Perşembe
14 Ekim 2011 Cuma
The Greenhouse Effect
Anyone who has either spent time in a greenhouse for plants or simply gotten into a car on a hot summer day has personally experienced the greenhouse effect. Heat enters an enclosed area and then reflects back and forth building upon itself. While the ambient temperature outside might be 85 degrees Fahrenheit, inside an automobile the temperature easily zooms upward to 130F. Simply put, the greenhouse effect is what happens when heat is trapped in one way or another and then increases as more heat radiation is added.
This is fine if you are an orchid or other tropical plant. But living things, including people, require set parameters of climate. When we discuss the greenhouse effect as regarding global warming we place the effect into a specific environment. That is the Earth’s atmosphere. When referencing the Earth, our entire planet becomes the interior of an automobile in the heat of summer. The Earth of course does not have a metal roof or a glass dome around it to trap heat and reflect solar radiation back to its surface. Indeed when drawings depict and descriptions explain the greenhouse effect the principle is simplified to imply that this is the case. Actually the greenhouse effect for the Earth is somewhat different.
When solar radiation passes through out atmosphere the molecules that constitute our air absorb it. The majority of solar heat is absorbed by our planet’s surface. Different types of surfaces absorb or reflect heat in different ways. A white blanket of snow will reflect much more heat than freshly paved asphalt. Still everything that the sun’s rays fall upon either absorbs or reflects heat. In the case of out snowy Polar Regions that heat is reflected back from the planet. In the case of our cities it is trapped on the surface. From there it radiates outward where living things attempt to adjust to the relative heat or cold. Our planet’s original design was for a balance of all the components. Our atmosphere absorbs enough heat to keep us warm but hopefully not bake us. The angle of the sun in areas such as the poles creates an environment suited to North and South Pole inhabitants. The people, creatures and plant life at the Earth’s equator have acclimated to their section of the world.
The greenhouse effect occurs planet wide when solar radiation either bounces off of or is radiated forth from the earth and instead of passing through our atmosphere and outward into space, is absorbed by all kinds of extra amounts of and extraneous gases and particles. These gases et al absorb heat and then radiate it outward in all directions, one of those directions, being the surface of the Earth. From there the process repeats itself until we have a global version of a car with the windows rolled up parked in the noonday sun.
This is fine if you are an orchid or other tropical plant. But living things, including people, require set parameters of climate. When we discuss the greenhouse effect as regarding global warming we place the effect into a specific environment. That is the Earth’s atmosphere. When referencing the Earth, our entire planet becomes the interior of an automobile in the heat of summer. The Earth of course does not have a metal roof or a glass dome around it to trap heat and reflect solar radiation back to its surface. Indeed when drawings depict and descriptions explain the greenhouse effect the principle is simplified to imply that this is the case. Actually the greenhouse effect for the Earth is somewhat different.
When solar radiation passes through out atmosphere the molecules that constitute our air absorb it. The majority of solar heat is absorbed by our planet’s surface. Different types of surfaces absorb or reflect heat in different ways. A white blanket of snow will reflect much more heat than freshly paved asphalt. Still everything that the sun’s rays fall upon either absorbs or reflects heat. In the case of out snowy Polar Regions that heat is reflected back from the planet. In the case of our cities it is trapped on the surface. From there it radiates outward where living things attempt to adjust to the relative heat or cold. Our planet’s original design was for a balance of all the components. Our atmosphere absorbs enough heat to keep us warm but hopefully not bake us. The angle of the sun in areas such as the poles creates an environment suited to North and South Pole inhabitants. The people, creatures and plant life at the Earth’s equator have acclimated to their section of the world.
The greenhouse effect occurs planet wide when solar radiation either bounces off of or is radiated forth from the earth and instead of passing through our atmosphere and outward into space, is absorbed by all kinds of extra amounts of and extraneous gases and particles. These gases et al absorb heat and then radiate it outward in all directions, one of those directions, being the surface of the Earth. From there the process repeats itself until we have a global version of a car with the windows rolled up parked in the noonday sun.
Causes of Global Warming -1
Let us start our examination of Global warming with a study of its causes. Global warming is an overall state of existence that is the cumulative effect of hundreds of environmental factors. All of these join together in both a linear and random model to show global warming as a chain of events.
Most modern attention to the problem of global warming began with discussion of depletion of the Earth’s Ozone layer. Ozone (O3) is a molecular form of Oxygen. The Ozone layer is a relatively thin strata of these molecules set in the lower portion of the Earth’s stratosphere.
Depletion of the Earth’s Ozone layer has resulted in a large increase in Ultra Violet Radiation reaching the surface of the earth. Does this increase in UV rays equate to global warming? Not really. In fact most scientific opinion is that depletion of the Ozone layer results in cooling of both the stratosphere and troposphere. So why mention depletion of the Ozone layer as regards to global warming? Because it represents a needed balance between harmful radiation being allowed to reach the earth’s surface and our desire to stem the rapid increase in our air and water temperature. Remember, we are viewing global warming as a chain of events.
global-warming-3What is the most significant cause of global warming?
The primary cause of global warming is Carbon Dioxide emissions. CO2 is being pumped into our atmosphere at an insane pace; 8 billion tons of CO2 entered the air last year. Of course some of this is due to natural activity such as volcanic eruptions and people breathing. But the Earth is equipped to easily absorb those into the normal regenerative process. No, the beginning of global warming was caused by fossil fuels being burned and emitting plenty of CO2.
Currently in the world 40% of all CO2 emissions are caused by power plants. These are burning coal, natural gas and diesel fuel. Some power plants burn garbage. Some burn methane made from garbage. And discounting those super green electrical generating plants designed to issue negligible pollutants, all of our power plants let loose into the atmosphere CO2.
33% of all the CO2 sent forth is the product of cars and trucks. Internal combustion engines burning fossil fuels…gasoline and diesel spew forth a retching amount of CO2.
3.5% of all CO2 emissions are released from aircraft traveling our friendly skies. Unfortunately, jets and other aircraft deliver their payload of pollutants directly into the troposphere.
The numbers can be confusing
12% of all CO2 released into the atmosphere is related to buildings. This figure varies from one source to the next. Some place the percentage of emissions from buildings as high as 33%. What most of these figures do not address is the actual cause of the CO2 emissions. In newly constructed buildings, production of materials used in building and energy used during construction are sited as the cause of carbon dioxide emissions. In existing buildings the CO2 created by the energy upkeep of the building is the root of the emissions quotient. The general comparison is that buildings consume energy in the way that cars burn fuel. But the pollutants created in providing power for heating, air-conditioning, lights and other usage in buildings has already been factored. Honestly this double billing accounting is more the product of auto manufacturers looking to point the blame for global warming away from gas guzzling cars.
The point to remember is that 98% of all CO2 emissions are related to energy production and 80% of these emissions become greenhouse gases.
Continuing the chain…global-warming-5
Which now mentioned allows us to follow our chain of event’s leading to global warming into the next most defined cause… Methane gas. Methane is released into the atmosphere from a dozen major sources. These include natural and man made emissions. Natural release of Methane is primarily from wetlands, (including agriculture) termites, the ocean, and hydrates. Non-organic releases are based from, landfills, livestock, waste treatment, and biomass burning. (More energy production). Almost all of this is offset by the Earth’s ability to absorb around 97% of the methane released into the air. But that remaining 3% is a serious problem. The molecular structure of Methane makes it 20 times as powerful a Greenhouse gas than CO2. So while there is a great deal less Methane to contend with than CO2, it is still the second largest link in the global warming events chain.
Not every Greenhouse gas is as obvious a villain as Methane. The next most potent problem is simple H2O water. How can water be a cause of global warming? Our atmosphere contains a set parameter of water as vapor. This vapor absorbs and radiates heat as does every molecule in the air. But when the lower atmosphere (troposphere) has excess water vapor that gaseous H2O is a potent greenhouse gas.
Another of the more commonplace greenhouse gases is Nitrous Oxide. NO2 can make your car go faster, or make you relax at the dentist. It has quite few beneficial uses. But as a greenhouse gas all it manages to accomplish is to be one more ingredient in out atmospheric soup. Cars using catalytic converters, fertilizer plants, manufacture of nylon, and nitric acid as well as being produced naturally in our oceans and rain forests, produce Nitrous Oxide.
All of the above plus quite a few other greenhouse gases comprise the foundation of global warming. As above and in all discussion of global warming they are cumulatively referred to as greenhouse gases. To understand the importance of these as the start and endpoint of global warming we must digress into a brief explanation of the greenhouse effect.
Most modern attention to the problem of global warming began with discussion of depletion of the Earth’s Ozone layer. Ozone (O3) is a molecular form of Oxygen. The Ozone layer is a relatively thin strata of these molecules set in the lower portion of the Earth’s stratosphere.
Depletion of the Earth’s Ozone layer has resulted in a large increase in Ultra Violet Radiation reaching the surface of the earth. Does this increase in UV rays equate to global warming? Not really. In fact most scientific opinion is that depletion of the Ozone layer results in cooling of both the stratosphere and troposphere. So why mention depletion of the Ozone layer as regards to global warming? Because it represents a needed balance between harmful radiation being allowed to reach the earth’s surface and our desire to stem the rapid increase in our air and water temperature. Remember, we are viewing global warming as a chain of events.
global-warming-3What is the most significant cause of global warming?
The primary cause of global warming is Carbon Dioxide emissions. CO2 is being pumped into our atmosphere at an insane pace; 8 billion tons of CO2 entered the air last year. Of course some of this is due to natural activity such as volcanic eruptions and people breathing. But the Earth is equipped to easily absorb those into the normal regenerative process. No, the beginning of global warming was caused by fossil fuels being burned and emitting plenty of CO2.
Currently in the world 40% of all CO2 emissions are caused by power plants. These are burning coal, natural gas and diesel fuel. Some power plants burn garbage. Some burn methane made from garbage. And discounting those super green electrical generating plants designed to issue negligible pollutants, all of our power plants let loose into the atmosphere CO2.
33% of all the CO2 sent forth is the product of cars and trucks. Internal combustion engines burning fossil fuels…gasoline and diesel spew forth a retching amount of CO2.
3.5% of all CO2 emissions are released from aircraft traveling our friendly skies. Unfortunately, jets and other aircraft deliver their payload of pollutants directly into the troposphere.
The numbers can be confusing
12% of all CO2 released into the atmosphere is related to buildings. This figure varies from one source to the next. Some place the percentage of emissions from buildings as high as 33%. What most of these figures do not address is the actual cause of the CO2 emissions. In newly constructed buildings, production of materials used in building and energy used during construction are sited as the cause of carbon dioxide emissions. In existing buildings the CO2 created by the energy upkeep of the building is the root of the emissions quotient. The general comparison is that buildings consume energy in the way that cars burn fuel. But the pollutants created in providing power for heating, air-conditioning, lights and other usage in buildings has already been factored. Honestly this double billing accounting is more the product of auto manufacturers looking to point the blame for global warming away from gas guzzling cars.
The point to remember is that 98% of all CO2 emissions are related to energy production and 80% of these emissions become greenhouse gases.
Continuing the chain…global-warming-5
Which now mentioned allows us to follow our chain of event’s leading to global warming into the next most defined cause… Methane gas. Methane is released into the atmosphere from a dozen major sources. These include natural and man made emissions. Natural release of Methane is primarily from wetlands, (including agriculture) termites, the ocean, and hydrates. Non-organic releases are based from, landfills, livestock, waste treatment, and biomass burning. (More energy production). Almost all of this is offset by the Earth’s ability to absorb around 97% of the methane released into the air. But that remaining 3% is a serious problem. The molecular structure of Methane makes it 20 times as powerful a Greenhouse gas than CO2. So while there is a great deal less Methane to contend with than CO2, it is still the second largest link in the global warming events chain.
Not every Greenhouse gas is as obvious a villain as Methane. The next most potent problem is simple H2O water. How can water be a cause of global warming? Our atmosphere contains a set parameter of water as vapor. This vapor absorbs and radiates heat as does every molecule in the air. But when the lower atmosphere (troposphere) has excess water vapor that gaseous H2O is a potent greenhouse gas.
Another of the more commonplace greenhouse gases is Nitrous Oxide. NO2 can make your car go faster, or make you relax at the dentist. It has quite few beneficial uses. But as a greenhouse gas all it manages to accomplish is to be one more ingredient in out atmospheric soup. Cars using catalytic converters, fertilizer plants, manufacture of nylon, and nitric acid as well as being produced naturally in our oceans and rain forests, produce Nitrous Oxide.
All of the above plus quite a few other greenhouse gases comprise the foundation of global warming. As above and in all discussion of global warming they are cumulatively referred to as greenhouse gases. To understand the importance of these as the start and endpoint of global warming we must digress into a brief explanation of the greenhouse effect.
What is global warming? -1
While some would call global warming a theory, others would call it a proven set of facts. Opinions differ vehemently. Let us consider global warming to be both a premise that the environment of the world as we know it is slowly, but very surely increasing in overall air and water temperature, and a promise that if whatever is causing this trend is not interrupted or challenged life on earth will dynamically be affected.
The prevailing counter opinion is that all that is presently perceived to be global warming is simply the result of a normal climactic swing in the direction of increased temperature. Many proponents of this global warming ideology have definitive social and financial interests in these claims.
Global warming and climate change are aspects of our environment that cannot be easily or quickly discounted. Many factions still strongly feel that the changes our Earth is seeing are the result of a natural climatic adjustment. Regardless of one’s perspective the effects of global warming are a quantifiable set of environmental results that are in addition to any normal changes in climate. That is why the effects of global warming have catastrophic potential. Global warming may well be the straw that breaks the camel’s back. It could turn out to be the difference between a category three hurricane and a category four. Global warming as caused by greenhouse gas emissions can lead us to a definite imbalance of nature.
The premise of global warming as an issue of debate is that industrial growth coupled with non-structured methods we as humans use to sustain ourselves has created a situation where our planet is getting progressively hotter. We have seemingly negatively effected our environment by a cycle of harmful processes that now seem to be feeding upon themselves to exponentially increase the damage to our ecosystem.
6 Ekim 2011 Perşembe
U.S. Climate Policy
The Federal government is using voluntary and incentive-based programs to reduce emissions and has established programs to promote climate technology and science. This strategy incorporates know-how from many federal agencies and harnesses the power of the private sector.
EPA plays a significant role in helping the Federal government reduce greenhouse gas emissions and greenhouse gas intensity. EPA has many current and near-term initiatives that encourage voluntary reductions from a variety of stakeholders. Initiatives, such as ENERGY STAR, Climate Leaders, and our Methane Voluntary Programs, encourage emission reductions from large corporations, consumers, industrial and commercial buildings, and many major industrial sectors. For details on these and other initiatives as well as other aspects of U.S. policy, visit the U.S. Climate Policy section of the site.
Top of page
Greenhouse Gas Emissions
In the U.S., our energy-related activities account for over 85 percent of our human-generated greenhouse gas emissions, mostly in the form of carbon dioxide emissions from burning fossil fuels. More than half the energy-related emissions come from large stationary sources such as power plants, while about a third comes from transportation. Industrial processes (such as the production of cement, steel, and aluminum), agriculture, forestry, other land use, and waste management are also important sources of greenhouse gas emissions in the United States.
For a better understanding of where greenhouse gas emissions come from, governments at the federal, state and local levels prepare emissions inventories, which track emissions from various parts of the economy such as transportation, electricity production, industry, agriculture, forestry, and other sectors. EPA publishes the official national inventory of US greenhouse gas emissions, and the latest greenhouse gas inventory shows that in 2008 the U.S. emitted slightly less than 7 billon metric tons of greenhouse gases (a million metric tons of CO2 equivalents (MMTCO2e) is roughly equal to the annual GHG emissions of an average U.S. power plant.) Visit the Emissions section of this site to learn more, or review the answers to some frequent emissions questions.
Top of page
Health and Environmental Effects
Climate change affects people, plants, and animals. Scientists are working to better understand future climate change and how the effects will vary by region and over time.
Scientists have observed that some changes are already occurring. Observed effects include sea level rise, shrinking glaciers, changes in the range and distribution of plants and animals, trees blooming earlier, lengthening of growing seasons, ice on rivers and lakes freezing later and breaking up earlier, and thawing of permafrost. Another key issue being studied is how societies and the Earth's environment will adapt to or cope with climate change.
In the United States, scientists believe that most areas will continue to warm, although some will likely warm more than others. It remains very difficult to predict which parts of the country will become wetter or drier, but scientists generally expect increased precipitation and evaporation, and drier soil in the middle parts of the country. Northern regions such as Alaska are expected to experience the most warming. In fact, Alaska has been experiencing significant changes in climate in recent years that may be at least partly related to human caused global climate change.
Human health can be affected directly and indirectly by climate change in part through extreme periods of heat and cold, storms, and climate-sensitive diseases such as malaria, and smog episodes. For more information on these and other environmental effects, please visit the Health and Environmental Effects section of this site, or review the answers to some frequent effects questions.
EPA plays a significant role in helping the Federal government reduce greenhouse gas emissions and greenhouse gas intensity. EPA has many current and near-term initiatives that encourage voluntary reductions from a variety of stakeholders. Initiatives, such as ENERGY STAR, Climate Leaders, and our Methane Voluntary Programs, encourage emission reductions from large corporations, consumers, industrial and commercial buildings, and many major industrial sectors. For details on these and other initiatives as well as other aspects of U.S. policy, visit the U.S. Climate Policy section of the site.
Top of page
Greenhouse Gas Emissions
In the U.S., our energy-related activities account for over 85 percent of our human-generated greenhouse gas emissions, mostly in the form of carbon dioxide emissions from burning fossil fuels. More than half the energy-related emissions come from large stationary sources such as power plants, while about a third comes from transportation. Industrial processes (such as the production of cement, steel, and aluminum), agriculture, forestry, other land use, and waste management are also important sources of greenhouse gas emissions in the United States.
For a better understanding of where greenhouse gas emissions come from, governments at the federal, state and local levels prepare emissions inventories, which track emissions from various parts of the economy such as transportation, electricity production, industry, agriculture, forestry, and other sectors. EPA publishes the official national inventory of US greenhouse gas emissions, and the latest greenhouse gas inventory shows that in 2008 the U.S. emitted slightly less than 7 billon metric tons of greenhouse gases (a million metric tons of CO2 equivalents (MMTCO2e) is roughly equal to the annual GHG emissions of an average U.S. power plant.) Visit the Emissions section of this site to learn more, or review the answers to some frequent emissions questions.
Top of page
Health and Environmental Effects
Climate change affects people, plants, and animals. Scientists are working to better understand future climate change and how the effects will vary by region and over time.
Scientists have observed that some changes are already occurring. Observed effects include sea level rise, shrinking glaciers, changes in the range and distribution of plants and animals, trees blooming earlier, lengthening of growing seasons, ice on rivers and lakes freezing later and breaking up earlier, and thawing of permafrost. Another key issue being studied is how societies and the Earth's environment will adapt to or cope with climate change.
In the United States, scientists believe that most areas will continue to warm, although some will likely warm more than others. It remains very difficult to predict which parts of the country will become wetter or drier, but scientists generally expect increased precipitation and evaporation, and drier soil in the middle parts of the country. Northern regions such as Alaska are expected to experience the most warming. In fact, Alaska has been experiencing significant changes in climate in recent years that may be at least partly related to human caused global climate change.
Human health can be affected directly and indirectly by climate change in part through extreme periods of heat and cold, storms, and climate-sensitive diseases such as malaria, and smog episodes. For more information on these and other environmental effects, please visit the Health and Environmental Effects section of this site, or review the answers to some frequent effects questions.
Climate Change
The Earth's climate has changed many times during the planet's history, with events ranging from ice ages to long periods of warmth. Historically, natural factors such as volcanic eruptions, changes in the Earth's orbit, and the amount of energy released from the Sun have affected the Earth's climate. Beginning late in the 18th century, human activities associated with the Industrial Revolution have also changed the composition of the atmosphere and therefore very likely are influencing the Earth's climate.
The EPA climate change website has four main sections on climate change issues and another section on "What You Can Do" to reduce your contribution. A "Frequent Questions" section is available, and EPA has provided a frequent questions database where users can search for more specific questions and answers on climate change. An eight-page brochure entitled Frequently Asked Questions About Global Warming.
Science
For over the past 200 years, the burning of fossil fuels, such as coal and oil, and deforestation have caused the concentrations of heat-trapping "greenhouse gases" to increase significantly in our atmosphere. These gases prevent heat from escaping to space, somewhat like the glass panels of a greenhouse.
Greenhouse gases are necessary to life as we know it, because they keep the planet's surface warmer than it otherwise would be. But, as the concentrations of these gases continue to increase in the atmosphere, the Earth's temperature is climbing above past levels. According to NOAA and NASA data, the Earth's average surface temperature has increased by about 1.2 to 1.4ºF in the last 100 years. The eight warmest years on record (since 1850) have all occurred since 1998, with the warmest year being 2005. Most of the warming in recent decades is very likely the result of human activities. Other aspects of the climate are also changing such as rainfall patterns, snow and ice cover, and sea level.
If greenhouse gases continue to increase, climate models predict that the average temperature at the Earth's surface could increase from 3.2 to 7.2ºF above 1990 levels by the end of this century. Scientists are certain that human activities are changing the composition of the atmosphere, and that increasing the concentration of greenhouse gases will change the planet's climate. But they are not sure by how much it will change, at what rate it will change, or what the exact effects will be. See the Science and Health and Environmental Effects sections of this site for more detail, or review the answers to some frequent science questions.
The EPA climate change website has four main sections on climate change issues and another section on "What You Can Do" to reduce your contribution. A "Frequent Questions" section is available, and EPA has provided a frequent questions database where users can search for more specific questions and answers on climate change. An eight-page brochure entitled Frequently Asked Questions About Global Warming.
Science
For over the past 200 years, the burning of fossil fuels, such as coal and oil, and deforestation have caused the concentrations of heat-trapping "greenhouse gases" to increase significantly in our atmosphere. These gases prevent heat from escaping to space, somewhat like the glass panels of a greenhouse.
Greenhouse gases are necessary to life as we know it, because they keep the planet's surface warmer than it otherwise would be. But, as the concentrations of these gases continue to increase in the atmosphere, the Earth's temperature is climbing above past levels. According to NOAA and NASA data, the Earth's average surface temperature has increased by about 1.2 to 1.4ºF in the last 100 years. The eight warmest years on record (since 1850) have all occurred since 1998, with the warmest year being 2005. Most of the warming in recent decades is very likely the result of human activities. Other aspects of the climate are also changing such as rainfall patterns, snow and ice cover, and sea level.
If greenhouse gases continue to increase, climate models predict that the average temperature at the Earth's surface could increase from 3.2 to 7.2ºF above 1990 levels by the end of this century. Scientists are certain that human activities are changing the composition of the atmosphere, and that increasing the concentration of greenhouse gases will change the planet's climate. But they are not sure by how much it will change, at what rate it will change, or what the exact effects will be. See the Science and Health and Environmental Effects sections of this site for more detail, or review the answers to some frequent science questions.
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