Wind Energy Basics

Energy From Wind
Wind is simple air in motion. It is caused by the uneven heating of the earth's surface by the sun. Since the earth's surface is made of very different types of land and water, it absorbs the sun's heat at different rates.

During the day, the air above the land heats up more quickly than the air over water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds. At night, the winds are reversed because the air cools more rapidly over land than over water.

In the same way, the large atmospheric winds that circle the earth are created because the land near the earth's equator is heated more by the sun than the land near the North and South Poles.

Today, wind energy is mainly used to generate electricity. Wind is called a renewable energy source because the wind will blow as long as the sun shines.

How Wind Power Is Generated
The terms "wind energy" or "wind power" describe the process by which the wind is used to generate mechanical power or electricity. Wind turbines convert the kinetic energy in the wind into mechanical power. This mechanical power can be used for specific tasks (such as grinding grain or pumping water) or a generator can convert this mechanical power into electricity to power homes, businesses, schools, and the like.

Wind Turbines
Wind turbines, like aircraft propeller blades, turn in the moving air and power an electric generator that supplies an electric current. Simply stated, a wind turbine is the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity.

Wind Turbine Types
Modern wind turbines fall into two basic groups based on the direction of the rotating shaft (axis); the horizontal-axis variety, like the traditional farm windmills used for pumping water, and the vertical-axis design, like the eggbeater-style Darrieus model, named after its French inventor. Most large modern wind turbines are horizontal-axis turbines.

Turbine Components
Horizontal turbine components include:
- blade or rotor, which converts the energy in the wind to rotational shaft energy;
- a drive train, usually incuding a gearbox and a generator;
- a tower that supports the rotor and drive train; and
- other equipment, including controls, electrical cables, ground support equipment, and interconnection equipment.

Wind turbines are often grouped together into a single wind power plant, also known as a wind farm, and generate bulk electrical power. Electricity from these turbines is fed into a utility grid and distributed to customers, just as with conventional power plants. The world’s largest wind farm, the Horse Hollow Wind Energy Center in Texas, has 421 wind turbines that generate enough electricity to power 230,000 homes per year.

Wind Turbine Size and Power Ratings
Wind turbines are available in a variety of sizes, and therefore power ratings. The largest machine has blades that span more than the length of a football field, stands 20 building stories high, and produces enough electricity to power 1,400 homes. A small home-sized wind machine has rotors between 8 and 25 feet in diameter and stands upwards of 30 feet and can supply the power needs of an all-electric home or small business. Utility-scale turbines range in size from 50 to 750 kilowatts. Single small turbines, below 50 kilowatts, are used for homes, telecommunications dishes, or water pumping.

Wind resources are characterized by wind-power density classes, ranging from class 1 (the lowest) to class 7 (the highest). Good wind resources (e.g., class 3 and above, which have an average annual wind speed of at least 13 miles per hour) are found in many locations. Wind speed is a critical feature of wind resources, because the energy in wind is proportional to the cube of the wind speed. In other words, a stronger wind means a lot more power.

Advantages and Disadvantages of Wind-Generated Electricity

A Renewable Non-Polluting Resource
Wind energy is a free, renewable resource, so no matter how much is used today, there will still be the same supply in the future. Wind energy is also a source of clean, non-polluting, electricity. Unlike conventional power plants, wind plants emit no air pollutants or greenhouse gases. According to the U.S. Department of Energy, in 1990, California's wind power plants offset the emission of more than 2.5 billion pounds of carbon dioxide, and 15 million pounds of other pollutants that would have otherwise been produced. It would take a forest of 90 million to 175 million trees to provide the same air quality.

Cost Issues
Even though the cost of wind power has decreased dramatically in the past 10 years, the technology requires a higher initial investment than fossil-fueled generators. Roughly 80% of the cost is the machinery, with the balance being site preparation and installation. If wind generating systems are compared with fossil-fueled systems on a "life-cycle" cost basis (counting fuel and operating expenses for the life of the generator), however, wind costs are much more competitive with other generating technologies because there is no fuel to purchase and minimal operating expenses.

Environmental Concerns
Although wind power plants have relatively little impact on the environment compared to fossil fuel power plants, there is some concern over the noise produced by the rotor blades, aesthetic (visual) impacts, and birds and bats having been killed (avian/bat mortality) by flying into the rotors. Most of these problems have been resolved or greatly reduced through technological development or by properly siting wind plants.

Supply and Transport Issues
The major challenge to using wind as a source of power is that it is intermittent and does not always blow when electricity is needed. Wind cannot be stored (although wind-generated electricity can be stored, if batteries are used), and not all winds can be harnessed to meet the timing of electricity demands. Further, good wind sites are often located in remote locations far from areas of electric power demand (such as cities). Finally, wind resource development may compete with other uses for the land, and those alternative uses may be more highly valued than electricity generation. However, wind turbines can be located on land that is also used for grazing or even farming.

The Future of Wind Power
With increasingly competitive prices, growing environmental concerns, and the call to reduce dependence on foreign energy sources, a strong future for wind power seems certain. The World Wind Energy Association projects global wind capacity will double in size to over 120,000 MW by 2010, with much of the growth happening in the United States, India, and China. Turbines are getting larger and more sophisticated, with land-based turbines now commonly in the 1-2 MW range, and offshore turbines in the 3-5 MW range. The next frontiers for the wind industry are deep-water offshore, and land-based systems capable of operating at lower wind speeds. Both technological advances will provide large areas for new development.

As with any industry that experiences rapid growth, there will be occasional challenges along the way. For example, beginning in 2005, high demand, increased steel costs (the primary material used in turbine construction), increased profit margins, and certain warranty issues have lead to turbine shortages and higher prices. There are also concerns about collisions with bird and bat species in a few locations. And the not-in-my-backyard (NIMBY) issue continues to slow development in some regions. But new manufacturing facilities, careful siting and management practices, and increased public understanding of the significant and diverse benefits of wind energy will help overcome these obstacles.

© Wind Energy EIS, EIA

Global Impacts

Global warming affects many different facets of life on Earth. There will be winners and losers, even within a single region. But globally the losses are expected to far outweigh the benefits.

The regions that will be most severely affected are often the regions that emit the least greenhouse gases. This is one of the challenges that policy-makers face in finding fair international responses to the problem.

Explore some of the possible impacts of global climate change, including an in-depth look at sea level rise, in the following sections:

• Sea Level Rise
  Water expands as it warms. Therefore, sea level will rise as the top few hundred meters of the oceans warm and swell. Meltwater from polar and mountain glaciers is another potential source of sea level rise.
  
  The oceans, which cover 71% of the Earth’s surface, warm slowly in response to greenhouse warming because it takes a long time to heat their great mass. But measurements indicate that the oceans are warming, and projections suggest that the warming will continue for many centuries.
  
  Sea level is currently rising at a rate of 1/10 inch per year. Due to the CO2 already in the atmosphere, sea level is projected to continue rising for several centuries. Projections for the year 2100 show great uncertainty, ranging from several inches to nearly three feet. The impacts of rising sea level include loss of coastal ecosystems, flooding of cities, displacement of coastal inhabitants, and increased vulnerability to storm surges. And the effects would be magnified if the frequency of severe storms increases, as some climate models project.
  
  Wealthy countries, such as the United States, will be much better able to adapt to sea level rise than developing nations that lack the resources to build new coastal protections and infrastructure.
  
  
• Impacts of Sea Level Rise on Humans
  The impacts of global warming will be felt across the globe. These are a few of the many examples of the impacts of sea level rise on humans.
  
  Flooding Bangladesh
  One of the poorest nations in the world is projected to lose 17.5% of its land if sea level rises about 40 inches (1 m). Tens of thousands of people are likely to be displaced, and the country’s agricultural system will be adversely affected. Coastal flooding will threaten animals, plants, and fresh water supplies. The current danger posed by storm surges when cyclones hit Bangladesh is likely to increase.
  
  Disappearing Islands
  The Majuro Atoll in the Pacific Marshall Islands is projected to lose 80% of its land with a 20-inch (0.5m) rise in sea level. Many of the islands will simply disappear under the rising seas. A similar fate awaits other islands throughout the South Pacific and Indian Oceans, including many in the Maldives and French Polynesia. Coral reefs, which protect many of these islands, will be submerged, subjecting the local peoples to heightened storm surges and disrupted coastal ecosystems. Tourism and local agriculture will be severely challenged.
  

  Urban Flooding
  Thirteen of the world’s fifteen largest cities are on coastal plains. Many smaller cities, such as Alexandria, Egypt’s ancient center of learning, also face a severe risk of inundation with a 39-inch (1m) rise in sea level. Parts of San Jose and Long Beach, California, are about three feet below sea level and New Orleans is about eight feet below sea level today. Cities at risk cover a wide range of economic circumstances, yet many will require extensive infrastructure development to minimize the potential impacts of flooding, particularly from storm surge.
  
  Adapting to Rising Seas
  Rising sea level requires many different local responses. Urban areas on the U.S. coastline could be surrounded by rising sea water. Cities may require extensive infrastructure development to assure fresh water supplies, secure transportation, and protect people from flooding and storm surge.
  
  Sea walls can be built to protect cities and roads from rising seas. More robust building construction may also be required to withstand the increasingly intense storms that are likely to result from global warming. Fresh water supply is a concern as sea water penetrates ground water aquifers, which become brackish and less usable further inland.
  
  Regional Challenges
  The United States could lose 10,000 square miles of dry land if sea level rises two feet (0.6m). But the impacts of rising sea level vary from one region to another. These maps identify areas along the U.S. Gulf and Atlantic Coasts that are vulnerable to a 5–10 feet (1.5–3m) rise in sea level. The U.S. Pacific Coast is far less vulnerable to coastal flooding because the land rises more abruptly from the sea.
  
  Ecological Tradeoffs
  Building sea walls is an effective way to protect roads and cities from rising sea level. Sea walls literally prevent sea water from encroaching inland and provide a buffer against storm surges.
  
  Unfortunately, sea walls disrupt coastal ecosystems. The abrupt transition between sea water and concrete eliminates the beaches and tidal areas that support life along the coasts. This may be particularly problematic in barrier island ecosystems, such as along the southeastern coast of the United States.

• Impacts of Sea Level Rise on Nature
  The impacts of global warming will be felt across the globe. These are a few of the many examples of the impacts of sea level rise on nature.
  
  Disappearing Wetlands
  Coastal wetlands are especially vulnerable because they are within a few feet of sea level. In the United States, a sea level rise of one foot (0.3m) could eliminate 17–43% of today’s wetlands, with more than half the loss in Louisiana. As sea level rises, new wetlands will form further inland, but the total area will probably be reduced. In developed areas, dikes and other structures will prevent new wetlands from forming.
  
  Coral Bleaching
  Corals weakened by a variety of stresses are susceptible to “bleaching.” This occurs when the microscopic algae that give corals their brilliant color die. In 1997 and 1998, a large El Niño event contributed to bleaching in tropical corals around the world. Over the next century, warming of the oceans, in combination with other stressors such as sea level rise and water pollution, could lead to an increase in bleaching events.
  


Coastal Erosion
Over the past century, approximately 70% of the world’s shorelines have been retreating due to sea level rise and increased erosion. Over the next century, increased erosion is likely as sea level rises. Erosion will increase along different types of unprotected shoreline, including the low-lying barrier dunes of the southern U.S. Atlantic Coast and the soft cliff coasts of California.

• Flooding in Eastern Maryland
  Climate models project rising sea level during the 21st century due to greenhouse warming. Sea level is not expected to rise as much as shown here by the year 2100, but it will likely be rising for centuries to come, especially as polar ice melts. Much of eastern Maryland is low-lying, leaving vast areas vulnerable to flooding.
  


Natural processes might reduce the impact in some areas. If sea level rises slowly enough, plants that grow upward to remain above the water level might amass large root systems that trap enough sand and soil to prevent wholesale flooding of low-lying areas. However, these natural responses in regions such as eastern Maryland are not assured.



• Water Resources
  The impacts of global warming will be felt across the globe. These are a few of the many examples of the impacts of climate change on water reources.
  
  The 1930s Dust Bowl was a relatively minor drought by prehistoric standards, yet tens of thousands of people were displaced. Today, farms and cities in the western United States could face a similar water shortage. This region relies heavily on the Colorado River for fresh water. The river, which is fed by the mountain snows, is overtaxed during dryer periods. Decreasing snow pack in the high mountains threatens to create severe water shortages throughout the southwestern U.S., and reduce the ability to generate hydroelectric power during the warmer summers.
  


Disappearing Glaciers
Glaciers are complex, and a short-lived advance or retreat of one or a few glaciers could have many causes. But almost all of the mountain glaciers on Earth have shrunk over the last century. The temperature increase needed to explain the rate of glacier disappearance agrees with warming estimated from thermometers.

Will Melting Ice Trigger an Ice Age?
Not likely. But, remember the Younger Dryas? Melting polar ice may have poured fresh water into the North Atlantic and interrupted the deep ocean circulation pattern, which may have sent the Northern Hemisphere into a 1,000-year cold period. Today, fresh water flow into the Arctic Ocean from Siberia’s four great rivers has increased, and oceanographers observe a slight decrease in the salinity of the North Atlantic. Although climate models do not project that these trends will lead to anything like an ice age, some indicate that over the next few hundred years deep ocean currents may be disrupted, which would affect regional temperature and precipitation patterns over North America and Europe.



• Traditional Cultures
  The impacts of global warming will be felt across the globe. These are a few of the many examples of the impacts of climate change on traditional cultures.
  
  Disappearing Ice Packs
  Wildlife in the arctic regions will be seriously affected as warmer temperatures affect the ocean ice cover. Polar bears rely on sea ice to hunt seals, which use the ice for rearing their young. The native peoples also rely on the ice to hunt these species and walruses. Observations of walrus in 1996-99 showed them to be thin and in poor condition, partly due to receding sea ice.
  
  Livestock Farming
  Over the past several thousand years, traditional livestock farmers in Africa have developed a variety of ways to cope with large climate variations. These coping mechanisms include keeping diverse species of livestock, moving temporarily to more lush grasslands, maintaining economic diversity, and distributing drought-induced hunger across the stronger members of the community. Coping with climate changes over the next century will be increasingly difficult as human populations increase and available grazing land decreases.
  
  Limited Resources
  Many indigenous peoples live in harsh climatic environments to which they have adapted. However, when climate changes occur rapidly, populations with limited resources can be the first to suffer from famine and disease. Adaptation techniques include altering crop mixes and water infrastructure to deal with drought, and improving public healthcare systems to reduce the harm caused by climate-related disease outbreaks.
  
  
• Health and Disease
  The impacts of global warming will be felt across the globe. These are a few of the many examples of the impacts of climate changes on health and disease.
  
  Infectious Diseases
  Cold winter weather reduces the spread of infectious diseases by killing infectious organisms and carrier species, such as mosquitoes. Warmer, wetter weather could increase the spread of malaria, dengue fever, and yellow fever. The possible increase in flooding and damage to water and sewage infrastructure can further encourage the spread of disease.
  
  Increased Air Pollution
  Three out of four of the world’s highest-density cities are in rapidly developing countries, where vehicle pollution is high. In Central Europe alone, 21,000 deaths are tied to air pollution each year. The concentration of photochemical pollutants, such as ozone, tends to increase with warmer temperatures. Ozone damages lung tissue and is especially harmful to people with asthma and other lung conditions.
  



Hotter Summers & Warmer Winters
A 1995 heat wave killed more than 500 people in the Chicago area, and heat intensity is likely to rise in the future. Statistical studies estimate that a temperature rise of 2°F could double or triple the number of heat-related deaths in Atlanta, in part because the heat index will increase exponentially as temperature rises. But warmer weather may save lives in the winter by reducing hypothermia and driving-related fatalities.



• Agriculture
  The impacts of global warming will be felt across the globe. These are a few of the many examples of the impacts of climate change on agriculture.
  
  American Crops
  Agriculture in the United States is relatively well positioned to adapt to climate change, due in part to the advanced technologies available to U.S. farmers. The overall system is regionally diverse and has already adapted to a wide range of growing conditions. On the whole, U.S. crop production could increase, unless warming becomes great or the frequency of extreme weather increases.
  


Isolated Arid Regions
Peoples most at risk of famine live in agriculturally isolated, arid or semi-arid regions, such as sub-Saharan Africa and Latin America. African agriculture was already unable to keep pace with population growth during the last decades of the 20th century. And climate models generally predict that mid-continental summer soil moisture will tend to be lower with greenhouse warming.

CO2 Fertilization
Because plants require CO2, rising levels may actually help plant growth. However, the increased plant growth requires adequate water supply and other fertilization, such as nitrates. Experiments in which crops are grown in CO2-rich air show that the CO2 fertilization effect could become small after a few years.



• Ecosystems
  The impacts of global warming will be felt across the globe. These are a few of the many examples of the impacts of climate change on ecosystems.
  
  American Ecosystems
  Earlier spring – A study observing 36 species in the central U.S. documented advances in flowering dates by an average of 7.3 days from 1936 to 1998.
  
  Northward Shift – A study projecting responses to a doubling of atmospheric CO2 found that tree habitats in the eastern U.S. may migrate northward more than 50 miles on average. However, the ability of trees to shift might be limited in regions where forests are only found in isolated patches.
  
  Shifting Penguin Populations
  Adélie penguin populations decreased 22% during the last 25 years, while Chinstrap penguins increased by 400%. The two species depend on different habitats for survival: Adélies inhabit the winter ice pack, whereas Chinstraps remain in close association with open water. A 7°–9°F rise in midwinter temperatures on the western Antarctic Peninsula during the past 50 years, and associated receding sea-ice pack, is reflected in their changing populations.
  
  

  

  Tiger Losses
  It is estimated that only about 3,000 – 4,500 Bengal tigers remain in the wild. The number in Bangladesh is projected to decrease as a result of rising sea levels. For tigers and the many other species that inhabit the forested wetlands of Bangladesh, migration to higher ground probably would be blocked by human habitation of adjacent lands.

©National Academy of Sciences

The Natural Climate Cycle

Climate Is Changed by Many Processes
Climate change may result from both natural and human causes. The importance of human causes has been increasing during the past few decades.

Causes
The major causes of climate change are described in the following sections.

1. CO2 and Other Greenhouse Gas Variations
Many natural and human-made gases contribute to the greenhouse effect that warms the Earth's surface. Water vapor (H2O) is the most important, followed by carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and the chlorofluorocarbons (CFCs) used in air conditioners and many industrial processes.

The increasing atmospheric CO2 concentration is likely the most significant cause of the current warming. Other greenhouse gases along with other factors discussed in the following sections also contribute.

2. Human Activity and Greenhouse Gas
The world’s economy runs on carbon: the “fuel” in fossil fuels. Coal, oil, and natural gas contribute energy to nearly every human endeavor in industrialized nations, and carbon dioxide (CO2) is a by-product of burning these fuels. Immediately eliminating CO2 emissions would literally stop the industrial world. This graph illustrates how thoroughly fossil fuels and CO2 emissions are integrated into American life.

CO2 contributes more to the recent increase in greenhouse warming than any other gas. CO2 persists in the atmosphere longer and longer as concentrations continue to rise.

Other chemicals such as methane, nitrous oxide, and halocarbons also contribute to the global greenhouse effect. A number of additional chemicals related to urban pollution, such as low-level (tropospheric) ozone and black soot, can have a strong regional and perhaps global warming effect. Sulfate aerosols may have a cooling effect.

3. Reducing Other Greenhouse Gases :. Bessy’s Stomachs
Methane is the second most significant cause of greenhouse warming, behind carbon dioxide. Bessy, the science cow, and her many brothers and sisters are one of the greatest methane emitters. Bessy’s grassy diet and multiple stomachs cause her to produce methane, which she exhales with every breath. The sheer size of her herds makes a significant contribution to global warming.

4. Ocean Circulation
A. Direct Effect of Oceans on Climate
The atmospheric circulation (winds) and ocean currents carry heat from the tropics toward the poles. Many processes can alter these circulation patterns, changing the climate regionally or even over the whole world.
Interactions between the ocean and atmosphere can also produce phenomena such as El Niño, which tends to recur every two to six years. Changes in deep ocean circulation can produce longer-lived climate variations that endure for decades to centuries. The ice age cycles may have been influenced by changes in ocean circulation arising from changes in the Earth’s orbit around the Sun.

B. Effect Of Oceans On Greenhouse Gases
The oceans play an important role in determining the atmospheric concentration of CO2. CO2 gas in the atmosphere and CO2 dissolved in the ocean surface reach a balance. Changes in ocean circulation, chemistry, and biology have shifted this balance in the past. Such changes may affect climate by slowly moving CO2 into or out of the atmosphere.

5. Volcanic Eruptions
A volcanic eruption may send ash and sulfate gas high into the atmosphere. The sulfate may combine with water to produce tiny droplets (aerosols) of sulfuric acid, which reflect sunlight back into space. Large eruptions reach the middle stratosphere (19 miles or 30 kilometers high). At this altitude, the aerosols can spread around the world.

A massive volcanic eruption can cool the Earth for one or two years. The 1982 El Chichon eruption and the 1991 Pinatubo eruption caused the globally averaged surface temperature to cool less than 1°F.

6. Solar Variations
The Sun is the source of energy for the Earth’s climate system. Although the Sun’s energy output appears constant from an everyday point of view, small changes over an extended period of time can lead to climate changes. Some scientists suspect that a portion of the warming in the first half of the 20th century was due to an increase in the output of solar energy.

Learning how the Sun changed before modern instruments were available is not easy, but it appears that changes in the output of solar energy have been small over the last million years, and probably even longer.

8. Orbital Variations
Slow changes in the Earth’s orbit lead to small but climatically important changes in the strength of the seasons over tens of thousands of years. Climate feedbacks amplify these small changes, thereby producing ice ages.

Eccentricity
Earth’s orbit oscillates very slightly between nearly circular and more elongated every 100,000 years. This cycle is evident in the glacial/interglacial cycles of roughly the same period.

Tilt
The Earth spins around an axis that is tilted from perpendicular to the plane in which the Earth orbits the Sun. This tilt causes the seasons. At the height of the Northern Hemisphere winter the North Pole is tilted away from the Sun, while in the summer it is tilted toward the Sun. The angle of the tilt varies between 22° and 24.5° on a cycle of 41,000 years. When the tilt angle is high, the polar regions receive less solar radiation than normal in winter and more in summer.
Wobble
There is a slow wobble in the Earth’s spin axis, which causes the peak of winter to occur at different points along the Earth’s elliptical orbital path. This variation in the seasons occurs on an approximately 23,000-year cycle.

9. Land Use Changes
When humans transform land from forests to seasonal crops or from natural to urban environments, the regional climate system is altered. For example, clear-cut hillsides are significantly warmer than forests. Urban environments are also islands of heat produced by industry, homes, automobiles, and by asphalt’s absorption of solar energy. Land use changes are not likely to have a large, direct effect on global average temperature.

Changing uses of the land are also associated with changes in the usage and availability of water, as well as the production of greenhouse gases. Deforestation can significantly increase the amount of atmospheric CO2, which warms the planet.

Amplifiers
Factors that can amplify or reduce the effect of the causes of change are known as "feedbacks." Some of the key feedbacks are described in the following sections. These feedbacks consist of interconnected processes in which a change in one leads to a change in another, which ultimately leads to further changes in the first.

1. Aerosols
Small particles in the air (aerosols) may have warming or cooling effects, depending on their characteristics. Sulfate (SO4) aerosol, for example, is light-colored and reflects sunlight back into space. The cooling effect of volcanic aerosols from the Mt. Tambora eruption of 1815 caused North America’s “year without a summer” in 1816. Sulfate aerosol is also produced by fossil fuel burning.

Black soot, which is a familiar component of urban smog and smoke from wild fires, has the opposite effect. The dark particles absorb the Sun’s energy in much the same way that dark asphalt roads become warm on sunny days.
Aerosol concentrations change for many reasons, including volcanic eruptions, spread of fires, increased windiness, drying of damp soils, changes in industrial processes, and more. Accurately projecting the extent and effect of aerosols is one of the major challenges in modeling the future of climate change.

2. Clouds
Like aerosols, clouds can either warm or cool the Earth, depending on their density and altitude. Their behavior demonstrates the intricate interactions at work within the climate system.

Very small differences in clouds may produce large feedbacks. An increase in high, thin clouds produced by greenhouse warming would further increase the warming. This is because high, thin clouds are relatively effective in trapping infrared radiation (heat) while allowing the Sun’s energy to pass through. In contrast, an increase in thick, low clouds could lessen the warming because these clouds reflect sunlight efficiently.

Changes in clouds result from changes in the distribution of water vapor, temperature, and winds. The effects of global warming on these factors are complex and not well understood.

In addition, aerosols may also play a role in cloud formation. Tiny aerosol particles can “seed” clouds by providing the “nuclei” around which cloud droplets are formed. High concentrations of some aerosol types may affect the character of clouds by causing many tiny droplets to form rather than a few big ones. Clouds with more tiny droplets reflect more solar energy and tend to produce less rainfall.

3. Water Vapor
Today, water vapor produces two-thirds of the world’s greenhouse effect. All of the other gases – carbon dioxide, methane, nitrous oxide, halocarbons, etc. – contribute the other third. The effect of water vapor is so significant that the global average temperature would be below freezing without it.

Warm air can contain more moisture than cold air. This is the basis of the water vapor feedback. As the atmospheric temperature rises and the amount of water vapor increases, the greenhouse effect is enhanced, further increasing temperature.

The water vapor feedback is critical for producing the glacial/interglacial cycles. Uncertainty in the magnitude of the water vapor feedback is an important source of uncertainty in projecting future climate warming.

A Common Source of Confusion
Does the water vapor added to the atmosphere by cooling towers and smokestacks contribute to global warming?

These sources are tiny compared to natural evaporation from the land and ocean. However, the water vapor feedback is important in increasing water vapor concentration and the greenhouse effect.

4. Ice-Reflectivity
Ice-free surfaces tend to absorb more solar energy than ice-covered surfaces. Therefore, snow and ice cover have a cooling effect on the Earth. If global warming reduces the global snow and ice cover, the warming will be enhanced because more solar energy will be absorbed. This ice-reflectivity feedback does not operate in polar regions during the winter, when it is always dark or the Sun is very low in the sky.
© National Academy of Sciences

Carbon Cycle

The Earth's Carbon Cycle
The Earth maintains a natural carbon balance. When concentrations of carbon dioxide (CO²) are upset, the system gradually returns to its natural state. This natural readjustment works slowly, compared to the rapid rate at which humans are moving carbon into the atmosphere by burning fossil fuels. Natural carbon removal can't keep pace, so the concentration of CO2 in the atmosphere increases.

In the following sections, we will examine the Earth's natural carbon balance and how humans are affecting this balance.

1. The Natural Carbon Balance
Carbon continually exchanges within a closed system consisting of the atmosphere, oceans, biosphere, and landmass. There are short- and long-term cycles at work.

Short-Term Cycles:
Carbon is exchanged rapidly between plants and animals through respiration and photosynthesis, and through gas exchange between the oceans and the atmosphere.

Long-Term Cycle:
Over millions of years, carbon in the air is combined with water to form weak acids that very slowly dissolve rocks. This carbon is carried to the oceans where some forms coral reefs and shells. These sediments may be moved deep into the Earth by drifting continents and eventually released into the atmosphere by volcanoes.

2. Upsetting The Balance :. Human Impact
Like all other animals, humans participate in the natural carbon cycle, but there are also important differences. By burning coal, oil, and natural gas, humans are adding carbon dioxide (CO²) to the atmosphere much faster than the carbon in rocks is released through natural processes. And clearing and burning forests to create agricultural land converts organic carbon to carbon dioxide gas. The oceans and land plants are absorbing a portion, but not nearly all of the CO2 added to the atmosphere by human activities.

Human Impact On The Carbon Cycle
The red arrow, representing rapid fossil fuel burning, indicates the main way in which humans affect the natural carbon cycle. Carbon dioxide (CO²) levels are increasing because the natural system cannot keep pace with this new emission source. The natural processes that permanently remove this additional carbon – ocean uptake and sedimentation – work extremely slowly.

Time
Natural changes to the carbon cycle have been very slow compared to the rate at which humans are adding CO² to the atmosphere. The redistribution of the added CO2 between the atmosphere, oceans, and biosphere takes hundreds of years, and the removal of the added carbon from the short-term cycle by the long-term cycle takes thousands of years.

© National Academy of Sciences

The Greenhouse Effect :. Natural & Amplified Warming

Natural Warming
The greenhouse effect is a natural warming process. Carbon dioxide (CO2) and certain other gases are always present in the atmosphere. These gases create a warming effect that has some similarity to the warming inside a greenhouse, hence the name “greenhouse effect.”

1. Sunlight brings energy into the climate system; most of it is absorbed by the oceans and land.
   THE GREENHOUSE EFFECT:
2. Heat (infrared energy) radiates outward from the warmed surface of the Earth.
3. Some of the infrared energy is absorbed by greenhouse gases in the atmosphere, which re-emit the energy in all directions.
4. Some of the infrared energy further warms the Earth.
5. Some of the infrared energy is emitted into space.
   AMPLIFIED GREENHOUSE EFFECT:
6. Higher concentrations of CO2 and other "greenhouse" gases trap more infrared energy in the atmosphere than occurs naturally. The additional heat further warms the atmosphere and Earth’s surface.

Amplified Warming
Increasing the amount of greenhouse gases intensifies the greenhouse effect. Higher concentrations of CO2 and other greenhouse gases trap more infrared energy in the atmosphere than occurs naturally. The additional heat further warms the atmosphere and Earth’s surface.

© National Academy of Sciences

Things you can do today to reduce Global Warming

There are many simple things you can do in your daily life — what you eat, what you drive, how you build your home — that can have an effect on your immediate surrounding, and on places as far away as Antactica. Here is a list of few things that you can do to make a difference.

1. Use Compact Fluorescent Bulbs
Replace 3 frequently used light bulbs with compact fluorescent bulbs. Save 300 lbs. of carbon dioxide and $60 per year.

2. Inflate Your Tires
Keep the tires on your car adequately inflated. Check them monthly. Save 250 lbs. of carbon dioxide and $840 per year.

3. Change Your Air Filter
Check your car's air filter monthly. Save 800 lbs. of carbon dioxide and $130 per year.

4. Fill the Dishwasher
Run your dishwasher only with a full load. Save 100 lbs. of carbon dioxide and $40 per year.

5. Use Recycled Paper
Make sure your printer paper is 100% post consumer recycled paper. Save 5 lbs. of carbon dioxide per ream of paper.

6. Adjust Your Thermostat
Move your heater thermostat down two degrees in winter and up two degrees in the summer. Save 2000 lbs of carbon dioxide and $98 per year.

7. Check Your Waterheater
Keep your water heater thermostat no higher than 120°F. Save 550 lbs. of carbon dioxide and $30 per year.

8. Change the AC Filter
Clean or replace dirty air conditioner filters as recommended. Save 350 lbs. of carbon dioxide and $150 per year.

9. Take Shorter Showers
Showers account for 2/3 of all water heating costs. Save 350 lbs. of carbon dioxide and $99 per year.

10. Install a Low-Flow Showerhead
Using less water in the shower means less energy to heat the water. Save 350 lbs. of carbon dioxide and $150.

11. Buy Products Locally
Buy locally and reduce the amount of energy required to drive your products to your store.

12. Buy Energy Certificates
Help spur the renewable energy market and cut global warming pollution by buying wind certificates and green tags.

13. Buy Minimally Packaged Goods
Less packaging could reduce your garbage by about 10%. Save 1,200 pounds of carbon dioxide and $1,000 per year.

14. Buy a Hybrid Car
The average driver could save 16,000 lbs. of CO2 and $3,750 per year driving a hybrid

15. Buy a Fuel Efficient Car
Getting a few extra miles per gallon makes a big difference. Save thousands of lbs. of CO2 and a lot of money per year.

16. Carpool When You Can
Own a big vehicle? Carpooling with friends and co-workers saves fuel. Save 790 lbs. of carbon dioxide and hundreds of dollars per year.

17. Don't Idle in Your Car
Idling wastes money and gas, and generates pollution and global warming causing emissions. Except when in traffic, turn your engine off if you must wait for more than 30 seconds.

18. Reduce Garbage
Buy products with less packaging and recycle paper, plastic and glass. Save 1,000 lbs. of carbon dioxide per year.

19. Plant a Tree
Trees suck up carbon dioxide and make clean air for us to breathe. Save 2,000 lbs. of carbon dioxide per year.

20. Insulate Your Water Heater
Keep your water heater insulated could save 1,000 lbs. of carbon dioxide and $40 per year.

21. Replace Old Appliances
Inefficient appliances waste energy. Save hundreds of lbs. of carbon dioxide and hundreds of dollars per year.

22. Weatherize Your Home
Caulk and weather strip your doorways and windows. Save 1,700 lbs. of carbon dioxide and $274 per year.

23. Use a Push Mower
Use your muscles instead of fossil fuels and get some exercise. Save 80 lbs of carbon dioxide per year.

24. Unplug Un-Used Electronics
Even when electronic devices are turned off, they use energy. Save over 1,000 lbs of carbon dioxide and $256 per year.

25. Put on a Sweater
Instead of turning up the heat in your home, wear more clothes Save 1,000 lbs. of carbon dioxide and $250 per year.

26. Insulate Your Home
Make sure your walls and ceilings are insulated. Save 2,000 lbs. of carbon dioxide and $245 per year.

27. Air Dry Your Clothes
Line-dry your clothes in the spring and summer instead of using the dryer. Save 700 lbs. of carbon dioxide and $75 per year.

28. Switch to a Tankless Water Heater
Your water will be heated as you use it rather than keeping a tank of hot water. Save 300 lbs. of carbon dioxide and $390 per year.

29. Switch to Double Pane Windows
Double pane windows keep more heat inside your home so you use less energy. Save 10,000 lbs. of carbon dioxide and $436 per year.

30. Buy Organic Food
The chemicals used in modern agriculture pollute the water supply, and require energy to produce.

31. Bring Cloth Bags to the Market
Using your own cloth bag instead of plastic or paper bags reduces waste and requires no additional energy.

32. Turn off Your Computer
Shut off your computer when not in use, and save 200 lbs of C02. Conserve energy by using your computer's "sleep mode" instead of a screensaver.

33. Be a Meat Reducer
The average American diet contributes an extra 1.5 tons of greenhouse gases per year compared with a vegetarian diet. Eliminating meat and dairy intake one day a week can make a big difference.

34. Ditch the Plastic
2.5 million individual plastic water bottles are thrown away every hour in the US. Start using a reusable water bottle and just say no to plastic!

Source: www.stopglobalwarming.org

The impact of global warming in South America

A science-based world map depicting the local and regional consequences of global climate change. The map was produced as a collaborative project by several environmental organizations, and has been peer-reviewed by scientists.

The people of South America are heavily dependent on the continent's natural resources—from the rangelands at the foothills of the Andes, to the plants and animals of the Amazon rainforest, to the fisheries off the coast of Peru. The region's ecosystems are particularly vulnerable to the changes in water availability expected with a changing climate. Higher global temperatures along with more frequent El Ni'os may bring increased drought, and melting glaciers in the Andes threaten the future water supply of mountain communities. Signs of a warming climate have already appeared both at high elevations—in glacial retreat and shifting ranges of disease-carrying mosquitoes—and along the coast—in rising sea level and coral bleaching.

Fingerprints: Direct manifestations of a widespread and long-term trend toward warmer global temperatures.

45. Recife, Brazil -- Sea-level rise. Shoreline receded more than 6 feet (1.8 m) per year from 1915 to 1950 and more than 8 feet (2.4 m) per year from 1985 to 1995. The dramatic land loss was due to a combination of sea-level rise and loss of sediment supply following dam construction, harbor dredging, and other coastal engineering projects.

64. Andes Mountains, Peru -- Glacial retreat accelerates seven-fold. The edge of the Qori Kalis glacier was retreating 13 feet (4.0 m) annually between 1963 and 1978. By 1995, the rate had stepped up to 99 feet (30.1 m) per year.

92. Chiclayo, Peru - Large increase in average minimum temperatures. Average minimum temperatures along Peru's north coast increased 3.5°F (2°C) from the 1960s to 2000. The temperature in the high plateau region in extreme southeastern Peru has also risen 3.5°F (2°C), from an average of 48°F (9°C) in the 1960s to 52°F (11°C) in 2001. Northwestern South America has warmed by 0.8-1.4°F (0.5-0.8° C) in the last decade of the 20th century.

101. Tropical Andes (Ecuador, Peru, Bolivia, and northernmost Chile) - Increase in average annual temperature. Average annual temperature has increased by about 0.18°F (0.1°C) per decade since 1939. The rate of warming has doubled in the last 40 years, and more than tripled in the last 25 years, to about 0.6°F (0.33°C) per decade.

128. Argentina - Receding glaciers. Glaciers in Patagonia have receded by an average of almost a mile (1.5 km) over the last 13 years. There has been an increase in maximum, minimum, and average daily temperatures of more than 1.8°F (1°C) over the past century in southern Patagonia, east of the Andes.

132. Venezuela - Disappearing glaciers. Of six glaciers in the Venezuelan Andes in 1972, only 2 remain, and scientists predict that these will be gone within the next 10 years. Glaciers in the mountains of Colombia, Ecuador, and Peru show similar rapid rates of retreat. Temperature records in other regions of the Andes show a significant warming of about 0.6°F (0.33°C) per decade since the mid-1970s.

Harbingers: Events that foreshadow the types of impacts likely to become more frequent and widespread with continued warming.

15. Andes Mountains, Columbia -- Disease-carrying mosquitoes spreading. Aedes aegypti mosquitoes that can carry dengue and yellow fever viruses were previously limited to 3,300 feet (1,006 m) but recently appeared at 7,200 feet (2,195 m).

36. Monteverde Cloud Forest, Costa Rica -- Disappearing frogs and toads. A reduction in dry-seson mists due to warmer Pacific ocean temperatures has beenlinked to disappearances of 20 species of frogs and toads, upward shifts in the ranges of mountain birds, and declines in lizard populations.

47. Pacific Ocean, Panama -- Coral reef bleaching.

53. Caribbean -- Coral reeef bleaching.

58. Galapagos -- Coral reef bleaching..

86. Nicaragua -- 2.2 million acres (890,308 hectares) burned, 1998. Over 15,000 fires burned in 1998, and the blazing acreage included protected lands in the Bosawas Biosphere Reserve.

117. Argentine Islands - Antarctic flowering plants changes. The populations of two native Antarctic flowering plants increased rapidly between 1964 and 1990, coincident with the strong regional warming over the Antarctic Peninsula. The Antarctic pearlwort population increased 5-fold while the Antarctic hairgrass increased 25-fold. The unusually rapid increases are attributed to warmer summer temperatures and/or a longer growing season, which enhance the plant's ability to reproduce.

125. Galapagos, Ecuador - Coral reef bleaching, March/April 2002. Sea-surface temperatures rose above 81.5°F (27.5°C) several times, causing repeated coral bleaching events. Repeated and prolonged bleaching episodes - expected as tropical water temperatures warm with climate change - eventually kill corals and cause a decline in associated marine species.

143. Pampas region, Argentina/Uruguay - Worst flooding on record, August to October 2001. Nearly 8 million acres (3.2 million hectares) of land in the Pampas region were flooded after 3 months of high rainfall. Mean annual precipiation in the humid Pampa increased by 35% in the last half of the 20th century.

145. Buenos Aires, Argentina - Heaviest rains in 100 years, May 2000. 13.5 inches (34.2 cm) of rain, more than 4 times the average monthly rainfall, fell in just 5 days. Northeastern Argentina is exhibiting a long-term trend of increasing precipitation.

146. Venezuela - Heaviest rainfall in 100 years, December 1999. The heaviest rainfall in 100 years caused massive landslides and flooding that killed approximately 30,000 people. Total December rainfall in Maiquetia, near Caracas, was almost 4 feet (1.2 m), more than 5 times the previous December record. The high death toll was attributed to population growth in vulnerable areas and forest clearing on steep hill slopes.

153. Argentina - Fire outbreak. 3.7 million acres (1.5 million hectares) burned in La Pampa province, sustained by record temperatures and persistent drought. Annual average temperature in Argentina has increased by nearly 1.8°F (1°C) over the last century.

© Environmental Defense, Natural Resources Defense Council, Sierra Club, Union of Concerned Scientists U.S. Public Interest Research Group, World Resources Institute, World Wildlife Fund

The impact of global warming in Oceania

A science-based world map depicting the local and regional consequences of global climate change. The map was produced as a collaborative project by several environmental organizations, and has been peer-reviewed by scientists.

The Oceania region ranges from the lush tropical rainforests of Indonesia to the interior deserts of Australia. The climate is strongly influenced by the ocean and the El Niño phenomenon. Small island nations and the coastal regions—where much of the population is concentrated—are very vulnerable to increasing coastal flooding and erosion due to rising sea level. Warming sea temperatures in recent years have damaged many of the region's spectacular coral reefs, threatening one of the world's most diverse ecosystems.

Fingerprints: Direct manifestations of a widespread and long-term trend toward warmer global temperatures.

2. Christchurch, New Zealand -- Warmest February on record, 1998. Daily temperatures averaged near 67°F (19.4°C).

43. Fiji -- Sea-level rise. Reports from local inhabitants at 16 sites indicate that the island's average shoreline has been receding half a foot (0.15 m) per year over at least the past 90 years.

44. American and Western Samoa -- Land loss. Western Samoa has experienced shore recession of about 1.5 feet (0.46 m) per year for at least the past 90 years.

67. New Zealand -- Retreating glaciers. The average elevation for glaciers in the Southern Alps has shifted upslope by more than 300 feet (91.4 m) over the past century.

129. Heard Island (Australia) - Rising temperatures; retreating glaciers. Since 1947 the island's 34 glaciers have decreased by 11% in area and 12% in volume, with half the loss occurring in the 1980s. Air temperature has risen 1.3°F (0.7°C) between 1947 and 2001.

Harbingers: Events that foreshadow the types of impacts likely to become more frequent and widespread with continued warming.

18. Indonesia -- Malaria spreads to high elevations. Malaria was detected for the first time as high as 6,900 feet (2,103 m) in the highlands of Irian Jaya in 1997.

48. American Samoa -- Coral reef bleaching.

49. Papua New Guinea -- Coral reef bleaching.

50. Philippines -- Coral reef bleaching.

51. Indian Ocean -- Coral reef bleaching (inclues Seychelles; Kenya; Reunion; Mauritius; Somalia; Madagascar; Maldives; Indonesia; Sri Lanka; Gulf of Thailand [Siam]; Andaman Islands; Malaysia; Oman; India; and Cambodia).

56. Australia, Great Barrier Reef -- Coral reef bleaching.

75. New South Wales, Australia -- Wettest August on records, 1998. On August 15-17, a storm dumped nearly 12 inches (30.5 cm) of rain on Sydney, over 8 inches (20.3 cm) more than what normally falls during that entire month.

87. Indonesia -- Burning rainforest, 1998. Fires burned up to 2 million acres (809,371 hectares) of land, including almost 250,000 acres of primary forest and parts of the already severely reduced habitat of the Kalimantan orangutan.

100. Australia - 2002 - Warmest April on record. This occurred in the context of an average annual temperature increase of 0.9-1.8°F (0.5-1.0°C) per decade over the past century. There has also been an increase in warm days and a decrease in cold winter days.

123. New Zealand - Ocean warming. The oceans around New Zealand have been warming over the past decade at a rate not seen since the 1930s. Over the last century the average ocean temperatures around New Zealand increased by about 1.8°F (1°C), slightly more than the global average. Despite 20 years of cooling from the 1970s through the early 1990s - due to longer and stronger El Niño events affecting the regional ocean temperatures - New Zealand's ocean temperature increase over the 20th century is consistent with the global average upward trend. Sea level along the country's shoreline has been rising accordingly by an average of 0.04-0.08 inches (1-2 mm) per year.

124. Fiji - Coral reef bleaching, 2000. A new wave of coral bleaching events has been observed during the southern summer in Fiji and on many other South Pacific atolls. Satellite measurements by the National Oceanic and Atmospheric Association documented unusually high temperatures across much of the Pacific. The 1990s has seen several major bleaching events. Repeated and prolonged bleaching episodes - expected as tropical water temperatures warm with climate change - eventually kill corals and cause a decline in associated marine species.

© Environmental Defense, Natural Resources Defense Council, Sierra Club, Union of Concerned Scientists U.S. Public Interest Research Group, World Resources Institute, World Wildlife Fund

The impact of global warming in North America

A science-based world map depicting the local and regional consequences of global climate change. The map was produced as a collaborative project by several environmental organizations, and has been peer-reviewed by scientists.

The vast North American continent ranges from the lush sub-tropical climate of Florida to the frozen ice and tundra of the Arctic. Within these extremes are two wealthy industrialized countries with diverse ecosystems at risk. Yet the United States and Canada are two of the largest global emitters of the greenhouse gases that contribute to a warming climate. Examples of all 10 of the "hotspot" categories can be found in this region, including changes such as polar warming in Alaska, coral reef bleaching in Florida, animal range shifts in California, glaciers melting in Montana, and marsh loss in the Chesapeake Bay.

For North America we have many more hotspots than for some other regions of the world, although impact studies have been emerging in larger numbers in recent years from previously under-studied regions. This higher density of early warning signs in the US and Canada is due in part to the fact that these regions have more readily accessible climatic data and more comprehensive programs to monitor and study environmental change, in part to the disproportionate warming that has been observed over the mid-to-high-latitude continents compared to other regions during the last century, and in part to capture the attention of North Americans who need to take action now to reduce greenhouse gas emissions.

Fingerprints: Direct manifestations of a widespread and long-term trend toward warmer global temperatures.

4. Edmonton, Canada -- Warmest summer on record, 1998. Temperatures were more than 5.4°F (3°C) higher than the 116-year average.

7. Glasgow, Montana -- No sub-zero days, 1997. For the first time ever, temperatures remained above 0°F (-17.8°C) in December. The average temperature was 10.9°F (6°C) above normal.

8. Little Rock, Arkansas -- Hottest May on record, 1998.

9. Texas -- Deadly heat wave, summer 1998. Heat claimed more than 100 lives in the region. Dallas temperatures were over 100°F (37.8°C) for 15 straight days.

10. Florida -- June heat wave, 1998. Melbourne endured 24 days above 95°F (35°C); nighttime temperatures in Tampa remained above 80°F (26.6°C) for 12 days.

11. USA -- Late fall heat wave 1998. An unprecedented autumn heat wave from mid-November to early December broke or tied more than 700 daily-high temperature records from the Rockies to the East Coast. Temperatures rose into the 70°F (20°C) as far north as South Dakota and Maine.

12. Eastern USA -- July heat wave, 1999. More than 250 people died as a result of a heat wave that gripped much of the eastern two-thirds of the country. Heat indices of over 100°F (37.8°C) were common across the southern and central plains, reaching a record 119°F (48.3°C) in Chicago.

13. New York City -- Record heat, July 1999. New York City had its warmest and driest July on record, with temperatures climbing above 95°F (35°C) for 11 days -- the most ever in a single month.

39. Chesapeake Bay -- Marsh and island loss. The current rate of a sea-level rise is three times the historical rate and appears to be accelerating. Since 1938, about one-third of the marsh at Blackwater National Wildlife Refuge has been submerged.

40. Bermuda -- Dying mangroves. Rising sea level is leading to saltwater inundation of coastal mangrove forests.

42. Hawaii -- Beach loss. Sea-level rise at Waimea Bay, along with coastal development, has contributed to considerable beach loss over the past 90 years.

65. Glacier National Park, Montana -- All glaciers in the park will be gone by 2070 if retreat continues at its current rate.

68. Interior Alaska -- Permafrost thawing. Permafrost thawing is causing the ground to subside 16-33 feet (4.9-10 m) in parts of interior Alaska. The permafrost surface has warmed by about 3.5°F (1.9°C) since the 1960's.

69. Barrow, Alaska -- Less snow in summer. Summer days without snow have increased from fewer than 80 in the 1950's to more than 100 in the 1990's.

71. Bering Sea -- Reduced sea ice. Sea-ice extent has shrunk by about 5 percent over the past 40 years.

72. Arctic Ocean -- Shrinking sea ice. The area covered by sea ice declined by about 6 percent from 1978 to 1995.

135. Canadian Rockies - Disappearing glaciers. The Athabasca Glacier has retreated one-third of a mile (0.5 km) in the last 60 years and has thinned dramatically since the 1950s-60s. In British Columbia the Wedgemont Glacier has retreated hundreds of meters since 1979, as the climate has warmed at a rate of 2°F (1.1°C) per century, twice the global average.

136. Alaska - Increasing rate of retreat. A study of 67 glaciers shows that between the mid-1950s and mid-1990s the glaciers thinned by an average of about 1.6 feet (0.5 m) per year. Repeat measurements on 28 of those glaciers show that from the mid-1990s to 2000-2001 the rate of thinning had increased to nearly 6 feet (1.8 m) per year. Alaska has experienced a rapid warming since the 1960s. Annual average temperatures have warmed up to 1.8°F (1°C) per decade over the last three decades, and winter warming has been as high as 3°F (2°C) per decade.

Harbingers: Events that foreshadow the types of impacts likely to become more frequent and widespread with continued warming.

16. Mexico -- Dengue fever spreads to higher elevations. Dengue fever has spread above its former elevation limit of 3,300 feet (1,006 m) and has appeared at 5,600 feet (1,707 m).

19. Central America -- Dengue fever spreads to higher elevations. Dengue fever is spreading above its former limit of 3,300 feet (1,006 m) and has been reported above 4,000 feet (1,219 m).

23. Lake Mendota, Wisconsin -- Fewer days of ice cover. The number of days per year with ice cover has decreased by 22 percent since the mid-1800s.

24. Mirror Lake, New Hampshire -- Earlier spring ice-out. The ice-covered period has declined by about half a day per year during the past 30 years.

25. Nenana, Alaska -- Early river thaw. During 82 years on record, four out of the five earliest thaws on the Tanana River occurred in the 1990's.

26. Washington, D.C. -- Cherry trees blossoming earlier. Average peak bloom from 1970-1999 came April 3, compared to April 5 from 1921-1970.

28. California -- Butterfly range shift. Edith's Checkerspot Butterfly has been disappearing from the lower elevations and southern limits of its range.

31. Olympic Mountains, Washington -- Forest invasion of alpine meadow. Sub-alpine forest has invaded higher-elevation alpine meadows, partly in response to warmer temperatures.

33. Alaska -- Sea bird population decline. The black guillemot population is declining from 1990 levels because melting sea ice has increased the distance the birds must fly to forage for food and reduced the number of resting sites available.

34. Canadian Arctic -- Caribou die-offs. Peary caribou have declined from 24,000 in 1961 to perhaps as few as 1,100 in 1997, mostly because of major die-offs that have occurred in recent years after heavy snowfalls and freezing rain covered the animals' food supply.

35. Monterey Bay , California -- Shoreline sea life shifting northwards. Changes in invertebrate species such as limpets, snails, and sea stars in the 60-year period between 1931-1933 and 1993-1994 indicate that species' ranges are shifting northwards, probably in response to warmer ocean and air temperatures.

36. Monteverde Cloud Forest, Costa Rica -- Disappearing frogs and toads. A reduction in dry-seson mists due to warmer Pacific ocean temperatures has beenlinked to disappearances of 20 species of frogs and toads, upward shifts in the ranges of mountain birds, and declines in lizard populations.

38. U.S. West Coast -- Sea bird population decline. A decline of about 90 percent in sooty shearwaters from 1987 to 1994 corresponds to a warming of the California Current of about 1.4°F (0.78°C).

46. Pacific Ocean, Mexico -- Coral reef bleaching.

53. Caribbean -- Coral reeef bleaching.

54. Florida Keys and Bahamas -- Coral reef bleaching.

55. Bermuda -- Coral reef bleaching.

76. New England -- Double normal rainfall, June 1998. Rainfall in Boston on June 13-14 broke a 117-year-old record, closing Logan Airport and two interstate roads. Vermont, New Hampshire, Rhode Island, and Massachusetts each received more than double their normal monthly rainfall.

78. Black Hills, South Dakota -- Record snowfall, 1998. At the end of February, the Black Hills received 102.4 inches (260 cm) of snow in five days, almost twice as much snow as the previous single-storm record for the state.

79. Texas -- Record downpours, 1998. Severe flooding in southeast Texas from two heavy rain storms with 10-20 inch (25.4-50.8 cm) rainfall totals caused $1 billion in damage and 31 deaths.

80. Santa Barbara, California -- Wettest month on record, 1998. 21.74 inches (55.22 cm) of rain fell in February, the most rain in a month since record keeping began.

81. Mount Baker, Washington -- World record snowfall, 1999. 1,140 inches (2,896 cm) of snow fell between November 1998 and the end of June 1999, a world record for most snowfall in a single winter season.

82. Florida -- Worst wildfires in 50 years, 1998. Fires burned 485,000 acres (196,272 hectares) and destroyed more than 300 homes and structures.

84. Florida, Texas, Louisiana -- Driest period in 104 years, April-June 1998. San Antonio received only 8 percent of its normal rainfall in May. New Orleans suffered its driest and hottest May in history.

85. Mexico -- Worst fire season ever, 1998. 1.25 million acres burned during a severe drought. Smoke reaching Texas triggered a statewide health alert.

86. Nicaragua -- 2.2 million acres (890,308 hectares) burned, 1998. Over 15,000 fires burned in 1998, and the blazing acreage included protected lands in the Bosawas Biosphere Reserve.

89. Eastern USA -- Driest growing season on record, 1999. The period from April-July 1999 was the driest in 105 years of record-keeping in New Jersey, Delaware, Maryland, and Rhode Island. Agricultural disaster areas were declared in fifteen states, with losses in West Virginia alone expected to exceed $80 million.

102. North America - Genetic adaptation to global warming in mosquito. Ecologists have identified the first genetic adaptation to global warming in the North American mosquito Wyeomyia smithii. Modern mosquitoes wait nine days more than their ancestors did 30 years ago before they begin their winter dormancy, with warmer autumns being the most likely cause. Higher temperatures, enhancing mosquito survival rates, population growth and biting rates, can increase the risk of disease transmission.

109. Colorado - Earlier emergence from hibernation. Marmots are emerging from hibernation on average 23 days earlier than 23 years ago. This coincides with an increase in average May temperatures of about 1.8°F (1°C) over the same time period.

110. Southeast Arizona - Earlier egg-laying. Mexican jays are laying eggs 10 days earlier than in 1971. The earlier breeding coincides with a nearly 5°F (2.8°C) increase in average nighttime temperatures from 1971 to 1998.

114. Alaska - Changing vegetation patterns. Comparison of photographs taken in 1948-50 to those taken in 1999-2000 of the area between the Brooks Range and the Arctic coast show an increase in shrub abundance in tundra areas, and an increase in the extent and density of spruce forest along the treeline. The increased vegetation growth is attributed to increasing air temperatures in Alaska, on average 1.8°F (1°C) per decade over the last three decades.

115. Western Hudson Bay, Canada - Stressed Polar Bears. Decreased weight in adult polar bears and a decline in birthrate since the early 1980s has been attributed to the earlier spring breakup of sea ice. Rising spring temperatures have shortened the spring hunting season by two weeks over the last two decades.

116. Banks Island, Canada - Expanded Ranges. The Inuit now regularly see species common much further south that previously were never seen on the island, such as robins and barn swallows. Thunder and lightning, never before recorded in Inuit oral history, have also been reported.

© Environmental Defense, Natural Resources Defense Council, Sierra Club, Union of Concerned Scientists U.S. Public Interest Research Group, World Resources Institute, World Wildlife Fund