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Frequently Asked Questions

What is Global Warming?

Global warming is the increase in the average surface air temperature of the planet that is a result of the buildup of heat-trapping or "greenhouse" gases in the atmosphere. Back to the top.


planttree What is the "Greenhouse Effect"?

The greenhouse effect is an important natural process that makes life on earth possible. Because the atmosphere always contains heat-trapping gases like carbon dioxide, water vapor, and methane, much of the heat from the sun's radiation is "trapped" in the atmosphere rather than radiating back into space -- much like how the panes of glass in a greenhouse hold heat inside the greenhouse. As a result, the atmosphere remains warm enough to support human, plant, and animal life as we know it. Without greenhouse gases, Earth would be about 60 degrees (F) colder and uninhabitable. Unfortunately, as humans burn fossil fuels like coal, oil and natural gas, we are increasing the amount of carbon dioxide and other greenhouse gases in the atmosphere. This is causing more of the sun's heat to be trapped, thus causing the intensification of the greenhouse effect known as global warming.


What is causing Global Warming?

Scientists contend that anthropogenic additions of greenhouse gases, mainly CO2, greatly enhance the natural warming of the earth. Use of fossil fuels (e.g. driving a car, drawing electricity from a coal-fired power plant, heating a home with oil or natural gas) is the main human source of CO2 and other greenhouse gases released into the atmosphere. The second most important source of heat-trapping gases is land-use changes, such as deforestation. The concentration of CO2 since pre-industrial times has increased by 31%. Also, agricultural activities such as growing rice and raising cattle has had a large influence in the 151% rise of atmospheric methane. With these considerable increases in greenhouse gases, more heat from the sun and earth's surface is trapped in the atmosphere, causing the phenomenon known as global warming.


How much warming is likely to occur?

The Intergovernmental Panel on Climate Change (IPCC) predicts a warming in the range of 2.5 to 10.4 degrees Fahrenheit by the year 2100.


How much warming has already occurred, and what are some of the global impacts we are seeing as a result?

During the 20th century the global average surface temperature has increased about 1 degree Fahrenheit. This is likely to have been the largest increase of any century during the past 1,000 years. As a result we are already observing various effects of this warming. Snow and ice cover are decreasing, including a widespread retreat of mountain glaciers in non-polar regions during the 20th century. Sea level is rising and the heat content of the oceans has increased. Precipitation and extreme weather events also appear to be increasing.


What is the IPCC?

The Intergovernmental Panel on Climate Change is a scientific organization established by the United Nations Environment Program (UNEP) and the World Meteorological Organization in 1988. The IPCC brings together the world's top scientists in all relevant fields, to survey and synthesize peer-reviewed scientific studies of climate change, and to provide an authoritative assessment of the state of knowledge regarding global warming. There have been three such assessments conducted. The first one was released in 1990, the second in 1995, and the third in 2001. The IPCC is made up of 2500 of the world's top climate scientists. There are three different "working groups" within the IPCC. Working Group I assesses available scientific information on climate change. Working Group II assesses the environmental and socioeconomic impacts of climate change, and Working Group III assesses possible solutions or response strategies.


How do we know levels of Carbon Dioxide and other Greenhouse Gases are increasing in the atmosphere?

Since the late 1950's we have been directly measuring the amounts of carbon dioxide in the atmosphere. We can also measure amounts from previous eras using ice core samples and other techniques. There is no scientific doubt that carbon dioxide levels have been increasing. According the IPCC's third assessment, the atmospheric concentration of carbon dioxide (CO2) has increased by 31% since 1750. The current CO2 concentration has not been exceeded during the past 420,000 years, and most likely was not exceeded during the last 20 million years. The atmospheric concentration of methane (CH4), a potent greenhouse gas, has increased by 151% since 1750, and continues to increase.


What is causing the rising levels of CO2 in the atmosphere?

According to the IPCC about three-quarters of the human-caused emissions of CO2 is due to the combustion (or burning) of fossil fuels. The rest is primarily due to deforestation and other land use changes.



How do we know that the atmospheric build-up of CO2 is due to human activity?

The nuclei of carbon atoms in carbon dioxide emitted by combustion of fossil fuels differ from the nuclei of carbon atoms in carbon dioxide emitted under natural conditions, in that the carbon dioxide emitted from natural sources on the Earth's surface retains a measurable radioactive portion, while the carbon dioxide emitted by fossil fuel combustion does not. As carbon dioxide has been emitted through fossil fuel combustion, the atmospheric levels of CO2 have increased, but the radioactive fraction of carbon in the atmosphere has decreased.


How do we know the warming is a result of the buildup of Greenhouse Gases in the atmosphere from human activity, and not the result of natural climate variability or some other natural cause?

The search for exactly that kind of proof has gone on during the 1990s, and is sometimes referred to as the search for the "Greenhouse Fingerprint." Typically, what we are looking for is some sort of "Greenhouse Signal" that emerges against a backdrop of noise. The noise is the natural variability in climate data or trends. To find such a signal requires identifying some distinctive results that would only be likely to occur as a result of warming caused by the increase of greenhouse gases in the atmosphere. Climate models could predict certain results that should be expected, and then actual data would be examined to see if they conform closely enough to the expected results to be statistically significant. The science bearing on this issue has been reviewed in each of the 3 assessments conducted by the Intergovernmental Panel on Climate Change (IPCC). In its first assessment, in 1990, the IPCC concluded that we could not yet tell with any certainty that humans were responsible for the observed warming. Between the first assessment and the second assessment, however, some new studies had begun to detect a clear "greenhouse fingerprint". In the second assessment the IPCC stated that its review of the science showed that "the balance of evidence suggests a discernible human influence on global climate," but also noted that "the anthropogenic signal was still emerging from the background of natural climate variability." Presumably, over time, as the human causes of global warming increase (as CO2 concentrations continue to rise), the signal should become more easily detectable. In fact, the third assessment released earlier this year, found that "there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities."


What nations produce the most Greenhouse Gas emissions?

The United States is the world leader, producing almost 25% of the total CO2 emissions worldwide. China shows the most rapid increase in CO2 emissions, and Canada is the world leader in per capita CO2 emissions (truly a dubious distinction). Table #1 below, compares the CO2 emissions of the top 10 nations.


Is Global Warming connected to the hole in the Ozone Layer?

Although Global Warming and ozone depletion are two separate threats, they do bear some relation. The enhanced greenhouse effect causing global warming takes place in the lower part of the atmosphere known as the troposphere. However, ozone depletion is a crisis occurring in the upper atmosphere known as the stratosphere. Stratospheric ozone is responsible for keeping out the sun's ultraviolet radiation that causes harm to life on earth. Because the ozone layer traps heat, its destruction not only lets in dangerous radiation but also cools the upper atmosphere, thereby disturbing weather patterns of the upper atmosphere. The two problems are related in that some human-made gases, called chlorofluorocarbons, both trap heat and rise into the stratosphere to destroy the ozone layer. Chlorofluorocarbons, however, are a larger contributor to ozone depletion than to global warming. Although any effort to reduce ozone-depleting gases is essential to preventing further devastation to the ozone layer, it will not solve the crisis of global warming at the same time. Nonetheless, working to eliminate many different types of emissions in order to regulate global warming may also have a positive effect on saving the ozone layer.



Is it too late to stop Global Warming altogether?

To be blunt, yes. Scientists of the IPCC have concluded that earth's temperature has already begun to rise unnaturally. The ten warmest years on record have occurred in the last 15 years. The 20th century experienced a global average surface temperature rise of about 1 degree Fahrenheit, possibly the largest increase experienced by any century in the last 1,000 years. The latter half of the 20th century saw a decrease in snow cover and the retreat of mountain glaciers. However, it is not too late to slow down the process of global warming, and to reduce the amount of warming that ultimately occurs. Scientists and economists have identified many cost-effective alternatives that would reduce greenhouse gas emissions. These alternatives include investments in energy-efficiency technologies, clean energy sources, and zero-emission vehicles, thus easing away from a dependence on oil and coal as main energy resources.


What needs to be done to reduce Global Warming?

Americans have played a large role in the anthropogenic addition of greenhouse gases. California, the U.S., and the world need to achieve a large reduction of emissions from fossil fuels. Governments should adopt more stringent energy efficiency standards, eliminate subsidies that promote coal and oil use, and support a trend toward renewable sources of energy (e.g., solar and wind power). While cutting CO2 emission levels is by far the most important factor in reducing global warming, the protection and restoration of forest ecosystems, which serve as important storehouses for carbon, can also help. Probably the single most important step that the federal government could take would be to increase federal fuel economy standards for new cars, trucks and SUVs. California should lead the nation in tackling global warming by formally authorizing the state's Air Resources Board (ARB) to reduce CO2 emissions from California's passenger cars and SUVs. California should also adopt a "Renewable Portfolio Standard" which would promote renewable energy sources by requiring that energy suppliers generate 20% of their power from renewable sources (like solar and wind power) by 2010.


What is CAFE?

CAFE stands for Corporate Average Fuel Economy and refers to federal automobile fuel efficiency standards. Improving automobile fuel efficiency would greatly decrease the United State's oil dependency because over 40% of the oil used in the country goes toward fueling our cars and trucks. Enhanced fuel efficiency would not only reduce our oil dependency, but it would also significantly reduce CO2 emissions. The standards set in 1975, requiring new cars to average 27.5 miles per gallon and light trucks to average 20.7 miles per gallon (mpg), was achieved in the 1980s, despite carmakers complaints that the requirements would impede product design. Today, a coalition of consumer, safety, and environmental advocates are calling for further improvement in CAFE standards. These new standards would be 45 mpg for cars and 34 mpg for light trucks over the next 10 years. Legislation has also been introduced to subject SUVs to the same CAFE standards as passenger cars. This is Senate Bill 804 introduced by Senators Feinstein and Snowe. The bill would require SUVs to incrementally reach current car standards of 27.5 mpg by 2007. By 2002, SUVs would need to average 22.5 mpg, 25 mpg by 2005, and finally 27.5 in 2007. Carmakers complain that in order to reach CAFE standards, they would need to reduce the size of the vehicles they produce. But, according to Department of Energy analysts, 86% of the fuel economy improvements for the 1975 standards came from efficient packaging, better aerodynamics, better fuel injections and other technologies. Only 2% of the improvements resulted from reducing the size of cars. In order to reach the new proposed standards, carmakers can use multi-valve engines, lean burn energy technology (allowing the car to burn less fuel under low power demand), high strength/ lightweight materials, low friction lubricants, and more. Because CAFE calls for averages on the fuel efficiency of an automaker's vehicle fleet, not all models need to reach the standard as long as enough vehicles exceed the standard in order to maintain the fleet average. Raising fuel economy requirements is the largest single step we could take to cut global warming emissions and save oil. In addition, strong CAFE standards would alleviate pressure to drill in wildlife preserves, enhance national security by attenuating our reliance on foreign imports, and save individuals money at the gas pump.



Should cities and counties play a role in reducing Global Warming?

Yes, absolutely. Climate Change can be successfully reduced only if all levels of government participate in finding ways to reduce greenhouse gas emissions. Cities and counties can adopt many policies that promote energy efficiency and renewable energy resources. They can also adopt a municipal Climate Action Plan that inventories a city's own contribution to greenhouse gas emissions, and sets a goal for reducing municipal emissions of greenhouse gases. Such plans often include specific measures for improving the energy efficiency of city buildings and streetlights, vehicle fleets, and even commercial and residential buildings throughout the city. They can include provisions for bicycle patrols, solar-heating at municipal swimming pools, and capturing methane to create electricity at landfills. And the good news is that most of these ideas will pay for themselves in reduced energy costs in just a few years.


What can individuals do?

Every individual can take action and do their part to curb global warming. Probably the most significant environmental decision a consumer can make is which car to drive. For every single gallon of gasoline burned, 20 pounds of CO2 enters the atmosphere. A person can help by choosing a highly fuel-efficient car or an electric or hybrid car and by carpooling, walking, biking, and using public transit. Also, a person contributes to global warming whenever they use electricity. Buying energy-efficient appliances and reducing daily energy use can make a difference as well. Compact fluorescent light bulbs use one-quarter the energy and last 5-10 times longer than standard incandescent light bulbs. Halogen lights are very inefficient. Avoid purchasing halogen lighting and choose compact fluorescent lights instead. And join organizations like the Coalition for Clean Air that are fighting for clean renewable energy resources, and clean, fuel-efficient cars and trucks. For more on what you can do as an individual, check out our Energy Tips.