About the Green Rating

The Green Rating measures a vehicle's environmental friendliness on a scale of 1 to 100. The higher a vehicle's Green Rating, the "greener" it is and the lower its harm to both human health and the health of the planet.
A Yahoo! Autos exclusive, the Green Rating was developed in consultation with Environmental Defense, a leading nonprofit that finds practical ways to protect the planet. The Green Rating covers all the major environmental costs of a motor vehicle, including:
• Unhealthy smog that comes from tailpipes.
• Emissions of greenhouse gases that cause global warming.
• The fuel a vehicle consumes.
• Pollution from manufacturing the vehicle and its components.
More and more car shoppers care about how their choices affect the planet. Yahoo! Autos' Green Rating makes it easy for anyone to comparison shop with the environment in mind.

Because all vehicles -- sedans, coupes, vans, SUVs, trucks, etc. -- are rated on a single 1 to 100 scale, you can use the Green Rating to find the most environmentally friendly vehicle that meets your needs. For example, a 3-point gain in Green Rating between SUVs that score 40 and 43, cuts pollution just as much as a 3-point Green Rating gain between compact cars that score 60 and 63.
You might already look at fuel efficiency when you compare vehicles. But since the Green Rating also reflects tailpipe emissions and other factors, it simplifies the task of weighing the many aspects of a car's environmental friendliness. Some car shoppers think that they need to buy a hybrid, use an alternative fuel or buy a small car in order to buy green. While such vehicles can indeed tread more lightly on the planet, the Green Ratings can help you make a greener choice no matter what kind of car you choose.
How are the Green Ratings derived?
Automobiles degrade the environment in many ways. Because vehicles stay on the road a long time, the largest effects occur during driving. Car pollution includes greenhouse gases, which cause global warming, and smog-related emissions, which trigger asthma attacks and raise the risks of heart and lung disease. Pollution also occurs when vehicles and their parts are manufactured, and again when a vehicle is scrapped at the end of its life.
A vehicle's total environmental impact
A scientific method for adding up all of the environmental damages associated with a product is known as lifecycle assessment. The Green Ratings were developed following principles of lifecycle assessment, using publicly available information to evaluate all vehicles uniformly. Thus, the ratings represent "apples-to-apples" comparisons between different makes and models. The Green Ratings rely on government-certified data and do not consider marketing assertions, "promises," or other unverifiable claims about environmental friendliness.
Major pollutants covered in the ratings include:
• Greenhouse gases, primarily carbon dioxide (CO2)
• Fine particles (particulate matter, PM)
• Nitrogen oxides (NOx)
• Hydrocarbons (HC)
• Carbon monoxide (CO)
These pollutants are emitted from tailpipes as well as during the production and distribution of fuel. Environmental impacts from auto manufacturing are incorporated by basing part of the Green Rating's derivation on a vehicle's weight.
Scientists evaluate car pollution in two broad categories: greenhouse gases that cause global warming (such as CO2) and emissions that directly harm human health (such as PM, NOx, HC and CO). The Green Rating gives equal importance to these two categories. A vehicle's global warming pollution depends largely on fuel consumption, so it is calculated from fuel economy data. A vehicle's health-harming pollution depends largely on the emissions standard that it meets, which forms the basis for that part of the calculation. In others words, a "green" vehicle is one that is both clean and fuel-efficient.
The data behind the ratings
The data used to derive the Green Ratings are a vehicle's official fuel economy numbers and emissions standards as certified by the U.S. Environmental Protection Agency (EPA), plus curb weight. Fuel economy and emissions information comes from tests performed by automakers and accepted by the EPA, with a vehicle subject to recall, penalty or withholding of the certification required for legal sale in the United States if the data are found to be false or misleading. Thus, Green Ratings are based on the most accurate and unassailable data available for all cars and light trucks, ensuring fair comparisons among competing models.
Because of concerns that the EPA miles-per-gallon (MPG) numbers overstate the fuel economy that most consumers experience, the agency is updating the way fuel economy ratings are determined. Revised MPG numbers are planned for model year 2008. Pending EPA's revisions, the Green Rating calculations adjust the fuel economy numbers downward. Because the adjustment is applied across the board, it does not bias comparisons among vehicles or types of vehicles relative to the official EPA numbers. This adjustment will be dropped in future model years once revised MPG data become available.
The Green Rating rates just the vehicle, not how you use it
In interpreting the Green Ratings, keep in mind that they are intended strictly for vehicle-to-vehicle comparisons. For example, a vehicle's Green Rating does not improve if you carry four passengers in it instead of just yourself, even though the per-person environmental impact will clearly decrease. Similarly, the Green Rating doesn't go down if you drive aggressively, even though the environmental damage due to your driving goes up.
To enable fair comparisons among vehicles regardless of how they are used, the Green Ratings are based on uniform assumptions about how far the vehicle is driven over its lifetime and good maintenance practices. Your own effect on the planet when using a car, of course, depends on how you drive, how well you maintain the vehicle, and how many miles you drive it.
Unless a vehicle is designed for exclusive use on a particular fuel (such as a car that runs only on natural gas, like the Honda Civic GX), its Green Rating is based on commonly available motor fuel (gasoline or diesel). While Green Ratings are designed for fair comparisons among vehicles in the showroom, you might reduce your own vehicle's pollution by using an alternative fuel. For example, a flexible-fuel vehicle able to run on E85 (a blend of 85% ethanol and 15% gasoline) can have lower greenhouse gas emissions when using E85 rather than gasoline. Similarly, biodiesel can emit less global warming pollution than regular diesel produced from petroleum.
Because most of today's biofuels were not originally developed to solve global warming, their greenhouse gas reductions vary. Farmers and refiners are working on new ways to produce cleaner fuels that will provide greater climate-protection benefits as time goes on. Consumers should stay tuned.
More information on the pollutants factored into the Green Ratings
Greenhouse gases
Greenhouse gases include carbon dioxide (CO2) and other emissions from the production and use of fossil fuels as well as deforestation. These global warming pollutants are accumulating in the atmosphere and causing the Earth to heat up at an unprecedented rate. Global warming brings many dangers and its consequences are already being felt. Glaciers and mountain snow packs are melting. Sea ice is thinning. Many communities will experience more sweltering days. Hazards from extreme weather events, such as intense hurricanes, are rising -- as is sea level, which heightens the impact of coastal storms and risks human tragedies and economic ruin for the many population centers located near a shoreline. Other dangers of global warming include spread of tropical diseases, destruction of habitat and disruptions to forestry and agriculture, bleaching of coral reefs, and adverse impacts on wildlife and fisheries.
Fine particles
Also called particulate matter (PM) and sometimes "soot," fine particles from car and truck fuel combustion are generally invisible. Many are so small they are labeled "ultra-fine." Fine particles are an especially deadly form of air pollution that can affect breathing, aggravate existing respiratory and cardiovascular disease, weaken the body's immune defenses, and contribute to cancer and premature death. Fine particles are especially hazardous for children, the elderly, asthmatics and people with cardiovascular or chronic obstructive pulmonary disease.
Nitrogen oxides
Nitrogen oxides (NOx) are harmful in many ways. In addition to being a direct irritant, NOx are key contributors to ozone smog, which damages lung tissue, worsens asthma, and recently has been found to increase the risk of premature death. Smog alerts bring health risks not only for people with asthma and other conditions that make them sensitive to air pollution, but even for normally healthy adults and children who can experience lung inflammation and shortness of breath if they are active in smoggy air. NOx contributes to fine particle pollution, with its dangers as noted above, and is also a cause of acid rain.
Hydrocarbons
There are many kinds of hydrocarbons (HC), and the hazardous ones emitted by cars fall into categories known as "volatile organic compounds" or "reactive organic gases." These pollutants are another key contributor to ozone smog, bringing all of the health dangers noted above for NOx. Some forms of HC directly irritate the lungs; many contribute to fine particle pollution and some hydrocarbons are also air toxics, including compounds having known cancer risks.
Carbon monoxide
Carbon monoxide (CO) is a poisonous gas that is deadly in high concentrations, notorious for sometimes killing people who leave a vehicle running in a closed garage, for example. CO is colorless and odorless, and when inhaled, it impairs the blood's ability to supply oxygen to the body. Even short of fatal exposures, exposure to too much CO can cause physical, mental and visual impairment and presents grave risks to individuals who have cardiovascular disease.

Source: http://autos.yahoo.com/green_center-article_144/?p=2

See also: http://autos.yahoo.com/green_center-top100/

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