EPA's Endangerment Finding

Frequently Asked Questions

What has EPA determined in these Findings?

The Administrator finds that under section 202(a) of the Clean Air Act greenhouse gases threaten both the
public health and the public welfare, and that greenhouse gas emissions from motor vehicles contribute to
that threat.

This final action has two distinct "findings," which are:

1)	The "Endangerment Finding," in which the Administrator finds that the mix of atmospheric
concentrations of six key, well-mixed greenhouse gases threatens both the public health and the public
welfare of current and future generations. These six greenhouse gases are: carbon dioxide (C02), methane
(CH4), nitrous oxide (N20), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur
hexafluoride (SF6). These greenhouse gases in the atmosphere constitute the "air pollution" that threatens
both public health and welfare.

2)	The "Cause or Contribute Finding," in which the Administrator finds that the combined greenhouse
gas emissions from new motor vehicles and motor vehicle engines contribute to the atmospheric
concentrations of these key greenhouse gases and hence to the threat of climate change.

Will these Final Findings impose any requirements under the Clean Air Act?

The action does not itself impose any requirements on industry or other entities. It does, however, pave
the way for EPA to finalize the proposed greenhouse gas emission standards for light-duty vehicles,
which were proposed in conjunction with the Department of Transportation's Corporate Average Fuel
Economy (CAFE) standards earlier this year.

Why is EPA issuing these findings?

By issuing this action, EPA is responding to the April 2007 Massachusetts v. EPA Supreme Court
decision, in which the court found that greenhouse gases are air pollutants under the Clean Air Act. The
Court held that EPA must determine whether or not emissions of greenhouse gases from new motor
vehicles cause or contribute to air pollution which may reasonably be anticipated to endanger public
health or welfare, or whether the science is too uncertain to make a reasoned decision. (See
htto://epa. gov/climatechan ge/endangerment/downloads/timeline .pdf)

What is EPA's rationale for making the finding that the elevated concentrations of greenhouse gases in
the atmosphere endanger both public health and welfare of current and future generations?

EPA considered both observed and projected effects of greenhouse gases in the atmosphere, their effect
on climate, and the public health and public welfare risks and impacts associated with such climate
change. The assessment focused on both public health and public welfare impacts within the United
States, but noted that the current and expected impacts of climate change in other parts of the world can
adversely affect the United States.

How is EPA defining the "air pollution" caused by greenhouse gas emissions
under the Clean Air Act?

The word "air pollution" is defined as the six well-mixed and directly emitted greenhouse gases that
together constitute the root of the air pollution problem that is causing climate change. These include

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carbon dioxide (C02), methane (CH4), nitrous oxide (N20), hydrofluorocarbons (HFCs),
perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).

What is EPA's rationale for making the finding that emissions of greenhouse
gases from on-road vehicles cause or contribute to the climate change problem?

The greenhouse gas emissions from section 202(a) source categories (essentially all on-road vehicles)
account for about 4 percent of total global greenhouse gas emissions and just over 23 percent of total U.S.
greenhouse gas emissions. Greenhouse gas emissions from the on-road vehicles are the second largest
greenhouse gas emissions source in the United States, behind the electricity generating sector. U.S.
emissions from on-road vehicles are also greater than the total greenhouse gas emissions from every other
individual nation with the exception of China, Russia, and India. EPA's determination treats emissions of
the six key greenhouse gases collectively as an "air pollutant" under the Clean Air Act and paves the way
for regulating emissions from cars.

What are the impacts of climate change that endanger public health and welfare?

The impacts of climate change that will cause hann to human health and welfare of current and future
generations include but are not limited to: increased drought; more heavy downpours and flooding; more
frequent and intense heat waves and wildfires; greater sea level rise; more intense storms; and harm to
water resources, agriculture, wildlife, and ecosystems.

What information did EPA review in forming this judgment?

EPA gave careful consideration to all of the scientific and technical information in the record and relied
primarily on published, well-vetted climate change assessment literature. That information, including the
recent assessment of the U.S. Global Change Research Program, released in June 2009, is summarized in
the Technical Support Document (TSD). In addition, EPA reviewed and considered scientific literature
and views submitted through public comments and provided responses in EPA's Response to Comment
document. All these documents together form the basis for the final determinations.

Did the public comment process result in any change to the findings since the
proposal?

The key elements of the proposal remain unchanged in the final findings: concentrations of greenhouse
gases threaten both public and welfare, and emissions of greenhouse gas air pollutants from cars
contribute to that threat. Based on EPA's careful review of the public comments, EPA has concluded that
the science remains overwhelmingly consistent that current and future greenhouse gas concentrations in
the atmosphere do endanger both public health and public welfare.

Why didn't EPA include black carbon in the definition of air pollution in this
finding?

Black carbon is now recognized as an important climate-forcing agent with particular impact on the
Arctic region. Scientific data on its contribution to the climate change problem is growing. Under this
action, the definition of air pollution includes six well-mixed greenhouse gases that share common
properties and are the best understood drivers of climate change. EPA recognizes the importance of black
carbon and is committed to fully evaluate its role on climate change.

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What requirements are imposed by this action? How do these findings relate to
other proposed Clean Air Act rules for greenhouse gases?

This action does not itself impose any requirements on industry or other entities. It does allow EPA to
finalize the greenhouse gas emission standards for light-duty vehicles proposed jointly with the
Department of Transportation's Corporate Average Fuel Economy (CAFE) standards on September 15,
2009.

Are stationary source permits under the Prevention of Significant Deterioration
(PSD) and Title V operating permit programs triggered by this action?

No, this action does not trigger PSD or Title V permitting. Final ization of the GHG emission standards
for motor vehicles, proposed 011 September 15, 2009 would trigger these programs. EPA proposed a PSD
and Title V GHG Tailoring Rule 011 September 30, 2009 to address this issue.

Did EPA rush to issue these finding?

No. It has been over 2-Vz years since the Supreme Court determined that greenhouse gases are pollutants
under the Clean Air Act. It has been more than 14 months since EPA issued its Advance Notice of
Proposed Rulemaking on this issue. Finally, it has been more than 10 years since the original petition for
rulemaking that led to the Supreme Court's decision was filed. Since that time, EPA has been evaluating
the entire body of scientific literature, which has become increasingly compelling that the root cause of
global warming is greenhouse gas concentrations in the atmosphere and that the impacts of climate
change threaten both public health and welfare.

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