U.S. EPA Technical Support Document: Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act

Published April 17, 2009

This U.S. Environmental Protection Agency's Climate Change Division report, released on April 17, 2009, states that, "This document provides technical support for the endangerment analysis concerning greenhouse gas (GHG) emissions that may be addressed under the Clean Air Act." The EPA Administrator's proposal, released along with this technical support document, can be accessed here.

Among its findings on impact of greenhouse gas emissions: "The primary focus of this document is on the observed and potential future impacts associated with elevated GHG concentrations and associated climate change within the U.S. However, EPA has considered the global nature of climate change in at least two ways for purposes of this document.

First, GHGs, once emitted, remain in the atmosphere for decades to centuries, and thus become, for all practical purposes, uniformly mixed in the atmosphere, meaning that U.S. emissions have climatic effects not only in the U.S. but in all parts of the world. Likewise, GHG emissions from other countries can influence the climate of the U.S., and therefore affect human health, society and the natural environment within the U.S. All observed and potential future climate change impacts within the U.S. reviewed in this document consider climate change driven by global anthropogenic GHG emissions.

Second, despite widely discussed metrics such as global average temperature, climate change will manifest itself very differently in different parts of the world, where regional changes in temperatures and precipitation patterns, for example, can deviate significantly from changes in the global average. This regional variation in climate change, coupled with the fact that countries are in very different positions with respect to their vulnerability and adaptive capacity, means that the impacts of climate change will be experienced very differently in different parts of the world. In general, the relatively poor nations may experience the most severe impacts, due to their heavier reliance on climate-sensitive sectors such as agriculture and tourism, and due to their lack of resources for increasing resilience and adaptive capacity to climate change (see Parry et al., 2007). In addition to the fact that U.S. GHG emissions may contribute to these impacts (see Section 2 for a comparison of U.S. total and transportation emissions to other countries’ emissions), climate change impacts in certain regions of the world may exacerbate problems that raise humanitarian and national security issues for the U.S."

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