Climate Change Indicators in the United States, 2012, presents 26 indicators to help readers better understand observed trends related to the causes and effects of climate change. This document updates a report published by EPA in 2010. Various government agencies, academic institutions, and other organizations contributed data critical to the development of this report. EPA also received feedback from a diverse group of scientists, researchers, and communications experts in the public and private sectors. This feedback helped to inform the content and new features of this 2012 report. All of the indicators in this report are based on data that have been collected and compiled according to protocols accepted by the scientific community. The indicators were chosen using a standard set of criteria that considered usefulness, objectivity, data quality, transparency, ability to meaningfully communicate, and relevance to climate change. Most of the indicators in this report focus on the United States, but some include global trends to provide context or a basis for comparison, while others have a regional focus. Geographic coverage depends on data availability and the nature of what is being measured. For example, greenhouse gas concentrations in the atmosphere are studied on a global scale. The indicators span a range of time periods, depending on data availability.