The Earth's climate is changing. Scientists are confident that many of the observed changes in the climate can be linked to the increase in greenhouse gases in the atmosphere, caused largely by people burning fossil fuels to generate electricity, heat and cool buildings, and power vehicles. Current and future emissions will continue to increase the levels of these gases in our atmosphere for the foreseeable future. One way to track and communicate the causes and effects of climate change is through the use of indica-tors. An indicator, such as a record of Arctic sea ice extent, represents the state or trend of certain envi-ronmental conditions over a given area and a specified period of time. Scientists, analysts, decision-makers, and others use environmental indicators, including those related to climate, to help monitor environmental trends over time, track key factors that influence the environment, and identify effects on ecosystems and society. The climate change indicators in this report present compelling evidence that the composition of the atmosphere and many fundamental measures of climate in the United States are changing. Temperatures are rising, snow and rainfall patterns are shifting, and more extreme climate events-like heavy rainstorms and record high temperatures-are taking place. Similar changes are occurring around the world."