The Earth's climate is changing. Temperatures are rising, snow and rainfall patterns are shifting, and more extreme climate events-like heavy rain-storms and record high temperatures-are already taking place. Scientists are highly confident that many of these observed changes can be linked to the climbing levels of carbon dioxide and other greenhouse gases in our atmosphere, which are caused by human activities. The climate change indicators in this report look at the composition of the atmosphere, fundamental measures of climate, and the extent to which several climate-sensitive aspects of the oceans, snow and ice, human health, society, and ecosystems are changing. Together, these indicators present compelling evidence that climate change is happening now in the United States and around the world."