New observations and new research have increased our understanding of past, current, and future climate change. The 4^th National Climate Assessment confirms prior assessments in concluding that the climate on our planet, including the United States, is changing, and changing rapidly. Observational evidence for a changing climate abounds, from the top of the atmosphere to the depths of the oceans. Documented changes include surface, atmospheric, and oceanic temperatures; melting glaciers; disappearing snow cover; shrinking sea ice; and rising sea level. Many lines of evidence demonstrate that human activities have been the dominant cause of the observed warming since the mid-20th century. Changes in the characteristics of extreme events are particularly important for human safety, infrastructure, agriculture, water quality and quantity, and natural ecosystems. Some extremes have already become more frequent, intense, or of longer duration, and many extremes are expected to continue to increase or worsen, presenting substantial challenges. The Earth’s climate is projected to continue to change over this century and beyond. This presentation provides an overview of the science of climate change from the 4^th National Climate Assessment, and discusses what this means for the American people and our planet.