Long-term records from weather stations, satellites, ocean buoys, tide gauges, and many other data sources all confirm that the world is warming. Precipitation patterns are changing, the frequency and intensity of some extreme weather events are increasing, sea level is rising, and the oceans are becoming more acidic. Many lines of independent evidence demonstrate that the rapid warming and associated climatic changes over recent decades are due primarily to human activities. The observed climatic changes are triggering wide-ranging impacts across the globe.