This resource provides an overview of the concept of climate change and discusses past climate changes, as evidenced by sea sediments and sedimentary rock studied by paleoclimatologists. More recently, ice cores, tree rings, and historical records tell of changes such as interglacial periods and the little ice age. Other factors like volcanoes, changes in the Earth’s orbit, comets, and meteorites that may alter the energy balance, change the greenhouse effect, or cause climate forcing are also explored in these pages.