This document answers some of the most commonly asked questions about climate change, including whether the Earth has warmed, which human activities are contributing to climate change, what further climatic changes are expected to occur, and what effects these changes may have on humans and the environment. First, however, several issues have to be clarified: what the Earth's climate is how climate differs from weather, and what processes influence climate, Climate is the average weather including seasonal extremes and variations, either locally, regionally, or across the globe. In any one tocation. weather can change very rapidly from day to day and from year to year even within an unchanging climate. These changes involve shifts in, for example, temperatures, precipitation, winds, and clouds. In contrast to weather. climate is generally influenced by slow changes in features like the ocean, the land, the orbit of the Earth about the sun, and the energy output of the sun.