Climate change is specifically the variation of global and regional climates along an extended period of time, reflecting changes in the average atmosphere state. According to international organizations, climate change refers to changes caused by external forces (i.e. sunlight intensity). internal processes (i.e. the movement of plate tectonics) and also human activities. Climate change also refers to the phenomenon known as global warming. In order to specify the variations which are not caused by human activities, some organizations call it as "climate variability".
Climate changed drastically in the past, considering, for example, the ice ages. In these cases, interglacial periods might have happened because of the rise of the global temperature as a consequence of increasing greenhouse gases. In the past, it was caused by natural events, like volcano activity. However, greenhouse gases emissions increased since the 19th century, causing the well-known global warming event, which has been subject of great concern because of its consequences on Earth.