According to the U.S. Environmental Protection Agency
"Climate change refers to any significant change in the measures of climate lasting for an extended period of time. In other words, climate change includes major changes in temperature, precipitation, or wind patterns, among other effects, that occur over several decades or longer."
Watch this video from the EPA explaining the basics of climate change.
View official reports from the Intergovernmental Panel on Climate Change (IPCC), an international body established by the United Nations for assessing the science related to climate change. Access the full reports here:
Highlighted report:Special Report on Global Warming of 1.5 Degrees Centigrade