The most general definition of climate change is a change in the statistical properties of the climate system when considered over long periods of time, regardless of cause.Accordingly, fluctuations over periods shorter than a few decades, such as do not represent climate change.The term sometimes is used to refer specifically to climate change caused by human activity, as opposed to changes in climate that may have resulted as part of Earth's natural processes. In this sense, especially in the context of environmental policy, the term climate change has become synonymous with anthropogenic global warming.