Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging frome decades to millions of years. It may be a change in average weather conditions, or in the distribution of weather around the average conditions (i.e. more or fewer extreme weather events).
Scientists actively work to understand past and future climate by using observations and theoretical models. 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 "El Niño", do not represent climate change.
