Change in global climate over time.
Climate change is measured by changes in temperature in the atmosphere. In some periods the temperature change is very slow, in other periods the change can be quite fast.
Climate change can have natural causes or it can be caused by human activity. Purely natural causes include volcanic activity, ocean variability, and solar variation. Humans have no influence on these.
When climate change is caused by humans it is sometimes called anthropogenic climate change.
Most experts agree that the main contributors to climate change today are greenhouse gases. There has been a big increase in the emission of greenhouse gases since the time of industrialization. This increase is due only to human activity. Most of the increase is due to CO2 produced by the use of fossil fuels.
The amount of methane in the atmosphere has also increased a lot since industrialization. Today more than half of all methane emissions stem from human activities.
Often human activities will speed up natural processes leading to accelerated climate
Predictions about future long term changes in climate are made by using climate models. These models use supercomputers to process gigantic amounts of data from the past and the present in an attempt to predict future climate.
Data from short term changes in climate are used by meteorologists in climate models to predict changes in weather. This is called weather forecasting.
The study of climate and climate change is climatology and it includes all the factors that can affect the climate.
The UNFCCC defines climate change more narrowly as the change in climate caused by human activity. Therefore the UNFCCC definition is only dealing with climate change that has taken place recently.