There is much evidence that supports the theory of global warming, including:
Evidence of recent and ongoing increases in GMST (Global Mean Surface Temperature), measured in degrees celsius.
Evidence of increased concentrations of Carbon Dioxide (and other gases) in the atmosphere, measured in particles per million.
The record of atmospheric gas concentrations, trapped in ice, giving an understanding of the historical changes in Carbon Dioxide levels. This can be corelated to other evidence such as changes in fossilised pollen concentrations, from which temperature changes can be inferred. This type of evidence shows a relationship between "warm periods" and periods where there were higher Carbon Dioxide concentrations.
Knowledge of how certain gases (including Carbon Dioxide) will affect electomagnetic radiation, by "trapping" outgoing infra-red wavelengths.
Observation of reductions in polar ice and glaciation.
Observations of changes in weather-patterns.
Observations of historical and contemporary changes in plant and animal lfe behaviour, including migraton.