Question

what are the main causes of global warming?

Answer 1

the drastic increase in the emission of CO2 (carbon dioxide) within the last 30 years caused by burning fossil fuels has been identified as the major reason for the change of temperature in the atmosphere (click the following link for a summary and graphs about the cause and effects of global warming 

Answer 2

Increase of pollution , deforestation , usage of ac's fridges which emmits cfc clorofluorocarbons burning of fossil fuels is a main cause