Global warming is caused by two main factors: greenhouse gases trapping heat (greenhouse effect) and pollution blocking sunlight (solar radiation effect). Researchers used weather data from 1959-2002 to estimate these effects. They found that the greenhouse effect warms the Earth by 1.87○C, while the solar radiation effect cools it by -1.09○C. This means that the true impact of greenhouse gases on global warming may be underestimated due to the cooling effect of pollution blocking sunlight.