Global warming is the continuing rise of the average temperature of the Earth's atmosphere and oceans. Global warming is caused by the increased concentrations of greenhouse gases, resulting from human activities and the burning of fossil fuels.
"This finding is recognized by the national science academies of all the major industrialized countries and is not disputed by any scientific body of national or international standing." -wikipedia.org
The rise in temperature is not noticeable physically to humans; only about a degree in Fahrenheit in the last century.
Links on the subject: