It is extremely hard to look to an unbiased forum to understand what global warming exactly as, but, in general, global warming is described as:
Carbon dioxide and other air pollution that is collecting in the atmosphere like a thickening blanket, trapping the sun's heat and causing the planet to warm up. Coal-burning power plants are the largest U.S. source of carbon dioxide pollution -- they produce 2.5 billion tons every year. Automobiles, the second largest source, create nearly 1.5 billion tons of CO2 annually.
Here's the good news: technologies exist today to make cars that run cleaner and burn less gas, modernize power plants and generate electricity from nonpolluting sources, and cut our electricity use through energy efficiency. The challenge is to be sure these solutions are put to use (NRDC, 2006)
As Krugman (2006) writes that in "his new movie, 'An Inconvenient Truth', Al Gore suggests that there are three reasons it's hard to get action on global warming. The first is boiled-frog syndrome: because the effects of greenhouse gases build up gradually, at any given moment it's easier to do nothing.