Average global surface temperatures swelled about 1.33 degrees Fahrenheit the last century. That might not sound like a lot, but it is when it builds up over thousands of years. Global warming will cause the ice caps to melt, which will in turn, rise sea levels. For over the past 2 centuries, burning fossil fuels and deforestation have made greenhouse gases, gases in the atmosphere, more concentrated. This creates the greenhouse effect. The greenhouse effect is what happens when the atmosphere thickens. Heat from the sun bounces off the earth, bound for space, but is held back by the atmosphere. Heat cannot escape from Earth, so it makes Earth hotter.