Climate Change ProCon.org – Our popular website on the climate change debate has been revised and expanded with new pro and con arguments, an updated background section, interesting Did You Know? facts, and more, with 170 sources cited. The pro side argues that rising levels of atmospheric greenhouse gases are a direct result of human activities such as burning fossil fuels, and that these increases are causing significant and severe climate changes. The con side argues human-generated greenhouse gas emissions are too small to substantially change the earth’s climate and that 20th century warming resulted primarily from natural processes. Explore both sides and decide for yourself.