Global warming is a natural process, not likely the result of human activities, argued more than 100 internationally prominent environmental scientists in papers presented at the 2008 International Conference on Climate Change, which concluded here today. The conference, organized by the Heartland Institute, sought to refute the contention promoted by Al Gore and the U.N. that there is an “established scientific consensus” that human beings are causing the earth to warm catastrophically. The event attracted more than 500 people, including scientists, economists, policy experts and members of the public from around the world.