Gas and oil giant ExxonMobil has increased its donations to organizations that oppose government regulations to limit greenhouse gas emissions and question the notion that humans cause global climate change. Although the company has pledged $10 million a year for 10 years to climate research at Stanford University, it is also giving generously to the likes of the Competitive Enterprise Institute, Frontiers of Freedom, and other groups that challenge the scientific consensus on global warming. Exxon is the largest corporate donor to some of these groups, accounting in some cases for more than 10 percent of their annual budgets. In many cases, Exxon’s donations to such organizations increased by more than 50 percent from 2000 to 2002. Exxon’s stance marks a widening gap between it and other companies in the industry, such as BP, Shell, and ChevronTexaco, which have backed away from challenging global warming and developed strategic plans that include renewable energy, carbon trading, and emissions reductions.