Climate change risks are real and Exxon Mobil takes the threat serious, but the world still needs "all viable energy sources" to function, an executive said. Exxon published reports Monday to its shareholders on the risk of climate change. Exxon's reports followed an assessment from the Intergovernmental Panel on Climate Change that found climate change was linked to human activity, notably the burning of fossil fuels. William Colton, vice president in charge of strategic planning for Exxon, said increasing energy efficiency and financing ways to curb greenhouse gas emissions may help tackle the threat, though the world still needs to burn fossil fuels. "Our analysis and those of independent agencies confirms our long-standing view that all viable energy sources will be essential to meet increasing demand growth that accompanies expanding economies and rising living standards," he said in a statement. The transportation sector is expected to be the largest driver in global demand for energy, with countries in the Asia-Pacific region leading the rest of the world. Exxon said a growing world population, which it said should approach 9 billion people in 2040, will need 35 percent more energy than today. The IPCC report said most policymakers were addressing past consequences of climate change rather than preparing for the future. "The risk of climate change is clear and the risk warrants action," Colton said.