redOrbit: Two Rice University researchers are calling on policymakers to encourage the transition from coal-based electricity production to a system based on natural gas through a carbon tax. Such a mechanism would help limit carbon dioxide (CO2) emissions. At the United Nations Climate Change Conference in Copenhagen last December, the United States pledged to reduce the 2005 levels of CO2 emissions by 17 percent by 2020. Dagobert Brito, the George A. Peterkin Professor of Political …