Bloomberg: A U.S. carbon-trading program would slow reductions in industrial greenhouse gases as volatile carbon prices discourage anti-pollution investments, said Exxon Mobil Corp. Chief Executive Officer Rex Tillerson. Since December, Tillerson has been publicly telling lawmakers that adoption of a carbon-trading system akin to that used in the European Union would be ruinous to the U.S. economy. A carbon tax would work better because it would eliminate most of the volatility inherent in …