A bill going to the U.S. Senate next week seeking deep cuts in U.S. greenhouse gases by 2050 is a "first step" but not enough to avert damaging climate change, the head of the U.N. Climate Panel said on Friday. Rajendra Pachauri also said that even tougher plans by some other developed nations to rein in emissions were insufficient to head off some projected impacts of global warming, ranging from more heatwaves and droughts to rising seas. The U.S. bill, sponsored by Sen. Joe Lieberman, a Connecticut independent and Sen. John Warner, a Virginia Republican, seeks to cut U.S. emissions...