By Timothy Gardner WASHINGTON (Reuters) -U.S. scientists on Tuesday revealed a breakthrough on fusion energy that could help curb climate change if companies can scale up the technology to a commercial level in the coming decades. Scientists at the Lawrence Livermore National Lab in California on Dec. 5 for the first time briefly achieved a net energy gain in a fusion experiment using lasers, the U.S. Energy Department said. The scientists focused a laser on a target of fuel to fuse two light atoms into a denser one, releasing the energy. Kimberly Budil, the director of Lawrence Livermore, tol…