Did “An Inconvenient Truth” pique your curiosity about global climate change? If so, check out a free public lecture by renewable energy guru Nathan Lewis at 4 p.m. Friday, May 4, in Rowland Hall Room 104. Lewis, a professor at California Institute of Technology, will speak on “Scientific Challenges in Sustainable Energy Technology,” hosted by the UC Irvine Department of Chemistry. Lewis will discuss the challenges — technical, political and economic — involved with widespread adoption of energy technology that harnesses the power of wind, water and sun.