Complex sentence: William L. Steffen, born 1947, is the Executive Director of the ANU Climate Change Institute at the Australian National University and the Australian federal government's chief climate science adviser.
Split into simpler sentences: William L. Steffen, born 1947, is a climate science expert and researcher. He is the Executive Director of the ANU Climate Change Institute at the Australian National University, and is the Australian federal government's chief climate science adviser.