MIT World Video from the 2007 ESI/CGCS Symposium "Earth System Revolutions: Key Turning Points in the History of our Planet"If you'd asked Ronald Prinn a decade ago whether human activity played a significant part in global warming, he would have given you an "equivocal" answer. Today, he is no longer straddling the line, and indeed, has amassed forceful evidence that post-industrial society has brought about enormous change in earth systems, and may cause irreparable damage as this century progresses.