and with easter this sunday we abouturn to philip yancey. his new tome, the question that never goes away. when accidents and tragedy strikes. that conversation right now. ♪ >> and by contributions to your pbs station from viewers like you. thank you. tavis: the extent of the damage to the world's resources and what action governments should take continues to create acrimony. as auditions argue about what should be done, what is clear to leading scientists is that immediate actions must be taken to preserve the earth's resources. among those sounding the alarm, ken caldeira. from stanford university and one of the leading experts on climate change and our nation and the world. good to have you on this program. i want to make the best use of our time. how bad is the problem and to jump to what we should do. how bad is the situation? >> on hundred million years ago around. dinosaurs were we can recreate the kind of that existed 100 million years ago. this is a radical alteration of the earth. tavis: in what way? caps will rise -- milk and the