Climate scientist Michael Mann runs down the list of bad global warming news: The world is spewing greenhouse gases at a faster rate. Summer Arctic sea ice is at record lows. The ice sheets in Greenland and West Antarctica are melting quicker than expected.

Is he the doomsayer global warming skeptics have called him? Mann laughs. This Penn State University professor — and many other climate scientists — are sunny optimists. Hope blooms in the hottest of greenhouses.