CBC: Global warming is once again becoming a hot topic for Americans, new data suggests. A U.S. national survey released Tuesday finds that public concern about global warming is increasing, with public belief that it is occurring rising to 61 per cent, up from 57 per cent since January. And 50 per cent of Americans believe the phenomenon is caused by people — an increase of three points. Fifty-three per cent of respondents now worry about the impact global warming will have (an …