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One of the major unanswered questions about climate change is whether hurricanes have become more frequent and stronger as the world has warmed. Until now, there hasn’t been enough evidence to settle the question, but a report published Monday in Proceedings of the National Academy of Sciences may have changed all that. Using an entirely new method of tallying hurricane power and frequency, a team of scientists say that hurricanes are, indeed, more of a danger when ocean temperatures are higher. “In particular, we estimate that Katrina-magnitude events have been twice as frequent in warm years compared with cold years," the report says.