Monday, March 28th, 2005 — Nature, not mankind, is to blame for a period of increased hurricane activity that could last for another 20 or 30 years, tropical weather expert William Gray said Thursday. "We think it’s ocean circulation patterns," Gray said in an interview. "It’s not human-induced global warming. It’s related mainly, as we see it, to the global ocean conveyor belt circulation." Although the number of major hurricanes — Category 3 through 5 — has been up during the past 10 years, only three of those bigger storms reached the United States from 1995 through 2003.