That’s just a little taste of things to come. Whatever the cause—greenhouse gases, natural warming, or both—-rising temperatures and sea levels already are breeding bigger, more intense hurricanes and more dangerous storm surges. Former vice president Al Gore, the teller of so many inconvenient truths about climate change, says it is “absolutely” a national-security issue. “We can expect continued increases in the frequency and severity of extreme floods, droughts, wildfires, storms and other events,” he says. “We need to -begin the process now of preparing for the disasters that are to come.”

According to Gore, “some scientists are considering adding a Category 6 classification to the Saffir-Simpson hurricane scale, which uses wind speed to measure hurricane intensity.” (Irene hit the Northeast as a low-grade Category 1 and then was downgraded to a tropical storm; Katrina hit New Orleans as a Category 3. A Category 5 hurricane has sustained winds greater than 155 miles per hour; Category 6 would be upwards of 175 or 180mph.) And each notch on that scale means an exponential increase in destructive power.

“The rules of risk assessment are being rewritten right before our eyes,” Gore says. “This year alone, in the United States, we have had 10 $1 billion–plus disasters. FEMA [the Federal Emergency Management Agency] is already nearly out of money.”