A revised paper from NOAA using advanced modeling contains a mixed bag for US coasts and other regions vulnerable to tropical cyclones. Here’s one of the key grafs:
A review of existing studies, including the ones cited above, lead us to conclude that it is likely that greenhouse warming will cause hurricanes in the coming century to be more intense globally and have higher rainfall rates than present-day hurricanes.
The paper concludes that warming seas and air might result in fewer tropical cyclones for the Atlantic basin, but the remaining storms will on average be more intense. That’s a big potential problem if it pans out, because the lion’s share of damage done by hurricanes comes from the rare major storm that makes landfall. Here’s the Saffir-Simpson hurricane intensity scale by max sustained winds:
- Category 1 — 74 to 95 mph
- Category 2 — 96 to 110 mph
- Category 3 — 111 to 130 mph
- Category 4 — 131 to 155 mph
- Category 5 — 156 mph and above
The reason hurricane categories are clustered every 20 to 14 mph apart after the category 1 threshold is reached is because of how wind operates on physical objects at these velocities. Wind imparts momentum on an object proportional to the square of its velocity (In fact, in some cases what fluid physicists and meteorologists call the Power Dissipated scales to the cube of the wind!). So a 200 mph wind exerts almost nine times the force of a 70 mph wind even though it is only three times faster. In addition the terminal velocity of human sized objects clusters around the 110 – 130 mph range. That means a 100 mph gale will knock the average person down, but a 130 mph wind will pick them and slam them into the side of a house, and a 150 mph wind can toss them over a house; a 180 mph wind can pluck a human off the ground like feather and catapult their remains hundreds of feet.
Likewise, the difference on structures of those wind speeds is enormous. A 100 mph wind can rip shingles off a roof, a 130 mph wind can take all or part of the roof off, a 180 mph wind can knock over a multistory office building. That’s why intensity is a big headache for emergency planners and property/life insurance companies. The difference between a direct hit from a category 1 and category 5 hurricane, ignoring debris damage, on a typical cinder block hurricane rated home in Florida is more likely than not to be negligible, usually requiring at most minor repair, vs. total destruction of the home in a cat 5 right down to the foundation and the loss of life for everyone sheltering inside.
Even some skeptics admit there could be more than a 10 percent increase in intensity because of global warming. Some of the higher estimates approach 40 percent, which would almost double the wind force. Twice the wind can translate into an order of magnitude increase or more in dollar damages. The increase in tragedy is immeasurable.
More at MillWX’s diary on Daily Kos
The effect of hurricanes on the BP spill via WeatherUnderground