On August 23, 2005, a tropical depression formed 175 miles southeast of Nassau. By the next day, it had grown into tropical storm Katrina and was intensifying rapidly. Early in the evening on August 25, Hurricane Katrina made landfall near North Miami Beach. Even though it was only a Category 1 storm, with sustained wind speeds of about 80 miles per hour, it caused significant damage and flooding, and took 14 lives.

The hurricane’s quick nighttime trip across Florida barely fazed the storm. Entering the Gulf of Mexico’s warm waters quickly kicked Katrina into overdrive, like a supercharged engine on high-octane fuel. Hurricanes fuel themselves by continually sucking in and spinning up warm, moist air.

On August 28, Katrina reached Category 5 status, with sustained wind speeds of 160 mph and a pressure of 908 millibars. A few hours later, wind speeds hit 175 mph, which they maintained until the afternoon.

At 4:00 p.m., the National Hurricane Center warned that local storm surges could hit 28 feet, and “Some levees in the Greater New Orleans Area could be overtopped,” a warning that was tragically ignored by federal, state, and local emergency officials. Over the next 14 hours, Katrina’s strength dropped steadily. When the hurricane’s center made landfall Monday morning, it was a strong Category 3, battering coastal Louisiana with wind speeds of about 127 mph. The central pressure of 920 millibars was the third lowest pressure every recorded for a storm hitting the U.S. mainland.

The devastation to the Gulf region was biblical. The death toll exceeded 1300. The damage exceeded $100 billion. [Combined with the effects of Hurricane Rita] two million people were forced to leave their homes, more than were displaced during the 1930’s Dust Bowl. One of the nation’s great cities was devastated.

About 20 miles to the west of the second Gulf landfall was the small town named Pass Christian, Mississippi, where my brother lived with his wife and son.

Tropical cyclones in the northern hemisphere rotate counterclockwise, and so the most intense storm surge is just to the east of the eye, because the surge represents the intense winds pushing the sea against the shore. A 30-foot wall of water with waves up to 55 feet crashed over the town. Although my brother and his family lived one mile inland, their house was ravaged with water up to 22 feet high, leaving the contents of the house looking like they had been churned “inside of a washing machine,” in my brother’s words. While they lost virtually all their possessions, they were safe in a Biloxi shelter.

Thanks to the generosity of many people, my brother’s family was able to find a temporary home in Atlanta. But like many families whose lives were ripped apart by the storm, they had difficult choices in the ensuing months. Perhaps the toughest decision was whether to rebuild their home or to uproot themselves and try to create a new life somewhere else.

I very much wanted to give my brother an expert opinion on what was likely to come in the future. After all, climate change was my field, and while my focus has been on climate solutions, I had done my Ph.D. thesis on physical oceanography.

As I listened and talked to many of the top climate experts, it quickly became clear that the climate situation was far more dire than most people-and even many scientists, myself included-realized. Almost every major climate impact was occurring faster than the computer models had suggested. Arctic sea ice was shrinking far faster than every single model had projected. And the great ice sheets of Greenland and West Antarctica were shedding ice decades earlier than the models said. Soils appear to be losing their ability to take up carbon dioxide faster than expected. At the same time, global carbon dioxide emissions and concentrations were rising faster than most had expected.

As for hurricanes, global warming had been widely projected to make them more intense and destructive, but again the recent increase in intensity was coming sooner than the computer models had suggested. Why is that a concern? Since 1970, the temperature of the Atlantic Ocean’s hurricane-forming region has risen 0.5 °C (0.9 °F). Over the path of a typical hurricane, this recent ocean warming added the energy equivalent of a few hundred thousand Hiroshima nuclear bombs. On our current emissions path, the Atlantic will warm twice as much, another 1 °C, by mid-century, and perhaps another 2 °C beyond that by century’s end. Who can even imagine the hurricane seasons such warming might bring?

This is what I ultimately told my brother, the same advice I would give anyone contemplating living near the Gulf Coast:

Only a quarter of Atlantic hurricanes make U.S. landfall, and while there is no question that the frequency of intense Atlantic hurricanes is rising, it is somewhat random as to where they will actually go any given year.

That said, the Gulf of Mexico is going to get warmer and warmer, as is the Atlantic Ocean, and so hurricanes that enter the Gulf are likely to start out and end up far more destructive than usual. I would not bet that the Mississippi Gulf Coast will get hit by a super-hurricane in any particular year, but I would certainly plan on it being hit again some time over the next ten years; I wouldn’t be surprised if it were hit by more than one.

Coastal dwellers from Houston to Miami are now playing Russian roulette with maybe two bullets in the gun chamber each year. In a couple of decades, it may be three bullets.

[This is excerpted from my book, Hell and High Water. The description of Katrina is from two terrific sources: Grauman et al., Hurricane Katrina: A Climatological Perspective, Technical Report 2005-01, NCDC, October 2005, update Jan 06, and Richard D. Knabb, Jamie R. Rhome, and Daniel P. Brown, Tropical Cyclone Report: Hurricane Katrina, 23-30 August 2005, National Hurricane Center 20 December 2005.]

Subsequently, the scientific literature has supported the view that human-caused global warming is “more likely than not” partly responsible for the fact that “In the period 1971–2005, since the beginning of a trend towards increased intense cyclone activity, [economic] losses excluding socio-economic effects show an annual increase of 4% per annum” (see here).

I have further elaborated on the growing threat to the Gulf from warming-driven superstorms:

• Why global warming means killer storms worse than Katrina and Gustav, Part 1
• Why future Katrinas and Gustavs will be MUCH worse at landfall, Part 2

And the literature also supports that analysis:

• Nature: Hurricanes ARE getting fiercer — and it’s going to get much worse

Needless to say, sea level rise will turn many other coastal cities into sitting ducks pre-Katrina New-Orleans:

• Startling new sea level rise research: “Most likely” 0.8 to 2.0 meters by 2100
• Sea levels may rise 5 feet by 2100
• US Geological Survey stunner: Sea-level rise in 2100 will likely “substantially exceed” IPCC projections