The era of hurricanes fuelled by the climate crisis arguably began with Katrina.
In late August 2005, Katrina hit the US Gulf Coast, the eye passing over New Orleans, with storm clouds stretching out across Louisiana, Alabama, Mississippi and Florida.
Over eight inches of rain doused southern Louisiana, while winds whipped over 110 miles per hour (177 kilometres per hour). Coastal waters surged over 10 feet (3 metres) in Mississippi and Alabama. Levees, separating New Orleans from a network of waterways, collapsed and the city flooded.
In its wake, Katrina left behind over $100billion in damages and nearly 2,000 people dead.
Eight years later, a group of scientists published a paper studying how damaging Katrina would have been in the year 1900 instead of 2005 — before the effects of the greenhouse gases. The scientists found that if the same hurricane had formed 105 years earlier, the storm surge could have been up to 60 per cent lower in some coastal areas.
These results point to what climate scientists say is a trend in hurricanes, cyclones and typhoons — different names for tropical storms that form a whirling shape over the world’s oceans.
As the global average temperature increases and the world’s oceans rise, scientists say, these kinds of storms are liable to get stronger — and the damage more intense.
Similar research to the Katrina study has been done for storms including 2017’s Hurricane Harvey in Texas, finding that planetary warming made rainfall during the days-long deluge 15 per cent more intense. Another study on 2019’s Typhoon Hagbis in Japan found that the climate crisis added at least $4bn in additional damages.
Sea-level rise is one way that the climate crisis is making these storms more dangerous. As the oceans rise, due to melting polar ice sheets and increased heat causing water to expand, coastal cities like Tokyo and New Orleans will be more likely to be inundated during storms.
Since the 19th century, the global sea level has risen by about eight inches – threatening coastal communities and increasing the risk of flooding when storms push water inland.
Rising sea levels can also wipe out natural defences that coastlines have against incoming hurricanes, such as wetlands of marshes and swamps that buffer storm surges and winds.
One 2020 study found that in nearly 90 US tropical storms from 1996 to 2016, counties with more wetlands had less property damage. The authors of that study put a value on those wetlands — an average of $1.8m of damage protection per square kilometre per year.
But as the seas rise, those wetlands — which sit at sea level — may start to disappear if they can’t rebuild quickly enough to follow the receding shoreline.
Another study looked at communities around Chesapeake Bay in the Northeast and found that in a climate scenario with a lot of sea level rise, losing wetlands could more than quadruple flooded areas from a storm and add more than $8bn in damage.
Even without sea-level rise, hurricanes are expected to become destructive as the ocean heats up.
Greenhouse gases, caused by burning fossil fuels, are trapping more heat near the Earth’s surface. Scientists have calculated that about 90 per cent of the excess heat generated from emissions is being absorbed by the ocean.
Since 1901, the top layer of the ocean has become about 1.5C hotter, according to the Woods Hole Oceanographic Institution.
Warmer air and water fuel hurricane growth, powering intense winds and sending water into the clouds. The US National Oceanic and Atmospheric Administration (NOAA) says that the climate crisis’s impact on hurricane power is “like adding fuel to a fire.”
Over the past four decades, the proportion of yearly cyclones that reach at least Category 3 in strength — meaning wind speed at least 111 mph (178 kph) — has increased, says the United Nations’ Intergovernmental Panel on Climate Change (IPCC), the leading authority on global climate science.
In addition to storm intensity, hurricanes often cause more damage if they linger over the coast, and this slowdown may also be a result of the climate crisis. One study found that, since 1949, hurricanes have slowed by 10 per cent — but there isn’t scientific consensus on why.
Hurricane Harvey was notoriously slow to dissipate, hanging around the Texas Gulf Coast for days and dropping upwards of 40 inches of rain in some spots.
With such intense, sustained storms, flooding can be devastating. During Harvey, floods in the Houston area lasted for days, with thousands of homes damaged or destroyed and more than 100 people dead.
There is one measure of hurricanes that may not be getting worse with the climate crisis. Despite recent years with an above-average number of hurricanes in the Atlantic, the IPCC says that there isn’t a strong trend toward more tropical storms per year.
According to Yale Climate Connections, some research indicates that there might even be slightly fewer hurricanes as the climate crisis worsens, due to changing wind patterns.
Conditions vary from year to year. In 2022, for example, NOAA has predicted a higher-than-average Atlantic hurricane season partly due to warmer ocean waters and ongoing La Niña conditions.
For the most part, scientists are telling the public to brace for harsher storms with more severe impacts.
In the past four years, the world has faced down major crises like Hurricane Laura in Louisiana, Hurricane Dorian in the Bahamas, Tropical Cyclone Idai in Mozambique and Typhoon Mangkhut in the Phillippines — all of which caused intense destruction and significant loss of life.
In 2017 alone, Hurricanes Harvey, Irma and Maria hit in the Atlantic, devastating Texas, the Caribbean and Puerto Rico. Cyclone Ockhi, which hit India and Sri Lanka that same year, killed over 900 people.
As the world keeps warming, the era of climate-supercharged hurricanes is only likely to get worse.