While scientists are uncertain about whether climate change caused by humans will result in more active hurricane seasons in future, there is wide agreement on one thing: Global Warming is changing storms.
Scientists believe that storm activity has been boosted by unusually warm Atlantic surface temperatures. “It’s very likely that human-caused climate change contributed to that anomalously warm ocean,” said James P. Kossin, a climate scientist with the National Oceanic and Atmospheric Administration. “Climate change is making it more likely for hurricanes to behave in certain ways.”
Here are some examples.
1. Higher winds. There’s a solid scientific consensus that hurricanes are becoming more powerful.
Hurricanes are complex. However, the ocean surface temperature is one of the main factors that determines how strong a storm will become. Because warmer water supplies more energy to storms, it is difficult to predict the outcome.
“Potential intensity is going up,” said Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology. “We predicted it would go up 30 years ago, and the observations show it going up.”
Stronger winds lead to downed powerlines, roof damage and worse coastal flooding, especially when they are combined with rising sea level.
“Even if storms themselves weren’t changing, the storm surge is riding on an elevated sea level,” Dr. Emanuel said. He used New York City as an illustration, where the sea level has risen by approximately a foot in the last century. “If Sandy’s storm surge had occurred in 1912 rather than 2012,” he said, “it probably wouldn’t have flooded Lower Manhattan.”
2. More rain. Warming also increases the atmospheric water vapor. Each degree Celsius of warming actually allows for about 7 percent more water to be held in the air.
We can expect future storms that will bring more rain.
3. Storms are usually slower. Researchers are still not able to explain why storms are moving slower, but they are. Some suggest that the slowdown in global atmospheric circulation (or global winds) could be partially to blame.
Dr. Kossin reported in a 2018 paper that the speed of hurricanes over the United States has slowed to 17 percent since 1947. He stated that storms are causing a 25% increase in rainfall in the United States because of the rise in rain rates.
Flooding is also worsened when it rains more slowly and is wetter. Dr. Kossin compared the problem to walking around your backyard while spraying water on the ground with a hose. If you walk fast, the water won’t have a chance to start pooling. But if you walk slowly, he said, “you’ll get a lot of rain below you.”
4. Wider-ranging storms. Warmer water fuels hurricanes. Climate change is expanding the area where hurricanes can form.
There is a “migration of tropical cyclones out of the tropics and toward subtropics and middle latitudes,” Dr. Kossin said. This could lead to more storms hitting higher latitudes, such as Japan and the United States.
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5. More volatility. Researchers predict that storms will intensify as the climate warms. They are still unsure about why it’s happening, but the trend appears to be clear.
In a 2017 paper based on climate and hurricane models, Dr. Emanuel wrote that storms that intensify rapidly — the ones whose wind speed increases by 70 miles per hour or more in the 24 hours before landfall — were rarefrom 1976 through 2005. Their likelihood was about once per century, he calculated.
He discovered that these storms could form once in five to ten years by the end of 21st century.
“It’s a forecaster’s nightmare,” Dr. Emanuel said. If a tropical storm or Category 1 hurricane develops into a Category 4 hurricane overnight, he said, “there’s no time to evacuate people.”
Source: NY Times