What made these storms so intense? Scientists are now trying to figure that out—including what role, if any, climate change may have played.
“People always want to know is it climate change or is it not?” says Katharine Hayhoe, a climate scientist at Texas Tech University. “The answer is, it’s in between.”
While climate change didn’t necessarily cause Harvey or Irma, many scientists say, it likely made an already bad situation worse, deepening the storms’ impact.
Hurricanes form over warm oceans, drawing their destructive power from the hot moist air evaporating upward. Over the past century, the Earth and its oceans have gotten warmer, creating more opportunities for tropical storms and hurricanes.
Most scientists say the planet is getting warmer because of a rise in greenhouse gases. Some of these gases occur naturally; others are produced by human actions. For example, the burning of fossil fuels like oil and coal—mostly from cars and power plants—creates carbon dioxide, the main greenhouse gas.
Greenhouse gases let sunlight through but also trap heat in the atmosphere, acting like a greenhouse. In the past century, Earth’s average temperature has risen about 1.5 degrees Fahrenheit (see graph). And for three years straight, the planet has broken its record for highest global average surface temperature, according to NASA.
Harvey didn’t behave like a typical hurricane, meteorologists say, because it continued to gain momentum even as it neared shore. Harvey also stayed intact for several days on land, and its punishing 115-mile-per-hour winds and rain were concentrated in the same area. Storms usually move steadily inland or back out to sea, so their damage is spread out.