Hurricanes drive heat deep into the ocean's water column boosting long-term warming.
What we discovered is that hurricanes ultimately help warm the ocean, too, by enhancing its ability to absorb and store heat. And that can have far-reaching consequences.When hurricanes mix heat into the ocean, that heat doesn’t just resurface in the same place. We showed how underwater waves produced by the storm can push the heat roughly four times deeper than mixing alone, sending it to a depth where the heat is trapped far from the surface. From there, deep sea currents can transport it thousands of miles. A hurricane that travels across the western Pacific Ocean and hits the Philippines could end up supplying warm water that heats up the coast of Ecuador years later.
Imagine the tropical ocean before a hurricane passes over it. At the surface is a layer of warm water, warmer than 80 degrees Fahrenheit (27 degrees Celsius), that is heated by the sun and extends roughly 160 feet (50 meters) below the surface. Below it are layers of colder water.
The temperature difference between the layers keeps the waters separated and virtually unable to affect each other. You can think of it like the division between the oil and vinegar in an unshaken bottle of salad dressing.
As a hurricane passes over the tropical ocean, its strong winds help stir the boundaries between the water layers, much like someone shaking the bottle of salad dressing. In the process, cold deep water is mixed up from below and warm surface water is mixed downward. This causes surface temperatures to cool, allowing the ocean to absorb heat more efficiently than usual in the days after a hurricane.
For over two decades, scientists have debated whether the warm waters that are mixed downward by hurricanes could heat ocean currents and thereby shape global climate patterns. At the heart of this question was whether hurricanes could pump heat deep enough so that it stays in the ocean for years.
By analyzing subsurface ocean measurements taken before and after three hurricanes, we found that underwater waves transport heat roughly four times deeper into the ocean than direct mixing during the hurricane. These waves, which are generated by the hurricane itself, transport the heat deep enough that it cannot be easily released back into the atmosphere.
Once this heat is picked up by large-scale ocean currents, it can be transported to distant parts of the ocean.
It is also possible that the excess heat from hurricanes stays within the ocean for decades or more without returning to the surface. This would actually have a mitigating impact on climate change.
As hurricanes redistribute heat from the ocean surface to greater depths, they can help to slow down warming of the Earth’s atmosphere by keeping the heat sequestered in the ocean.
Scientists have long thought of hurricanes as extreme events fueled by ocean heat and shaped by the Earth’s climate. Our findings, published in the Proceedings of the National Academy of Sciences, add a new dimension to this problem by showing that the interactions go both ways — hurricanes themselves have the ability to heat up the ocean and shape the Earth’s climate.
But when it comes to climate science, what researchers “expect” can be a sketchy concept. “We know the overall path we’re on,” Alex Ruane, a climate scientist at NASA, told me, but “things don’t always change in a nice, gradual way.” Although the global situation is deteriorating at about the rate that leading models would predict, more specific, local changes may come as a surprise. Climate change is, at its core, a destabilizing force: Think of its effects as being predictably unpredictable. For example, the total surface area of the Antarctic sea ice is currently more than four standard deviations smaller than the average for this time of year. That’s not just breaking the record since measurements began in the 1970s; that’s shattering the record. Why exactly this has happened now—and whether it will end up as a terrifying blip or a permanent state—is still an open question. Likewise, scientists do not yet fully understand how climate change affects the way that weather systems move across the globe. A storm may be diverted from a drought-stricken region to an already sodden town, or a scorching atmosphere may stall out in a single place, as we’re seeing with the heat dome that has settled over Phoenix.
Even if those disasters do play out exactly as expected, the scientists I spoke with said they’ve noticed shifts in how Americans are discussing them. “People are no longer talking about climate change in the future tense,” Ruane said. “They’re talking about climate change in the present tense.” More and more of them have personal tales of climate woe. Disasters are no longer framed as harbingers; they’re simply understood to be the way things are. “These are not canaries in the coal mine,” Schmidt said. “The canaries died a long time ago.”