Photo: NOAA
This post was co-authored by EDF Postdoctoral Climate Science Fellow Tianyi Sun
Today Hurricane Laura made landfall in Louisiana as a Category 4 hurricane, causing death and destruction. Louisianans and Texans in its path are now mourning and looking ahead to a long and painful recovery.
Laura had winds up to 150 miles per hour, making it one of the strongest hurricanes on record to ever hit the Gulf Coast in the United States. It tied the record for how quickly it intensified, driving questions about the role of climate change in creating and fueling this monster storm.
A look at the latest science
Scientists have been actively studying how climate change affects hurricanes for decades, and the evidence that it can influence several aspects of hurricanes continues to grow.
Overall, climate change is making these already dangerous weather events even more perilous. They are stronger, wetter, slower, and intensify more rapidly. Major storms are occurring more often and piling on heavier rainfall, and scientists anticipate the strongest storms will continue to increase in frequency. Sea level rise, along with stronger winds, are also worsening storm surges, causing more coastal flooding.
All aspects of hurricanes – from formation to track to strength to damages – can be influenced to some degree by climate change, through warmer waters, more moisture in the atmosphere, changing air patterns, and sea level rise.
For some connections, such as how climate change affects hurricane strength and its damages, the science is simple and robust. For other connections, such as how climate change affects hurricane formation and track, the science is more complicated and nuanced.
Here we break down what we know about how climate change affects four key aspects of hurricanes
1. Hurricane formation – competing factors at play
How climate change affects whether or not a hurricane develops depends on the interaction of several features. On one hand, warmer ocean temperatures from climate change can make it more likely for hurricanes to develop. On the other hand, changing air patterns can have complicated and opposing effects on hurricane development. For example, changes in wind speeds over short distances and the shape of the jet stream – both of which can be influenced by climate change – can sometimes make it harder for storms to form.
Although the North Atlantic has seen more overall hurricanes since the 1970s, scientists do not say this is due to climate change. They attribute this pattern partly to decreasing emissions of aerosol particles such as sulfur from human activities, that had previously blocked sunlight from warming the ocean. Natural factors likely also played a role.
While the frequency of hurricanes overall does not seem to be increasing from climate change, scientists have found that climate change has likely led to more storms becoming major hurricanes (Category 3 to 5). Researchers suggest that the most damaging U.S. hurricanes are now three times more frequent than 100 years ago, and that the proportion of hurricanes that are Category 3 or above in the Atlantic Ocean has doubled since 1980.
In the future, the best available science suggests that the strongest hurricanes (Category 4 and 5) will increase in frequency, but not the overall number worldwide.
2. Hurricane strength – the science is clear
Warmer water and more moisture in the atmosphere, due to climate change, provide fuel for storms to grow more powerful. Both these aspects of climate change can also trigger rapid intensification if high-level winds are light.
Scientists are virtually certain that climate change has increased the intensity of hurricanes across the globe since the 1970s. How fast hurricanes intensify has also increased in the Atlantic since the 1980s due to climate change. Hurricane Laura and Dorian are prime examples of this, as both went through rapid intensification close to landfall, which made it harder to predict their landfall intensity and evaluate potential danger ahead of time.
With continued warming, we expect hurricane intensity and intensification rates to continue to increase throughout the century.
3. Hurricane track – it’s complicated
Shifting weather and large-scale air circulation patterns due to climate change can affect the location and path of a hurricane. However, the physics is complex, and this remains an active area of research.
There is growing evidence that stagnant weather patterns linked to climate change can cause slower-moving storms, and scientists have found that tropical cyclones worldwide have been moving 10% slower since 1949. Some scientists also expect storms to continue moving slower with future warming, although it remains an open research question. That means more time to dump immense amount of rain and wind on an area. For example, we saw this with Hurricane Harvey in 2017.
In addition, the average locations where hurricanes and other tropical cyclones reach their peak strength has moved away from the equator, meaning further north in the Northern Hemisphere and south in the Southern Hemisphere, at a rate of 30 to 40 miles per decade over the last 30 years. However, the speed and direction of this migration has a lot of variation across the globe.
4. Hurricane damages – they’re piling up
High wind speeds, heavy rainfall and flooding from storm surges all drive damages from hurricanes, and climate change is worsening all three of these components.
First, higher windspeeds and therefore higher ‘category’ storms are considered a direct impact of climate change.
Next, more moisture in the atmosphere can lead to more rainfall during a storm, and stagnant weather patterns linked to climate change lead to slow-moving storms that cause the rain to be dumped over an area for a longer period of time (such as Hurricane Harvey in 2017).
Finally, higher sea level from melting ice and warmer oceans contributes to more damaging storm surges that cause severe coastal flooding – not just because the sea level is closer to the height of the land, but also because deeper water makes it is easier for wind and waves to push water onshore. Higher windspeeds also push more water inland, contributing to the additional flooding caused by sea level rise and heavier rainfall.
Scientists have found that recent storms had heavier rainfall due to climate change. Research shows that Hurricane Harvey in 2017 rained 15% more and Hurricane Florence in 2018 rained 50% more in its heaviest precipitating part due to climate change. With sea levels already rising several inches to over a foot along the U.S. coast, storm surges are undoubtedly worse. We expect to see even heavier rainfall and worsening storm surges with future hurricanes as warming and sea level rise continue.
How do we prevent hurricanes from getting worse?
The best way to ensure we avert the trend of ever more destructive hurricanes and build a safer future is to limit additional warming by as much as we possibly can. This means drastically cutting climate pollution such as carbon dioxide and methane. Thankfully, we have the tools and solutions today to move to a 100% clean economy.
At the same time, we must take proactive steps to protect communities on the front lines of stronger storms, sea level rise and other climate impacts that are already occurring. By emphasizing solutions such as natural infrastructure along our coasts and prioritizing pre-disaster mitigation, we can build communities that are safer, more prosperous and more resilient
Let’s get to work.