Are Hurricanes Getting Stronger Because of Climate Change? Weather Analysis

Hurricanes and the havoc they wreak aren't expected to abate any time soon.

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Are hurricanes getting stronger in our warming world? Given that climate change is affecting everything from droughts to sea levels, it may come as little surprise that the answer is "yes." Here, we explore the latest research, how hurricanes are measured, and what we can expect in the future.

How Hurricanes Are Intensifying

A study examining global trends in tropical cyclone intensity over the past four decades found that Category 3, 4, and 5 "major" hurricanes have increased by 8% per decade, globally—meaning they're now nearly a third more likely to occur. Zoom in on the Atlantic Ocean alone, and this increase climbs to a whopping 49% per decade.

In addition to making the strongest storms stronger, climate change is also causing rapid intensification (that is, the increase in maximum sustained winds of 35 mph or more within a 24-hour period) of storms. According to a 2019 study in Nature Communications, the 24-hour intensification rates of the strongest 5% of Atlantic hurricanes increased by 3-4 mph per decade between 1982 and 2009. 

And with trends in global average temperatures projected to increase into the 2050s and beyond, hurricanes and the havoc they wreak aren't expected to abate any time soon.

How Is Hurricane Strength Measured?

Before we delve into the science of how and why global warming yields hulked-out hurricanes, let’s revisit the many ways hurricane strength is measured.

Maximum Wind Speed

One of the most popular ways to measure hurricane intensity is by using the Saffir-Simpson Hurricane Wind Scale, which bases strength on how fast a storm's maximum sustained winds blow and the potential damage they can inflict on property. Storms are rated from weak but dangerous Category 1s with winds of 74 to 95 miles per hour, to catastrophic Category 5s with winds of more than 157 mph.

When the Saffir-Simpson scale was created in 1971, it didn't include a Category 6 rating because it was reasoned that once winds cross the Category 5 mark, the outcome (total destruction of most property types) would likely be the same no matter how many miles per hour over 157 mph a storm's winds measure.

At the time of the scale's creation, only one Atlantic hurricane, the 1935 Labor Day hurricane, had ever reached enough to be considered a Category 6. (Since the difference between categories is roughly 20 mph, a Category 6 would have winds of more than 180 mph.) But since the 1970s, seven Category 6-equivalent storms have occurred, including Hurricanes Allen (1980), Gilbert (1988), Mitch (1998), Rita (2005), Wilma (2005), Irma (2017), and Dorian (2019).

It's worth noting that of the eight Atlantic storms that have reached such lofty wind speeds, all but one have occurred since the 1980s—the decade when global average temperatures rose more sharply than in any preceding decade since 1880 when reliable weather records began.

Size vs. Strength

It's often thought that a storm's size—the distance its wind field stretches across—indicates its strength, but this isn't necessarily true. For example, the Atlantic's Hurricane Dorian (2019), which intensified into a top-end Category 5 cyclone, measured a compact 280 miles in diameter (or the size of Georgia). On the other hand, the Texas-sized, 1,000-mile wide Superstorm Sandy didn't strengthen beyond a Category 3. 

The Hurricane-Climate Change Connection

How do scientists connect the above observations to climate change? Largely through an increase in ocean heat content.

Sea Surface Temperatures

Hurricanes are fueled by heat energy in the upper 150 feet (46 meters) of the ocean and require these so-called sea surface temperatures (SSTs) to be 80 degrees F (27 degrees C) in able to form and thrive. The higher that SSTs rise above this threshold temperature, the more potential exists for storms to intensify and to do so more rapidly.

As of the publication of this article, half of the top ten most intense Atlantic hurricanes when ranked by lowest pressure have occurred since the year 2000, including 2005's Hurricane Wilma, whose pressure of 882 millibars ranks as the basin's record lowest.

The barometric pressure at a hurricane's geographical center or eye region also indicates its overall strength. The lower the pressure value, the stronger the storm.

According to the 2019 IPCC Special Report on the Ocean and Cryosphere In a Changing Climate, the ocean has absorbed 90% of the excess heat from greenhouse gas emissions since the 1970s. This translates to an increase in global average sea surface temperature of approximately 1.8 degrees F (1 degree C) over the past 100 years. While 2 degrees F may not sound like much, if you break down that amount by basin, the significance becomes more apparent.

Intense Rainfall Rates

A warmer environment not only encourages stronger hurricane winds but also hurricane rainfall. The IPCC projects human-caused warming could increase the intensity of hurricane-related rainfall by as much as 10-15% under a 3.6 degree F (2 degree C) global warming scenario. It's a side effect of warming supercharging the water cycle’s evaporation process. As air warms, it is able to “hold” more water vapor than air at cooler temperatures. As temperatures rise, more liquid water evaporates from soils, plants, oceans, and waterways, becoming water vapor.

This additional water vapor means there’s more moisture available to condense into raindrops when conditions are right for precipitation to form. And more moisture spells heavier rain.

Slower Dissipation After Landfall

Warming isn't just affecting hurricanes while they're at sea. According to a 2020 study in Nature, it's also affecting hurricane strength after landfall. Ordinarily, hurricanes, which draw their strength from the ocean's heat and moisture, decay rapidly after striking land.

However, the study, which analyzes intensity data for landfalling storms over the past 50 years, found that hurricanes are staying stronger for longer. For example, in the late 1960s, a typical hurricane weakened by 75% within 24 hours of landfall, whereas today's hurricanes generally lose only half of their intensity in this same timeframe. The reason why isn't yet well understood, but scientists believe warmer SSTs could have something to do with it.

Either way, this occurrence hints at a dangerous reality: The destructive power of hurricanes could extend increasingly farther inland the farther into the future (and into climate change) we trek.

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