Last updated September 20, 2017

Increased Frequency Intense Cyclones, Hurricanes and Typhoons

Hurricanes are fueled by ocean heat. As climate change warms sea surfaces, the heat available to power hurricanes has increased, raising the limit for potential hurricane wind speed and with that an exponential increase in potential wind damage.  There is strong evidence that climate change may be responsible for the recent observed increase in the intensity and wind speed of tropical cyclones. Separately, sea level rise has elevated and dramatically extended the storm surge driven by hurricanes - the main driver of damage for coastal regions. And climate change has been found to have significantly increased the rainfall in tropical cyclones. Warmer air holds more moisture, feeding more precipitation from all storms including hurricanes, significantly amplifying extreme rainfall and increasing the risk of flooding.

Global trends

Warming seas are increasing the limits for powerful storms

Tropical cyclones are fueled by available heat. Warming seas are increasing the potential energy available to passing storms, effectively increasing the power ceiling or speed limit for these cyclones.[1] And there has been a global increase in the observed intensity of the strongest storms.[2] However, there is an extremely wide range of natural variability in tropical cyclone activity, and other factors affected by climate change, such as wind shear and the global pattern of regional sea surface temperatures, also play controlling and potentially contradictory roles. The balance of all these factors is not fully known.[3] Nevertheless the fingerprint of global warming in the intensity of tropical cyclones has been identified in one ocean basin: the Northwest Pacific. In 2015, accumulated cyclone energy (ACE) in the western North Pacific was extreme, and human-caused climate change "largely increas[ed] the odds of the occurrence of this event," according to an assessment study conducted by a large group of scientists led by NOAA and published in the fifth edition of "Explaining Extreme Events from a Climate Perspective" by the Bulletin of the American Meteorological Society.[4]

Most of the published scientific work concerns the expected response of tropical cyclones to climate change and anticipates that such storms will become stronger and perhaps less frequent, but at a rate that should not be formally detectable until mid-century. Yet there is clear satellite-based evidence of increasing incidence of the strongest storms, as theory dating back to 1987 predicted.[5]

- Kerry Emanuel, Professor of Atmospheric Science, MIT

 

While there is little scientific evidence that there will be more (or fewer) hurricanes or more hurricanes hitting the U.S., there is strong theoretical and statistical evidence that the strongest hurricanes are getting stronger as the oceans heat up due to global warming from the emission of greenhouse gases. In fact, there is statistical evidence that the magnitude of economic damage in the U.S. from hurricanes increases with rising ocean temperature.[5]

- James Elsner, Professor, Florida State University

As seas warm and offer more heat energy, there has also been a global increase in the observed intensity of the strongest storms over recent decades. The link between warming ocean temperatures and stronger storms may be reflected in the close correlation between observed trends in recent sea surface temperatures and observed trends in the intensity of tropical cyclones.[6][7][2] The increase is well-documented and is consistent with models projecting the future climate, but the correlation between these two trends is not fully understood and scientists are still working to better understand the relation between these two trends.[1]

The US National Climate Assessment (2014) reports that "the intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest hurricanes, have all increased since the early 1980s."  A reconstruction of North Atlantic hurricanes dating back to the the late 1800s adjusts the historical record in an attempt to account for hurricanes that went unrecorded in the early years, and after adjustment finds that there has been no century-scale trend. However, prior bouts of increased hurricane activity due to natural variation do not rule out a role for global warming the current period of increased activity since the early 1980s.  For a detailed, consensus synthesis of the science published through 2014 on climate change and tropical cyclones see, "Tropical cyclones and climate change," by Walsh et al, 2015.[1]

Fewer but stronger storms would likely lead to an increase in overall damages

Damage incurred by tropical cyclones is overwhelmingly and disproportionately incurred by the most powerful storms, indicating that overall damage will increase as the climate warms.

Cyclone wind damage increases geometrically with an increase in speed.[8] A decrease in frequency would not be expected to offset the increase in damages incurred by increasing intensity. Moreover, damage escalates exponentially when storm strength crosses over the thresholds beyond which threatened infrastructure collapses.

It's the high end events that are the most destructive historically....More than half the damage that's been done in the United States by storms dating back to the middle of the 19th century has been done essentially by just eight events. So it really is the rare events, the Katrinas, the Sandys, that do the overwhelming amount of damage.  Your average run-of-the-mill hurricane will do some damage and be memorable in the local place that if affects, but it doesn't really amount to a hill of beans compared to what the big storms do.

Dr. Kerry Emanuel [9]

Higher storm surge

The most important impact of tropical cyclones in coastal regions is storm surge.[1] Increases in storm surge can be due to sea level rise and increasing wind speed.[1]

Climate change has already contributed about 8 inches (0.19 meters) to global sea level rise,[10] and this has amplified the impact of cyclones by increasing baseline elevations for waves and storm surge.[11]

Small vertical increases in sea level can translate into large increases in horizontal reach by storm surge depending upon local topography. For example, sea level rise extended the reach of Hurricane Sandy by 27 square miles, affecting 83,000 additional individuals living in New Jersey and New York City[12] and adding over $2 billion in storm damage.[14]

More extreme rainfall

Climate change is dramatically increasing the rainfall of tropical cyclones.[13] And an increase in rainfall rates is one of the more confident predictions of the effects of future climate change on tropical cyclones.[1]