Introduction
Although scientists are uncertain whether climate change will lead to an increase in the number of hurricanes, there is more confidence that warmer ocean temperatures and higher sea levels are expected to intensify their intensity and impacts. Stronger hurricanes will be far more costly in terms of damages and deaths without action to make coastal (and inland) areas more resilient.
Hurricanes are subject to a number of climate change-related influences:
Warmer sea surface temperatures could intensify tropical storm wind speeds, potentially delivering more damage if they make landfall. Based on complex modeling, NOAA has suggested that an increase in Category 4 and 5 hurricanes is likely, with hurricane wind speeds increasing by up to 10 percent. Warmer sea temperatures also are causing hurricanes to wetter, with 10-15 percent more precipitation from cyclones projected in a 2 degree C scenario. Recent storms such as Hurricane Harvey in 2017 (dropping over 60 inches in some locations), Florence in 2018 (with over 35 inches) and Imelda in 2019 (44 inches) demonstrate the devastating floods that can be triggered by these high-rain hurricanes.
Sea level rise is likely to make future coastal storms, including hurricanes, more damaging. Globally averaged, sea level is expected to rise by 1-4 feet in low and moderate emissions scenarios during this century, which will amplify coastal storm surge. For example, sea level rise intensified the impact of Hurricane Sandy which caused an estimated $65 billion in damages in New York, New Jersey, and Connecticut in 2012. Much of this damage was related to coastal flooding.
Areas affected by hurricanes are shifting poleward. This is likely associated with expanding tropics due to higher global average temperatures. The changing patterns of tropical storms (a shift northward in the Atlantic) could put much more property and human lives at risk, but much more research is required to build a better understanding of how these patterns might change.
The connection between climate change and hurricane frequency is less straightforward. It is likely the number of storms will remain the same or even decrease, with the primary increase being of the most extreme storms. For the 21st century, some models project no change or a small reduction in the frequency of hurricanes, while others show an increase in frequency. More recent work shows a trade-off between intensity and frequency – that as warmer oceans bolster hurricane intensity, fewer storms actually form.
Background on Hurricanes and Tropical Storms
A hurricane is a type of tropical cyclone, which is a general term for a low-pressure system with activity like thunder and lightning that develops in the tropics or subtropics. In the Northern Hemisphere, these storms rotate counter-clockwise. In the Southern Hemisphere, they rotate clockwise. Stronger systems are called “hurricanes” or “typhoons,” depending on where they form. Weaker tropical cyclones might be called “tropical depressions” or “tropical storms.”
The National Hurricane Center categorizes Atlantic hurricanes based on wind speed. A storm with winds exceeding 74 mph is a Category 1 hurricane. Storms with winds stronger than 111 mph are considered “major hurricanes” (Category 3 or higher). Wind speed is just one of many factors that contribute to a hurricane’s impact. Others include its track (the site where the storm makes landfall), size, storm structure, rainfall amount, duration, and the vulnerability of the area it affects.
Frequency and intensity vary from basin to basin. In the North Atlantic Basin, the long-term (1966-2009) average number of tropical storms is about 11 annually, with about six becoming hurricanes. More recently (2000-2014), the average is over 15 tropical storms per year, including about seven hurricanes. This increase in frequency is correlated with the rise in North Atlantic sea surface temperatures, which could be partially related to global warming.
Threats Posed by Hurricanes
Climate change is adding to the coast and threat of hurricanes. While there have been extreme storms in the past, recent history reflects the growing expense of hurricanes. Four of the 10 costliest hurricanes on record in the United States occurred in 2017 and 2018. Hurricane Katrina (2005) remains the most expensive hurricane on record costing $168 billion (2020 dollars).
The 2017 hurricane season was historic, with Hurricanes Harvey, Maria and Irma costing nearly $300 billion together (2020 dollars). It is important to note that while stronger hurricanes are more damaging, there are nearly 50 million homes and at least $1.4 trillion in assets within an eighth of a mile of the coast and a growing amount of property at risk in coastal areas. An important driver of the increased cost of hurricanes is increasing development in coastal areas. U.S. coastal populations grew by nearly 35 million people between 1970 and 2010. As more development occurs in harm’s way — regardless of climate change — the more likely the damage will grow.
In addition to damages to buildings, hurricanes threaten infrastructure, undermining energy systems, water and sewer systems, transportation, and flood management structures.
Stronger hurricanes pose a significant risk to public health and human lives. Hurricane Katrina caused over 1800 deaths, and Hurricane Maria in 2018 caused 2981 deaths mostly in Puerto Rico. Disruptions to water supplies and power systems can create risk for waterborne illness, environmental contaminants, mosquito borne illnesses and cause hospitals to close or affect care for patients.
How to Build Resilience
Reducing greenhouse gas emissions is one way to reduce the risk of the strongest storms in the future. Communities can also bolster their resilience to the impacts of hurricanes by:
- Preserving coastal wetlands, dunes, and reefs to absorb storm surge and ensure building and development does not occur in harm’s way.
- Replenishing beaches and improve infrastructure that affords coastal protection, such as seawalls.
- Elevating vulnerable buildings to reduce flood damage.
- Encouraging residents in areas that have had historically low hurricane risk to purchase flood insurance.
- Designing structures to be resilient to high winds and flying debris.
- Prepare directly prior to a storm’s arrival by boarding windows, clearing property of potential flying debris, and having an evacuation plan.
Originally published by the Center for Climate and Energy Solutions (C2ES), republished with permission for educational, non-commercial purposes.