New Orleans and sea-level rise
New Orleans, a unique city positioned below sea level, faces significant challenges due to rising sea levels and climate change. The legacy of Hurricane Katrina in 2005 underscored the city's vulnerability, as extensive flooding occurred when levees were breached, leading to a renewed focus on coastal disaster preparedness. Scientists predict that sea levels could rise between 0.3 to 1 meter over the next century, with estimates indicating that coastal flooding could increase significantly in frequency by 2050. Research has also suggested a correlation between higher sea surface temperatures and the strengthening of hurricanes, raising concerns about future storms' intensity.
In addition to rising waters, the loss of natural buffers like coastal wetlands has exacerbated the risks faced by New Orleans, as human activity and climate change accelerate land erosion and subsidence. While the U.S. government has invested in enhancing levee systems and coastal restoration, debates continue regarding the adequacy of these measures against the backdrop of ongoing climate change and the need for comprehensive solutions. These challenges extend beyond New Orleans, as many coastal communities in the U.S. face potential threats from rising tides and stronger storms. The plight of New Orleans serves as a crucial reminder of the far-reaching impacts of climate change, highlighting the urgent need for local and global action.
New Orleans and sea-level rise
After Hurricane Katrina devastated New Orleans in 2005, the city’s experience became a pivotal point for increasing interest in understanding and mitigating the contribution of global warming to future coastal disasters.
Background
New Orleans, the only major American city below sea level (2.4 to 3 meters below in some places), depends on a system of levees and natural buffers, such as coastal wetlands and barrier islands, for flood protection. When Hurricane Katrina’s breached and topped the city’s levees in the summer of 2005, 80 percent of New Orleans was flooded. Post-storm queries sought to determine how to assess and reduce the probability of future New Orleans disasters by better understanding the conditions that caused Katrina’s devastation. Additionally, some scientists have hypothesized that, since hurricanes’ high winds, rain, and tornadoes are created as they push water vapor up into the atmosphere, more sea surface heat should increase the storms’ power.
Rising Sea Levels and Hurricane Strength
Whether New Orleans will suffer future catastrophes that are similar or worse in magnitude than the one caused by Katrina depends on a number of factors, including the current and projected effects of climate change. There is a strong consensus among scientists that sea levels have increased because of global warming and will rise another 0.3 to 1 meter over the next one hundred years. Researchers for the Fifth National Climate Assessment estimated in 2023 that during the next thirty years (2020-2050), sea levels along the US coastline could rise by as much as 11 inches (28 centimeters). This is as much as the sea level rose during the last 100 years. Because of this, coastal flooding would occur five to ten times more often by 2050 than in 2020.
A study conducted at the Massachusetts Institute of Technology combined hurricane duration and wind speed to create the Power Dissipation Index to measure their intensity. The research report, which was published one month before Katrina hit, concluded that an examination of 1,557 Pacific and 558 Atlantic hurricanes over a thirty-year period showed a doubling of storm power, with a strong correlation between rising water temperatures and increasing hurricane strength. Research conducted at the Georgia Institute of Technology similarly showed that since the mid-1990s, the number of Category 4 or 5 hurricanes on the had doubled. According to a study by Climate Central in 2024, climate change strengthened the wind speed of the hurricanes from 2019 to 2023 by about 80 percent, which is about 18 miles per hour. Higher sea surface temperatures fueled these hurricanes. Three hurricanes strengthened into Category 5, the strongest classification, because of climate change: Lorenzo (2019), Ian (2022), and Lee (2023).
These and the conclusions of similar studies are not accepted by all scientists. Some meteorologists, including researchers at the National Oceanic and Atmospheric Administration, take the position that the Atlantic Multidecadal Oscillation (AMO) has created decades-long increases and decreases in sea temperatures, and the AMO is more responsible for the recent upsurge in hurricane strength than is global warming. These critics concede, however, that the AMO will cause decades of more powerful hurricanes.
Loss of Natural Protections
Historically, Southeast Louisiana’s coastal wetlands and barrier islands have served as natural buffers that reduced hurricane damage to New Orleans (the US Army Corps of Engineers asserts that 4.3 kilometers of wetlands dissipates 0.3 meter of storm surge). Soil subsidence, meanwhile, was counteracted by continuous silt deposits from the Mississippi River. Both human development and climate change have created the potential for extensive damage from future storms. Flood control and navigation projects stopped the land buildup from the Mississippi River in both the wetlands and the New Orleans area, while the channels created by the oil industry sped up the pace of coastal erosion.
The combined effects of sea level rise, land subsidence, and erosion have resulted in the loss of thousands of square kilometers of Louisiana’s coastal land, a one-meter increase in “relative sea level” for New Orleans over the past one hundred years (one-third due to sea rise and two-thirds due to soil compaction), and concerns that New Orleans may be on the coast in another one hundred years. The destruction of barrier islands has also increased (Katrina destroyed half of the Chandeleur Islands located east of New Orleans). Many experts claim that current and proposed coastal restoration efforts would only minimally reduce annual losses.
Government Responses and Calls for Action
Whether New Orleans can avoid future disasters of Katrina’s magnitude will depend on the effectiveness of measures that have been taken and the implementation of additional proposals for better protecting the city. The federal government began increasing the height and strength of the levees shortly after Katrina, and millions of dollars have been spent on coastal restoration programs. Critics argue that these measures cannot begin to counteract the ongoing effects of global warming. They propose that a comprehensive approach that includes billions of dollars in coastal restoration projects and local, national, and global efforts to significantly reduce greenhouse gas (GHG) emissions will be necessary to ensure New Orleans’s future survival. Private organizations have rebuilt neighborhoods in New Orleans using green construction to serve as pilot projects to promote energy-efficient housing everywhere and have joined with scientists and legislators in calling for the federal government to end its resistance to both increasing investment in renewable clean energy and participating in international agreements to reduce carbon dioxide emissions.
Between 2006 and 2018, the Army Corps of Engineers completed repairing and rebuilding of the Greater New Orleans Hurricane and Storm Damage Risk Reduction System (HSDRRS). The system included 350 miles of floodwalls and levees, a 1.8-mile surge barrier across Lake Borgne, 244 land-based flood gates, and 73 powerful pumping stations, all of which were designed to significantly reduce the risk of flooding during superstorms like Katrina. The $14 billion project was one of the largest public works projects in world history. The system was tested to some extent in 2020 by Hurricanes Laura, Delta, and Zeta before it faced Hurricane Ida, a Category 4 hurricane that struck New Orleans on August 29, 2021, the sixteenth anniversary of Katrina's landfall. The areas protected by HSDRRS successfully withstood Ida's storm surge and rainfall, but areas outside the network experienced flooding that trapped residents.
Context
Within the debate over the best ways to secure New Orleans’s future, there are those who assert that concerns about that city’s fate should be viewed as a wake-up call that draws attention to a much broader threat. They posit that, if the future effects of global warming occur as currently projected, all of America’s coastal areas, where half of the nation’s population resides, would be in danger from catastrophes caused by coastal erosion, higher sea levels, and strong storms. This could result in cities like New York and Miami being below sea level and dependent on levees for protection, as New Orleans’s improved system becomes obsolete and ineffective. The IPCC report asserts that, during the next century, coastal communities all over the world will be at risk of disasters like Katrina’s destruction of New Orleans. This report also states that current rates of ocean temperature increases could cause much higher sea levels as huge Antarctic and Greenland ice sheets melt.
Key Concepts
- Atlantic Multidecadal Oscillation: cyclical increases and decreases in sea temperatures that last for decades
- Power Dissipation Index: a measure of the total annual energy output of all hurricanes in a region
- Saffir-Simpson scale: a scale that ranks hurricanes from category 1 through category 5, based on their sustained wind velocity
- storm surge: rising water that is caused when a hurricane’s winds push the ocean’s surface inland
- U.S. Army Corps of Engineers: a government agency whose duties include flood control
Bibliography
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