The Effects of Sea Level Rise on Orange County Coastal Habitats

Coastal homes threatened by sea level rise. Photo Credits: Orange County Register.

Water covers 71% of the world, and about 50% of people live less than 100 miles from the coast with the ocean playing an important role in everyday life. The ocean is dynamic, with a global circulatory system, currents, and energy dispersal (waves and swells). It transports heat from the equator to the poles, regulating our climate and weather patterns (NOAA, 2024). The sea is used for transportation and recreation as well. Consequently, critical ocean issues, such as rising sea levels, impact all coastlines and many lives. Scientists attribute climate change for causing an increase in sea level, which is the average height of the ocean's surface. Another dynamic aspect of our oceans that is important to understanding sea level rise is sea surface temperature which varies with latitude, the warmest waters generally near the equator and the coldest in the Arctic and Antarctic regions.

How Does Global Warming Cause the Sea Level to Rise?

Global warming causes a rise in sea level in two significant ways; glacial/sea ice melt and thermal expansion. The first refers to worldwide glacial and sea ice melting adding water to the ocean. Glaciers are large ice masses created by snowfall that have transformed into ice by the accumulated snow's pressure. Sea ice is frozen ocean water that floats on the ocean's surface. Sea ice does not raise the sea level significantly since the ice is already floating in the ocean, but when it melts, it causes a lower albedo effect. The albedo effect is a measure of how much sunlight a surface reflects into space. Snow and ice demonstrate a high albedo effect, reflecting a large amount of sunlight due to their light color, while surfaces such as dark soil have a low albedo effect, absorbing more sunlight. Thus, changes in the Earth's surface will impact temperature and contribute to climate change. Currently, due to higher temperatures, there is a loss of sea ice, which means less sunlight is reflected into space, accelerating the sea’s warming and threatening ice shelves that hold back the continent's massive glaciers (Turcotte, 2023). Glaciers are crucial because they hold three-quarters of Earth’s freshwater, making them the second largest reservoir of water on Earth, according to USGS. When glaciers melt due to the warming of the climate, the sea level rises, and we lose freshwater that is stored in them.

Another way the sea level rises is through a process called thermal expansion. This refers to the natural process by which a material expands in size when its temperature increases. Thus, ocean volume expands as the water warms. The sea temperatures are warming up because of climate change, and every year, it gets warmer. This is due to the greenhouse effect, the natural process that warms the Earth’s surface by trapping heat from the sun in the atmosphere (DCCEEW, 2025). The ocean absorbs 90% of the excess heat trapped by greenhouse gases, which raises its temperature and increases its volume. Greenhouse gases, including carbon dioxide, water vapor, and methane, make up our atmosphere and are normally helpful. But increasing levels of carbon dioxide in the atmosphere have caused global temperatures to rise, therefore heating up our ocean and causing thermal expansion.

Illustration of thermal expansion. As ocean water warms, it increases in volume due to thermal expansion, contributing to sea level rise. Photo Credits: Pressbooks.

How do Scientists know Sea Level Rise is Happening?

Scientists measure the rise in sea level using two methods. A tide gauge measures the water's height along the coast relative to a specific point on land. This method has been used for collecting data for more than 100 years. They are often inside a special house called a “tide house” which shelters permanent tide gauges and takes measurements every six minutes (NOAA, 2017). These tide houses were primarily used before computers to record water levels, but are still used today. Another way to record sea level is by a satellite altimeter which is a technique that uses radar pulses to measure the height of the ocean’s surface and estimate the depth of the ocean. The altimeter has been used since the early 1990s. Both tide gauges and satellite altimeters provide scientists with a more comprehensive picture of how sea level trends have changed over time.

A tide gauge with a protective "tide house" that shelters water level recording instruments from harsh environmental conditions. Photo Credits: National Oceanic and Atmospheric Administration.

Why does this matter to us, particularly in Orange County?

With the sea level projected to increase, our coastlines and habitats here in OC will be affected. Rising sea levels will cause wetland destruction, an increase in erosion, species displacement, and even storm surge amplification. Huntington Beach is the second most vulnerable city to sea level rise in California (Coastkeeper, 2016). Sea level rise is projected to rise between 1.6 and 3.1 feet, perhaps even higher by 2100 in California, according to the California Ocean Protection Council. 

Wetlands are especially vulnerable because they are low-lying areas and the rising water can drown vegetation and convert the wetland into open water that cannot adapt quickly. In addition, wetlands are vital in filtering pollutants from water, controlling floods, serving as essential habitats for diverse wildlife, and acting as a natural carbon sink, meaning they remove carbon dioxide from the atmosphere and store it. About half of all wetlands across Southern California are projected to be permanently submerged by 2100 which would destroy vital habitat and ecosystem services (Stein, 2024).

Satellite Altimetry used to represent the ocean better. Photo credit: Copernicus Marine Service.

In addition to wetland destruction, it is predicted that the rise of sea level will cause significant coastal erosion, leading to the loss of a large portion of Southern California’s beaches. It is estimated that 24% to 75% of beaches could be lost by the year 2100 (Woelfle, 2023). Sea level rise gradually causes loss of the beach area and the shoreline retreats inland due to the higher water level, making beaches vulnerable to waves.

Some species that are vulnerable to sea level rise and will be displaced include shorebirds like the California least tern and western snowy plover, salt marsh plants, harbor seals, tidepool fish species, and even turtles. These animals live in and thus rely heavily on coastal habitats that will be impacted if the sea level rises since they will lose their nesting grounds and food sources. Salt marsh plants help stabilize the shoreline, reducing erosion, and provide habitat for many of these species, so they are vital. In addition, some of these species of animals are endangered, such as the California least terns and western snowy plover which nest on Orange County beaches.

The Western Snowy Plover (Charadrius alexandrinus nivosus) is a native shorebird that inhabits sandy dune habitats year-round along the Pacific Coast. It is listed as a threatened species under the U.S. Endangered Species Act. Photo credit: Ross Griswold.

Natural Resiliency Measures Versus Infrastructure Projects

Natural Resiliency measures are natural-based solutions that use natural features and processes to recover from a disturbance, such as sea level rise. Some examples of these measures are salt marshes, sand dunes, planting coastal vegetation and living shorelines (Aerts, et al., 2018). Natural resilience measures are often considered a better option than an infrastructure project that can cost more, impact the environment, and be only temporary. Natural resilience measures have benefits such as protecting the coastlines from erosion, mitigating flood damage, and enhancing biodiversity and are more cost-effective and last longer. 

The California Least Tern (Sternula antillarum browni) is a small migratory shorebird that nests in open, sandy or sparsely vegetated coastal habitats in Orange County. It is listed as an endangered species under the U.S. Endangered Species Act. Photo credit: Bill Halladay.

Infrastructure projects include levees, jetties, and seawalls. Levees are a man-made barrier that's primary purpose is to control flooding by containing and controlling water rise and reducing the frequency of flooding. Jetties are a man-made structure that extends from the land out into water. Seawalls are walls to prevent the sea from approaching an area of land. These can all have benefits but also have disadvantages. For instance, levees can cause increased water speed which increases erosion and reduces beneficial in-stream vegetation (Braunstein, 2012). Jetties can also cause sediment accumulation and erosion due to lack of transported sediments. For seawalls, disadvantages include erosion, cost, and structural damages over time. Infrastructure projects can help with the effects of sea level rise but can have damages to the environment.

Jetty at The Wedge, Newport Beach, California. Photo credit: CaliforniaBeaches.com

Conclusion

The future regarding sea level is that it is expected to rise, the California Ocean Protection Council anticipates sea level to rise anywhere from two to seven feet between now and 2100. Worst-case scenario, it can rise 10 feet and impact all coastlines in California as researchers warn. (Woelfle, 2023). Sea level rise is caused by two major factors which are glacial/ice melt and thermal expansion. As the ocean rises, Orange County’s coast will be impacted, as well as the animals that live there. Many plants and animal species are not adapted to the saltwater environment or having much water in their habitats causing them to be destroyed.

Seawall protecting Laguna Beach home. Photo credit: The Orange County Register.

Wetlands are at risk of becoming flooded, losing precious habitat for many species. Some of these species include the Western Snowy Plover and the California least terns which both are endangered and use the wetlands as their habitat. Wetlands are not only important to just animals they are also vital to humans as they remove carbon dioxide. However, natural-based solutions alongside infrastructure projects can help with sea level rise affecting the coast. It is crucial for everyone to know how and why the oceans are rising and why it will impact the environment and the future generations. If you want to help preserve local wetlands which act as natural resilience measures for our coast, OC Habitats hosts restorations events at Huntington Beach Wetland Conservancy and Upper Newport Bay to ensure the continuance of these important habitats.