The question of whether Florida is sinking or the water is rising is a complex one, and the answer involves both processes occurring simultaneously. The land mass is indeed experiencing a gradual lowering, a long-term geological reality tied to its very foundation. At the same time, the global ocean is expanding due to warming, which is causing the water level to climb. The resulting observable change on the Florida coast is the net effect of these two distinct, yet compounding, processes. Understanding this situation requires examining the deep geological history of the state alongside the modern effects of a changing climate.
Geological Reality: Subsidence and Karst Topography
Florida’s unique geology is rooted in a massive, porous underground foundation known as karst topography. This landscape is formed by the dissolution of a thick layer of soluble carbonate rock, primarily limestone, which underlies the entire state. The limestone bedrock is highly permeable, containing a vast network of interconnected fissures, conduits, and caves.
The natural process of dissolution and erosion of the limestone creates the state’s characteristic sinkholes and springs. Over millennia, the slow but constant flow of water through these subsurface voids causes the overlying sediment and rock layers to settle, a process known as natural subsidence. This lowering of the land surface is a long-term geological phenomenon, independent of human-caused climate change, but it contributes directly to the state’s vulnerability.
Localized subsidence can also occur in coastal regions built on reclaimed marshland as younger sediments naturally compact under the weight of development. Furthermore, a regional influence called glacial isostatic adjustment (GIA) plays a minor role, where the land continues to adjust after the last Ice Age. These geological mechanisms mean that Florida’s land surface is gradually losing elevation, creating a stationary target for the rising ocean.
Climate Reality: Global Sea Level Rise
While the land is naturally settling, the global ocean is actively rising due to two main effects driven by increasing global temperatures. The first mechanism is the thermal expansion of seawater. As the ocean absorbs heat from the warming atmosphere, the water molecules spread out, causing the total volume of the ocean basin to increase.
The second, and increasingly dominant, factor is the addition of water from melting land ice. Massive ice sheets and glaciers in places like Greenland and Antarctica are losing ice mass at an accelerating rate. When this ice melts, the resulting freshwater flows into the ocean, directly increasing the total volume of water.
This rise is a global phenomenon, but its impact is felt acutely in Florida because of the state’s extremely low-lying topography. Much of the peninsula sits only a few feet above the current sea level, making it highly susceptible to even small increases in ocean volume. This rising tide is now meeting the naturally subsiding land, creating a rapidly worsening scenario for the state.
The Combined Threat: Measuring Relative Sea Level Change
For coastal communities in Florida, the critical measurement is not the absolute rise of the ocean or the rate of land sinking in isolation. The critical factor is the combined effect known as Relative Sea Level Rise (RSLR). RSLR measures the net difference between the height of the ocean’s surface and the height of the adjacent land. When the land lowers and the water rises, the relative sea level changes at an accelerated rate.
Scientists monitor RSLR using a network of coastal tide gauges, which provide long-term records of local water levels. Key West, for instance, has one of the longest continuous records in the Western Hemisphere, showing a long-term RSLR trend of approximately 2.64 millimeters per year. Modern measurements also incorporate satellite data, such as the Continuously Operating Reference Stations (CORS) and Interferometric Synthetic Aperture Radar (InSAR), to precisely track vertical land motion.
Current projections for Southeast Florida indicate an acceleration in RSLR. Observed sea levels are rising in the range of one to two inches per decade. Short-term projections for Southeast Florida suggest a rise of 10 to 17 inches by the year 2040, using the 2000 mean sea level as a baseline. This metric drives planning and policy, as it represents the true rate at which the ocean is encroaching on the state’s coastline.
Immediate Impacts on Water and Infrastructure
The most immediate consequence of Relative Sea Level Rise is the inland migration of the saltwater boundary, known as saltwater intrusion (SWI). As the sea level rises, it exerts increasing pressure on the freshwater aquifers, like the Biscayne Aquifer, which supply drinking water to millions of residents. This forces the denser saltwater deeper into and farther inland within the porous rock structure, contaminating potable water sources and requiring costly relocation or treatment of wells.
The rising water table also directly affects infrastructure and daily life in coastal cities. Increased frequency of “sunny day flooding”—tidal flooding that occurs without rain or storm surge—is common, as the high tide simply exceeds the elevation of the land. Storm drainage systems and septic tanks, which rely on gravity and a lower water table to function, become ineffective.
Roads and other infrastructure suffer damage as the rising groundwater saturates the subsurface, causing stress and deterioration. The inundation of septic systems poses a public health threat by mobilizing contaminants and fecal coliform bacteria into the surrounding environment, especially during high-tide events. These effects are already observable and represent a growing challenge for coastal resilience.