Union of Concerned Scientists

South Florida landscape
Before it was drained, the landscape of South Florida was a mosaic of habitats connected by fresh water. The water flowed in rivers, streams, and shallow sheet flows across the gently sloping landscape below Lake Okeechobee, through sawgrass interspersed with tree islands and tangled mangrove forests, to shallow estuaries, and out to the coral reefs off shore. Wading birds, alligators, sawgrass plains, mangroves, and tropical hardwood hammocks are still among the most recognizable features of this landscape.

The natural evolution of this landscape mosaic has been driven by the slow relative rise in sea level over the past three thousand years, as well as extreme episodic events—in particular, fires, freezes, tropical storms, hurricanes, floods, and droughts. The large differences in rainfall from year to year can bring excessive flooding in some years and drought in others. However, this natural year-to-year variability, along with the normal seasonal variability in rainfall, is a major contributor to the high productivity and biodiversity of these wetlands.

Human pressures
The same episodic events that control the natural landscape also affect human populations. To protect the growing population from severe storms and to support agriculture (especially the sugar industry), South Florida developed one of the world's most extensive water management systems. These engineering efforts have caused a change in the timing and supply of clean water flows, reducing the Everglades to a degraded remnant that continues to decline. The natural variability of surface water flows has been altered dramatically, so that now in very wet years, massive amounts of fresh water are discharged through canals and enormous pumps into a few coastal estuaries. The historical sheet flows of water that used to occur along other parts of the coast have been reduced substantially, commonly resulting in saltwater intrusion and occasionally in overly salty conditions in systems such as Florida Bay.

Future changes
As a result of the water management system, the Greater Everglades is an endangered ecosystem whose sustainability is critically at risk. Global warming is likely to worsen the effects of human pressures on the Greater Everglades ecosystem, although a great deal of uncertainty remains about the specific impacts that will occur. Among the impacts that can be expected are ecosystem shifts due to sea-level rise and the increased spread of invasive exotic species. Other major effects could result from more frequent or more intense hurricanes or from more frequent or intensive droughts, which would increase the risk of major wildfires.

The greatest risks the Everglades face from climate change may well be accelerated sea-level rise and the damaging impacts of elevated storm surges. Since the flow of water is the most critical factor in the survival of the region's mosaic of habitats, any changes in water balance will certainly affect this unique and valuable landscape.