The Keys mark the last outposts of the Everglades lands. Once hummocks of higher vegetation set in a prehistoric swamp, they have struggled against the rising sea. Mangroves on their perimeters collect silt and organic material, building a barricade secure against all but the most severe hurricane winds and tides. In the Everglades and Big Cypress Swamp, there is a strong contrast between the seasons. From early spring well into autumn, they have ample rainfall, averaging 50 inches per year.
Winter is a time of drought and fire, and saltwater penetrates farther inland.
Already stressed by water diversions, invading species of plants and animals, and the natural phenomena of drought, flood, and storms, these ecosystems will be stressed further by climate change. A 20-inch sea level rise would cause large losses of mangroves in southwest Florida. Increased salinity, resulting from rising saltwater into the Everglades from Florida Bay, also would damage freshwater ecosystems containing sawgrass and slough. Communities of wet prairie also would decline with the rise in sea level. Climatic conditions in central Florida may become suitable for subtropical species such as Gumbo-limbo, now confined to subtropical hummocks in the southern part of the peninsula and the Keys.