The effects of climate change are far reaching - what changes can you see today?

Florida has a reputation of being flat and that is certainly true of South Florida. Here, a few inches difference in elevation determines which habitats can form. Historically covering much of the southern half of the state, the Everglades is a vast watershed where water flows south-southwest from Lake Okeechobee into Florida Bay and the Gulf of Mexico. As water moves through the Everglades, it flows around the high elevation ridges and is channeled through the low elevation sloughs.

Where you are standing now is in the middle of Taylor Slough, the second largest slough in Everglades National Park. Sloughs are important deep-water channels that deliver water to the estuaries lining the southern coast. They should remain wet in all but the driest years. Unfortunately, people have altered the flow of water into the park, which led to devastating consequences for the plants and animals here and even caused subsidence in some areas, but Everglades Restoration seeks to repair water flow into the park.

Another way that people are affecting the Everglades is through climate change.

In addition to having a reputation for being flat, South Florida also has a tropical reputation, but it actually has a sub-tropical climate and cold fronts can occasionally bring low, even freezing temperatures. However, with climate change, the frequency and severity of these cold fronts may change, though the extent of change is unclear. What is clear is that average temperatures, especially the average low temperatures, are increasing every year.

Another unique feature of South Florida is that it lies in a transition zone from tropical to sub-tropical and temperate zones. This leads to a unique mix of species that cannot be seen side-by-side elsewhere in their ranges. For temperate species, the Everglades is the southern extent of their range, anything farther south being too hot for them. For tropical species, the Everglades is the northern extent of their range and anything farther north is too cold for them. Examples include American alligators and live oak trees, which are temperate species and American crocodiles and gumbo limbo trees, which are tropical species.

Cold fronts really keep tropical species from expanding their ranges northward, but if these become less severe, that could allow species to persist farther north than they have historically. Changing climate also opens a region up to additional vulnerability to invasive species.

Florida’s warm climate and busy international shipping ports and airports, which are the main entry point for goods, agriculture, and aquaculture, make it especially vulnerable to invasion from species native to tropical regions of the world. Climate change will increase the potential for future and ensure the continued prevalence of already established invasive species in South Florida, particularly those species native to tropical regions.

In the past, cold fronts have led to die-off events for invasive animals like Burmese pythons and cichlid fishes. In contrast to many of the native freshwater fishes of the Everglades, which evolved in temperate regions of the United States and are able to survive cold winter temperatures, many of these nonnative fishes evolved in tropical regions where minimum temperatures are warmer and so they are physiologically incapable of surviving when temperatures drop below certain levels. Unfortunately, an invasive animal could survive a drop in temperatures if one finds itself, on purpose or on accident, in a pocket of warmth called a thermal refuge.

Deep bodies of water like sloughs or retention ponds offer thermal refuges for tropical fish in South Florida. In 2010, Burmese pythons that remained underground or were otherwise insulated from ambient temperatures, were able to survive freezing temperatures. As temperatures increase and cold fronts with freezing temperatures potentially lessen, more and more tropical invasive animals will be able to survive, reproduce, and spread in the region, without needing thermal refuges.

Other effects of climate change, namely sea level rise and resulting saltwater intrusion, could help some invasive species with higher salt tolerances outcompete some native freshwater species with lower saltwater tolerances. Saltwater intrusion is the process where seawater pushes against and infiltrates underground freshwater reservoirs called aquifers. South Florida’s Biscayne aquifer is a surficial aquifer because it lies just below the surface and is replenished by groundwater and rainfall. South Florida’s porous bedrock means that there is often interchange between the aquifer and both ground and surfacewater. This means that saltwater intrusion could eventually make freshwater wetlands near and far from the coast saltier while allowing the invasive species that are more tolerant of saltwater than some of the native freshwater species to thrive.

Canals dug into the Everglades in order to drain it offer refuges for invasive fish species and they are often overrun by them. Until Everglades Restoration is accomplished, sever droughts will cause man-made canals and borrow pits, or areas where rock was mined to use as fill for nearby roadbeds, to be the only places with water available for aquatic species like fish. If saltwater intrusion also makes those canals saltier, it would mean that even fewer native freshwater species will persist.