200 
Figure 4. Sunspot cycles and numbers [Redrawn from Wilson (1989).]. 
El Nino events. For unknown reasons, moderate El Nino events appear to occur preferentially 
near the sunspot minimum and when annual sunspot numbers are low. Strong El Nino events 
appear to preferentially occur during the declining portion of the sunspot cycle. 
It has been found recently that the solar radius is variable, with variations on an ~80 yr time 
scale, and that these variations may result in large changes in solar luminosity (Gilliland, 
1982). This ~80 yr cycle, as well as the shorter 11-yr solar sunspot cycle and 22-yr Hale 
cycle of solar magnetic reversals may explain hemispheric temperature trends. A third 
possible cycle is the 18.6-yr lunar nodal cycle in which tidal influences may play an important 
role. 
5.5. Sea level change 
Global sea level has been rising since the last glacial maximum approximately 18,000 yrs ago 
and this rise has not been uniform. Wanless et al. (1994) has shown that the sea level rise for 
the past few thousand years has been about 0.04 cm/yr compared to that of the Holocene, 
approximately 0.25 cm/yr. Maul and Martin (1993) have determined the sea level rise at Key 
West using instrument records from 1846 - 1987. The linear sea level rise has been about 30 
cm and there is a statistically weak but consistent indication that the rate of rise has increased 
slightly since the 1920s (Figure 5). 
6. ENVIRONMENTAL CHANGES 
6.1. Species status 
There are several threatened and endangered species in Florida Bay under Federal and state 
protection. These include the key silverside, the green sea turtle, the loggerhead sea turtle, 
hawksbill sea turtle, the Kemp's Ridley sea turtle, the leatherback sea turtle, the manatee, the 
American crocodile, the brown pelican, the southern bald eagle, the osprey, the South 
American kestryl, the Florida sandhill crane, the white crowned pigeon, and others. The Florida 
Committee on Rare and Endangered Plants and Animals listed 72 taxonomic species of birds, 
twenty seven of which occur within the terrestrial and freshwater wetlands of the lower 
Everglades (Schomer and Drew, 1982). The Florida coast serves as turtle nesting habitat, 
supporting the second largest nesting population of loggerhead turtles in the world (Thompson, 
25 
