FORT LAUDERDALE — The debate over global warming tends to focus on future perils — scary maps of flooded suburbs, the northward creep of tropical diseases, rich farmland turning into desert.
But some of the effects of global warming have already arrived in South Florida, as coastal cities flood more frequently and overheated corals turn white and die. The region's temperatures have not gone up, however, and many scientists say climate change has had little effect on hurricanes.
While most climate scientists agree the Earth has warmed over the past century, they say it's difficult to assess the impact of slight temperature increases on complex natural systems.
"There is general consensus among scientists that climate change is occurring and that human activities are influencing that," said James W. Jones, director of the Florida Climate Institute at the University of Florida. "A lot of the controversy stems from the fact there's a lot of uncertainty about how much it's changing and how fast it's changing. … We need to go into the middle of this debate and not say nothing is going to happen and not say the sky is falling."
The most immediate, easily measured and incontrovertible impact of global warming on South Florida is a rise in sea levels that has already generated flooding in coastal cities.
The tide station in Miami Beach has registered an increase of seven inches since 1935, according to the National Oceanic and Atmospheric Administration. An older station in Key West has measured an increase of eight inches since 1920.
Although South Florida is considered among the most vulnerable parts of the United States to climate change, the region has so far escaped the most obvious consequence: higher air temperatures.
"That raises complacency that climate change is not affecting us so why should we care," said Misra Vasu, assistant professor of meteorology at Florida State University's Center for Ocean-Atmospheric Prediction Studies. "That's a dangerous attitude to take. Climate change has no borders."
Higher ocean temperatures have killed corals along the garland of reefs that stretch from Martin County to the Dry Tortugas, vital elements of the marine environment and major tourist draws that support fishing, diving and snorkeling.
A major coral die-off in the Keys took place after corals bleached, expelling the algae which give them color and nutrition, said Richard Dodge, director of the National Coral Reef Institute of Nova Southeastern University.
The number of major hurricanes — defined as those with sustained winds of 110 mph or more — has more than doubled since 1995.
Chris Landsea, science and operations officer for the National Hurricane Center, said the slight increase in global temperatures is dwarfed by factors such as La Nina, the eastern Pacific cooling that nurtures Atlantic hurricanes.
Global warming has probably added 1 or 2 miles per hour to current hurricane wind speeds, he said.
Landsea, Kerry Emanuel of the Massachusetts Institute of Technology and other prominent hurricane researchers collaborated on an article last year that says global warming will lead to less frequent but more powerful hurricanes by the year 2100.