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South Florida
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The Rising TideHow does global warming lead to sea level rise? A warmer climate causes water at the surface of the ocean to expand and adds large quantities of freshwater runoff from melting glaciers and ice sheets. In areas where the land is sinking, as it is along much of the southern Atlantic and Gulf coasts, the effects of rising seas are even more pronounced.
South Florida's sea level has risen about 12 inches since 1846. It is still rising today, at a rate that is equivalent to 8-16 inches per century. That rate is 6-10 times faster than the average rate of sea level rise along the south Florida coast during the past 3,000 years.
"Competition [for diminishing freshwater resources] will surely result in a no-win situation for humans and the Everglades under a scenario of global warming and rising sea level."
- Intergovernmental Panel on Climate Change, 1995 |
If the current trend were to continue without any additional global warming, the sea along the south Florida coast would climb another 3 inches by 2025 and 10 inches by 2100. But the global warming predicted for the decades ahead is expected to accelerate sea level rise. During the next 25 years, the sea is likely to rise 5 inches rather than 3. By 2100, the best available science indicates that south Florida seas will be approximately 20 inches higher than they were in 1990. There is even a 5 percent chance that the sea will rise by as much as 36 inches.
Rising seas may cause the Everglades system to drain more sluggishly. Saltwater may move up rivers and into aquifers, contaminating freshwater ecosystems and groundwater. Mangroves may spread inland and invade formerly freshwater marshes. Rising sea levels in conjunction with storms are likely to increase coastal flooding and erosion, causing more particulate matter, dissolved organic matter, and nutrients to flow into bay waters, affecting animal and plant life in the bays and coral reefs.
Looking beyond the next century, EPA researchers estimate that the sea in south Florida probably will rise 30 inches above 1990 levels by the year 2150. At those levels, most of Everglades National Park could essentially become an extension of Florida Bay. South Florida's key deer, alligators, panthers, and other wildlife would be squeezed into a shrinking habitat bounded by the shoreline advancing inland from the south and west, suburban development expanding from the east, and agricultural development in the north.
What is Global Warming?The Earth's climate has changed in the past, and will continue to change naturally in the future. Ice ages, long warm periods, and short-term fluctuations in temperature and precipitation are all elements of the global climate's natural variability.
Today, the average global temperature is rising. Is that natural? Some of the temperature increase can be explained by natural factors. But many scientists believe that a portion of the warming trend may be caused by humans. Human activities are creating a buildup of greenhouse gases — primarily carbon dioxide, methane, and nitrous oxide — in the atmosphere. The heat-trapping property of these gases is undisputed. Although scientists do not know exactly how the Earth's climate responds to increases in greenhouse gases, they do know that the current warming trend is consistent with changes that would be expected from the increase in greenhouse gases.
Scientists generally believe that the burning of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide in the atmosphere. Fossil fuels burned to run cars and trucks, heat homes and businesses, and power factories are responsible for almost 99 percent of U.S. anthropogenic carbon dioxide emissions and about 20 percent of our nitrous oxide emissions. Of the carbon dioxide emissions, industrial activity accounted for 33 percent in 1997. Personal and commercial transportation accounted for 30 percent, and residential and commercial energy use accounted for 19 and 16 percent, respectively. Increased agriculture, deforestation, landfills, industrial production, and mining also contribute a significant share of carbon dioxide, methane, and other greenhouse gas emissions.
Average global temperatures at the Earth's surface have increased 0.6-1.2°F since the late 19th century. The 10 warmest years in the 20th century all occurred in the last 15 years. Snow cover in the northern hemisphere, floating ice in the Arctic Ocean, and the areas covered by mountain glaciers have all decreased. Globally, sea level has risen 4-10 inches during the past century. Worldwide precipitation over land has increased by about 1 percent, and the frequency of extreme rainfall events has increased throughout much of the United States.
Although it is impossible to predict future changes in climate with certainty, many scientists believe that the continued addition of greenhouse gases to the atmosphere is likely to raise the Earth's average temperature by several degrees in the next 100 years. Rising global temperatures are expected to raise sea level and change precipitation and other local climate conditions. Changing regional climate could alter forests, crop yields, and water supplies. It also could threaten human health and harm birds, fish, and many types of ecosystems. |
Changes in StoreIn addition to the rising seas, scientists expect global warming to lead to changes in temperature and precipitation that will affect plants and wildlife.
Although it is impossible to predict with certainty the future climate of a small region, computer models suggest that the overall climate in Florida may warm and that extremely hot days in summer may become more frequent. A warmer climate could allow heat-loving pest species, such as the invasive Australian Melaleuca tree, to expand their range northward in Florida. However, if warmer winters lead to fewer frosts, tropical plants and trees that are vulnerable to cold temperatures may benefit.
Increases in the atmospheric concentration of carbon dioxide, one of the primary greenhouse gases responsible for global warming, may affect competition and dominance among plant species. Carbon dioxide generally promotes plant growth, but not all species respond alike to higher concentrations of the gas.
Many people wonder if global warming will affect rainfall, hurricanes, or the severe weather events associated with El Niņo and La Niņa. Rainfall has indeed declined in the Keys and parts of south Florida over the last 100 years, while increasing in central Florida and the Florida Panhandle. But scientists do not know to what extent these changes are related to global warming. If rainfall continues to decline in the future, water supplies for south Florida residents could be threatened. Past droughts have led to mandatory water restrictions in the region, a situation that could be exacerbated in the future as sea level rise causes saltwater to infiltrate aquifers.
Scientists also are not certain whether global warming would affect the frequency and severity of hurricanes and tropical storms, or if it would change the frequency and strength of El Niņo and La Niņa events. El Niņo has been linked to the drought and subsequent wildfires that occurred over much of Florida during 1998.
We do know that global warming and sea level rise will add yet another stress to south Florida ecosystems already threatened by urban development, agriculture, air and water pollution, water management practices, and invasions by exotic species. Some researchers are concerned that climate change and sea level rise could help push endangered species like the Florida panther and key deer even closer to extinction, because the remaining populations of these species may be squeezed between the rising sea and human populations. There are 16 endangered and six threatened wildlife species in the four national parks and preserves of south Florida.
Florida BayFlorida Bay is the world's largest sea grass bed and a nursery ground for at least 22 species of commercially and recreationally harvested fish. The bay is a crucial nesting area for American crocodiles and provides year-round habitat for manatees, ospreys, bald eagles, and wading birds.
Florida Bay will be affected by climate change and sea level rise. The bay is likely to become deeper than it is now. As storms superimposed on higher sea levels cause increased erosion of the coastline, Florida Bay's waters may become cloudy with eroded sediments. During the next several centuries, many of the undeveloped keys that currently dot the waters of Florida Bay may disappear as the sea rises.
 Plants and animals that live in the bay are sensitive to changes in the proportion of fresh to salty water. During the 20th century, water management projects in south Florida increased the salinity of Florida Bay by diverting freshwater that formerly flowed in from the Everglades. Salinity is especially high in drought years. High salinity may have played a role in recent mass die-offs of more than 100,000 acres of seagrasses in Florida Bay. Highly saline water from Florida Bay also can harm coral reefs in the Keys.
Scientists are not certain how global warming will affect the salinity of Florida Bay. On the one hand, sea level rise would increase the bay's salinity by adding more seawater to the bay. Warmer temperatures would increase evaporation, making the bay even saltier. But if global warming also causes precipitation to increase, more freshwater could enter Florida Bay during the rainy season. Under that scenario, seagrasses and other plants and animals in the bay could be harmed, since too much freshwater is as harmful as too little.
What Can Be Done?Prevention of human-induced climate change also is an important strategy. Some global warming probably will occur no matter what we do, because some of it is natural. But also, humans have become dependent on fossil fuels. The burning of fossil fuels emits greenhouse gases, which may remain in the atmosphere for years, decades, or even centuries, exacerbating the natural warming. But we as individuals can take action now to reduce our own consumption of fossil fuels by improving energy efficiency and using alternative energy sources. (See "Searching for Solutions" and "What People Can Do"). |
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