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Chesapeake Bay
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Other Changes in StoreThe loss of marshes, beaches, and islands are only some of the potential impacts of global warming in the Chesapeake Bay region. Other changes also are possible, including warmer temperatures, increases in precipitation, more frequent and more damaging floods from coastal storms, lower oxygen levels in the bay, and lower water quality. Not all of the changes may be harmful: for example, an increase in rainfall could bolster the region's freshwater supply. Scientists cannot predict future climate or its effects with certainty, but the best research available today suggests that global warming could have significant impacts on the mid-Atlantic region.
The diverse habitats of Chesapeake Bay and its surrounding watershed — including underwater grass beds, salt marshes, forested wetlands, and upland forests — provide homes for more than 2,700 species of animals and plants. Many of these habitats will be affected by climate change.
During the past 100 years, the average temperature in the mid-Atlantic region has risen by nearly 1°F, and precipitation has increased by up to 10 percent. Compared with today's temperatures, climate models project that the region's climate may become approximately 2°F warmer by 2030, with an additional 3°F to 8°F average temperature increase by the end of the 21st century. Models project that precipitation in the region also will increase during the next 100 years.
More precipitation might bring more freshwater and nutrient runoff into Chesapeake Bay, which may reduce the bay's salinity and the amount of oxygen available for fish and other aquatic life. High nutrient levels can lead to algal blooms, reducing the water's clarity and the amount of light available to submerged aquatic vegetation. Excess nutrients also stimulate the growth of algae on the leaf blades of submerged vegetation, further reducing the amount of light available to the plants for growth.Finally, high nutrient levels in the bay may be linked to outbreaks of the toxic organism Pfiesteria, which some scientists believe killed many bay fish in 1997.
Oysters also may suffer if bay waters become fresher. The enormous volume of freshwater that entered Chesapeake Bay from Tropical Storm Agnes in 1972 killed an estimated 2 million bushels of market-size oysters and eliminated most oyster larvae in the bay.
On the other hand, sea level rise may cause water in the bay to become saltier, encouraging the spread of oyster diseases. Warmer water temperatures, especially in winter, are also linked to oyster diseases. The oyster diseases MSX and Dermo are caused by warm-water parasites.
Chesapeake Bay has very low levels of dissolved oxygen, due in part to the heavy load of nutrients from agricultural runoff and municipal wastewater treatment discharges in the freshwater that flows into the bay. The low oxygen levels make life difficult for fish and other aquatic animals. Global warming may make it even harder for them to survive. For each degree Fahrenheit that the bay's water warms, the capacity of water to dissolve oxygen decreases by about 1.1 percent. Higher water temperatures also raise the metabolic rates — and hence the oxygen requirements — of cold-blooded aquatic animals, such as invertebrates and fish.
Warmer waters could be harmful for Chesapeake Bay species that are at the southern end of their range, such as the soft clam. But warming also could help warm-water species at the northern end of their range survive by reducing the severity of cold snaps during winter.
Higher sea levels would allow storm surges to penetrate farther inland than they do today, placing more structures and people at risk.
Finally, the impacts of climate change will come on top of the many stresses that already affect plants and animals in Chesapeake Bay, such as excess sediment and nutrients, overharvesting, toxic pollutants, and habitat loss from land development by humans.
What is Global WamringThe 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. |
What Can Be Done?To address the threat of climate change, first we have to understand the risks. Many scientists are analyzing the potential impacts of climate change in the Chesapeake Bay region. Their findings will help identify the areas of risk to people, animals, and plants in the bay, Assateague Island, and other important ecosystems in the area.
Efforts to restore the bay, such as the federal-state Chesapeake Bay Program, can help reduce current stresses on life in the bay and make natural ecosystems more resilient to some impacts of climate change.
The Maryland and Virginia state governments could help coastal areas adapt to rising sea levels by enacting plans indicating the areas that will be protected and those that will be abandoned to the sea. Some areas may require regulations to prohibit revetments or bulkheads, specify erosion-based setback rules for new construction, or require buildings to be moved landward as the sea rises. Other areas may need structural protection, landfill, or beach nourishment.
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".)
Assateague IslandAssateague Island stretches along the Atlantic coast of the Delmarva Peninsula, between Chesapeake Bay and the ocean. Assateague is one of many barrier islands that rim the eastern coast of the United States. Barriers are narrow islands that run parallel to the continental shoreline, with a protected bay lying between the island and the shore. The bay shores of barrier islands typically are lined with salt marshes.
Like other barrier islands, Assateague is constantly changing shape and geographical position. At one time, it lay far seaward of where it is today.
Large undeveloped barrier islands like Assateague are likely to narrow and "roll" landward during the next century. Sea level rise and storms will cause Assateague Island to erode until it becomes narrow enough for storms to push sand over onto the bay side. Like a rug being rolled up, the island will remain above sea level and roll gradually toward the land.
The bays on the landward side of the island — Sinepuxent and Chincoteague Bays — will expand inland as the sea rises, flooding the coastal plain. The future Assateague Island and its bays may look generally similar to what we see today, but they will be farther inland. The birds and other wildlife that attract so many visitors to Assateague National Seashore and Chincoteague National Wildlife Refuge should still find good habitat conditions as the island migrates landward. However, many of today's popular visitor sites, such as the wildlife loop road that encircles Snow Goose Pond at Chincoteague refuge, eventually will disappear.
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"Assateague Island National Seashore is one of the most dynamic environments administered by the National Park Service."
- Robert Dolan, Bruce Hayden, Jeffrey Heywood, Atlas of Environmental Dynamics,
Assateague Island National Seashore, October 1977 |
Some barrier islands may not be as lucky as Assateague: If the sea level rises too quickly, islands can break up and drown in place. The Isles Dernieres barrier chain along the Louisiana coast was once a single island. Storm erosion and a relative sea level rise of three feet per century broke Isle Dernier into five smaller islands that are expected to be completely submerged by the year 2020. Due to the rapidly subsiding land along Louisiana's coast, the sea level relative to the land level is rising faster than in other parts of the country.
The northern end of Assateague may be more vulnerable to sea level rise than the rest of the island, as it has been sand-starved for many decades by jetties at Ocean City Inlet that trap the sand. Personnel at Assateague National Seashore are working with the U.S. Army Corps of Engineers and the State of Maryland to create a system that will restore sand transport to northern Assateague.
Condominiums, hotels, shops, and other coastal development on barrier islands will become increasingly at risk of flooding and storm damage as the sea rises. Ocean City, Maryland, is built on the lower end of Fenwick Island, which is just north of Assateague. For the past 10 years, Ocean City has had to bring in sand to replenish its eroding beach. The beach needs replenishing more frequently now than it did only a few years ago because of increased erosion, and sea level rise could double the rate of erosion in the next 30 years.
A powerful northeaster that hit the mid-Atlantic coast in early March 1962 caused an estimated $7.5 million in property damage to Ocean City. A similar storm today would cause hundreds of millions of dollars in damage because the island has become densely developed over the past 20 years. Future storms may cause even more harm because storm surges and waves will be superimposed on higher sea levels.
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