By Festa, David
“. . . Ocean surface temperatures worldwide have risen on average 0.9[degrees]F, and ocean waters in many tropical regions have risen by almost 2[degrees] over the past century. This is 30 times the amount of heat that has been added to the atmosphere. . . .” MARINE BIOLOGIST Chris Rader recalls childhood summers when his father, Environmental Defense scientist Doug Rader, would take him diving in the Virgin Islands: “Schools of butterfly fish and Queen angelfish would swim by,” remembers Rader. “I learned to identify hundreds of tropical reef fish.”
Later, as a student at the University of North Carolina, the younger Rader was snorkeling off the Tar Heel coast to study temperate-water fish. Much to his surprise, he saw some of the same tropical fish he had seen in the Caribbean. ‘This was not what I was expecting at all-warm-water fish so far north,” he relates. Yet, the elder Rader confirms that tropical fish showing up’ in temperate waters no longer is a rarity. Ocean specialists have spotted larvae of butterfly fish, angelfish, and other tropical sea life floating in coastal waters as tar north as Woods Hole, Mass. This evidence points to fish shifting their ranges in response to wanning waters.
Observations show that the oceans have been heating up since 1975. Ocean surface temperatures worldwide have risen on average 0.9[degrees]F, and ocean waters in many tropical regions have risen by almost 2[degrees] over the past century. This is 30 times the amount of heat that has been added to the atmosphere, a significant number, even though the ocean has a lot more mass than the atmosphere. Moreover, the incidence of coral bleaching has increased worldwide since 1979, and scientists now generally link these mass events to global warming. The largest bout of coral bleaching ever (1997-98) occurred during the wannest-at least up until that time- 12-month period on record, and in nearly every region of the world. It was a wake-up call that global warming is not just a distant threat.
Scientists have known for a long time that the ocean plays a huge role in climate. Covering 70% of the globe, it stores 1,000 times more heat than the atmosphere, but often overlooked in the public debate on climate change is the ocean’s synergistic role-how it responds to the growing amount of heat-trapping gases in the atmosphere.
“Even five years ago, most people had no inkling of the extent to which global warming was affecting the oceans but, slowly, over the years a consensus has been building,” asserts Environmental Defense marine ecologist Rod Fujita. “Today, we are witnessing impacts that we largely attribute to warming-like the bleaching of corals, changing fish habitat. We’ve gone from denial to talking about how to manage the impacts and reduce the threat of climate change.”
A tidal wave of studies has swept through the scientific community, making headlines and setting off alarm bells that global warming is happening and its impacts are playing out in the ocean right now. One groundbreaking study about the relationship between oceans and the climate, published in Science, “goes a long way in laying to rest the arguments that atmospheric warming is caused by anything other than man-made greenhouse gases accumulating in the atmosphere,” maintains Bill Chameides, chief scientist at Environmental Defense. “This study is a critical piece of the global warming ‘jigsaw puzzle’-one of the pieces that enables us to see the overall picture more clearly.”
In anotner headlining study pointing to the rise in temperatures in the Earth’s oceans, Scripps Institution of Oceanography scientist Tim Barnett declares, “This is perhaps the most compelling evidence yet that global warming is happening right now and it shows that we can successfully simulate its past and likely future evolution.” The findings project water shortages in the western U.S., western China, and the Andes Mountains due to changing rainfall patterns and less snowpack. Two other studies show that, even if we were to stabilize greenhouse gases at 2000 levels, the Earth’s temperature and sea levels would continue to rise over the next 100 years.
“The ship is already in motion, and it will take immediate action to turn it away from the danger ahead,” sums up Environmental Defense climate scientist James Wang.
Since humans began burning fossil fuels like coal and gas for power, huge amounts of carbon dioxide and other heat-trapping gases have been released. From the beginning of the Industrial Revolution, the concentration of these greenhouse gases in the atmosphere has soared to levels higher than at any time in the last 420,000 years, warming the Earth on average by 1[degrees] over the last century.
Oceans and forests naturally absorb COz, and sometimes are referred to as “carbon sinks.” Seawater absorbs heat as well-it can store four times more heat per unit mass than air. In modern times, human activities have pumped CO2 into the atmosphere at a dramatic rate. The oceans have absorbed huge amounts of carbon dioxide and heat in the last 40 years, but not enough to keep these two elements from building up in the atmosphere.
Fujita points out that, because of the huge amount of heat soaked up by water, “The oceans are saving us from faster climate change- in essence, they are a big flywheel that delays rapid overheating of the Earth, putting a brake on the climate system. That’s the good news. The bad news is that the oceans only slow the atmospheric warming down. Once the oceans come to equilibrium with a greenhouse- gas warmed Earth, the excess heat will remain in the atmosphere and things will get much hotter.”
Oceans take up the slack
In effect, the oceans are taking up the slack for the atmosphere and delaying the full impacts of global warming, but where and how the oceans release this accumulated heat is uncertain at this point. What scientists do know is that, even if we cut our emissions of heat-trapping gases today, it would take centuries for gases now in the air to fall to more historically balanced levels-and it appears that changes are afoot in global ocean dynamics which could have profound ecological impacts. Significant changes loom for seabird and fish communities, ocean circulation patterns, and basic processes of ocean chemistry. Without emissions cuts, the effects will be even worse. “The natural vagaries of climate plus greenhouse effects add up to substantial changes we will need to deal with-and plan for,” contends Doug Rader.
Scientists cannot predict exactly how climate change will affect the ocean. “The impacts of global warming are likely to vary tremendously in different regions, due to the complexities of ocean circulation, chemistry, and biology. Increased temperatures, altered wind patterns, and increased carbon dioxide concentrations will interact in surprising ways, no doubt,” Fujita explains in his book, Heal the Ocean.
The oceans’ global system of currents is propelled by the force of cold, salty (and denser) waters sinking in the North Atlantic. This great volume of water falling downward, sort of a giant underwater waterfall, pulls water at the surface of the Atlantic Ocean north and creates a current that flows along the bottom of the seas. This movement is called the ocean conveyor-and what powers all that falling water is cold temperatures in the polar region and salinity.
Changes are under way in the mix of the ocean’s salt and freshwater that dramatically could affect this system of currents. The mix of salty and fresher water is determined by rainfall and evaporation patterns (or hydrological cycle). Changes in patterns of precipitation and evaporation have been altering the seas’ saltiness and freshness. The system of currents takes 1,000 years to go full cycle. Warm water is chilled in the far North Atlantic and sinks. The cold, salty current flows south near the bottom.
As average temperatures rise worldwide, glaciers and sea ice are melting, and evaporation and precipitation patterns are shifting. With more freshwater pouring into some regions and more evaporation occurring in others, parts of the ocean are becoming fresher, while others are becoming saltier at a visible pace. Studies indicate that tropical Atlantic and Pacific waters have become saltier, while Arctic waters have become fresher. In one study, authors Ruth Curry (of the Woods Hole Oceanographic Institution) and Cecilie Mauritzen (of the Norwegian Meteorological Institute) suggest that, by the end of the century, the freshening of Northern Atlantic waters could slow or disrupt the ocean conveyor.
From 1965-95, a volume of freshwater almost as large as that in the Great Lakes melted from the glaciers in the Arctic and flowed into the normally salty North Atlantic. That nearly is 20,000 cubic kilometers of freshwater. By comparison, the entire outflow from the Mississippi River each year is about 500 cubic km. If the North Atlantic loses too much salinity, one of the primary forces driving circulation could weaken. Since fresher water is less dense, it does not sink in saltier water. If waters were to stop sinking in the North Atlantic, existing currents could slacken or change course, leading to altered climate patterns. A slackening of the conveyor could slow or change the course of the Gulf Stream-a warm current that gives northwestern Europe a milder climate than it normally would have so far north-plunging Europe into a colder era even as the rest of world experiences warmer temperatures, more droughts, and excess flooding. Circulation patterns also deliver nutrientrich waters to strategic parts of the ocean. A disruption of the ocean conveyor would interfere with this delivery system of nutrient supplies to sea animals and could have dire consequences for the intricate web of marine life. As surface waters heat up, the vertical layers of sea water could mix less with each other, an effect called vertical stratification. Upwellings of cold, nutrient- rich waters would become less frequent, thus diminishing blooms of phytoplankton, microscopic plants that anchor the marine food chain. On top of that, phytoplankton use carbon dioxide for photosynthesis. If plankton become depleted, the oceans could not remove as much carbon dioxide from the atmosphere.
The marine food chain already may be showing signs of breaking down. In 2005, on the West Coast of the U.S., and, in 2004, in Great Britain, hundreds of thousands of seabirds failed to breed. Dead cormorants and Cassin’s auklets have washed up on beaches. Juvenile rockfish counts are the lowest they have been off California in more than 20 years. Most alarming, small crustaceans like krill-the base of the ocean’s food web-have suffered steep declines.
The culprit for the collapse appears to be slackening upwellings, which have decreased phytoplankton blooms in these coastal areas. Fewer phytoplankton mean fewer fish, leaving the birds to face mass starvation. Scientists speculate that this decrease in food supply could be an effect of global warming. With no mixing, nutrients at the surface would be used up in about 50 years. Beyond that, “Deep waters would be deprived of oxygen and food from the surface,” emphasizes Fujita, “and many deep sea animals could be affected.” Monitoring of ocean waters off Hawaii over the last 20 years shows that waters in the area are indeed more stratified and upwellings are decreasing.
El Nino events are natural variations in weather patterns that normally occur about every four or five years and last for one to two years. They are tied to trade winds. This peculiar weather pattern sometimes triggers severe weather changes across the Pacific Ocean and other parts of the world. During an El Nino, patches of unusually warm water develop in the tropical Pacific near the Galapagos Islands off South America. Weaker trade winds cause fewer upwellings and less deep mixing of cold and warm waters. El Ninos promote warmer ocean and land temperatures. “Such a strong global event has profound effects,” notes Fujita. For one, productivity in tropical waters drops. The nutrient-poor warm water does not fuel the food web like the nutrient-rich cold water from the deep does.
Pacific salmon populations fell sharply during a strong El Nino in 1997-98, when ocean temperatures rose 6[degrees]. Many rockfish species did not fare well, either, although there were some winners during the same event. Pacific hake, cod, herring, and sardines reproduced well. During the same period, the most widespread and severe coral bleaching event on record took place.
Rainfall and evaporation patterns change during an El Nino. Many normally arid areas get more rainfall and heavy thunderstorms: to wit, California and Peru often experience heavy rainfall and flooding, while normally wet Indonesia may suffer drought and massive forest fires. El Ninos have become more frequent since 1976. Many ocean specialists say that these events possibly will occur more frequently and last longer as the Earth heats up.
Warmer waters already are affecting marine life. “Shifts in distributions of fish and other creatures are one impact of global warming that is pretty obvious,” according to Fujita. For example, off the coast of central California near Monterey over the last 60 years, southern warm water species generally have increased in abundance, while northern cold water species have declined. From 1951-93, water temperatures rose an average of 2.7[degrees] and Zooplankton declined by 70%. During that same period, Pacific salmon fisheries collapsed. Warmer waters and poor fisheries management were contributors. Sea birds, fur seals, sea lions, and gray whales died in unusually high numbers during record warm years since there was less plankton.
Doug Rader is studying the Albemarle and Pamlico sounds in North Carolina to see “what global warming means for real places.” He sees evidence that Atlantic species of fish are responding to changes in water temperatures. “We’ve seen a decline in black sea bass in southeast U.S. waters but, farther north, black sea bass is more abundant.” Rader also is witnessing large increases in Gray triggerfish, a warm water reef fish, and, as noted earlier, he and other ocean specialists have spotted larvae of butterfly fish, angelfish, and other tropical species floating in northern coastal waters. “These kinds of larvae would normally be killed off by the cold, although we don’t know if, over the long term, these species will survive in higher-latitude waters.”
As waters warm, the more native species’ ranges are likely to shift and habitats become more vulnerable to invasive non-native species. “We do know that waters in the mid Atlantic are now suitable for exotic invasive tropical species to survive without natural predators,” continues Rader. Populations of Pacific red lion fish, a “big showy venomous fish popular for saltwater aquariums,” have exploded in the mid Atlantic, apparently escaping in large enough numbers to thrive. “This fish was not around in the 1980s, and they are now breeding from Florida to North Carolina,” Rader reports.
Rising seas also will have cascading effects on fish habitats, insists Rader. In North Carolina, the sea level has risen by slightly more than one foot since the 1920s, a rate of 1.5 feet per century. Scientists say the rate will double within a century. As seas rise, more salt water will penetrate fresh and brackish sounds, converting freshwater into brackish water, and brackish marsh into salt marsh. It also will “drown” some marshes that cannot keep up with the rising waters. These changes could devastate key feeding and nursery grounds from Florida to Maine for a wide variety of marine life, including dolphins, snappers, shad, and river herring. This means “profound consequences for the commercial and recreational fisheries sustained by these estuaries,” proclaims Rader.
Slackening upwellings of nutrient-filled waters on the West Coast have had dire consequences for fish and seabirds. In July 2005, The San Francisco Chronicle reported that “plankton have largely disappeared from the waters off Northern California, Oregon, and Washington” and, in “perhaps the most ominous development, seabird nesting has dropped significantly on the Farallon Islands off San Francisco, the largest Pacific Coast Seabird rookery south of Alaska.” The collapse of the nesting season has not been seen in the 30 years of record-keeping for the islands’ seabirds. In 2004, hundreds of thousands of Scottish seabirds failed to breed, which never has happened in the time that they have been monitored. Scientists link this phenomenon to global warming, specifically the dearth of phytoplankton blooms. Fish starve, leaving no food for seabirds. “If this trend continues, that does not bode well for many fish and seabirds,” cautions Wang.
Coral reefs are taking hits around the world from many stresses- pollution, destructive fishing practices, disease-but perhaps the most damaging is warmer water. Corals host tiny algae called zooxanthellae that give them their color as well as a food source. When stressed by excessive heat or cold, many corals expel their algae and “bleach.” Corals are very sensitive to temperature changes and thrive within a narrow band of heat and cold: a temperature increase of 1.8[degrees] can trigger them to bleach. After severe bleaching, they often die.
A mass bleaching of corals occurred during a very warm 1997-98. About 16% of the world’s reefs seriously were damaged. Coral reefs that had persisted for as long as 1,000 years simply perished. Continued wanning could make mass bleachings an annual event. “Within a century,” asserts Doug Rader, “very large portions of coral reefs could be gone.” Rader has spent years diving and snorkeling in the Caribbean and has seen firsthand the decimation to reefs: “The damage is bad enough from coral and sea urchin disease, which has nearly destroyed elkhom and staghorn reefs throughout the region; then you add to that more frequent bleaching events and the fact the seas are unable to support reef-forming coral because waters are absorbing too much carbon dioxide. It seems hard to believe that it is happening-and happening on our watch.”
Yet, there remains a sliver of hope. “Corals are sensitive but also very resilient-if conditions are right,” relates Fujita. “If we can reduce some of the other direct stresses from human activities on coral reefs, like pollution from nonpoint sources, perhaps that may also enable reefs to cope better with indirect threats like climate change.”
Creating more protected areas for coral reefs may help them better withstand the rigors of too-warm water and be less vulnerable to mass bleachings. Kelp forests seem to be able to cope with warmer water better in marine reserves but, even so, cautions Fujita, “The number of corals that can adapt to or withstand such dramatic, rapid changes may be just a tiny fraction-coral reefs may likely prove to be the first ecological victims of unchecked global warming.”
Besides the incalculable loss of these “rain forests of the ocean” and the colorful reef fish, turtles, sharks, lobsters, shrimp, sea urchins, sea stars, anemones, and sponges that depend on them, the economic losses would be enormous in regions that depend on reefs for food and tourism income. Coral reefs provide an estimated $375,000,000,000 in economic benefits each year globally. Coral reefs face yet another threat induced by carbon dioxide pollution. A 2005 report by the U.K.’s Royal Society found that the increased CO^sub 2^ being absorbed by the ocean over the last two centuries is making it more acidic. When carbon dioxide dissolves into the ocean, it produces carbonic acid, which corrodes the limestone structures of coral reefs and shells of marine organisms. “The world’s seas are naturally alkaline,” explains Fujita, “and thousands of marine animals have evolved and flourished for eons in this environment. Many of these creatures will not survive in an acid sea.” In acidic water, “there is a greater tendency for seashells to dissolve, like putting them in vinegar, but not quite as dramatic,” explains Wang.
Tropical reefs in danger
As waters become more acidic, coral reefs and other marine ecosystems could suffer. The report’s panel of scientists points out that acidification hurt tropical and subtropical reefs the most, but that cold water corals are in danger as well. Since acidification is “irreversible in our lifetimes, the only practical step is to reduce emissions of carbon dioxide as quickly as possible to minimize large- scale, long-term harm to the world’s oceans and marine ecosystems,” the report warns.
The debate over global warming has shifted from whether it is happening to how to avoid catastrophic damage. “We’re facing warming waters and major alterations in many oceanic processes and ocean chemistry, damage to coral reefs, and effects from sea level rise on marine ecosystems,” affirms Doug Rader. “These are impacts we need to plan for and develop strategies for adaptation.” Rader, who played a key role in developing North Carolina’s Coastal Habitat Protection Plan, says similar “road maps” are needed for all coastal regions around the country-and ultimately the world. He is working on a blueprint for Pamlico and Albemarle sounds to project scenarios of how sea level rise, changing habitats, invasion of exotic species, pollution, and other impacts of human intervention will play out by the end of the century. “The bottom line is that the area will not look like what it does now-but what it will look like and what we can do to limit the damage is the big question?”
Rader is optimistic that North Carolina is up to the challenge and sees the state as one of the leaders in planning for broad- scale changes to ocean ecosystems. The South Atlantic Fishery Management Council has drafted the first-ever fishery ecosystem plan and the state passed a landmark bill to address climate change. Above all, Rader entreats, we need to invest in a new vision of the future-a national commitment to tackle climate change, one that engages diverse groups of stakeholders all working toward a common interest that seeks to balance economic gains with low-impact development and protection of critical habitats. “This would be an engagement similar to the plan to restore and protect the Everglades ecosystem, which was really quite remarkable in that so many different kinds of people managed to agree and get the plan off the ground”
For its part, Environmental Defense partnered with The Nature Conservancy and commercial fisherman to create no-trawl zones off California. (Trawlers are huge fishing boats that drag nets across the sea floor and damage habitat and catch sea life that is not used commercially.) Together, these groups protected nearly 4,000,000 acres of spectacular underwater habitat, from deep canyons and seamounts to coral gardens and reefs. The groups shared information on where the fish were and where the reserves should be. The protection of this vast area shows that bringing diverse groups together to forge creative solutions can work even on problems that seem impossible to solve. As broad and complex a challenge as global warming is, with a commitment to action, we can find ways to cope and head off the worst impacts.
Another tactic is to lessen other threats to marine ecosystems, especially in locales rich in biodiversity. Reducing destructive fishing practices, keeping habitats healthy, and curbing pollution may help sea life withstand global warming impacts. Creating marine protected areas (MPAs) based on careful scientific assessments can assist in buffering ecosystems as well. “We can help manage for resilience by working into protection plans factors such as siting the protected area around coral reefs known to be most resilient to warm water, and designating migration zones or migratory corridors for fish and marine plants, like those for land animals,” declares Fujita, a member of the Federal advisory committee working on a national network of MPAs.
Yet, all these measures only may serve merely to soften the blow of climate change if we do not act quickly to reduce emissions of carbon dioxide. “There is no question we need more money invested in ocean research-it is grossly underfunded,” argues Rader, “and there is so much about the oceans we don’t know. We need more high- quality data on fisheries and ecosystems, and we need more extensive monitoring to take the pulse of the ocean-that is, to measure temperature, salinity, currents, and biological processes.”
Still, we know enough today to take action now to address global warming. “Humanity may have only a narrow window of time leftperhaps a decade or so-to begin the emissions reduction needed to stabilize greenhouse gas concentrations at a level that can avert devastating and irreversible impacts from global warming,” Wang concludes.
“As average temperatures rise . . . glaciers and sea ice are melting, and evaporation and precipitation patterns are shifting. With more freshwater pouring into some regions and more evaporation occurring in others, parts of the ocean are becoming fresher, while others are becoming saltier at a visible pace.”
“Coral reefs are taking hits around the world from many stresses- pollution, destructive fishing practices, disease-but perhaps the most damaging is warmer water. . . . When stressed by excessive heat or cold, many corals expel their algae and ‘bleach.'”
“Reducing destructive fishing practices, keeping habitats healthy, and curbing pollution may help sea life withstand global warming impacts. Creating marine protected areas (MPAs) based on careful scientific assessments can assist in buffering ecosystems as well.”
David Festa is oceans program director for Environmental Defense, Washington, D.C. This article was adapted from the organization ‘s “Oceans Alive ” report.
Copyright Society for Advancement of Education Sep 2008
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