The Great Barrier Reef, Australia - The Weather of the Future - The Weather of the Future: Heat Waves, Extreme Storms, and Other Scenes from a Climate-Changed Planet - Heidi Cullen

The Weather of the Future: Heat Waves, Extreme Storms, and Other Scenes from a Climate-Changed Planet - Heidi Cullen (2010)

Part II. The Weather of the Future

Chapter 6. The Great Barrier Reef, Australia


Joanie Kleypas and I first met in 2001, when I moved to Boulder, Colorado. I had just completed my postdoc at Columbia University and had decided to head west to begin work as a research scientist at the NCAR. Kleypas, a marine ecologist and geologist who uses climate models to study the health of coral reefs, had an office down the hall from mine.

At the time, I was studying a drought that had devastated a large stretch of central and southwest Asia. More than 60 million people across the region were in dire need of rain; and Afghanistan had been especially hard hit, as the drought came after two decades of political instability and economic isolation. I was looking at how large-scale climate patterns, like El Niño, might potentially help predict big droughts in the future and prevent such devastation. Whenever I needed a break, I’d stop in at Joanie’s office to talk about her research on coral reefs. I remember thinking that Joanie was really lucky, because she studied beautiful places that were untouched by human activity. I loved listening to her talk about coral reefs and her travel to exotic places like Tahiti, the Caribbean, and, perhaps best of all, Australia’s Great Barrier Reef.

I checked in with Kleypas recently to see how things were going with the Great Barrier Reef as well as to get a sense of what kind of impact global warming was expected to have on reefs in the coming years. She wasn’t feeling so lucky. “I work on coral reefs, for God’s sake. The entire coral science community is depressed,” Kleypas admitted.

The Great Barrier Reef (GBR) is the largest tropical coral reef system in the world. It contains nearly 3,000 reefs built by more than 360 species of hard coral, and it attracts a wide variety of marine life. The GBR provides shelter to more than 400 types of sponges; 1,500 unique species of fish; 4,000 varieties of mollusks; 500 kinds of seaweed; and 800 types of echinoderms, which include starfish and sea urchins. It is bursting with activity, an oceanic metropolis analogous to Paris or New York. I grew up in New York, but given the choice, I would have much preferred growing up with a view of the GBR. It extends more than 1,200 miles along the northeast coast of Australia, and its area is about that of 70 million football fields, or half the size of Texas, which is where Kleypas is originally from.

As an undergraduate, Kleypas studied oceanography and marine biology at Lamar University in Beaumont, Texas. She had learned how to scuba-dive, thanks to her brother, and she dreamed of leaving the murky waters of the Gulf of Mexico for the majesty of the GBR. That dream came true when she received a Fulbright scholarship to study in Australia. She completed her PhD dissertation on the GBR and finally had a chance to see many of the things she only read about in textbooks. The GBR, home to six of the world’s seven species of marine turtle, 30 percent of the world’s soft coral varieties, and several hundred types of seabirds, became her backyard when she moved to Townsville, a small city of about 100,000 in the state of Queensland.

Townsville sits along the central part of the GBR and is a mecca for coral reef research. It’s the site of James Cook University, where Kleypas studied, as well as the Australian Institute of Marine Science and the Great Barrier Reef Marine Park Authority. Townsville is about as close as you can get to the GBR and still breathe air. It is on the edge of the GBR lagoon, the reef just a thirty-minute ferry ride away. Kleypas did the reverse ferry commute for a while when she moved to Magnetic Island, population 2,107. More than half of this 20-square-mile island, known as “Maggie” to the locals, is designated a national park, so chances are you’ll see more wallabies and koalas there than you will people. Kleypas rented a room from Lyndon DeVantier, one of the world’s best field taxonomists for corals. “I would take my bike on the ferry and ride to the university in Townsville every day. It was an idyllic existence and I would have loved to have stayed,” she says a little wistfully.

Kleypas began her career as a geologist interested in using corals to study changes in sea level. When she arrived at James Cook University, she and a team of researchers would go out for weeks at a time to remote sections of the GBR. They would cart out a small rig that allowed them to drill into the massive coral reef structures and extract cores. “Coral reefs are like big dipsticks,” Kleypas explains. “They can tell us a lot about the geologic history of reef growth as sea level goes up and down.” Despite being seasick from the strong currents and the 10- to 20-foot tides that swept the reef twice a day, Kleypas loved the GBR. And her hard work led to new insights about it. She and her team learned that since the end of the last ice age, the GBR had flourished or faltered depending on a delicate balance of conditions that included sea level, light, sediments, temperature, and circulation patterns. At the time, they weren’t even thinking about carbon dioxide. They are now.

Corals have probably existed on the GBR for more than 25 million years.1 The corals first formed during the geological era known as the Miocene. It was during the Miocene that India slammed into Asia and created the Himalayas. The Miocene also was a time when the Australian continent was on the move. As Australia tectonically made its way into the tropics, the shift to warmer ocean temperatures initiated the growth of some corals. Think of them as the very first version of the GBR, although back then the corals didn’t form large structured reefs.

According to the Great Barrier Reef Marine Park Authority (GBRMPA), the earliest record of complete reef structures dates back about 600,000 years. Research suggests that the current reef structure started growing above this older platform about 20,000 years ago, during the Last Glacial Maximum (LGM), the peak of the last ice age. At the time, much of the Earth’s water was locked up in the form of ice, so the sea level was about 390 feet lower than it is today.

As the ice age came to an end, global temperature began to increase and the ice slowly retreated to the poles and mountaintops where it had originated. By around 13,000 years ago, corals began to move into the hills of what had been Australia’s coastal plain but was now underwater. At the time, the sea level was still 200 feet lower than it is today, but the coastal plain had already been swallowed up by the sea: only a few islands protruded out of the water. As the little islands slowly became submerged beneath the ocean, the corals finally had a place to set up shop in earnest. Scientists estimate that the present-day, living reef structure is between 6,000 and 8,000 years old; in other words, it dates from the period during which the sea level is thought to have finally stabi- lized.

Think of the modern GBR as a living veneer draped over ancient limestone. “The reef is like a layer cake,” Kleypas explains; “every time the sea level rises, the reef adds a new layer.” Today, that big layer cake helps to feed hundreds of thousands of Australians, because it brings in about $6.9 billion annually from tourism and other sources. What Captain James Cook identified as the perfect spot for a prison colony in 1770, when he surveyed the place then called New Holland, is now recognized as a World Heritage Site. So much for first impressions.

It’s lucky for the GBR that Australia drifted into the tropics during the Miocene. Of all regions of the ocean, corals like the tropics best. Kleypas calls the reefs in this range, the band that stretches from 30°N to 30°S, the vacation reefs. The GBR alone has become a vacation destination for more than 2 million people each year.

You can find corals outside the tropics, too. A sturdy, brave few have inched their way out of their traditional comfort zone into places like Japan and Bermuda. But the farther poleward you go, the less the corals can build and actually reach the size associated with a true reef community. And it’s the reefs that contain all the staggeringly beautiful biodiversity. “They get puny as you move north,” Kleypas explains. “You can find single corals growing along the North Atlantic coast. But you’ll never find a reef.” The corals simply don’t like cooler temperatures; coolness slows their growth rate, and in some cases colder waters can actually kill them. It seems corals are a bit like Goldilocks; they don’t want things to be too hot or too cold.

By the time she left Australia in 1991 to begin her job at NCAR, Kleypas had fallen in love with the reef ecosystem that she had been using to reconstruct ancient sea levels. And so she shifted her focus from using the reefs as a tool to just studying the reefs themselves. And in the meantime, she’s become a reluctant expert on how global warming is affecting these magnificent ecosystems.

“I really do think the coral reef community is suffering from some form of depression,” Kleypas says. “It’s like this. Imagine you fall in love with the most beautiful, amazing person. And then that person comes down with cancer. It’s an incredibly sad thing. I fell in love with the reefs, not their disease.” But it’s the disease, the rising level of carbon dioxide in the atmosphere, that has captured the attention of an entire generation of marine scientists who are intent on saving the reefs. Kleypas is someone who uses climate models to study the reefs,2 but, ironically, she could never have predicted that her own research career would come to this. She never expected to be forecasting the eventual decline of coral reefs.

That’s not to say everything was perfect with corals before the impact of global warming became glaringly evident. Coral reefs were already showing signs of stress due to local-scale impacts such as agricultural runoff and destructive overfishing practices that include bottom trawling and dynamiting. The overall decline in water quality, due to pollution from coastal development, didn’t help matters either. “Basically, the reefs are in worse shape the closer they are to people. The farther out you go, the better they look,” Kleypas says.

But the global-scale stress due to climate change is adding a new dimension and a new threat to the overall resilience of the coral reef ecosystem. Global warming affects corals in two ways. The first is temperature: the oceans are warming up. The second is ocean chemistry: the oceans are also becoming more acidic.

Corals begin their lives as soft-bodied larvae that float through the water and eventually settle on a hard surface. As they settle, they also partner up with marine microalgae called zooxanthellae. Corals, which are animals, and their microscopic plant roommates are one of the prime examples of what scientists call a symbiotic relationship. Once the coral has partnered with the microalgae, it then sets to work building its skeleton by pulling dissolved calcium carbonate compounds out of the ocean water. The limestone skeleton forms the physical structure we think of as the reef.

A reef is the result of colonies of corals building their skeletons, like a bricklayer laying bricks, steadily over thousands of years. Shacking up with the algae turns out to be a big asset, as corals gain a second helping of food on top of what they are able to pull directly out of the water column. That second helping turns out to be very big. The zooxanthellae can provide up to 90 percent of the corals’ energy requirements. “It’s like if we had algae growing on our skin,” Kleypas explains. “Whenever we’d go out into the sun, we’d get a jolt of extra energy courtesy of that algae.” The corals get their energy from the plant by means of photosynthesis. This symbiotic relationship provides the extra boost that allows the corals to grow so large and form such elaborate reef structures. By definition, the symbiotic relationship benefits both partners. The microalgae get nutrients in the form of waste released by the coral. And of course it is the relationship with the algae that makes corals so pretty. The tissues of corals themselves are clear. Most of the beautiful colors of the coral reef, which can range from the palest pink to darkest black, are a gift from the zooxanthellae.

It’s true that coral reefs like warmth. Ideally, they are adapted to water temperatures ranging between 65°F and 90°F. But corals don’t like a quick spike in temperature. Go a little above the range they’re used to, and trouble starts. That trouble comes in the form of coral bleaching.3

Coral bleaching is the term scientists use to describe the loss of all or some algae and pigment by the coral. As the algae are ejected, the white calcium carbonate skeleton becomes visible through the translucent tissue layer. The coral is weakened because it has lost the food energy provided by the algae. Already, in many places of the world—such as the Maldives, the Seychelles, and Palau—coral bleaching has effectively destroyed more than 50 percent of reefs. In the Caribbean, the numbers are worse, with between 80 and 90 percent of the reefs destroyed by bleaching, disease, hurricanes, and a number of problems related to coastal development, fishing, and other human activities. And future climate model projections, the kind that Kleypas works on, indicate that coral bleaching events are expected to become more frequent and severe over the coming decades.

“Bleaching is what happens when the coral kicks the algae out,” Kleypas notes. “The way I have come to understand it is that the coral can usually handle the hot water, at least until you turn on the lights. When you add sunlight on top of a spike in ocean temperatures, photosynthesis kicks into overdrive.” One by-product of all this photosynthesis is the release of too many free oxygen radicals. Free radicals are the same agents involved in the process of aging in humans. Crank up the photosynthesis, and you crank up the free radical count. “All those free radicals hurt the coral,” Kleypas says. The coral can’t handle the imbalance, so it responds by evicting its tenant: kicking out the algae.

“It’s almost like diarrhea,” she says. “We have symbiotic microflora in our gut, and diarrhea is a common biological response when there is an imbalance.” The diarrhea then serves as a way to get rid of things that are normally good for us. This classic tale of a good relationship gone bad makes you wonder if it might be a metaphor for the larger relationship between the planet and us.

Almost every reef region in the world has suffered extensive stress and in some cases death from coral bleaching. In 1998, a severe bleaching episode took out upward of 16 percent of coral reefs worldwide. El Niño played an obvious role in that event. During El Niño conditions, ocean temperatures in the Indian Ocean and in the central to eastern Pacific Ocean increase. Along with the warmer ocean waters comes a stable mass of high pressure, exactly the kind of weather pattern that ushers in a prolonged period of hot, sunny days. What might look like perfect weather is actually a condition for extensive coral bleaching. El Niño turns the lights on in a very big way.

“As a general rule, corals on the Great Barrier Reef start bleaching once temperatures exceed the average yearly maximum by about 2°F,” Kleypas explains. In some cases it takes a much higher temperature spike to cause bleaching. But scientists say the range is generally between 2°F and 4°F. The actual temperature at which bleaching starts depends on how healthy a reef is to begin with, and how many other stressors, such as pollution and overfishing, are present. But as a general rule, if you crank up the temperature, you will most certainly crank up the stress level.

Average annual ocean temperature around the GBR varies from about 68°F to 79°F. A bleaching event is mostly likely to happen in January, February, and March—the southern hemisphere’s summer months. Conversely, June, July, and August—winter in the southern hemisphere—are cooler. The all-important maximum temperature, which sets the baseline for when bleaching can happen, ranges from about 79°F at the southern end to 86°F at the north- ern end.

The fact that there is a range within which bleaching can happen means that other factors, such as global warming and just plain bad luck, are important in determining the ultimate fate of a coral reef under stress. Add a heat wave or an El Niño event on top of a week where ocean temperatures are at a maximum, and you’ve drastically increased the risk of a coral bleaching event. Global warming is no different. It effectively starts you off at a point closer to the temperature at which corals bleach. Water temperature along the GBR has increased by about 0.7°F since 1850, and the central and southern portions of the reef have warmed up even more, about 1.2°F.

The mass bleaching event of 1998 represents a turning point, according to many experts. They say that mass coral bleaching events have increased in extent and severity worldwide over the last decade. Prior to 1998, many reef systems had never experienced a severe bleaching event. But since 1998, every region has seen severe bleaching, and many regions have experienced significant die-offs because of warmer ocean waters.

And although the GBR is recognized as one of the best-managed and best-maintained coral reef parks in the world, it too has felt the effects of severe bleaching. The 1998 event hit 50 percent of the GBR. Another bleaching event occurred in 2002; this time, 60 percent of the GBR was hit. Fortunately, the death toll was low, but about 5 percent of the GBR is gone. In 2006, another bleaching episode hit the GBR, but it was more localized.

The southern hemisphere summer of 2009 appears to have been another bad break for the GBR. On March 16, 2009, the Australian government reported that a “weather triple whammy” had led to yet another round of coral bleaching. Stifling heat in December, floods in January and February, and winds from the tropical cyclone Hamish arrived one after the other. Ocean temperatures across most of the reef rose 3.6°F to 5.4°F degrees above the December average.

Russell Reichelt, chairman of the Great Barrier Reef Marine Park Authority, said that the “triple whammy” raised serious concerns about global warming. “The forecasts are an increased frequency of extreme events,” he said. All these factors individually cause stress to the GBR. But, Reichelt added, it was their combined impact that was most worrying. “Historically, the reef has been resilient to events like this, but it is rare, possibly unprecedented, to have three such events in such a short period of time.”

Coral reefs are complex and stunningly beautiful ecosystems. And their beauty attracts significant tourist dollars: it is estimated that tourism associated with the GBR contributes more than $5 billion to the Australian economy. This figure doesn’t include other sources of revenue, such as commercial fishing. There are five main commercial fisheries operating in the GBR that together catch about 26,000 tons of seafood each year, with a total gross value of more than $220 million. But the reefs also provide benefits that don’t have a price tag. Coral reefs not only serve to protect Australia’s fragile coastlines from storm damage but also have been used to make several anticancer drugs. So it’s quite accurate to say that coral reefs save lives.

Ultimately, extreme weather on top of the long-term global warming trend spells trouble for the reefs as well as for Australia’s economy. Climate and economic models predict losses to the GBR tourism industry of between $95.5 million and $293.5 million by 2020, as a result of bleaching-related damage. And when you factor in the costs of all the other risks that warmer temperatures pose for Australia—extended droughts, heat waves, wildfires, and so on—you begin to sense that Australia is in grave danger.

Janice Lough, a researcher at the Australian Institute of Marine Science, explains the global warming effect as follows: “This seemingly modest increase in baseline temperatures has been sufficient to take corals over the bleaching threshold in 1998, 2002, and again in 2006. Modeling of future impacts suggest that a 1.8°F to 3.6°F warming of the GBR would result in about 80 to 100 percent bleaching compared to about 50 percent in 1998 and 2002.” In other words, global warming makes bad luck worse. Lough adds that maintaining the hard coral at the heart of the reefs requires corals to increase their upper thermal tolerance limits by 0.2°F to 1.8°F per decade. But how do you teach corals to become more heat tolerant?

Bleached corals aren’t dead; they’re just starving. The loss of their energy-providing zooxanthellae means they’re not getting enough food. If the stressful conditions come to an end soon enough—that is, if the weather changes and temperatures become cooler again—the algae can come back, and the corals can survive the bleaching event. But corals that do survive a bleaching event come out of it in a weakened state. As a result, they’ll be likely to experience reduced growth rates, decreased reproductive capacity, and increased susceptibility to diseases. Because it can take up to twenty years for reefs to fully recover, these recurring bleaching events are a kick in the teeth. Prolonged bleaching often leads to coral death.

Complicating matters is the fact that saving the reef from severe bleaching events requires patiently nursing it back to health. The recovery process is time-consuming and requires recolonization by coral larvae. Even under ideal conditions, coral recovery is slow and may take decades. You need sufficient connectivity of source reefs—reefs that export fertilized coral and fish eggs to other reefs downstream—as well as good water quality to make sure that the spawning and recruitment of larvae will succeed. Bleaching will actually kill the corals if the stresses are too severe or too persistent. This situation is really not so different from a prolonged drought. The condition of a coral when it enters a bleaching event is likely to determine its ability to survive the bleaching event.

Corals get a good bit of attention because a bleaching event is highly visible and because so much money is tied up in the reefs. But other parts of the reef ecosystem are also vulnerable to temperature. Seabird chicks have undergone severe die-offs during periods of unusually high sea temperatures. These die-offs, called nesting failures, result when parent birds can’t get dinner for their chicks. The fish they prey on follow productivity zones that are temperature-dependent. And when these fish change location, the birds can’t always find them. Sea turtles are also at risk. The sex ratio of turtle hatchlings is temperature-dependent, and continued warming could cause a significant bias toward females in future populations.

But again, temperature is just half of it. The other half of the global warming situation is ocean acidification (OA). Kleypas describes OA as the “silent problem” associated with increasing CO2. It’s also been described as “the other CO2 problem.” The other CO2 problem has scientists very worried. And, ironically, it comes as the result of a favor the oceans are doing us. No good deed goes unpunished.

Atmospheric CO2 is currently at 387 ppm, but it would actually be a lot higher if not for the oceans. Roughly 30 percent of the excess carbon dioxide released into the atmosphere by human activities since the industrial revolution has been absorbed by the oceans. That’s the favor. If not for the ocean uptake, atmospheric CO2 would be on the order of 450 ppm today, a level that would have led to even greater climate change than is already under way. But this favor provided by the oceans doesn’t come cheap. It has led to a roughly 30 percent increase in the concentration of hydrogen ions through the process of OA.4

This process, OA, is simply what happens when you add carbon dioxide to seawater. The additional CO2 causes a slight reduction in ocean pH, which is a measure of how acidic or basic a substance is. The pH scale ranges from 0 to 14. Pure water, for example, has a pH of 7 and is considered neutral. A pH less than 7, as in vinegar and lemon juice, is acidic. A pH greater than 7, as in ammonia or laundry detergent, is basic. The ocean is also slightly basic; the average pH of surface seawater today is about 8.1. But there is reason to believe that this is not the number it should be or the number it will remain.

The United States is the third-largest consumer of seafood in the world, with total consumer spending for fish and shellfish at about $60 billion per year. Coastal and marine commercial fishing generates as much as $30 billion per year, and nearly 70,000 jobs. Healthy coral reefs are the foundation of many of these viable fisheries. Needless to say, there are plenty of reasons to be worried about OA.

Although it is described as “silent,” OA is a straightforward consequence of rising atmospheric CO2. This condition doesn’t have a lot of the uncertainties that plague some other climate change forecasts. It’s freshman chemistry. And ocean pH is something we’re good at measuring. Since the 1980s, pH measurements collected in the North Pacific Ocean (near Hawaii) and in the Atlantic Ocean (near Bermuda) are registering a decrease in pH of approximately 0.02 unit per decade. Since preindustrial times, the average pH of ocean surface water has fallen by approximately 0.1 unit, from approximately 8.2 to 8.1, and it is expected to decrease further, depending on how high CO2 rises. If atmospheric CO2 concentrations reach 800 ppm, pH is predicted to rise an additional 0.3 to 0.4 pH unit.

What worries scientists is that even a slight decrease in pH does something funky to ocean chemistry, specifically to the amount of carbonate ions, a very important form of carbon. Corals pull in carbonate ions and secrete calcium carbonate (CaCO3). This is a process called calcification, and it uses the dissolved carbonate ions to form calcium carbonate minerals for shells and skeletal components. Once dissolved in seawater, CO2 gas reacts with the water to form carbonic acid (H2 CO3), which can then break apart by giving up hydrogen ions to form bicarbonate (HCO3-) and carbonate (CO32-). Increasing the amount of carbon dioxide dissolved in the oceans has a nasty side effect: it decreases the amount of carbonate ions in the water. Fewer carbonate ions means less material for building such things as calcium carbonate reefs and clamshells.

A study published in the journal Science in 2009 seems to confirm this.5 Experts at the Australian Institute of Marine Science in Townsville looked at coral samples from the GBR over the past twenty years to track changes in growth rates. Specifically, they measured the rate at which corals absorb calcium from seawater to build limestone skeletons. The study concluded that corals in the GBR are growing more slowly. The team of researchers investigated 328 colonies of massive porites corals from sixty-nine reefs covering coastal as well as oceanic locations spanning the entire length of the GBR. Because the porites coral lays down annual growth bands, it’s possible to count back to a specific year and correlate the growth during that year with the sea surface temperature over the same time period. Ten of the cores dated back to 1572.

The researchers sliced up the cores and used X-rays to measure three growth values: skeletal density, annual growth rate, and calcification rate. The values for growth and density allowed them to calculate annual calcification. They found that between 1900 and 1970 calcification rates increased 5.4 percent. But that’s when you could argue that the party ended. Calcification rates dropped 14.2 percent from 1990 to 2005, mainly owing to a slowdown in growth. Researchers measured calcification as decreasing from 0.56 inch per year to 0.49 inch per year. Scientists can’t confirm yet that what they are seeing is indeed the impact of increased OA, as opposed to other stressors such as coastal pollution. But the fact that the effect is seen on inshore as well as offshore reefs suggests to them that the cause is more likely to be global (for example, temperature and ocean acidification) than local (for example, pollution). It appears that not just the economy but also the GBR is in a recession.

And the impact of OA isn’t limited to corals. “There’s some very cool new research out there about clown fish,” Kleypas says. “Of course, it’s also very depressing.” The clown fish has become an iconic species ever since Disney’s blockbuster Finding Nemo gave kids a look at the biodiversity of the GBR. Interestingly, Phil Munday and his colleagues at James Cook University found that OA affects Nemo’s ability to find his way home. “Baby clown fish use their sense of smell to find a suitable habitat. And ocean acidification impacts their ability to differentiate between what is a suitable habitat and what isn’t,” Kleypas says. Recent research suggests that OA has impaired their sense of smell. “The baby fish aren’t getting the signal that says, ‘Bad habitat; don’t go there!’ and are less able to sense the proper habitat. And the researchers were not subjecting the fish to huge changes in pH. They were consistent with future projections,” Kleypas adds.

Research by Ken Caldeira, an ecologist, and his team at Stanford’s Carnegie Institution for Science suggests that ocean pH has not been more than 0.6 unit lower than today’s levels during any time over the past 300 million years. Yet the results obtained with the Stanford climate model show that the continued release of fossil fuel CO2 into the atmosphere could cause an eventual pH reduction of 0.7 unit over the next 300 years.6 An unprecedented change in pH over 300 million years is a lot easier to handle than the same change over three centuries. When CO2 changes over a time interval longer than 1 million years, ocean chemistry is buffered by interactions with carbonate minerals, and that buffering helps reduce the impact of acidification. Caldeira’s research suggests we’re talking about such a severe mismatch in timescales that adaptation is almost impossible.

When I asked Kleypas what she envisioned the GBR might look like by 2050, she said, “The distribution of reefs will be more patchy. Biodiversity will go down. There will be more algae and less hard coral. Erosion will become more noticeable. There will be fewer baby corals. It’s not all going to be dead; … the deeper parts of reefs may fare better.”

Climate models support this grim snapshot of the future. The models suggest that if CO2 emissions stay as they are, average water temperature in the GBR could increase by another 3.6°F to 5.4°F by 2100.7And studies have suggested that these increasing baseline temperatures, combined with the likelihood of more extreme weather events, like heat waves and flooding, could result in mass bleaching events every two to three years. Recent modeling studies indicate that if atmospheric CO2 levels hit 600 ppm, it will be very tough to save the corals. By 650 ppm, it will be impossible to save them.

Still, Kleypas thinks the overall outlook for impacts associated with increasing temperature is a little rosier than the outlook for impacts associated with OA. “We know corals can handle high temperature. We see them in the Red Sea and the Arabian Gulf. Corals can get used to warmer water, the same way people living in Arizona and Phoenix don’t suffer as much from heat stress.” In places like the Red Sea and the Arabian Gulf, corals don’t bleach until they reach temperatures about 18°F higher than their summer maxima, a much higher threshold than for similar species located in cooler regions. But there is one problem: the projected rate and magnitude of temperature increase will quickly outpace the conditions under which coral reefs have adapted and flourished during the past 500,000 years. Experts are worried that corals won’t be able to adapt fast enough to keep pace with even the most conservative projections for climate change. “The problem is,” Kleypas adds, “it takes time for corals to get used to the increased temperature.” And, unfortunately, time is not on their side.

With regard to finding an approach to help the coral adapt, coral bleaching reveals itself as the kind of problem where traditional management approaches that focus on minimizing or eliminating sources of stress don’t help much. The ocean is not like the heated pool at a hotel or motel: coral reef managers are constrained by a frustrating inability to directly turn down the ocean temperature when their reefs start to overheat. Needless to say, when you can’t control the single most significant factor affecting a bleaching event, you’re dealing with a challenging environmental management problem. To address the problem, in 2006 the Great Barrier Reef Marine Park Authority published A Reef Manager’s Guide to Coral Bleaching.8

Resilient reefs seem to share a few important qualities. One is location: they are located in a zone of cooler water. Some sites may have consistently cooler water because of upwelling or proximity to deep water. A second quality is shade: some reefs may be protected from bleaching because their exposure to the sun is limited by topographic or bathymetric features. Reefs shaded by cliffs or mountainous shorelines may also have a reduced risk of bleaching. Many reef areas are unlikely to have features that can provide shade, but fringing reef complexes around steep-sided limestone or volcanic islands, as in Palau and the Philippines, may have many shaded sites. A third quality is screening. Naturally turbid conditions may filter or screen sunlight, providing a measure of protection for corals exposed to anomalously warm water. Ongoing research suggests that organic matter in turbid areas may absorb ultraviolet (UV) wavelengths and screen sunlight. Corals at these sites may be less susceptible to bleaching.

The goal is to establish a network of marine protected areas (MPAs). If you can identify MPAs or reef areas that are likely to be more resistant to mass bleaching, then these are the places that have the best shot at survival in a warmer world. And if scientists can help set up a network of resilient coral reef refuges, then they can draw on these like a garden to reseed coral reefs that have been hurt by bleaching. In the context of mass coral bleaching, these refuges can serve as seed banks or source reefs for less resilient areas. But if the special reef refuges are to serve this role, they need to be effectively monitored and protected from local stressors such as anchor damage, overfishing, and pollution.

One such spot that scientists and conservationists are working hard to protect is an area called the Coral Triangle, which spans eastern Indonesia, parts of Malaysia, the Philippines, Papua New Guinea, Timor Leste, and the Solomon Islands and contains 53 percent of the world’s corals. It’s often compared to the Amazon rain forest of Brazil because it has such a high level of biodiversity. The Coral Triangle covers an area of 2.3 million square miles, about half the size of the United States. It has more than 600 reef-building coral species—75 percent of all species known to scientists—and more than 3,000 species of reef fish. It also has the greatest extent of mangrove forest of any region in the world. Both the mangroves and the coral reefs serve to protect fragile coastlines from damage by storms and tsunamis. Scientists feel that if they can protect this reef system, it will help them save other reef systems.

More than 120 million people live within the Coral Triangle, and about 2.25 million depend on its marine resources for their livelihood. Between the tuna fisheries and the tourism, the estimated total annual value of the coral reefs is $2.3 billion.

The MPAs are carefully selected areas where human development and exploitation of natural resources are regulated to protect species and habitats. By providing refuges for exploited fish stocks, MPAs provide benefits for commercial fisheries as well. Healthy fish stocks in MPAs replenish surrounding fishing grounds with eggs, larvae, and adult fish. Right now only 1 percent of the ocean is protected, compared with about 12 percent of the land. The question is whether the existing MPAs are in the right places and where we should put the next ones. Kleypas explains that finer-resolution climate models can help scientists select the optimal locations for MPAs. Implementing this principle in MPA design involves considering prevailing currents and adjacent non-reef areas. Linking MPAs along prevailing currents that carry larvae can replenish downstream reefs, increasing the probability of recovery at multiple coral reef sites. Adjacent non-reef areas are important to connectivity because they can become important staging areas for coral recruits as they move between reefs and into new areas.

“I call this high-CO2 window the Noah’s ark period. We have to save as many species as we can,” Kleypas says. “We also need to help make the reefs more resilient. The reefs that are in the best shape today are the reefs with the best management practices,” she adds. “I’d like to see some advances in coral reef restoration and coral farming.” In essence, this involves managing the ocean more as we do the land. It’s interesting to imagine coral reef farmers growing and tending to baby coral reefs. And this may be the best hope we have.

Another important part of management is monitoring the reefs using satellites. Coral Reef Watch, a program of the U.S. National Oceanic and Atmospheric Administration (NOAA), has developed tools to analyze satellite images and help reef managers assess the likelihood of mass coral bleaching events. It’s a little like a weather forecast for your coral reef, and it includes maps and indexes that track how warm conditions are getting in the tropics.

The maps use satellite data to show the intensity and duration of spikes in sea surface temperature. If you can monitor the intensity and duration of heat stress, you can get a sense of where a mass bleaching event might occur and how bad it might be. Both the intensity and the duration of heat stress are important factors in predicting the onset and severity of a mass bleaching event. The monitoring tool tracks the anomalous sea surface temperature, the difference between the observed ocean temperature and the highest temperature expected for a specific location, based on long-term monthly averages. It provides a useful reference point that shows the extent to which current temperatures vary from those that the corals are accustomed to experiencing at that time of year.

Temperature anomalies of 2°F to 4°F extending over a period of several days to several weeks should alert managers that there is a medium to high risk of bleaching. The NOAA Coral Reef Watch program also developed Tropical Ocean Coral Bleaching Indices to provide additional nearly real-time information for twenty-four reef locations worldwide.9 For each reef site, the closest 30-mile satellite data are extracted, including present sea surface temperature, degree heating weeks, climatology, and surface winds. Visual warnings are provided for each site when conditions reach levels known to trigger bleaching in vulnerable coral species. It’s a bit like the way forest rangers track the potential for wildfires on land.

There are also monitoring programs that encourage laypeople to serve as scientists. The sheer size and remoteness of many reef areas can be a substantial challenge for reef managers wishing to detect the onset of bleaching and monitor bleaching-related impacts. Reef users can help managers keep an eye on the reef during periods of high risk. A program in the GRB called BleachWatch engages people who love the reefs by teaching them how to help monitor coral bleaching events. BleachWatch provides an early warning system for coral bleaching and forms part of the Coral Bleaching Response Plan of the Great Barrier Reef Marine Park Authority’s (GBRMPA). The program is aimed at tour guides and allows them to go about their everyday work, be it guiding snorkel trails or diving, while taking a mental picture of their “home reef.” Back on the vessel, staff members fill in the monitoring form and send it back to the GBRMPA at no postage cost. In return for the monitors’ efforts, the GBRMPA analyzes the information and provides monthly site reports.

Experts like Kleypas also hope that high-resolution climate models might help in planning for the Noah’s ark period. The models can be used to fast-forward in time and get a better sense of what the reefs might look like as temperatures go up and pH goes down. The models might also be able to serve as a tool that allows a better understanding of which species are going to make it and which are more vulnerable. The species that are most resilient and most likely to survive can potentially be used to reseed reefs that have suffered from bleaching. Kleypas says that right now, most models look only at the surface ocean temperature. But when you begin to study the ocean at depth, the models could help identify places where the reefs are likely to survive. The models could actually help managers target specific areas to protect—areas like the Coral Triangle that will probably be used to help rebuild the reefs that are having a harder time.

Despite all these efforts, some people remain worried that corals simply will not have the resilience or the adaptive strength required to get past this high-CO2 window. Such people are calling for more dramatic measures. Some have recommended setting up an underwater repository of corals similar to the Svalbard Seed Bank, a cave on the Norwegian island of Spitsbergen that (as its name implies) preserves thousands of plant seeds from around the world. Svalbard is, in a sense, an underground “doomsday vault” built to serve as the ultimate safety net for the world’s seed collections, protecting them from a wide range of threats. In a repository, the corals would be saved from rising temperatures and OA, but Kleypas sees this as a last resort.

With all these tools and programs coming online, Kleypas is trying very hard to stay positive. As a scientist she is pragmatic, but as someone who is passionate about coral reefs, she conveys an uncommon sense of hope. “Scientists are very introverted people by nature. We don’t tend to be inspirational. We make future predictions based on the here and now. But I’ve been trying to give people hope. I hate to give a doomsday lecture and tell folks the reefs are all going to hell. People don’t know what to do with that information.”

On the other hand, she doesn’t want to come across as a Pollyanna. “We’ve already entered into this window of high CO2. So, we have to aim for mitigation. We can’t just stabilize emissions. We need to then get CO2 levels down. I like to tell people we don’t know how high the CO2 is going to be, because that level is fundamentally up to us.”

Kleypas is not one to shy away from the possibility of genetic engineering. “Scientists are thinking about the symbiotic algae,” she explains. “The question is: can we seed a reef with algae that are more resilient to temperature changes? One theory that has emerged is that the amount of bleaching that occurs at each reef may be influenced to some extent by the prevalence of stress-tolerant algae. And so scientists have begun surveying corals for the presence of stress-tolerant zooxanthellae within reefs. There’s still so much to learn about these symbiotic algae, but identifying which algae are most stress-tolerant may help managers to assess the potential resilience of different sites. We know how to engineer resilience in terrestrial species, but we know much less how to do it in marine ecosystems. And we need to figure it out,” she says with a sense of urgency. “This is one of the most remarkable times to be a scientist. Sure, we can just sit back and watch it happen and confirm that our predictions are coming true. But that would be embarrassing.” I suppose it’s fair to say that we’ve reached a point where we need to make our own luck.

The Great Barrier Reef, Australia: The Forty-Year Forecast—Coral Bleaching, Ocean Acidification, and Economic Struggle


Forecast March 2017

For several months, squadrons of scuba divers from all over the world had been heading out into the unusually warm waters off the coast of Townsville, tanks of air strapped to their backs and monitoring checklists dangling from their wrists. The divers were roaming the seas in search of bleached corals—a terrible job for anyone who loves the reefs. El Niño set off a worldwide coral bleaching event affecting hundreds to thousands of miles of reefs simultaneously. This El Niño came when ocean temperatures were already warmer than average and caused severe to extreme bleaching even along the very carefully managed and monitored GBR—with the result that more than half of the colonies turned completely white. The divers went out each morning to identify sick corals and came back each evening hoping that park officials wouldn’t need to come up with a catastrophic level for coral bleaching, too.

The Coral Reef Watch program set up by NOAA had been monitoring ocean surface temperature using satellites and was able to provide scientists and volunteers with almost up-to-the-minute information. Temperatures along the GBR ranged from 80°F to 84°F, and bleaching was widespread. Reports from volunteer groups, such as BleachWatch and Reef Check, warned that large sections of coral were bleaching at levels much higher than those seen in 1998, when waters heated by El Niño killed 15 percent of reefs worldwide. In the GBR alone, reef damage related to bleaching had caused losses to the tourism industry on the order of $250 million; and we had felt sick to think that when all was said and done, we might lose more than one-third of these beautiful reefs.

It was hoped that local solutions—for example, marine sanctuaries and volunteer monitoring efforts—might create lasting changes. But it’s tough to manage global warming locally. And in the end, the root cause of bleaching, warmer ocean temperatures, could be addressed only by a worldwide effort to reduce CO2 emissions. Scientists had hoped that the more remote reefs, safely isolated from human impact, might fare better. They were wrong. The bleaching event caused extensive mortality in nearly every coral reef region in the world. No man is an island—and no reef is safe from the long arm of climate change.

December 2019

As climate change continued to accelerate, the words severe and extreme were no longer adequate to describe the destructive potential of Australia’s wildfires. That’s why the residents of South Australia awoke on the first morning in December 2019 to face yet another sustained warning of catastrophic fire danger. The category catastrophic had been put in place by the Australian Bureau of Meteorology (BOM) in 2009, after the horrific wildfire called Black Saturday radically altered everyone’s definition of how bad a wildfire could get.10 The wildfires came on Saturday, February 7, 2009; and by the time the sun rose the next morning, they had killed 173 Australians and traumatized countless others. According to a report by the Victorian Bushfires Royal Commission,11 the fires generated winds so strong “that trees appeared to have been screwed from the ground.” At the time, no one dared imagine what Australia might look like if Black Saturday had gone on for a week. We found out in 2019. That catastrophic outbreak came to be known as Black December.

Fire marshals begged residents of the eastern Eyre Peninsula and the west coast districts in the state of South Australia to evacuate their homes immediately. If they had learned anything from Black Saturday—when many residents stayed on, hoping to defend their property but in the end losing their lives—it was that no one should attempt to be a hero. Fire authorities, however, had no official mandate, so they could not force people out of their homes; they could only beg the residents to leave.

It had been a brutal few months. In October, an ongoing drought had kicked up a thick wall of red dust that reduced visibility in Sydney to less than two city blocks. Snapshots taken of the Sydney Opera House—silent, ghostlike, and shrouded by a thick red veil—made their way around the globe, and the world looked on in fear and fascination. The ferocious wildfires, pervasive drought, and unbreathable air made Australia seem like hell on Earth. And for those who lived there it was.

In November, intense heat pushed the average temperature for the month into numbers never seen before. Towns throughout Victoria and southeast Australia were running 2°F to 4°F above the previous record, set in 2009. Melbourne was running 2°F above the record set during the previous November. The city’s chief meteorologist summed it up: “Usually when you break records like these you break them by a tenth of a degree. But we’re seeing we’re two, three, or even four degrees above previous records. This is not natural.” And by December, the heat and drought—together with low humidity and strong winds, created the perfect conditions for a catastrophic wildfire. Happy New Year, Australia.

January 2025

After the widespread bleaching event of 2017, the idea of setting up a coral bank began to gain traction. The Svalbard Global Seed Bank had proved to be successful. Why not try something similar with corals?

The Smithsonian Institution in Washington, D.C., finally received funding to set up the Smithsonian Global Coral Vault. Corals from tropical oceans were being placed in deep freeze at the Smithsonian to preserve them for posterity as they faced destruction from rising greenhouse gas levels. This coral cryobank would ultimately house hundreds of samples from each species. The funding came after new research suggested that most coral reefs would be largely dead by 2040, wiped out by a combination of rising temperatures and increasing acidity in the world’s oceans. The affected areas included Australia’s 1,600-mile GBR, Caribbean reefs, and reefs in the Coral Triangle—an area spanning Indonesia, the Philippines, Malaysia, Papua New Guinea, and East Timor. Carbon dioxide emissions had risen above the safe level for corals, and reefs around the world were showing the impact. The Smithsonian’s vault was a matter of reverting to plan B. And its very desperation reflected the despair among scientists about rising CO2 levels.

The coral vault applied a breakthrough deep-freeze technique developed by scientists to regenerate coral from frozen samples. The scientists took tiny biopsies from coral, froze them in liquid nitrogen at -330°F, and then thawed them to regenerate polyps. These scientists were proposing to do the same for every species of coral on the planet. There are about 1,800 known tropical corals and another 3,350 cold-water species. The Smithsonian would house about 1,000 samples of each coral in a large room in a subbasement of its museum in Washington, D.C. The facility was nicknamed the “Morgue of the Sea.”

December 2050

The overall acidity of the ocean continued to increase. Corals reached the point where they were dissolving more quickly than they were growing. Consequently, many coral reefs were unsustainable. It was expected that pH levels would continue falling. By 2100, climate models forecast a further drop in pH of 0.3 to 0.5 unit—which would make the world’s oceans more acidic than they had been in tens of millions of years. And while there might be thousands of coral polyps sitting in deep freeze at the Smithsonian, there was no ocean on the planet Earth that they could now call home.