Half the World’s Coral Reefs Already Have Been Killed by Climate Change
The oceans have long been the biggest buffer for humankind’s dangerous greenhouse-gas emissions. Around a quarter of all the carbon dioxide released into the atmosphere since the 1980s—from driving cars, running factories and churning out electricity with fossil fuels—has ended up sunk into the waters. As the planet has warmed from mounting emissions, the oceans warmed first and fastest, absorbing 90% of that excess heat. A report released last month by the UN-based Intergovernmental Panel on Climate Change, the foremost scientific authority on the subject, warned that damage to the oceans is accelerating and may be at the point of irreversibility.
That makes delicate coral reefs around the world something of a leading indicator for the collapse of the ocean ecosystem. Half of all reef systems have already been destroyed, putting a quarter of marine life at risk. Even if global warming is limited to the 1.5 degree Celsius target outlined in the 2016 Paris Agreement—a longshot goal, at the current rate of emissions—the IPCC now concludes that “almost all warm-water coral reefs are projected to suffer significant losses of area and local extinctions.”
In a perverse consequence, lost reefs will leave nearby coastlines even more vulnerable to erosion and storms, as well as from accelerating sea-level rise, which could go up by as much as two feet this century as a result of glacier melt.
Corals are so sensitive to rising sea temperatures that you can see their demise. When water is too warm, corals enter a stress response and lose the symbiotic algae that give them their distinctive colors—a process known as bleaching. If a coral is severely bleached, chances of disease and death increase.
In 2014, an El Niño-driven coral bleaching event swept the world’s reefs that lasted three years—the longest and most damaging of its kind on record. Bleaching was evident in 75% of tropical reefs and brought nearly 30% to mortality level.
Global Coral Bleaching
- No bleaching alert
- Alert
- High alert
- Coral reef
Reefs in the northern part of Australia’s Great Barrier Reef that had never bleached before lost nearly 30% of their shallow water corals in 2016. Reefs farther south lost another 22% in 2017. Only 7% of the reef avoided coral bleaching. In Japan’s Sekiseishoko Reef, East Asia’s largest, over 90% bleaching was observed, with 70% lost.
Severe bleaching was reported in Philippines, Indonesia, Taiwan, Thailand, Vietnam
Many reefs—including those in Guam, American Samoa and Hawaii—experienced their worst bleaching ever documented. In the Northern Line Islands in the South Pacific, between 80 and 98% of total coral cover was killed.
Severe bleaching was reported in Palau, Fiji, French Polynesia, Micronesia, Marshall islands, Kiribati, Marianas
High temperatures in 2015 impacted coral reefs throughout the western Atlantic, Gulf of Mexico and the Caribbean, with the western Caribbean hit hardest. In 2015 moderate to severe coral bleaching and disease impacted Florida’s coral reefs for the second year in a row.
Severe bleaching was reported in Belize, Gulf of Mexico, Saba, Yucatan
In early 2016, bleaching in the Seychelles reduced the reef’s hard-coral cover by about half.
Severe bleaching was reported in Kenya, Madagascar, Maldives, Mauritius, Mozambique, Reunion, Seychelles, Tanzania, Western India
Some of the planet’s most important habitats are within 12 nautical miles from shore—the coral reefs, seagrass and mangrove areas plied by over 50 million fishers for food and livelihood. Reefs that manage to survive the onslaught of warming and acidification will be left with less marine diversity, the IPCC warns, which will “greatly compromise” seafood supplies and tourism revenue.
That could leave 680 million people who live in low-lying coastal zones in a bind, especially those in smaller island states. Fishing and tourism contribute an estimated $16 billion annually to 52 economies particularly intertwined with coastal reefs. Almost 20% of gross domestic product in the Maldives is directly tied to reefs.
Reef Dependence
Even in high-income countries, the deterioration of this natural wonder can represent concrete economic loss. Australia’s Great Barrier Reef Marine Park attracts about 1.9 million visits each year, with prime tourist spots stretching most of the coast of Queensland. Reef tourism generates AUD$5.4 billion annually to Australia’s economy and supports 54,000 jobs.
Stressed Reefs
- Highly valued
- Bleaching alert
- High alert
- Marine Protected Area
Coral Sea
Cairns
Townsville
Mackay
QUEENSLAND,
AUSTRALIA
Rockhampton
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Coral Sea
Cairns
Townsville
QUEENSLAND,
AUSTRALIA
Mackay
Rockhampton
100 km
100 miles
Coral Sea
Cairns
Townsville
QUEENSLAND,
AUSTRALIA
Mackay
Rockhampton
100 km
100 miles
Bleaching is driven by a variety of stressors, which corals respond to differently depending on where they are. The Wildlife Conservation Society, a leading NGO working on coral reef protection, tested 226 sites globally and found a variation of about 50% in global bleaching patterns from the 2014–2016 event when measuring for thermal stress and exposure, habitat, depth and geography. And their survey of 2,500 Indo-Pacific reefs showed that “coral responses to global climate change may be changing as corals have different past experiences and tolerances to heat and stress,” said Tim McClanahan, co-author of the study.
But warming waters pose a dire threat that only seems to be getting worse. Under the influence of ever-increasing CO2 emissions, marine heatwaves have doubled in frequency since 1982 and are increasing in intensity. Their frequency will be 20 times higher at 2°C warming, compared to pre-industrial levels. If the current rate of emissions is left unchecked, these underwater heatwaves would occur 50 times more often than they do today.
Scientists are trying to keep up by monitoring ocean temperatures in real time. An early-warning system to identify impending bleaching events developed by the National Oceanic and Atmospheric Administration measures accumulation of temperature anomalies of more than 1 °C over a three-month window. But this comes with limitations since other environmental factors can impact bleaching outcomes. A section of the Great Barrier Reef, for example, survived the last bleaching event because it was protected by heavy cloud cover.
Designating marine protected areas, where no fishing is allowed, may not provide resistance against warming. But these restrictions can give marine habitats a chance to replenish and sustain local fisheries.
Next year the tiny Pacific island nation of Palau will close off from commercial fishing and mining 80% of their exclusive economic zone (EEZ), an area larger than California and home to more than 1,300 species of fish and 700 species of coral. About 20 percent of Palau’s waters will become a domestic fishing zone reserved for locals and small-scale commercial operators with limited exports.
For the sanctuary to be effective, it must be enforced. In 2015, fighting a rise of illegal fishing, Palau set fire to four Vietnamese boats caught poaching sea cucumbers and other marine life. The country has turned to partnerships, working with Vulcan’s Skylight, to track illegal fishing using satellite-based ship location data.
Palau National Marine Sanctuary
- Frequency of fishing, Jan.—Aug. 2019
- Proposed National Marine Sanctuary
HIGH SEAS
Palau
EEZ
HIGH
SEAS
INDONESIA
EEZ
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250 miles
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Palau EEZ
Philippines
EEZ
Micronesia EEZ
Restricted fishing
20% of EEZ
National Marine
Sanctuary
80% of EEZ
High seas
250 km
Indonesia EEZ
250 miles
High seas
Philippines
EEZ
Palau EEZ
Micronesia EEZ
Restricted fishing
20% of EEZ
National Marine
Sanctuary
80% of EEZ
High seas
Indonesia EEZ
250 km
250 miles
The motivation behind the sanctuary is a cultural desire to protect resources, which are vital for the tourism industry that supports 56% of Palau’s GDP. In the past decade foreign visitors have grown from 65,000 to 125,000 per year. Fishing, by contrast, contributes approximately 3% to the island’s economy.
The effort to reduce fishing is meant to bolster the abundant fish stocks needed to strengthen reefs and reef tourism. Of course, tourism is itself an environmental stressor that can damage reefs from uncontrolled development and poor waste management; divers and snorkelers are also known to damage reefs. And this doesn’t even begin to factor in the emissions associated with airplane travel.
Healthy reefs in Southeast Asia, the Indian Ocean and the Caribbean could support a maximum sustained yield of 4 tons of fish per square kilometer per year, according to the International Coral Reef Initiative. Yields from degraded reefs can drop as low as 0.7 tons per year. Shifts in the distribution of fish populations have already reduced the global catch potential, although the impact is uneven. In the future, tropical oceans could see further decreases while fish move into the warmer Arctic. Communities that depend on seafood may face risks to nutritional health and food security.
In the Philippines, there are 1.9 million registered municipal or small-scale fishers. It’s not easy to envision an alternative food source.
“These fisheries are also the most undervalued and undermanaged,” says Rocky Sanchez Tirona, a vice president of Rare for the Philippines. “Fish recovery takes time, and it’s hard to get people to hold out for a payoff that takes years before you see it.” One method Rare uses is to showcase the benefits that fishers get from “participating in the process and being listened to,” she says, while making available scientific data to inform local decisions on fishery management.
There are also efforts to set up saving clubs to give fishing families a financial buffer. In some cases, Tirona says, these cash reserves help generate small businesses.
The rationale for taking action to protect coral ecosystems goes beyond their economic value. A focus on oceans could play a significant role in cutting emissions deeply enough to keep global average temperatures from rising past 1.5 degrees Celsius by 2050.
A recent report by seven countries, including Australia and Fiji, found that the oceans can provide up to a fifth of annual emissions cuts needed for that target. The solutions don’t focus on corals, but most of the suggested measures would help there, too. The proposals include decarbonizing shipping, expanding ocean-based renewable energy and protecting mangroves and salt marshes to prevent a gigaton of CO2 from entering the atmosphere.
One of the recommendations: Switching away from emissions-intensive fishing and aquaculture operations to eating lower carbon sources of ocean protein, such as sustainably harvested fish, seaweed and kelp—which would go a long way toward bolstering the health of the coral reefs the world has left.