Climate Change, Silent Killer of the World’s Precious Coral Reefs

Environment Policy Brief #133 | By: Jacob Morton | October 22, 2021

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Policy Summary

14 percent of the world’s coral reefs perished within just ten years from 2009 through 2019, says a report released earlier this month by the International Coral Reef Initiative, a partnership of countries and organizations that works to protect the world’s coral reefs. The cause? Climate change. Pollution from human sewage and agricultural runoff, which cause harmful algal blooms, as well as heavy metals and other industrial chemicals from manufacturing industries, were cited as major contributors as well. Destructive fishing practices that harm coral reefs also earned a dishonorable mention.

The report presents an analysis of data collected by more than 300 scientists in 73 countries. Its editors concluded that “Since 2009, it’s a constant decline [of coral populations] at the global level.” According to the editors, what is particularly alarming is the trajectory of this decline. They point out that the first major global coral bleaching event occurred in 1998, but afterwards, most of the affected reefs seemed to bounce back. Today, they report, “That no longer appears to be the case.”

The report does note, however, that around 900 species of coral exist, and “some appear more resilient to the heat and acidification that accompany climate change.” Unfortunately, as researchers in the report point out, “those tend to be slower-growing and not the more familiar, reef-building varieties that support the richest biodiversity.” Despite this, editors of the report provide some optimism, stating that, “Many of the world’s coral reefs remain resilient and can recover if conditions permit.” They emphasize that if the world can limit the amount of global warming, these corals could still potentially recover, or at least regenerate over time.

Policy Analysis

According to the National Oceanic and Atmospheric Administration (NOAA) “Climate change is the greatest global threat to coral reef ecosystems,” and the clearly evidenced warming of the earth’s atmosphere and oceans “are primarily due to greenhouse gases derived from human activities.” NOAA explains that, “As temperatures rise, mass coral bleaching events and infectious disease outbreaks are becoming more frequent. Additionally, carbon dioxide absorbed into the ocean from the atmosphere has already begun to reduce calcification rates in reef-building and reef-associated organisms by altering seawater chemistry through decreases in pH,” a process known as ocean acidification.

A report by NOAA’s Florida Keys National Marine Sanctuary explains this process: “Rising (or even falling) water temperatures can stress coral polyps, causing them to lose algae (or zooxanthellae) that live in the polyps’ tissues. This results in “coral bleaching,” so called because the algae give coral their color and when the algae “jump ship,” the coral turns completely white. The algae also give coral polyps the food they need to survive.” The report adds that, “While a bleached coral is not dead, and corals can survive bleaching events, they are under greater stress, are less resistant to other threats such as disease, and are thus subject to mortality.”

Additionally, the ocean absorbs approximately one-third of the atmosphere’s excess carbon dioxide. As humans emit more carbon dioxide into the atmosphere, our oceans absorb more of the excess CO2, which alters the water’s pH, resulting in a more acidic ocean. “In order for a coral reef to grow, it must produce limestone (or calcium carbonate) at a rate that is faster than the reef is being eroded. Ocean acidification slows the rate at which coral reefs generate calcium carbonate, thus slowing the growth of coral skeletons.” Compounding these affects, as global warming worsens, “sea level rise; changes in the frequency, intensity, and distribution of tropical storms; and altered ocean circulation,” all create harsher conditions for coral reefs.

While the report by the International Coral Relief Initiative (ICRI) makes clear that tackling climate change should be our top priority for saving coral reefs, it stresses that “reducing pollution is also critical.” If corals are to be as healthy as is necessary to survive the warming temperatures that are already here to stay, we must reduce the amounts of pollution that cause algal blooms and murky and toxic waters in coral ecosystems.

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Coral reefs occupy a small percentage of the sea floor, but according to the ICRI report, they collectively support “an estimated $2.7 trillion per year in goods and services.” The fish that live amongst them supply a critical source of protein for human consumption; their large limestone branching formations protect coastlines from storms; and their well-known beauty attracts billions of dollars in tourism revenue.

According to Dr. David Obura, chairperson of the coral specialist group for the International Union for Conservation of Nature and a contributing editor to the ICRI report, the 14 percent decline in the planet’s living coral reefs that took place between 2009 and 2019, is deeply concerning. Obura says, “In finance, we worry about half-percent declines and half-percent changes in employment and interest rates.”

A 14 percent decline in an ecosystem that supplies so much revenue globally, should be concerning to everyone. As Obura points out, “Coral reefs are the canary in the coal mine telling us how quickly [things] can go wrong.”

Just a week after the release of the ICRI report, United Nations world leaders met to discuss a new global biodiversity agreement (much like the Paris Agreement on Climate Change), called the Post-2020 Global Biodiversity Framework (GBF). The UN’s draft GBF sets targets for protecting marine and land habitats and reducing pesticides and plastic waste. The agreement is expected to set “21 targets and 10 milestones for governments to meet by the end of the decade. These include protecting a minimum of 30% of the world’s oceans and land, reducing pesticide use by at least two-thirds, eliminating plastic waste, and increasing financial resources dedicated to biodiversity to at least US$200 billion annually.”

For coral reefs, some leaders are pushing to protect the most pristine reefs that still remain. Dr. Obura, however, says “this approach would not suffice.” Obura argues, “People are so dependent on reefs around the world, we need to focus a lot of effort on the mediocre reefs, or all the other reefs, as well. We need to keep them functioning so that people’s livelihoods can continue.” The UN’s GBF agreement is set to be finalized in Spring 2022.

Engagement Resources​

ICRI Logo Colour

The International Coral Reef Initiative (ICRI) – A global informal partnership between Nations and organizations which strives to preserve coral reefs and related ecosystems around the world.

center for biological diversity

The Center for Biological Diversity (The Center) – Because diversity has intrinsic value, and because its loss impoverishes society, we work to secure a future for all species, great and small, hovering on the brink of extinction. We do so through science, law, and creative media, with a focus on protecting the lands, waters, and climate that species need to survive.

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The International Union for Conservation of Nature (IUCN) – IUCN is a membership Union composed of both government and civil society organizations. It harnesses the experience, resources and reach of its more than 1,400 Member organizations and the input of more than 18,000 experts. This diversity and vast expertise make IUCN the global authority on the status of the natural world and the measures needed to safeguard it.

Writer’s Sources

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Einhorn, C. (2021, October 5). Climate change is devastating coral reefs worldwide, major report says. The New York Times. Retrieved October 22, 2021, from

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NOAA. (2011, April 4). Coral bleaching and ocean acidification are two climate-related impacts to coral reefs. How is climate change affecting coral reefs? Retrieved October 22, 2021, from

NOAA. (2015, March 3). How does climate change affect coral reefs? NOAA’s National Ocean Service. Retrieved October 22, 2021, from

GCRMN Logo cropped

The sixth status of corals of the world: 2020 report. GCRMN. (2021, October 8). Retrieved October 22, 2021, from

Willige, A. (2021, October 18). UN’s 2022 Global Biodiversity Framework could become the new ‘Paris agreement for nature’. ThePrint. Retrieved October 22, 2021, from

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