The Great Barrier Reef is one of the most biodiverse places in the entire world, worth billions of dollars.
But it's in real danger of being killed off as greenhouse gas emissions warm the water and make it more acidic, which causes coral bleaching and can kill it.
There's a real chance the Great Barrier Reef could be killed within the next couple of decades, leaving a dead structure that could take thousands of years of recover, if it ever can.
One of the most spectacular natural environments on the planet is also one of the most vulnerable, and if people aren't careful, there's a good chance it could be destroyed altogether.
Located off the northeastern coast of Australia, the Great Barrier Reef — made up of more than 3,860 separate coral reefs, according to some measures — is such a massive natural structure that it can be seen from space.
It's home to countless organisms and it's a huge draw for tourism. It's the most biodiverse of all UNESCO Heritage Sites and the most extensive coral reef ecosystem on the planet.
But just like all coral reefs, it's vulnerable to human activity, which means that it's in real danger of dying off.
It's not just local activities like fishing and pollution that damage the corals that make up the Great Barrier Reef, though those do have detrimental effects. The biggest overall threat to reef health — both off the coast of Australia and around the world — comes from the carbon dioxide emissions that cause climate change.
The broader consequences of reef loss are devastating, both for natural environments and for the people that depend on them.
As a recent study in the journal Nature Geosciences explained, the Great Barrier Reef has come back from near-death experiences before — five times in the last 30,000 years. That shows recovery is at least theoretically possible, but in those cases, it took hundreds or thousands of years.
Here's what's happening to make the Great Barrier Reef so vulnerable.
According to one recent study published in the journal Nature, the Great Barrier Reef is made up of 3,863 coral reefs, with over 400 species of coral building up those reefs.
Corals are animals — translucent creatures that form huge colonies and create a variety of structures
Certain types of algae populate the structures, which gives reefs bright colors and helps them derive energy from the sun as well as from nutrients and plankton in the water.
The environments these creatures create are crucial — a quarter of fish species spend some part of their life cycle in reefs, which means their loss could have catastrophic effects on fish populations and the many people who depend on them for food or income.
The Great Barrier Reef supports at least 1,500 fish species, 4,000 species of mollusk, 240 bird species, and thousands of other marine creatures.#
The Australian government has said the reef contributes at least $6.4 billion a year to the economy, and that at least 64,000 people have jobs that depend on the reef.
Estimates of the overall economic value of reefs suggest they contribute between $30 billion and more than $375 billion to the world economy annually, though some scientists say those figures are far too low.
Source: Business Insider
Local activity has contributed to damage of the Great Barrier Reef and other reefs.
Runoff and pollution from agriculture have damaged the reef, allowing harmful types of algae and predatory starfish to overwhelm parts.
But coral reefs are suffering even more from climate change.
As climate change causes water temperature to rise and seas become more acidic as they absorb carbon dioxide, the coral lose algae in a process called bleaching.
Bleaching slows corals' growth and makes them vulnerable to harmful types of algae, disease, and death.
One-third of the Great Barrier Reef died off after an extreme bleaching event caused by a catastrophic heat wave in 2016.
Another bleaching event in 2017 compounded the damage, leaving half the reef dead in just two years.
According to some estimates, similar conditions around the globe have killed off about half the world's coral reefs in the past 30 years. By 2030, 60% of all coral reefs are expected to be highly or critically threatened, and 98% of reefs will be exposed to potentially fatal conditions every year.
Source: World Resources Institute
The Australian government recently announced it will spend $379 million to limit agricultural runoff from farms and try to eliminate coral-devouring crown-of-thorns starfish, which liquify coral organisms.
Source: Business Insider
But experts say addressing these problems without dealing with climate change won't save the reef. The Great Barrier Reef and most other coral reefs around the globe could almost entirely die off within a few decades, leaving mostly dead structure in their places.
As they have in the past, these reefs might bounce back eventually, but that could take thousands of years — and is unlikely to happen until climate change is dealt with. That would leave the most vibrant —and in many ways, most important —parts of the ocean lifeless, which would have devastating effects on marine life and all the people who depend on it.
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