The Great Barrier Reef is sick. Almost half of its coral is already dead and a massive new coal mine, which was given final approval this week, will only cause further damage. This is not just an issue for Australia, it affects us all • The Great Barrier Reef: an obituary – interactive

These are dark days for Australia’s Great Barrier Reef. On 29 July, the last major regulatory hurdle facing the development of Australia’s largest coal mine was removed by Greg Hunt, minister for the environment. The Carmichael coal mine, owned by India’s Adani Group, will cover 200 sq km and produce 60m tonnes of coal a year – enough to supply electricity for 100 million people. Located in Queensland’s Galilee Basin, 400km inland from the reef, it will require a major rail line, which is yet to receive final approval, to transport the coal, which must then be loaded on to ships at the ports of Hay Point and Abbot Point, near Gladstone on the Queensland coast, adjacent to the southern section of the reef. Both ports require dredging and expansion to manage the increased volume of shipping. Once aboard, the coal must be shipped safely through the coral labyrinth that is the Great Barrier Reef, and on to India, where it will be burned in great coal-fired power plants.

The proposed development will affect the reef at just about every stage. Indeed, so vast is the project’s reach that it is best thought of not as an Australian, or even an Australian-Indian project, but one of global impact and significance.

Often hailed as one of the seven natural wonders of the world, the Great Barrier Reef stretches 1,400 miles along Queensland’s coast and covers an area the size of Germany. It is home to a truly extraordinary variety of living species. From giant grouper to tiny eels that inhabit the anuses of sea cucumbers, its creatures amaze the thousands who visit it each year, as well as the millions who watch it virtually through nature documentaries. But what fascinates scientists is the way the myriad reef organisms co-operate to create such a prolific ecosystem in what is an essentially unproductive sea. The trick lies in give and take: coral polyps and giant clams allow their tissues to be colonised by algae, which, in return for shelter and nutrients, provide food via photosynthesis. The reef organisms even co-operate to produce clouds, by releasing cloud-seeding molecules into the atmosphere, so that the reef is protected from ultraviolet radiation.

Remarkably, the earliest evidence of this astonishing ecosystem is found not in Australia, but in the green hills near Verona in northern Italy. There, 54-million-year-old sediments laid down in a shallow lagoon preserved the remains of the oldest coral reef fish known. Just a million years earlier, the planet had been devastated by a gargantuan eruption of natural gas, which caused unprecedented greenhouse warming. The oceans turned acidic, corroding the sea floor; the waters warmed, and countless organisms perished in a great extinction event. The first modern reef-building and inhabiting creatures appeared in the wake of this cataclysm, and they have flourished ever since.

Facebook Twitter Pinterest A coal loading terminal in Newcastle, Australia … a major new mining project in Queensland’s Galilee Bison will involve moving huge volumes of coal through ports adjacent to the southern section of the Great Barrier Reef. Photograph: Ian Waldie/Corbis

When the region around Verona was a tropical lagoon, a seaway known as the Tethys stretched from Europe all the way across Asia to Australia. Reef organisms flourished in the ancient seaway, laying the foundations for today’s pan-tropical coral reef communities. But it was off the Queensland coast that these organisms found conditions most to their liking, allowing them to build the greatest coral wonderland on Earth.

Today, the Carmichael mine development is occurring adjacent to what is now a very sick Great Barrier Reef. A 2012 study established that around half of the coral composing the reef is already dead – killed by pesticide runoff, muddy sediment from land clearing, predatory starfish, coral bleaching and various other impacts. The coal mine development will add significant new pressures. First will come the dredging for the new ports. The 5m or more tonnes of mud, along with whatever toxins they contain, will be dug up, transported and dumped into the middle of the reef area. Some studies suggest that the suffocating sediment will not drift far enough to harm the majority of the reef. But who can say what impact tides, currents or cyclones, which are frequent in the area, will have on the muddy mass?

The raw coal itself will be another pollutant. Coal dust and coal fragments already find their way from stockpiles, conveyor belts and loaders into the waters of the reef. Indeed, existing coal loaders have already dumped enough coal for it to have spread along the length and breadth of the reef. In areas near the loaders, enough has accumulated to have a toxic effect on the corals that grow there.

There is also the ever-present possibility of a coal ship running aground on the reef. The region is littered with wrecked vessels, and as the number of voyages increases such accidents become more probable. Even if the coal is safely shipped to India, and burned in coal-fired power plants there, the attack on the reef will continue. Within days or weeks, the carbon dioxide emitted from Indian smokestacks will have returned to the atmosphere over the reef. There it will have two major effects, best envisaged as heat and acid. The reef is exquisitely sensitive to global warming caused by greenhouse gases such as carbon dioxide because it sits atop a shallow and very broad continental shelf. Like a shallow saucer of water left in the sun, its waters warm rapidly, and are effectively cut off from cooler, deeper water that elsewhere helps dissipate the heat.

Facebook Twitter Pinterest Many scientists believe that most of the Great Barrier Reef will die if the planet warms by 1.5C above its pre-industrial average – we are perilously close to ­having emitted sufficient greenhouse gas to achieve that. Photograph: Ingo Arndt/Minden/Corbis

Corals die from a curious cause when the water in which they grow warms up. Unaided, the coral polyp is unable to feed itself sufficiently. So it shelters algae in its tissues, which capture sunlight and produce food using photosynthesis, which is then shared by the coral. In what is a kind of business partnership, the coral contributes nutrients and shelter in return. But the algae can only photosynthesise efficiently in relatively cool water. As the water warms, the algae produces less food, until the algae costs the coral organism more than it is worth to maintain. Then the polyp ejects the algae. Incidentally, it’s the algae that give the coral its colour; and so when it’s ejected, the coral takes on a ghostly white hue, giving rise to the term “bleaching”. If the hot water lingers for six weeks or more, the polyps die of starvation, and a green slime replaces the wonders of the reef.

The first bleached coral appeared on the Great Barrier Reef in the 1970s, and each decade since has seen more and more catastrophic bleaching events, some of which have killed up to 60% of the coral on the reef. You might think the corals could adapt, but studies show that the warming is now happening so fast that it is outstripping the ability of corals to migrate. Many scientists believe the vast majority of the reef will die if the planet warms by as little as 1.5C above its pre-industrial average. We are perilously close to having emitted sufficient greenhouse gas to achieve that.

As if the warming isn’t bad enough, some of the carbon dioxide is dissolved into seawater, where it forms carbonic acid, causing a phenomenon known as ocean acidification. This makes it vastly harder for organisms to lay down a calcareous skeleton. Our oceans are already 30% more acidic than they were at the beginning of the industrial revolution, and in sensitive regions this is already having catastrophic effects. The north Pacific is particularly vulnerable to acidification, and it may offer some insights into what is ahead for the reef. Already, large economic and natural impacts have been felt as the north Pacific has acidified. Oyster spat (young oysters) for the entire north-west Pacific oyster industry are cultivated at two large facilities. Beginning in 2008-09, mass mortality of the spat began to occur due to acute acidification of the seawater drawn into the growing tanks. The hatcheries have adapted their regimes so spat can now be raised, but wild organisms all feel the full effect of the acidity. The impacts of acidity on corals are only now beginning to be investigated. Much remains to be learned, but all stages of the coral lifecycle appear to be vulnerable, with fears that the effects will be greatest on eggs and spawn.

Facebook Twitter Pinterest Protesters in Sydney on a demonstration to save the Great Barrier Reef … Australians are ­waking up to the dire threat ­facing their reef, and particularly in the region around the reef itself, public sentiment is very much on the side of protection. Photograph: Richard Milnes/Demotix/Corbis

Australia’s cavalier attitude to its great reef makes little sense without knowing about its coal industry. It is powerful in a way that few industries globally are. Until recently, Australia controlled a greater proportion of the seaborne coal trade than Saudi Arabia did the oil trade. Domestically, coal-fired power plants provided 90% of the nation’s electricity. The coal barons have made it their business to ensure that nothing gets in the way of their profits. But much has changed in the past five years. Coal prices are at a historic low, and as electricity demand has fallen, and renewables have expanded, coal now supplies a mere 69% of the nation’s electricity. The industry has woken up to the threat it faces, and it’s now putting all its efforts into self-defence. What it sees as bureaucratic “green tape” – ie, environmental regulation – has been high on its agenda, as it tries to breathe new life into stalled coal projects.

This is not the first time the reef has been threatened with destruction. In the 1960s, proposals were developed by the premier of Queensland, Joh Bjelke-Petersen, to mine the reef for fertiliser for the state’s sugar cane fields, and to drill the corals for oil and gas. Were it not for the catastrophic consequences for marine life of the Torrey Canyon oil spill on the south-west coast of the UK in 1967, the proposal may have gone ahead. As it was, the Australian federal government granted the reef a measure of protection instead, creating the Great Barrier Reef Marine Park Authority to allow for wiser management in the future.

Today, ordinary Australians are waking up once more to the dire threat facing their reef. They are joined by a thriving tourism industry. With marine tourism alone earning $4bn a year for the local economy, it’s the most profitable business in the reef region. It is also a large employer, pushing local public sentiment very much on to the side of protection.

If the Carmichael coal mine is a global story, and the Great Barrier Reef a global asset, then the issue should not be left to Australia alone to decide. The citizens of the world deserve a say on whether their children should have the opportunity to see the wonder that is the reef. Opportunities to do this abound. Petitioning national governments to put climate change on the agenda of the G20 summit, to be held in Australia in November this year, is one. Pushing governments to play a constructive role at the 2015 climate negotiations in Paris is another, as is letting the Australian government know directly that everybody has a stake in the reef, and that it needs to act to secure its future. The Great Barrier Reef does not have to die in a greenhouse disaster like the one that devastated the world’s oceans 55 million years ago. But if we don’t act decisively, and soon, to stem our greenhouse gas emissions, it will.

This article was amended on 4 August 2014. An earlier version referred to carbolic acid. That has been corrected to carbonic acid