It is extremely difficult to divine what is happening below the water from what is visible at the surface. Ghost crab volcanoes rise from the sand beside a lagoon of duck-egg blue. The air is clear and still cool as the first sun touches the palm crowns. Noisy mynahs argue over the contents of a plastic bag stranded on a beach that is smoothed to perfection by the falling tide. Below the glassy surface, stingrays pass like shadows with movements so subtle they seem to glide without propulsion. A little offshore, sudden splashes and arcing cascades of silvered fish give away the primordial interplay of hunters and those hunted.

This coral reef in the Maldives lies at the heart of the Indian Ocean, where the fight for life goes on daily, as it has for countless millennia. But a new struggle is under way against an invisible force that has not been felt for millions of years, upending the relationship that built these reefs, a partnership first formed during the age of the dinosaurs between coral and a microbial seaweed. These seaweeds, called zooxanthellae, somehow evolved to live within the coral animal’s tissues. As plants, they gifted corals with abundant food produced by photosynthesis, enabling the corals to grow more rapidly than their predecessors, whose only source of food was passing plankton. In return, living deep within coral tissues cupped inside hard limestone skeletons, zooxanthellae gained protection and used exhaled carbon dioxide to make food. Photosynthetic calories fortified the corals as protein supplements do bodybuilders. Thus endowed, corals could lay down limestone fast enough to outpace the forces of destruction: rasping grazers, burrowing worms, snails and sponges, chemical dissolution and storm waves.

Over tens of thousands of years, corals built structures that criss-cross thousands of kilometres of ocean and descend hundreds of metres into the abyss. It is hard to reconcile the immense geological antiquity of the coral-seaweed partnership with its present susceptibility to disruption. Corals love warmth, basking in tropical seas that rarely dip below swimming-pool temperatures, but equally, they wilt under unusual heat. Although we rarely think of them this way, the oceans are afflicted by heatwaves too, and, just as on land, the frequency and duration of these are on the rise due to global warming. When oceanic temperatures increase just a degree or two above the typical maximum for a region, and stay there for a month or more, the relationship between coral animal and internal zooxanthellae turns nasty, swinging from benefit to cost. In this fevered state, for reasons that are still unclear, the corals must rid themselves of the zooxanthellae quickly or they will die. Because the seaweeds produce most of the colour in coral, when they are expelled the corals turn a deathly bone white in a phenomenon known as mass bleaching. A bleached coral is a starving coral, and since corals store little fat, unless temperatures fall quickly and they can regain more zooxanthellae, they perish.

The Maldives is a nation wholly dependent on coral. It consists of twenty-six atolls built upwards by coral growth over thousands of years as sea levels rose after the last ice age. The reefs are topped by 1,100 islands created from dead coral fragments and sand swept up by Indian Ocean waves and bound together by shrubs and palm trees. From space, the country appears as a double string of bright emerald rings that runs north to south across a thousand kilometres of dark sea. Zoom in closer and, inside the giant circles of reef that make up the main atolls, dozens of ring reefs rise from the bottoms of pale lagoons. This is one of the major coral provinces of the world, comparable to Australia’s Great Barrier Reef in size and complexity. The Maldives’ profusion of reefs, developed over a period that we know from the geological record, has been one of the most prolific eras of reef construction in planetary history. But in 1998, tragedy struck.

In December 1997, far away from the Maldives, an El Niño – a large-scale disturbance of oceanic and atmospheric circulation – began to spread a pool of warm water across the eastern Pacific. First it scorched the Galapagos Islands, then in early 1998 it spread like a hot tongue along the equator, wrapping around Australia and Indonesia before slipping into the Indian Ocean. By May the hot pool had crossed to the coast of East Africa and entered the southern Red Sea. As the heat engulfed reefs along its journey, the corals bleached before dying en masse. Indian Ocean reefs were devastated, losing between 70 and 95 per cent of their coral. In the Maldives, living coral plunged from covering between half and two-thirds of the reef to less than a twentieth.

With hindsight, we realise that this global mass mortality of coral was an early example of the immense planetary upheaval that is visible everywhere today. The world is changing in ways beyond experience. Places where benign climates have nurtured civilisations into life now see wildfire, drought or tempest in their midst; seas that have lapped the same shores since the end of the last ice age are rising again as glaciers are burned off mountainsides or surge into the ocean, unmoored from their rocky seabed anchors by probing warm water. There is a febrile atmosphere about these times, as the earth’s thermostat drifts upwards. Each broken record – each new disaster – is like a gasping whitecap on a steepening wave, the harbinger of a coming crash.

Climate sceptics (and there are still a few weaving fairy tales to explain away the implacable mountain of evidence) love to remind us that the planet has often changed throughout its history. During the early Eocene epoch, 50 million years ago, the climate was over 10°C hotter than now, there was no ice at the poles and the sea above the Arctic Circle was an improbable 20°C. The sceptics’ argument implies that today’s changing climate is somehow less serious because changes have occurred previously, but there are two crucial differences between past and present. The first is that changes today are happening faster than previously. Four of the past five mass extinction events were marked by a tremendous release of greenhouse gases leading to global warming and ocean acidification (from carbon dioxide dissolved into the sea). The mother of mass extinctions was the end-Permian collapse, brought on by vast reservoirs of lava bubbling up through today’s Siberia, vaporising coal measures and carbonate rocks into carbon emissions at a rate of a fifth to a third of a gigaton per year. Today’s emissions blow into the atmosphere thirty to forty times more rapidly.

The second vital difference between past and present is us. Past changes had natural causes, like volcanoes or orbital wiggles, but present warming is unequivocally our fault: you can’t release aeons of solar energy stored in fossil fuels without disruption. But the heat produced by these fuels is only a tiny part of the warming; it is the greenhouse effect, by which released carbon dioxide and gases like methane trap incoming solar energy, that makes the greatest difference. In the time that it takes you to read this sentence, the world will have trapped additional heat that is equivalent to the explosion of thirty Hiroshima-sized atomic bombs. Read that again, it wasn’t a misprint. By the time you have, the total will be sixty atomic bombs.

I first began to take my master’s students to the Maldives to experience its marvellous coral reefs in 2014. Sixteen years had passed since the El Niño warming had shrivelled its corals and their renewal was nearly complete. Just as a tree which falls in the forest can offer opportunities to others, space freed up on a reef is soon colonised by seaweeds and a riot of invertebrate life, including new corals. Coral growth is slow, typically ranging from about a centimetre a year for colonies with rounded stony shapes to twenty centimetres for the most vigorous arborescent species. Although visible scars remained, the wounds had more or less healed. Corals tumbled into the depths down slopes half obscured by moving clouds of fish. Table corals spread seaward from the reef front like stepped ledges, around which schools of snapper fish flowed in braided streams, their bodies lined with gold, dark eyes circled in glowing daffodil yellow. Such resilience was uplifting. I began to believe again that coral reefs might outlive today’s relentless human destruction.

Then in 2015, history repeated itself. A giant El Niño disturbance erupted in the eastern Pacific and spread towards Australia. By March 2016, the northern Great Barrier Reef had lost 60 per cent of its coral. By May, corals throughout the Maldives had bleached and, by July, 50 to 70 per cent were dead. One particularly exquisite reef near the island my students and I use as a base, a showpiece gem in a richly decorated crown, lost 99 per cent of its coral.

Three years on from this catastrophe, I am back with another class. We slip underwater with our scuba tanks and glide gently down to the reef. It is beginning to look healthier, less damaged. Fish that depend on coral for food or shelter suffered greatly when the corals died, but are coming back. Tiny Chromis, newly arrived from their drifting planktonic larval stage, fill the water like emeralds, their scales glinting and sparkling above their coral shelters. Black-and-white humbug fish, neat and rounded like the boiled sweets after which they are named, retreat among the branches of a coral head at our approach, then blossom outward again after we pass. Newly settled corals speckle the bottom, like young plants pushing up from recently thawed soil.

But despite the exuberant colours, the play of light and wondrous forms, I see the absences: animals that should be there but are not. These ghosts haunt me as I pass by towering columns that should be half-living coral but instead are rock spattered by sponges and tufted with hydroids or weed. Within their clefts, giant groupers and spangled emperor fish should be hiding. The occasional encounter with a hulking fish, round-bellied and scarred by age, only serves to remind that there should be more. Most of my students are fresh to the scene and revel in the immediacy of the experience. To them, the blanks are invisible.

I also see things that should not be there. The sponge that covers the bottom like fungus is a pretty turquoise patch to my students. To them, the matted algae that stain the seabed rust brown shiver in the current like waterweed in a summer river. For me, they are a cloak that chokes off recovery, snuffing out tiny corals before their lives have really begun.

The difference in our perceptions illustrates a phenomenon called ‘shifting baseline syndrome’. Shifting environmental baselines are intergenerational changes in how we perceive our world. Each generation sets its mental benchmark of normality by how the world looked when first encountered, often in youth, and sees change relative to this. Younger generations accept as normal a world that seems tainted and degraded to older people.

Shifting baselines weave through many aspects of life, usually unnoticed, since that is their power. In 1871, John Ruskin, the English critic and artist, railed in ‘The White-Thorn Blossom’ against what he saw as the desecration of a small piece of heaven in the Derbyshire hills by a railway viaduct:

There was a rocky valley between Buxton and Bakewell, once upon a time, divine as the Vale of Tempe; you might have seen the gods there morning and evening – Apollo and all the sweet Muses of the Light – walking in fair procession on the lawns of it, and to and fro among the pinnacles of its crags. You cared neither for gods nor grass, but for cash (which you did not know the way to get). You thought you could get it by what the Times calls ‘Railroad Enterprise’. You enterprised a railroad through the valley, you blasted its rocks away, heaped thousands of tons of shale into its lovely stream. The valley is gone, and the gods with it; and now, every fool in Buxton can be at Bakewell in half-an-hour, and every fool in Bakewell at Buxton; which you think a lucrative process of exchange, you Fools everywhere!

The twist in this tale is not Ruskin’s rage, which many of us feel daily at the destruction by commerce of natural wonders and beauty, but what happened a century later. By the 1960s, the railway had become uneconomical and the line was closed. Instead of taking swift advantage to remove the blight, the Headstone Viaduct was Grade II listed and preserved for its grandeur. Looking at photographs of this softly wooded valley, spanned by five elegant arches of moss-covered stone, I find it hard to agree with Ruskin: my baseline was set in a world where viaducts were admired, not castigated.

Shifting baselines have a darker side. The recent resurgence of right-wing ideology has been blamed on many things, with one view being that immigration and globalisation have placed immense strain on feelings of cultural and national identity, leading to a backlash. Another is that growing inequality breeds resentment and despair that usher the dispossessed into the arms of populist leaders. Such leaders are again spouting the fascist and authoritarian tropes used by Stalin, Mussolini and Hitler. Their words were taboo and almost unspoken by generations of people who lived through the horrors of two world wars or grew up in their aftermath, but younger people today are falling for the rhetoric in part because their personal experiences of peace and stability tell them little, or nothing, of its danger.

These are extraordinary times. The Renaissance heralded in a resurgence of art, literature and technology, expressions of the period’s renewed curiosity about how the world worked and our place in the universe. Not even the greatest minds of the day, however, predicted that within a few centuries we would transition from being at the mercy of nature to reshaping it. That headlong growth in understanding and influence – that fevered rebirth of culture between the Middle Ages and modern times – is itself a wonder of nature, but it far outstrips growth in our common sense. We know what we are doing to the world, we know how to stop the harm, but again and again we fall short when it comes to action. Like a teenager, our capacity for calamity has grown faster than our self-restraint, a mismatch that leaves us dangerously exposed.

The question of the age is whether we can adapt from fulfilling our own selfish interests to fulfilling the self-interest of humanity before it is too late. If we let the growing flood of human impact run its course, nature’s beauty and abundance will be pruned so savagely that there will be only remnants left. They will hint at past majesty, as a marble torso or shattered face pulled from the earth lets us glimpse the nobility of ancient Greece. Those of us who document nature’s struggle, as the boot of human progress presses ever harder upon the earth, look on with feelings of helplessness as the world did when the Taliban destroyed the Bamiyan Buddhas, or when ISIS sacked Palmyra. Each forest cleared is another assault; every coral bleaching, a silent tragedy.

Scientists are trained to record and report dispassionately, distancing themselves from the phenomena observed. But sometimes it is hard not to get caught up by emotion. I once dived off an island in the Arabian Gulf and found the reef pulverised to rubble by anchors thrown from fishing vessels. The anchor of a neighbouring boat had smashed a hole amid the delicate fawn branches of an Acropora thicket, lying within the hollow like an iron claw. A fragment-strewn path passed through the coral to the anchor, cut by dragging chain. The loss felt all the more heartbreaking because the destruction was not yet complete. Here and there turrets of living coral emblazoned with the liveries of a hundred species of invertebrates hinted at
past glories.

If humanity were to feel the cumulative burden of loss and damage over millennia, it would already be unbearable, but shifting baselines have a protective influence. The patch of bluebell woodland hemmed in by housing can bring as much pleasure as the heavy-timbered wildwood that was once there, perhaps more. Young Singaporeans grow up surrounded by skyscrapers and hanging gardens, and many prefer them to the ‘green hell’ of jungle they have replaced. For those who have seen pages torn from the book of their experience, or badly overprinted with vulgar development, the story is jarring and incomplete. But for those new to the scene, it’s a different tale.

You cannot regret the loss of something you never knew existed, but shifting baselines, while soothing the sting of loss, do not fully protect us from the consequences of today’s recklessness. We know what we have done. Unlike the dinosaurs, whose demise was no fault of ours, we rue the loss of the dodo, or great auk, or Atlantic grey whale, because we killed them all. Some of the most threatened species today are among the most iconic: Siberian tigers, Javan rhinoceros, vaquita porpoises, Amsterdam Island albatrosses and a menagerie of others. Imagine a future in which these animals exist only as virtual- reality holograms recreated from old television documentaries.

Losses to nature risk far worse than the impoverishment of human experience; they also threaten our well-being. As ecosystems disintegrate, we are seeing losses of critical functioning upon which life depends. For example, in degraded habitats plants and ocean phytoplankton produce oxygen and extract carbon dioxide less quickly from the atmosphere than in healthy intact habitats, accelerating greenhouse warming. Coastal habitats like coral reefs or mangrove forests, under assault from growing human pressures, protect coasts less strongly, just when rising sea levels mean we need their protection more. In September 2019, the Intergovernmental Panel on Climate Change reported on risks to the oceans and frozen parts of the planet. There is no scenario of greenhouse gas reduction that will stop sea level rise, they concluded. If the world were to shift to carbon-neutral energy production tomorrow, sea levels will carry on rising between one and three metres in the next 200 years. That is bad news for the 880 million people who live on very low-lying coasts. It is terrible news for global food production, which is disproportionately concentrated on fertile, low-lying river deltas and flood plains.

Here shifting baselines represent a clear danger, suppressing perceptions of harm and lowering ambition to reverse human impacts. A good example can be found in European marine protected areas. Many permit the continuation of extractive and damaging activities, like bottom-trawling for fish, dredging or mining for aggregate. The logic applied is that the wildlife present is resilient to these activities because they survive them today. This is often true, but it is because the habitats are a product of the activities, not because the activities are benign. We have mistaken altered and often heavily damaged habitats for the norm. That error seems improbable, but was easily made. Much of the damage occurred long before marine scientists began to look underwater in the second half of the twentieth century, so they assumed the habitats they found were natural and subject primarily to environmental forces. I was hoodwinked myself as a student taking my first, hesitant dives into the North Sea in the 1980s. I thought the monotonous backdrop of shifting sand, gravel and mud I encountered was the outcome of powerful waves and currents that prevented animals and plants from gaining a foothold. It was only decades later that I discovered the richness of life that carpeted the seabed where there was protection from trawling and dredging: moss-like bryozoans, feathery hydroids, lace nets of coralline algae, sponges of gaudy orange, purple and yellow, and the waving tentacles of burrowing anemones covered the bottom, while shoals of juvenile fish sheltered among dark thickets of seaweed.

The premise of present-day naturalness is almost always undone by reference to the past. For example, a report on Irish Sea fisheries from 1836 includes the following descriptions, among many similar, depicting a world in which marine life was far more abundant than today:

Turbot are so abundant in Dundrum Bay, that they are speared close to the dry strand.

The middle of [Carlingford] Loch is deep . . . and the bottom occupied by an immense bed of oysters, of which vast quantities are taken to Dublin and other towns.

[In a season] a Skerries boat may catch Ling to the extent of thirty or forty hundred weight, dried; twelve or fourteen hundred [weight] of Cod, of five score to the hundred [weight]; and thirty hundred [weight] of Skate.

The dense cod shoals, skate the size of tables and rugged oyster beds are all gone from the Irish Sea today.

It is salient also to examine fish catches from when records first began in 1889, as Ruth Thurstan, one of my former students, did. She looked at the productivity of bottom-trawl fisheries in England and Wales and was astonished to find that a fleet powered mainly by wind landed five times more fish annually in the late nineteeth century than the sophisticated modern vessels one hundred years later. When she accounted for the technological advances that made the modern fleets more powerful and efficient, the gulf was even greater: nineteenth-century boats landed seventeen times more fish per unit of fishing power expended than those of the twenty-first century. If a nineteenth-century fisherman could somehow be transported to the present, they would conclude that the sea had been emptied of fish and the bottom left barren.

Some fish have been almost eliminated from their former haunts. Thurstan’s figures suggest that halibut, a large and succulent flatfish, have undergone a greater than 99 per cent decline in the southern North Sea since 1889. Historical records from the 1830s show that sailing vessels deploying hook and line often caught a ton of halibut per day on the Dogger Bank alone, a sprawling underwater hill between England and the Continent, while today’s entire fishing fleet lands less than two tonnes of halibut in a full year of fishing the Dogger. Yet the conservation objective set for a recently established English marine protected area on the Dogger Bank was to maintain the habitat as it is today. Not only does such low ambition hold back the recovery of nature, it mandates that it should not happen.

As baselines shift across generations, we have forgotten the past so completely that few people question whether a different world is even possible, or desirable, today. There are two antidotes to this complacency. History supplies the first: more and more scientists and historians are disentangling the roles of human and natural causes in long-term environmental change. Their research tells us that the world was generally richer, ecosystems more complex and vibrant, and animals bigger and more abundant in the distant past. The second antidote is provided by protected areas. When areas are fully protected from extractive and damaging uses, remarkable transformations unfold. Fish and shellfish become more prolific, much bigger and more productive. Different habitats emerge, like kelp forests re-establishing on naked reefs, oyster beds scrambling upwards from the bottom, or the seabed blossoming again with the rich crusts of invertebrates that historical accounts describe. Nature has great resilience, and when given respite from human damage, it soon flourishes once more.

Rapid global change supplies an urgent imperative for a rethink of conservation practice. For the last several decades we have been losing on two fronts: as the planet heats up and the human imprint grows, the natural world is on the move and in retreat. Likewise, our efforts to save species and habitats are failing even to reduce the rate of biodiversity loss, let alone reverse it, while greenhouse gas emissions still rise long after we know they should have begun to fall. Like Nero, we fiddle as Rome burns.

What we are beginning to appreciate, belatedly, is that we cannot solve our problems by technology alone or live without nature. Saving biodiversity cannot be achieved by tokenism. At present, the international community has agreed to protect just 10 per cent of the sea and 17 per cent of land for nature. Wildlife needs far more space if it is to keep the planet habitable, and if we give it that space, it can help us out of our present troubles. In photosynthesis, evolution has produced the best means of extracting the greenhouse gas carbon dioxide from the air, releasing at the same time the essential by-product of oxygen. While we wrestle to bring down emissions, nature can slow the speed of warming and adapt to the consequences of climate change.

Again and again I have watched and carefully documented the vigorous resurgence of life given protection from hooks, nets, traps or dredges. Most of the protected areas I have studied are little more than hectares to a few square kilometres in size, like the coral reefs of St Lucia in the Caribbean. But they prove that nature is buoyant and prolific given a chance. These findings, now replicated in hundreds of protected areas scattered across almost all seas and oceans, make a compelling case for greater effort. A large-scale programme of protection, rewilding and habitat restoration is called for, more ambitious than anything attempted so far. Many of the world’s foremost scientists are calling for the safeguarding of a third to half the planet, and greatly improved management of the rest. This is not utopian fantasy. The fantasists are those who think we can somehow engineer a replacement environment, or believe we can thrive in a world of megacities and industrial agriculture alone. Our approach must shift rapidly from trying to save nature from ourselves to giving nature the space and freedom from human impact to save us. The draft text of a possible new international agreement for the next ten years of nature conservation sets out a vision for 30 per cent of land and sea to be protected by 2030. If adopted by the Convention on Biological Diversity, it would represent a major advance. But protected areas will need strong protection from extractive and destructive uses to make the difference we need.

I am an optimist at heart – how else could I be an environmentalist if I did not see hope as better than despair? But at some point, optimists must be pragmatists. Global change is racing away from us as the gulf widens between what we should do and what we are doing. The discomforting truth is that regardless of what we do, many of the changes under way today are unstoppable and accelerating, at least for the immediate future. That doesn’t mean we should give up. On the contrary, we must redouble our efforts to wean ourselves off fossil fuels, because how fast we do this will dictate how long the damage will endure. If we act decisively, there will be a few centuries of strife before more settled times return. We might even prevent the complete loss of coral reefs, if we’re lucky, but if we drag our feet, we condemn our descendants to thousands or tens of thousands of years of loss and turmoil.

Photograph © European Space Agency / Copernicus Sentinel / CC BY-SA 3.0 IGO, Ari Atoll, The Maldives, 2019