By 2100, Earth Will Have an Entirely Different Ocean
Pacific Ocean, NASA


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By 2100, Earth Will Have an Entirely Different Ocean

A complete guide to the hotter, higher, trashier, fish-free oceans of the near future.

The ocean is in the midst of a radical, manmade change. It can seem kind of crazy that one of the most immense properties on Earth—the ocean washes over 71 percent of the planet—could be completely transformed by a swarm of comparatively tiny, fleshy mammals. But humans are indeed remaking the ocean, in almost every conceivable way. The ocean we know today—that billions of people swim, fish, float, and surf in—that vast planetary body of water will be of an entirely different character by the end of the century.


"There is only one global ocean," as NOAA likes to say. While it's changing in different ways and to different degrees in different places, it's a single, huge, interconnected system. Trash dumped off the coast of Australia can end up in the great Pacific Garbage Patch. Pollution from China drifts overseas into North America. All of our carbon emissions end up partially absorbed by oceans everywhere—the actions of residents of Sheboygan, USA have affected, in some minute way, the future of the seas in Bangladesh. That's the thing about climate change.

It's not just that the ocean is absorbing more heat than at any point over the last 10,000 years, and that its levels are rising. It's also becoming more acidic. Its very chemical composition is changing. Ecosystems will be reordered, currents altered. To the billions who live closest to it, it will be more hostile. Coastal flooding will threaten cities, Arctic passageways will open new trade routes, and fishermen who depend on the seas will scramble to keep up with the shifting aquatic biomes.

"In a worst case scenario, i.e. one in which we pursue business-as-usual through the end of the century," the climatologist Michael Mann tells me, "the oceans will look something out of a post-apocalyptic Hollywood flick. We are talking about the depletion of fish populations by overfishing, the massive die-off of much other sea life due to water pollution and ocean acidification, the destruction of coral reefs by the twin impacts of ocean acidification and bleaching by increasingly warm ocean waters."


Which is why it's worth taking a look at the changes reshaping the body of water that defines our planet, and examining where our best predictive sciences say we'll end up at the end of the century—in the year 2100, which is as good a benchmark as any. It's a natural milestone, included in a lot of climate models' projections, policy-oriented synthesis reports, and research-based recommendations for political leaders.

By combing through the most recent science and reaching out to oceanographers and climate scientists, I tried to render a snapshot of what the future of our oceans might look like.

Rising Tides

Right now, the ocean is growing. That's due to two main factors; the melt of land ice—mostly from Arctic and Antarctic sheets, shelves, and glaciers—and thermal expansion. In the ocean, thermal expansion occurs when water warms. It leads to an increase in volume, but a decrease in density. Right now, the ocean is absorbing about 90 percent of the excess heat generated by climate change, and is getting fed by numerous thawing ice stocks in the Arctic and Antarctica.

So sea levels are rising—but by how much?

The head of NASA's Goddard Institute for Space Studies, Gavin Schmidt, told me that the best available roadmap for the future of our oceans under climate change is probably the Intergovernmental Panel on Climate Change's (IPCC) latest report. That 2014 behemoth of a survey is an invaluable resource, as it features an exhaustive synthesis of the latest body of ocean and climate science. Known for erring on the conservative side, it predicts a sea level rise of between a foot and a half to five feet by the end of the century, depending on whether we reduce our greenhouse gas pollution.


"For high emissions IPCC now predicts a global rise by 52-98 cm by the year 2100, which would threaten the survival of coastal cities and entire island nations," the oceanographer and climatologist Stefan Rahmstorf explains. The highest-emissions projections point us closer to 1.5 meters (5 feet) of sea level rise.

"But even with aggressive emissions reductions, a rise by 28-61 cm is predicted," Rahmstorf notes. "Even under this highly optimistic scenario we might see over half a meter of sea-level rise, with serious impacts on many coastal areas, including coastal erosion and a greatly increased risk of flooding." Even if we quickly and suddenly reduce emissions, in other words, expect the ocean to rise by at least a foot or two no matter what.

But other scientists warn of the prospect of sea levels that are much, much higher. The godfather of climate science, James Hansen, along with 16 respected co-authors, recently published new research that makes the case that land ice in Antarctica and Greenland will melt 10 times faster, and contribute 10 feet of sea level rise in a period as brief as 50 years (the study is controversial and is currently under peer review). Clearly, that would be disastrous for human civilization as it is currently organized—with the bulk of our population centers posted on the coast—many scientists believe that we're currently "locked in" to about that much sea level rise regardless, because of the inexorable melting of a giant ice sheet in West Antarctica. But it may take many decades beyond 2100.


So what does all this mean? What does 1.5 feet sea level rise look like, compared to 10? How should we envision this swelling of the oceans? There are a number of handy tools that help drive home how this saltwater creep will manifest: Climate Central, for instance, has a tool that uses Google Maps to demonstrate how much of US coastal cities and land will be swallowed by the rise. NOAA has a similar one.

Most of New Orleans will be underwater with 5 feet of sea level rise, as will large swaths of Miami and New York City. Some cities may be spared the swamping with expensive water management technologies; others will have to be relocated. Some, the poorer ones, no doubt, will be evacuated and abandoned.

So, by 2100, the oceans will include at least the remains of some human infrastructure in its shallows; beachfront property, docks, boardwalks, and some of the roads that we used to get there. To illustrate, here's Miami, under 10 feet of saltwater.

Hot Water

Water can absorb far more heat than air, which is why the ocean has sucked down the bulk of the heat that has resulted from climate change. This is a good thing for the climate; it means air temperatures aren't heating up as rapidly as they otherwise would—and it's the reason there was a so-called "pause" in planetary warming. But it also means the ocean is beginning to heat up in a serious way.

"Over the last 39 years, oceans have warmed at average rates of >0.1˚C per decade in the upper 75 meter and 0.015˚C per decade at 700 m depth," the IPCC report explains. This may not sound like much, but it is. Shallow waters are warming up, fast. By the end of the century, if warming continues apace, shallow waters may be a full degree Celsius (1.8˚F) warmer, on average, which could be dangerous to marine ecosystems and may help feed tropical storms.


Even incremental increases in temperature cause coral to bleach, for instance, a phenomenon plaguing the keystone species around the world. Combined with acidification, which we'll get to shortly, coral risks flat-out extinction by century's end. That's the conclusion of a 2012 study published in Science; "Nearly every coral reef could be dying by 2100 if current carbon dioxide emission trends continue."

Meanwhile, because warmer water is quicker to evaporate, it means the ocean can fuel more powerful storms. Combined with higher sea levels, by 2100, the ocean will be more prone to overwhelm nearby communities in the event of a hurricane or tropical storm. And while the warming waters will prove problematic everywhere, the heating will be most pronounced away from the equator.

"The strongest warming trends are found at high latitudes," the IPCC notes, away from the equator. Like the Arctic and Antarctic, where warmer water is melting icebergs and ice sheets from below, contributing to further sea level rise and robbing polar bears (still the most famous mascot of global warming), walruses, and other animals of their habitats. Last year, the lack of sea ice forced 35,000 walruses to crowd together for the first time in observed history, making for one of the most iconic examples of polar warming in recent memory.

The Arctic region is warming twice as fast as the global average; thus, according to projections of climate agencies like NOAA and the UK's Met office, Arctic sea ice may be all but gone in the summers by century's end. "In fact," NOAA states, "it is thought that the melting of the sea ice could accelerate through the 21st century, with very little summer sea ice remaining by the year 2100."


Warmer waters ripen conditions for invasive species, too, which is why crabs from the Caribbean are showing up in northern waters. Marine life all over is being driven northward—fish are heading towards the poles. Sharks are spawning further north.

Algae is more likely to bloom—warmer-than-usual temperatures in the Pacific have fueled the record-breaking toxic bloom currently stretching past California right now, for instance. "It's definitely the largest bloom of this particular algae seen on the West Coast, possibly anywhere, ever" Raphael Kudela, a professor of ocean sciences at the University of California Santa Cruz, recently told CBS News.

Finally, probably the most dire-sounding development of all: An expansion of marine dead zones, wherein oxygen levels become so low that little life can survive. Maybe the best known example is the massive dead zone in the Gulf of Mexico; it's about the size of Connecticut. A number of studies have linked warming waters to the expansion of these dead zones, also known as hypoxia—fixtures that will become more or less permanent in our future ocean.

"Any increase in dead zones from global warming will last for thousands of years. They will be a permanent fixture" of our oceans, Gary Shaffer of the University of Copenhagen, who studies dead zones, told National Geographic. His model "predicts that global warming could cause dead zones to grow by a factor of ten or more by the year 2100," according to NatGeo. "In the worst-case scenario, dead zones could encompass more than a fifth of the world's oceans."


That's just the most dire prediction; we may not see dead zones of that size, but we'll probably see a lot more of them than we do now. The bottom line is that as the ocean warms, it will transform in a host of very unpredictable, sometimes radical ways. So how hot does Gavin Schmidt think the oceans will be in 2100?

"Hot enough to boil a frog," he said. "Metaphorically." The frog in that metaphor, I think, is us.

Acid Splash

But we're not just boiling; we're risking an acid bath, too. About 30-40 percent of all carbon emissions are drawn down directly into the ocean, where it forms carbonic acid. As a result, the pH in the surface ocean today is 0.1 unit lower than it was before the Industrial Revolution. And the most recent research shows that ocean waters are on track to become much more acidic by 2100—up to 150 percent more so. In other words, by the end of the century, the ocean will be twice as acidic as it was in preindustrial times.

That's what Taro Takahashi, a professor at Columbia University's Earth Institute who studies ocean acidification, tells me. He said that he agrees with the landmark 2009 study by Richard Freely that attempted to project acidification levels into the future.

"The magnitude of acidification depends primarily on the amount of CO2 emitted into the air, and I agree with their prediction for the magnitude of acidification: the pH of surface ocean water decreases from today's about 8.1 to about 7.75 by 2100 (an increase of 225 percent in the hydrogen ion concentrations)," he tells me.


If we continue emitting carbon dioxide at the current pace, we're on target to hit 800 parts per million by the end of the century (we're at 400 ppm now). In that case, Freely explains, "surface water pH will drop from a pre-industrial value of about 8.2 to about 7.8… by the end of this century, increasing the ocean's acidity by about 150 percent relative to the beginning of the industrial era." (More recent studies have shown it could get even worse.) So what's the big deal? What ill is portended by slightly more acidic oceans?

For one thing, shellfish are in trouble. In some places, as in certain stretches of the Pacific, the ocean is already too acidic for some sea snails' shells to properly form. In 2100, entire ecosystems could be ravaged; not just corals and sea snails, but many creatures whose exoskeletons are made of calcium carbonate.

"The level of CaCO3 saturation would decrease by 50 percent or more, and colder oceans would become corrosive to CaCO3 shells," Taro says. Plus, the last time the oceans got this acidic this fast, 96 percent of marine life went extinct.

Garbage Islands and Falling Fish

It's not all carbon and climate change, either; humans are directly impacting the oceans, too, of course. We're covering it in garbage, for starters. Three major papers published in 2014 sought to tally up the amount of debris we've loaded into the ocean. As National Geographic explained, "There are 5.25 trillion pieces of plastic debris in the ocean. Of that mass, 269,000 tons float on the surface, while some four billion plastic microfibers per square kilometer litter the deep sea."


We have blanketed the seafloors, and sea-surface, with refuse, changing on every level the nature of those environments. And imagine what kind of trash that 85 years of nonstop development and free-market capitalism will churn out by 2100.

"A recent estimate of the amount of plastic that enters the ocean every year—8 million metric tons from 192 countries," NOAA's Asma Mahdi told me. "Those estimates don't differentiate between different kinds of plastic—it's very difficult, especially since waste management is so different across the country and the globe. If things remain as status quo, debris will fill our ocean."

If we continue to dump 8 million metric tons of trash into the ocean every year, it will total 680 million tons by 2100. Some of that will have been cleaned up, as NOAA notes, but some of it will continue to form grand artificial landmasses in the Pacific and elsewhere.

The ocean of 2100 will be packed with trash.

Perhaps it can take the place of the fish, many species of which are rapidly being fished into extinction oceanwide. A survey of the recent science by Pew found that "90 percent of the world's fish stocks are overfished or fully fished," and "Experts say populations of large predatory fish such as tunas and sharks have declined about 90 percent over the past 60 years." Even the most fearsome of fish, the sharks, are being finned into extinction, scientists worry: they estimate that a staggering 100 million are killed each year.


The EDF, a mainstream enviro group, claims that "Of all the threats facing the oceans today, overfishing takes the greatest toll on sea life—and people." That's probably true for now, as hundreds of millions of people depend on seafood for protein, and the fishing practices currently draining our oceans are pretty destructive—remember shrimp trawling?

A 2006 Science study showed that we were on pace to see the collapse of major fish stocks by midcentury, if overfishing continued. So far, it has. After the collapse, the study argues, we'd see just 10 percent of the original catch from 2050 on. Other studies offer a less grim portrait, but most agree that we're rapidly depleting major fish stocks upon which humans and other sea life rely.

By 2100, it's hard to say exactly how much will be left.

The Oceans of 2100

"Never turn your back to the ocean," my father used to say, whenever my brother and I would play too close to its waves. Two things strike me, about that nugget now—one is that it seems like, collectively, we've done exactly that: we've polluted, overfished, acidified, and warmed it. We've managed to trash the place, without necessarily intending to.

Second, it's a little strange to think just how different the ocean of 2100 will be from the one I was turning my back on, literally—the next generation, and the one after that, will come of age with an entirely different ocean than the one we couldn't bear to face. And how drastically it changes will depend a lot on how we decide to act right now; which policies and principles we choose to pursue.

That's why even Dr. Mann, who gave me one of the grimmest prognostications, nonetheless holds out hope.

"The good news is that this doesn't have to be our future," he said. "There is still time to act to save the oceans for future generations."

Hell or Salt Water is a series on Motherboard about exploring and preserving our oceans. Follow along here.