Today a baby girl was born. Consider the years of her life—how she’ll think back to her childhood in the ’20s (the 2020s) and become a teenager in the ’30s. If she’s an American citizen, she’ll cast her first vote for president in the 2040 election; she might graduate from college a year or two later. In the year 2050, she’ll turn 31, and she’ll be both fully grown up and young enough to look to the end of the century—and imagine she may get to see it.
We hold the fate of that girl—and of the society she inhabits—in our hands. That’s the message of a blockbuster new report, released today, from the United Nations–led Intergovernmental Panel on Climate Change (IPCC).
While the report covers how climate change is reshaping the oceans and ice sheets, its deeper focus is how water, in all its forms, is closely tied to human flourishing. If our water-related problems are relatively easy to manage, then the problem of self-government is also easier. But if we keep spewing carbon pollution into the air, then the resulting planetary upheaval would constitute “a major strike against the human endeavor,” says Michael Oppenheimer, a lead author of the report and a professor of geosciences and international affairs at Princeton.
“We can adapt to this problem up to a point,” Oppenheimer told me. “But that point is determined by how strongly we mitigate greenhouse-gas emissions.”
If humanity manages to quickly lower its carbon pollution in the next few decades, then sea-level rise by 2100 may never exceed about one foot, the report says. This will be tough but manageable, Oppenheimer said. But if carbon pollution continues rising through the middle of the century, then sea-level rise by 2100 could exceed 2 feet 9 inches. Then “the job will be too big,” he said. “It will be an unmanageable problem.”
This release concludes a trilogy of special reports from the IPCC. The first came last October, when it warned that even “moderate” warming of 1.5 degrees Celsius would generate irreparable damage; and the second was published last month, with a summary of how climate change will reshape the planet’s land surface. After this new report, the IPCC will fall silent until 2021, when it will publish its sixth major assessment of climate science.
In other words, the IPCC—whose recent reports have overthrown the climate conversation both in the United States and around the world—will publish nothing new until after the 2020 presidential election.
The headline finding of this report is that sea-level rise could be worse than we thought. The report’s projection of worst-case sea-level rise by 2100 is about 10 percent higher than the IPCC predicted five years ago. The IPCC has been steadily ratcheting up its sea-level-rise projections since its 2001 report, and it is likely to increase the numbers further in the 2021 report, when the IPCC runs a new round of global climate models.
Read: Are we living through climate change’s worst-case scenario?
But sea-level rise is only one of the bewildering consequences of climate change listed in the report, whose view stretched “from the highest mountains to the bottom of the ocean,” according to Ko Barrett, a vice chair of the IPCC and a scientist at the National Oceanic and Atmospheric Administration. What’s clear is that climate change is going to reshape every system made of water on Earth.
That means that as the ocean warms, seafood safety will decline: Mercury will accumulate in fish, and the toxic bacteria Vibrio will become more common. And climate change will sicken people. In the Arctic, where indigenous people rely on seafood diets, food- and waterborne illnesses are already increasing.
Climate change will also prompt extreme coastal-flooding events—think of Hurricane Harvey or Katrina—to surge in frequency. Floods that used to happen every century will now happen, in some places, every year. It will push the worst rainstorms, including tropical cyclones and hurricanes, to dump even more water. And it will increase the frequency of extreme El Niño and La Niña events like the “monster El Niño” that struck in 2016. This threatens to induce intense “whiplash between wet and dry periods,” Andrea Dutton, a climate scientist at the University of Wisconsin, told me.
At the same time, climate change’s effects seem to be speeding up. The seas are now rising at a pace “unprecedented over the last century,” the report warns. The rate of global sea-level rise was 2.5 times faster from 2006 to 2016 than it was for nearly all of the 20th century. “In the Antarctic ice sheet, the rate of mass loss had tripled relative to the previous decade,” Dutton said. “In Greenland, it’s doubled over the past decade.”
The oceans act like a massive sponge in the planetary system, and they have so far absorbed most of the warmth trapped by greenhouse gases. Since 1993, the rate of ocean warming has more than doubled. Marine heat waves—when the ocean becomes so hot that it can kill plants and animals—happen twice as frequently now, and they have grown in intensity, duration, and size.
This is prompting invisible bonfires to break out across the ocean’s most pristine environments. Tropical coral reefs contain most of the ocean’s biodiversity: They are the so-called rainforests of the ocean. Yet they are dying more surely than the Amazon in Brazil. “Almost all warm-water coral reefs are projected to suffer significant losses of area and local extinctions, even if global warming is limited to 1.5 degrees Celsius,” the IPCC writes.
From 2016 to 2018, half the coral in the Great Barrier Reef died, Australia’s lead coral scientist told me last year. It will take at least 15 years to recover—and given the pace and spread of marine heat waves, it probably never will. A child born today in Australia may never know the Great Barrier Reef as an adult. That is not a hyperbolic statement; that is an assessment of the facts.
Even beyond reefs, life is fleeing the tropical ocean. Since the 1950s, entire populations of fish and seafloor creatures have moved toward the poles at a rate of up to 50 miles a decade. This is an incredible figure when you consider that it is unplanned, unorganized, and unhabitual: The population is relocating itself all at once.
Read: Seven ways to understand the IPCC’s warning about climate change and land
And this ecological upheaval of climate change is not limited to the seas. “Many glaciers, particularly in Washington State and the Mountain West, will disappear within the next decade and—at the latest—within a century,” said Regine Hock, an author of the report and a geophysicist at the University of Alaska Fairbanks, at a press conference this week. That has implications for water security across huge portions of the American West: Phoenix and Los Angeles both rely, to some extent, on water from mountain glaciers.
There are two immense stores of water on the planet. The first, covering more than two-thirds of its surface, are the oceans. The second, blanketing the poles, are the rocklike ice caps. (Hence the pithy observation, beloved by some oceanographers, that we call our home world “Earth” only out of a kind of species-level vanity. It would be far more accurate to call it “Sea.”)
It’s not common, across Earth’s history, for ice to sit on the surface as a permanent presence. It’s happened only three times in the past 550 million years, the same time period that complex, multicellular life has ruled the surface. It denotes that we are living in an Ice Age, scientifically, even if glaciers are not choking off Manhattan. The entire span of the human species has happened in an Ice Age. It’s an open question of whether climate change will end the one we are currently in.
But we can already detect one key change in how those two stores of water interrelate. For decades, the biggest driver of sea-level rise was heat itself, because as the ocean gets hotter, it literally takes up more space. (Scientists call this principle “thermal expansion,” and it applies to matter more generally: You demonstrate it at home whenever you run a jar under hot water to loosen the lid.) But in the past few years, meltwater from Greenland and Antarctica has overwhelmed this effect. Oceans are rising today primarily because they have more water in them.
“We’ve been saying all along that ice sheets would become dominant, and that signal is starting to appear,” Dutton said. (Dutton is having a busy week: She won a MacArthur genius grant this morning.)
And while this is a dramatic change, there’s a question in the middle of the report that portends an even more cataclysmic event. Hanging over the report, like an icy Damocletian saber, dangles the question: Will the Antarctic ice sheet collapse?
Read: After decades of losing ice, Antarctica is now hemorrhaging it
In 1978, the glaciologist John Mercer issued a warning in the scientific journal Nature. If people kept burning fossil fuels at the present rate, he wrote, then within 50 years they could set off the “rapid deglaciation” of West Antarctica. The process he identified—called “marine ice-sheet instability”—has haunted climate scientists for the past four decades.
Mercer’s problem begins with a simple fact: Ice floats in water. Many glaciers in West Antarctica have “wet feet,” as Dutton put it, meaning their front face sits in the water. Just like ice in a water glass, these glaciers want to float. But they don’t. The weight of the ice above the waterline keeps the entire glacier stuck to the seafloor.
But as it gets farther from the ocean, the bedrock of West Antarctica slopes downhill. If the glacier were to start retreating, then more and more of its mass would fall below the waterline. Eventually, the mass above the waterline would no longer keep the glacier stuck to the seafloor. The glacier would float off its foundation, the ice floe behind it would quickly spill out into the sea, and the glacier would quickly become so many melting ice cubes.
Once this process starts, it’s irreversible. It has never been observed—because we’ve never observed wrenching global climate change before. But since about 2006, more and more evidence has suggested that Mercer’s process is real and has happened in the past, Oppenheimer said.
And just in the past decade, glaciologists have added another potentially irreversible process to the mix, called “marine ice-cliff instability.” Its proponents argue that ice is structurally unstable. As West Antarctic glaciers retreat, their ice fronts could eventually tower so high above the bedrock that they would crumple under their own weight. While this hypothesis is far more recent, this glacial brittle collapse would further accelerate the melting of the Antarctic ice sheet.
Right now, the IPCC authors believe that the Antarctic ice sheet probably won’t collapse. But that is not exactly reassuring. Some measurements suggest that the ice sheet is already unstable. And the IPCC is clear that if Antarctica’s glaciers do begin to disintegrate, then its projections about future “likely” sea-level rise will be far too small. If Antarctica totally collapses, then it could loose 13 feet of sea-level rise into the ocean, at a rate of more than three feet a century, Oppenheimer said. This scenario, he added, “is unmanageable.”
We don’t know how much climate change might trigger runaway collapse—but generally, the less carbon pollution, the better. “If there’s a threshold out there, we’re much better landing in 1.5-degree-Celsius trajectory,” Oppenheimer said.
What’s crucial is that decisions about these pathways are being made now; the little girl’s future is being locked in, even as we speak. In the United States, President Donald Trump’s campaign to repeal virtually every climate regulation is nudging us toward the higher, more disastrous path, and making climate action more expensive for other countries.
“This [report] drives home the message that policies that curb greenhouse gases today can have a strong effect on future sea-level rise, particularly in terms of what happens after 2050,” Dutton said. We cannot abandon this Ice Age without risking a new, and far more dangerous, epoch.
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