23 February 2021  15:49

Dr Helena Martins


23.02.2021 | 3:49pmGUEST POSTSGuest post: The threat of high-probability ocean ‘tipping points’ 

This guest post is by:

Dr Helena Martins, science communicator in the Rossby Centre at the Swedish Meteorological and Hydrological Institute.

Climate change is profoundly altering our oceans and marine ecosystems. Some of these changes are happening quickly and are potentially irreversible. Many are taking place silently and unnoticed.

In recent years, tipping points – thresholds where a small change could push a system into a completely new state – have increasingly become a focus for the climate research community.

However, these are typically thought of in terms of unlikely changes with huge global ramifications – often referred to as “low probability, high impact” events. Examples include the slowdown of the Atlantic Meridional Overturning Circulation and the rapid disintegration of the West Antarctic ice sheet

In a new paper, published in the Proceedings of the National Academy of Sciences, my co-authors and I instead focus on the potential for what we call “high probability, high impact” tipping points caused by the cumulative impact of warming, acidification and deoxygenation.

We present the challenge of dealing with these imminent and long-lasting changes in the Earth system, and discuss options for mitigation and management measures to avoid crossing these tipping points.

Warming, acidification and deoxygenation

The ocean is a giant reservoir of heat and carbon. Since the beginning of the industrial revolution, the oceans have taken up around 30-40% of the carbon dioxide (CO2) and 93% of the heat added to the atmosphere through human activity. 

Without ocean uptake, the scale of atmospheric warming would already be much larger. But this comes with a high cost in the form of ocean warmingacidification – where the alkaline ocean becomes more acidic – and deoxygenation – where the oxygen content of the ocean falls. 

The potential impact of these processes on the marine environment is well documented. However, in some cases, they could trigger a number of regional tipping points with potentially widespread consequences for marine ecosystems and ocean functioning.

Here are some examples:


Each species has an optimal temperature range for their physiological functioning. Like humans, most marine organisms are vulnerable to warming above their optimal temperature. Without adaptation, some species will be hit hard by ocean warming. A well-known example is the threat to tropical coral reef systems, such as Australia’s Great Barrier Reef, to mass coral bleaching from extreme heat. 

Bleached corals in shallow water in Papua New Guinea
Bleached corals in shallow water in Papua New Guinea. Credit: Nature Picture Library / Alamy Stock Photo.

These coral reef systems play an important role for fisheries, for coastal protection, as fish nurseries, and for a number of other ecosystem services. This serves as an example of how the impact of ocean warming extends far beyond the most sensitive marine organisms, with range shifts being observed across the food web from phytoplankton to marine mammals.


Most marine organisms can only exist in seawater with sufficiently high concentrations of dissolved oxygen. Warming of the ocean decreases the solubility of oxygen in the water and slows down ocean mixing, which, in turn, decreases oxygen transport from the surface into the ocean interior. 

In addition, run-off of nutrients from the land – such as from agriculture and domestic waste – increases the biological productivity in coastal areas, disrupting ecosystems and enhancing deoxygenation. Consequences for marine organisms are huge, with species distribution, growth, survival and ability to reproduce negatively affected.


Besides being the primary driver of global warming, CO2 also changes ocean chemistry, causing the acidification of seawater. Many marine organisms have shells or skeletal structures made of mineral forms particularly vulnerable to ocean acidification. A well-known example are pteropods – free-swimming sea snails and sea slugs – that live in the upper 10 metres of the ocean, which are a keystone species in the marine food web. 

Currently observed acidification conditions are already unprecedented within the last 65m years, and are projected to continue and aggravate for many centuries even with the reduction of carbon emissions to net-zero.

High-probability, high-impact ocean tipping points

While these different processes are individually a danger to marine life, in combination with other threats – such as overfishing, high nutrient input from land and invasive species – they have the potential to cause ecosystem-wide regime shifts.

In addition, extreme events – such as marine heatwaves or high-acidity, low-oxygen events – lead to severe consequences for marine biodiversity. Across the globe, the observed local and regional changes already add up to a substantial regional – and possibly global – problem. Examples include coastal acidification and anoxic ocean “dead zones”. 

The figure below highlights some of the regions of the world ocean that are under threat from these impacts.

High probability ocean tipping points
Map showing potential candidates for high-probability, high-impact marine tipping elements that concern warming, deoxygenation and ocean acidification, as well as their impacts. Source: Heinze et al. (2021). The numbers refer to cited studies in this paper.

While these impacts already need dealing with today, ocean circulation patterns mean that they are also being stored up for the future.

The upper ocean mixes on a timescale of decades, while the deep ocean water masses are renewed from the surface on a much longer timescale – from hundreds to thousands of years. The present-day accumulation of heat and carbon are initially largest at the ocean surface. But, through mixing and ocean currents, this excess of heat and carbon is transported away from the surface and into deeper layers.

These short and long-term timescales have two consequences. The first is that mixing is not fast enough to prevent the accumulation of heat and carbon in the upper ocean.

The second is that deep mixing transports some of the surface excess heat and carbon to greater depths, where long-lasting changes can gradually build up. Consequently, the deep ocean can be altered by climate change irreversibly for thousands of years, even under strong emission reduction scenarios. These impacts are incredibly difficult to monitor at such depths.

Can these ocean tipping points be avoided?

While the threats to the ocean from human-caused climate change are many and varied, there is still time for them to be minimised. We highlight a few action points where scientists are contributing to the development and implementation of mitigation actions.

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First, scientists are using models and observations to determine the regions where the most severe hazards have occurred, are occurring, and may occur in the future. Laboratory and in-situ experiments can help identify vulnerabilities in organisms and ecosystems.

Second, progress is being made to define important thresholds in the physiological tolerance of key organisms for changes in temperature, oxygen concentration, nutrient levels and acidity. This also draws attention to the need for metrics of global change that go beyond atmospheric CO2 concentration and global average surface temperature. Keeping a close watch on potential ocean tipping points means tracking ocean temperature changes, acidification, deoxygenation and marine productivity.

Third, communication of these threats is improving. While there is still much progress to be made – for example, in building climate and ocean literacy and working with indigenous groups – research into empowering science communication to address global challenges is growing.

While headway is being made, much more action is needed. We suggest four system management and societal transformation actions for minimising the likelihood of encountering high-probability, high-impact ocean tipping points:

  • The highest priority for ocean damage limitation is the immediate and drastic reduction of greenhouse gas emissions – particularly CO2.
  • To achieve emission reductions, human societies need to shift to a decarbonised energy production, sustainable use of land and ocean, and climate-friendly urban and regional planning.
  • The implementation of mitigation measures needs to be enabled through adequate governance structures and seamless interagency action.
  • And, finally, these transformations need to be carried out increasingly fast.

Warming oceans are trapping shellfish in hotspots they can’t escape

A new study has found marine creatures like mussels could be vulnerable to a phenomenon known as "elevator to extinction," in which increasing temperatures are driving them towards new, less secure habitats
A new study has found marine creatures like mussels could be vulnerable to a phenomenon known as “elevator to extinction,” in which increasing temperatures are driving them towards new, less secure habitats

Many species are expected to be displaced as the world continues to warm and natural habitats are transformed, and this is true both on land and at sea. Scientists studying more than half a century of data on bottom-dwelling shellfish have uncovered evidence of a destructive feedback loop, in which generations of these marine creatures are becoming trapped in warmer areas that threaten their survival.

The research was carried out at Rutgers University and throws up some counter-intuitive revelations concerning the migration of marine species. Many creatures will respond to warming waters by traveling to cooler areas for refuge, but the scientists found a number of species that do just the opposite, a phenomenon they call “wrong-way migration.”

These include sea scallops, blue mussels, clams and quahogs, which the team notes are valuable resources for the shellfish industry, with the team drawing its conclusions from more than six decades of data on more than 50 species off the north-east coast of the US. Around 80 percent of the species studied could no longer be found in their traditional habitats, turning up in shallower, warmer waters instead.

“These deeper, colder waters of the outer shelf should provide a refuge from warming so it is puzzling that species distributions are contracting into shallower water,” says lead author of the study Heidi Fuchs.

Once there, they are already less likely to survive, but the ones that do and go on to reach adulthood become part of a destructive feedback loop, with these warmer regions again causing the earlier spawning of their larvae, and the cycle then repeats.

While this study only looks at bottom-dwelling invertebrates from one general location, the findings are consistent with trends observed in other animals whose habitat is being affected by climate change. This is sometimes called the “elevator to extinction” phenomenon, where animals like birds and butterflies are driven to higher and higher altitudes to escape increasing temperatures until they can no longer be found in areas they originally inhabited.

Seabed fossils show the ocean is undergoing a change not seen for 10,000 years

ocean circulation may have caused a shift in Atlantic Ocean ecosystems not seen for the past 10,000 years, new analysis of deep-sea fossils has revealed.

This is the striking finding of a new study led by a research group I am part of at UCL, funded by the ATLAS project and published in the journal Geophysical Research Letters. The shift has likely already led to political tensions as fish migrate to colder waters.

The climate has been quite stable over the 12,000 years or so since the end of the last Ice Age, a period known as the Holocene. It is thought that this stability is what allowed human civilisation to really get going.

In the ocean, the major currents are also thought to have been relatively stable during the Holocene. These currents have natural cycles, which affect where marine organisms can be found, including plankton, fish, seabirds and whales.

Yet climate change in the ocean is becoming apparent. Tropical coral reefs are bleaching, the oceans becoming more acidic as they absorb carbon from the atmosphere, and species like herring or mackerel are moving towards the poles. But there still seems to be a prevailing view that not much has happened in the ocean so far – in our minds the really big impacts are confined to the future.

Looking into the past

To challenge this point of view, we had to look for places where seabed fossils not only covered the industrial era in detail, but also stretched back many thousands of years. And we found the right patch of seabed just south of Iceland, where a major deep sea current causes sediment to pile up in huge quantities.

Scientists gathered fossils from an area with lots of seabed sediment. Peter SpoonerAuthor provided

To get our fossil samples we took cores of the sediment, which involves sending long plastic tubes to the bottom of the ocean and pushing them into the mud. When pulled out again, we were left with a tube full of sediment that can be washed and sieved to find fossils. The deepest sediment contains the oldest fossils, while the surface sediment contains fossils that were deposited within the past few years.

One of the simplest ways of working out what the ocean was like in the past is to count the different species of tiny fossil plankton that can be found in such sediments. Different species like to live in different conditions. We looked at a type called foraminifera, which have shells of calcium carbonate. Identifying them is easy to do using a microscope and small paintbrush, which we use when handling the fossils so they don’t get crushed.

Electron microscope image of the tiny fossil plankton G. bulloides, a type of foraminifera found during the study. Alessio Fabbrini, UCLAuthor provided

recent global study showed that modern foraminifera distributions are different to the start of the industrial era. Climate change is clearly already having an impact.

Similarly, the view that modern ocean currents are like those of the past couple of thousand years was challenged by our work in 2018, which showed that the overturning “conveyor belt” circulation was at its weakest for 1,500 years. Our new work builds on this picture and suggests that modern North Atlantic surface circulation is different to anything seen in the past 10,000 years – almost the whole Holocene.

The effects of the unusual circulation can be found across the North Atlantic. Just south of Iceland, a reduction in the numbers of cold-water plankton species and an increase in the numbers of warm-water species shows that warm waters have replaced cold, nutrient-rich waters. We believe that these changes have also led to a northward movement of key fish species such as mackerel, which is already causing political headaches as different nations vie for fishing rights.

Members of the team collect ocean sediment. Ian Hall, Cardiff UniversityAuthor provided

Further north, other fossil evidence shows that more warm water has been reaching the Arctic from the Atlantic, likely contributing to melting sea ice. Further west, a slowdown in the Atlantic conveyor circulation means that waters are not warming as much as we would expect, while furthest west close to the US and Canada the warm gulf stream seems to be shifting northwards which will have profound consequences for important fisheries.

One of the ways that these circulation systems can be affected is when the North Atlantic gets less salty. Climate change can cause this to happen by increasing rainfall, increasing ice melt, and increasing the amount of water coming out of the Arctic Ocean. Melting following the peak of the Little Ice Age in the mid 1700s may have triggered an input of freshwater, causing some of the earliest changes that we found, with modern climate change helping to propel those changes beyond the natural variability of the Holocene.

We still don’t know what has ultimately caused these changes in ocean circulation. But it does seem that the ocean is more sensitive to modern climate changes than previously thought, and we will have to adapt.

‘We Should Be Worried’: Study Confirms Fear That Intense Ocean Acidification Portends Ecological Collapse

“We have been warned.”

A new study regarding fossil records reveals that ocean acidification could cause mass extinction. (Photo: Rodfather/Flickr/cc)

The acidification of the Earth’s oceans, which climate scientists warn is a dangerous effect of continued carbon emissions, was behind a mass extinction event 66 million years ago, according to a new study.

Small-shelled marine organisms survived the meteorite that struck the Earth and wiped out the dinosaurs, according to researchers at the GFZ geosciences research center in Potsdam, Germany, but the subsequent sharp drop in pH levels in the ocean caused the marine life to go extinct.

“We show ocean acidification can precipitate ecological collapse,” Michael Henehan, who led the study, told The Guardian.

Researchers examined shell fossils in sediment dating back to the time period just after the meteorite struck the planet, which showed that the oceans’ pH dropped by about 0.25 units in the 100 to 1,000 years after the strike.

“In the boundary clay, we managed to capture them just limping on past the asteroid impact,” Henehan said.

But, the newspaper reported, “It was the knock-on effects of acidification and other stresses, such as the ‘nuclear winter’ that followed the impact, that finally drove these foraminifera to extinction.”

“We have been warned,” climate campaigner Ed Matthew tweeted with a link to the research, which was published in the Proceedings of the National Academy of Sciences.

Today, climate scientists warn that the continued burning of oil, gas, and coal is causing ocean acidification that, left unchecked, could cause a pH drop of 0.4 units.

If policymakers are able to help limit the warming of the globe to two degrees Celsius by ordering that fossil fuels be left in the ground and shifting to a renewable energy economy, the ocean’s pH level could drop just 0.15 units.

“If 0.25 was enough to precipitate a mass extinction, we should be worried,” Henahan told The Guardian.

As Common Dreams reported in July, MIT researchers also recently turned their attention to ocean acidification as well. The researchers released data showing that today’s carbon levels could be fast approaching a tipping point threshold that could trigger extreme ocean acidification similar to the kind that contributed to the Permian–Triassic mass extinction, which occurred about 250 million years ago.

UN Climate Report: Oceans Also F-cked

A new report from the IPCC is yet another wake-up call for world leaders to take the climate crisis seriously

PERITO MORENO, ARGENTINA - APRIL 5: A piece of the Perito Moreno glacier, part of the Southern Patagonian Ice Field, breaks off and crashes into lake Argentina in the Los Glaciares National Park on April 5, 2019 in Santa Cruz province, Argentina. The ice fields are the largest expanse of ice in the Southern Hemisphere outside of Antarctica but according to NASA, are melting away at some of the highest rates on the planet as a result of Global Warming. (Photo by David Silverman/Getty Images)

A piece of the Perito Moreno glacier, part of the Southern Patagonian Ice Field, breaks off and crashes into lake Argentina in the Los Glaciares National Park on April 5th, 2019.

David Silverman/Getty Images

Climate activists and world leaders have gathered this week in New York for the United Nations Climate Summit. But on Wednesday attention was focused across the Atlantic, where in Monaco the UN’s Intergovernmental Panel on Climate Change presented a special report on the “unprecedented” impact warming temperature will have on the world’s oceans. It’s not good. The report — compiled by over 100 authors from 36 countries citing close to 7,000 accredited sources — paints a grim picture of the effect warming oceans and the cryosphere will have on humanity, especially if nothing is done to curb emissions.



The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate , was presented today in Monaco🇲🇨

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The ocean has played a critical role in warding off the effects of climate change by absorbing close to 25 percent of CO2 emissions. The report warns that as the temperature continues to rise and the ocean traps more heat, it will become more acidic, less oxygenated, less productive, less hospitable to life, and more likely to give rise to tropical storms and hurricanes, which will occur with greater frequency and intensity. The report notes that with any additional degree of warming, intense sea events that used to occur once per century will in certain regions once per year by the middle of the 21st century.

Connected to the fate of the world’s oceans is the fate of the world’s frozen areas, or the cryosphere, on which close to 1.5 billion people’s lives directs depend. As parts of the cryosphere melt (glaciers, for instance), the global sea level will continue to rise, dramatically altering life for those living in coast regions, if not making those regions uninhabitable. The sea level is rising twice as fast as it did during the 20th century, and that the rate is increasing, the report notes, explaining that the Antarctic ice sheet will contribute more to sea level rise by 2100 than was previously expected. In the next 80 years, the sea level could increased by up to 60 centimeters if greenhouse gas emissions are dramatically reduced, and 110 centimeters if they are not.

It isn’t just glaciers and rising sea levels, either. As permafrost, snow, and ice melt, the frequency of landslides, avalanches, rockfalls, floods, and wildfires will increase. Water availability could also be thrown into flux as glaciers retreat, impacting agriculture.

“The world’s ocean and cryosphere have been ‘taking the heat’ from climate change for decades, and consequences for nature and humanity are sweeping and severe,” IPCC Vice Chair Ko Barett said in a statement. “The rapid changes to the ocean and the frozen parts of our planet are forcing people from coastal cities to remote Arctic communities to fundamentally alter their ways of life.”

Despite the realities detailed in the report, it was structured around the idea that many of these consequences can be mitigated with “timely, ambitious and coordinated action” to reduce emissions and pursue sustainable development. Unfortunately for humanity, China and the United States, the world’s two largest emitters of greenhouse gases, have largely ignored he climate crisis. Neither cared to contribute possible solutions at the UN’s Climate Summit this week.

The Oceans We Know Won’t Survive Climate Change

Vast piles of dead fish in Rio de Janeiro
Warmer oceans are leading to die-offs, such as this one in Rio de Janeiro.SERGIO MORAES / REUTERS
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.

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.

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.

Warming waters have bleached out corals in French Polynesia. (Alexis Rosenfeld / Getty)

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.

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.”)

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?

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.

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.

This Is Exactly What Will Happen After the Last Fish in the Ocean Dies

The devastation of the vast majority of the world’s marine life is much closer than we think.

By Mike Pearl; illustrated by Cathryn Virginia
Sep 20 2019, 3:00am

Picture a beach along the same vast ocean you know today—the same powerful waves and shifting tides, reflecting the same beautiful sunsets, even the same green-blue water. Now imagine a crowd gathered at the shoreline, standing in a big circle, gawking at something that just washed up. Kids tug on their parents’ shirt sleeves, asking questions about the dead creature lying on the sand. Reporters arrive. The story is momentous even if the takeaway isn’t much fun. Everyone knows there used to be fish in the oceans—kind of like the ones that still live in some rivers and lakes, except they could be much bigger, sometimes meaner, more diverse, more colorful, more everything. But those mythical ocean fish all died. Except maybe this one. This one was alive in there, and now it’s dead too.

According to Stanford University paleobiologist Jonathan Payne, an expert in marine mass-extinction events, a scenario where all the ocean’s fish, mammals, and other creatures—even tiny animals like krill—are all gone is far from science fiction. The type of die-off that would lead to a largely lifeless ocean has happened before, and we’re well on our way to seeing it happen again.

To get into Payne’s frame of mind, we have to look at two areas of history. First, there’s pre-dinosaur times, where we can find a precedent for the kind of huge-scale extinction we’re seeing now. Then, we have to look at the past few hundred years, to understand why our fishless future kind of looks like, uh, the present.

We know that, about 250 million years ago, some extremely bad stuff happened, because almost everything on Earth that was alive at that time died very quickly, taking only a few million years to die off. This event is not to be confused with the meteorite impact that happened 65 million years ago—the one that supposedly wiped out the dinosaurs. That was nothing. A lot of those dinosaurs never went truly extinct; they’re now known as “birds,” and quite a few mammals made it, and evolved into humans, in pretty short order. This earlier event, the Permian–Triassic Extinction, is frequently called “the Great Dying” by paleontologists who like historical events to sound like Morrissey album titles. It made the Earth pretty quiet for a while—the oceans quietest of all.

In 2017, Payne and several colleagues looked into the source of the aforementioned extremely bad stuff that led to the Great Dying. They concluded that temperature-dependent hypoxia—loss of oxygen due to changes in temperature—caused about 70 percent of the losses. An oddly familiar culprit was fingered for this temperature change: “rapid and extreme climate warming.” Payne and his pals weren’t the first to draw comparisons between the events leading up to the Great Dying and the changes we’re seeing today. A previous study had found that the Great Dying had resulted from rising carbon emissions—caused at that time by geothermal events—that occurred over the span of two to 20 millennia; in other words, the blink of a geological eye.

“The relevant thing we know from these recent results is that the patterns of warming, and loss of oxygen from the ocean that can account for the extinction at the end of the Permian are the same features we’re starting to see right now,” explained Curtis Deutsch, a chemical oceanographer at the University of Washington and one of Jonathan Payne’s colleagues on that 2017 study.

This is adapted from an excerpt out of The Day It Finally Happens. To buy this book, go here.

Thanks to our species’ multi-pronged and comprehensive approach, humanity’s present day “Kill All the Marine Life” project is going extremely well. Here’s a quick cheat sheet listing our main strategies:

  • We dump several metric tons of plastic garbage into the oceans every year.
  • Bottom trawling, or dragging fishing equipment across the seafloor, is turning “large portions of the deep continental slope into faunal deserts and highly degraded seascapes” according to a 2014 report on the long-term effects of this widespread practice
  • The planet is heating up really fast, and the resulting extinctions are happening in real time. (Although, for the record, at this rate it will take a few more centuries for this effect to reach the lifeforms at the deepest depths of the oceans.)
  • Ocean acidification—the other major side effect of CO2 emissions besides global warming—is causing countless die-offs, most famously in corals, the backbone of coral reefs, the most biodiverse ecosystems on earth.
  • Fertilizer and pesticides poison the ocean, and when combined with the above factors, they help create “dead zones,” nearly oxygen-free patches of ocean where almost nothing can live. According to a 2018 paper published in Science magazine, dead zones make up four times as much of the oceans as they did in 1950.
  • We eat the sea’s living creatures—which is the number-one cause of their declining numbers. There are rates at which we can supposedly fish sustainably—meaning in such a way that we don’t run out—but the fishing industry operates in volumes that meet, or surpass the peak equilibrium rate. (Right now, we’re hauling up 90 percent of fish stocks globally, according to the UN.) In other words, we’re killing as many fish as we possibly can as a byproduct of our industries, and then on top of that, we’re also eating as many as we can.

To be clear, the Great Dying wasn’t 100 percent caused by warming either. But whatever the cause, 286 out of 329 marine invertebrate genera we know of died back then. All the trilobites and blastoids died, for instance. Every single one! But no one mourns the trilobites and blastoids, and that actually helps illustrate why we fail to grasp that we’re annihilating life in the oceans. There’s actually a sociological term for this phenomenon: it’s called a shifting baseline.

“Shifting baselines” have to do with everyone’s gut-level perception of the natural world. The term refers to our tendency to perceive our own early experiences of ecology as the norm, in contrast to what we see later in life. To explain with a non-oceanic example, my own childhood memories of summers in California’s Inland Empire include street gutters choked with thousands of California toads. Twenty years later, those toads are mostly gone—likely decimated by chytrid fungus infections. Their loss leaves me with the false impression that the natural order in Southern California has vanished in a very short time, when actually, the damage humanity has caused here is of much longer duration and much larger in scale than the loss of one species of toad (a species that arguably wasn’t “supposed to be there” in the first place). Much more serious losses of biodiversity have been rolling out for centuries, but I don’t miss animals like the Southern California kit fox, which went extinct over a century ago, because my own baseline never included them.

Similarly, according to Deutsch, we won’t collectively care about the death of all the fish, because when it finally happens, our baselines will have shifted so much that the lack of fish will seem normal.

So back to the first question I asked those scientists: what will the fishless ocean look like?

Aesthetically, it won’t be very different, according to Payne. A point I came across again and again in my research is that crystal-clear blue waters are often relatively lifeless. It’s rare to look at the ocean and see strong indications of life—even plant life. “It’s not carpeted in green, there aren’t cells everywhere photosynthesizing,” Payne said. “The color you see is mostly just the physics of light absorption and water.” So in most places, you wouldn’t actually see anything at all by looking at the ocean, just as a flight over the Great Plains doesn’t tell you anything about the decline of the American buffalo.

Holistic accounting of the numbers of various species in the oceans have only begun recently, so it’s hard to pin down exact numbers, but according to a 2015 report by the World Wildlife Fund, the oceans lost 49 percent of all vertebrates in just the time between 1970 and 2012. So rather, we should try and imagine the perspectives of people who saw the oceans when they were teeming with life, and Deutsch suggests reading accounts from the Age of Exploration. If they could time travel, Deutsch said, the Spanish explorers who first visited the New World would look at our ocean today, and say, Wow, that’s dead.

“They would describe coming in on their ships through the Gulf of the Caribbean and not even being able to get to shore because the backs of the sea turtles were just so thick they couldn’t get their boats in,” Deutsch said. Indeed, when Columbus arrived, there were so many turtles, they thunked against the hull of his ship all night, keeping his crew awake. Today, spotting a sea turtle is a momentous event, because the number of sea turtles in the Caribbean is down to about 3 to 7 percent of what it was before Europeans arrived.

I have seen precisely one wild sea turtle in my entire life, and that was because I was searching for one.

I was off the northeast coast of Queensland, Australia, at the time, snorkeling in the Great Barrier Reef in the hopes that it might at least partially correct my own shifting baseline vis-a-vis ocean biodiversity. Even if you’ve never had the extreme privilege of visiting a coral reef, you’ve undoubtedly seen one, as magnificently CG-rendered in Finding Nemo, or majestically photographed for the BBC’s Blue Planet TV series, which means you know the broad strokes of what a coral reef is—a place so teeming with life that it’s one of the rare places for which the word “teeming” seems appropriate.

But don’t picture a technicolored Disney wonderland. Unless you have the right lens filters and the weather is just so, a coral reef just looks like what it is: a section of ocean with, well, a lot of life—like any part of the ocean you’ve ever seen, except with more brown and yellow (alive) stuff in there. When you look closely, there are the charismatic, photogenic animals down among the corals, and inside the anemones. Your expedition guide will call out when there’s something to see, “Does anyone want to see Nemo?” they’ll ask, and show off the clownfish, because clownfish are to the reef as the Eiffel Tower is to Paris. But the clownfish down there look pale and brown, and impossibly tiny, nothing like the bright red cartoon characters brought to you by Disney and Pixar. (I’m not implying that the Great Barrier Reef is anything other than breathtakingly beautiful; just that when you see it, it looks more “normal” than you might think.)

Meanwhile closer to the surface, thousands of indifferent, brownish fish dart around in schools that change directions in twitchy unison. In some parts, you can busy your hands at a coral reef by reaching out and gently closing your hand around a fish, feeling it squirm away, and then immediately grabbing another. The sheer density of “biomass” had a mounting emotional effect on me, particularly when my thoughts inevitably drifted to just how much below me had already died. Recently, 30 percent of the coral died in one year, bringing estimates of the total loss to about 50 percent. When I visited in 2018 there hadn’t been much coral bleaching recently, and lots of fish were around. The way the future is shaping up, though, finding a lot of life there is likely to become rarer and rarer.

After three hours spent touching what’s essentially a closed-off memorial to the living ocean we once had, you inevitably leave, and this gives you an opportunity to test your original perception of the ocean against your fresh memories of a marine wonderland. When you look down at the seafloor off the coast of California, you see the exact opposite of the Great Barrier Reef: bupkis. No visible fish at all. Not all patches of coastal ocean can be the Great Barrier Reef, but that doesn’t mean they should all look like lifeless deserts. To assume they should be this lifeless isn’t natural at all; that’s just your already-shifted baseline talking.

If the Great Dying is our model, the process of environmental degradation wouldn’t just mean dead marine fish, but massive die-offs in most of the plants and animals eaten by fish, meaning algae and kelp, along with many plankton, krill, worms, and everything else we tend to lump into “the bottom of the food chain.” That carnage would, in turn, devastate species that rely on small fish, like most whales, dolphins, seals, penguins, and many humans.

It’s a good time to pause and point out that some of fish species, like the coelacanth, a deep sea cave-dwelling monster fish, made it through the Great Dying and survived all the way to the present unchanged—so no, the Great Dying didn’t kill all the fish on Earth, “great” though it may have been. It was just a very large-scale mass extinction. But as long as we’re being pedantic, keep in mind that fish can’t all be lumped into any single taxonomic category like phylum, class, order, or family. From a certain genetic perspective, a shark has more of an obvious connection to its fellow cunning predator the seahorse (look it up) than with a coelacanth, and a coelacanth shares DNA with a salamander that it doesn’t share with a shark. So when I say “fish” I’m casting a very wide net (pun intended) that includes all marine vertebrates with gills that aren’t tetrapods—so no salamanders. That might not mean much to you, but if any jargon-crazed biologists are reading this, they’ll be glad I’m making this distinction.

And with the Great Dying as our model, we’re imagining the disappearance of about 96 percent of all life in the ocean—not just fish, but just about everything down there with eyes (and a lot of blind species, too). What happens?

Well, in some ways this will be a vastly improved business environment for large corporations. Just as the overabundance of marine life in oceans around the New World was bad for business, today’s ships also run into problems.

For one example, let’s look at retailers that ship globally like Walmart, Amazon, and Alibaba, which increasingly face regulations aimed at preserving marine animal habitats. The container ships—which are the size of a small town—that move merchandise currently have to plot out inconvenient routes to circumvent certain animal habitats, and to avoid some forms of water pollution caused by their 100,000 horsepower diesel engines. And they must carve a path through the seas without making sounds that are too loud, or that fall below 100 hertz because animals like whales use those frequencies to communicate. In the heated, acidified ocean that has killed all fish, baleen whales will have certainly starved to death long ago, obviating the need for any such regulations. The die-off will also allow for the easing of regulations against sewage dumping, and—needless to say—negate most of the public’s antipathy toward oil spills.

That’s not to say that businesses will make more money and that’s that. Environmental remediation, a term that means “cleaning up after businesses that pollute,” is currently a growing industry, with some market researchers claiming it’ll be worth as much as $123.13 billion by the year 2022—an amount that’s almost equal to Google’s 2017 revenue. Some of those profits will obviously fall away when there’s much less demand for oil spills to be cleaned up. But it’s not clear how long the mostly dead oceans could be treated as free and open spaces to dump things.


We can safely predict one very large effect of all that dumping: the marine fishing industry will no longer involve “fishing.” It may nonetheless survive with the help of fish aquaculture.

Fish farms appear to be a growing business. Just look at “Bluefin tuna,” the marketing term used to describe several giant, silvery fish—all endangered or threatened—that we hoist onto ships, carve up by the thousands every day to extract the $15 morsels of fatty tuna we label on menus with the Japanese word “toro,” and serve for the gustatory pleasure of the wealthy inhabitants of coastal cities around the world. Those morsels are about to become even more effective advertisements of wealth when the three or four species of fish they come from go extinct in the wild sometime in the next few decades, and prices skyrocket.

To mitigate this inconvenience, projects exist today to grow Bluefin tuna in tanks, like the ones at Yoni Zohar’s marine technology lab at the University of Maryland, Baltimore County. The purpose, currently, is to grow fish larvae, including bluefins, along with smaller species like sea bass, into viable juvenile fish that can be taken out in boats and tossed into overfished bluefin habitats to replenish the depleted population. But this plan will only work as long as the ocean can sustain schools of wild tuna, which it won’t be able to for much longer. The death knell has been sounded for even the more plentiful albacore, and the yellowfin species marketed as “ahi,” both of which are declining in number as well. That means tanks like Zohar’s have to evolve if these luxury consumer goods are going to continue to exist. Tuna will have to survive in their tanks for multiple decades—long enough to transform from a microscopic and inedible hatchling to a 400 kilogram titan with fatty, palate-pleasing jowl meat. Making the feat even more problematic is that they never stop swimming, which is no big deal when the fish are tiny, but will be harder to accommodate in a tank when they’re capable of swimming at speeds exceeding 70 kilometers per hour.

In the case of something like a dolphin, this sort of small-tank captivity is viewed as cruel, but fish taste better than dolphins, and don’t squeak happily at children, so, much as has been the case with cows in the U.S., it’s doubtful anyone will take an interest in their welfare. We can probably expect vast factory farms full of tuna, along with any other large marine fish humans want to continue to eat in the future since there’s no alternative, apart from not eating them.

But if we move away from looking at the ocean as a business, it bears mentioning that not eating any fish whatsoever is decidedly not an option for a vast swath of humanity. “You’d be looking at a lot of starvation,” Payne, the Stanford paleobiologist, told me. According to a 2016 op-ed in Science magazine by public health researcher Christopher Golden, 845 million people—about a tenth of the global population—face some form of malnutrition in the near future when traditional fishing ceases to be a viable source of food for many of the world’s poor.

We’re also in for more big changes to the weather, Payne said. Part of the reason the oceans work as a “carbon sink” is that plankton consume carbon as a part of photosynthesis, turning them into organic matter. A reduction in photosynthesis means more carbon will just stay in the atmosphere and speed up global warming, particularly in the vast dead zone around the equator—a probable cause of the extreme ocean temperatures of the Great Dying; areas that are now usually around 28 degrees Celsius were 40 degrees Celsius or more back then.

Apart from heat, Payne said, “one thing you would see very quickly is the effect of storms on coastal systems would change, because with nothing living on the reefs, the reefs will start to fall apart. That will reduce their ability to protect coastal systems from waves during big storms.” This means huge changes in the terrestrial climate near these coastal systems, particularly in places like Australia and the Bahamas.

But even with the combined ocean ecosystem more or less converted into a giant marine desert, there’s a very good chance we’ll always have a man-made oasis or two. A 2017 proposal by the consortium of tourism businesses and Australia’s Reef and Rainforest Research Centre would protect six particularly profitable sites along the reef by literally pumping in cold water at a cost of millions of dollars to lessen the effects of climate change. The idea has been regarded as perverse, with critics noting that pumping cold water into a few areas of the Great Barrier Reef would be nothing but a band-aid, and that large scale action is needed. But large scale action isn’t happening, and the mass die-off is proceeding.

Since it appears we lack the willpower to curb our worst impulses when it comes to the oceans, a few band-aids may be all we can hope for.

Adapted from an excerpt from The Day It Finally Happens by Mike Pearl. Copyright © 2019 by Mike Pearl. Reprinted by permission of Scribner, an Imprint of Simon & Schuster, Inc.

While we debate geoengineering the ocean, it seems we’re already doing it

While we debate geoengineering the ocean, it seems we’re already doing it

Human activities such as industry and fossil fuel burning are likely contributing extra iron to some parts of the world’s oceans, according to a study published June 14 in Nature Communications.

Iron is an important nutrient for the growth of phytoplankton, tiny single-celled plants at the base of the ocean food chain. But iron is not very soluble in seawater and tends to be scarce in marine environments; the lack of this element limits phytoplankton growth in up to one-third of ocean waters worldwide.

These observations have led to proposals to “fertilize” the ocean with iron to stimulate phytoplankton growth. The idea is that the increased phytoplankton growth would remove some of the excess carbon dioxide we’ve released into the atmosphere, and thus help to mitigate climate change.

Like other forms of geoengineering, oceanic iron fertilization is controversial. So it’s a bit unsettling to realize that this process might already be happening, albeit unintentionally.

Researchers in the United States analyzed iron in air samples collected on a research cruise in the North Atlantic Ocean. They used stable isotopes—forms of the same chemical element with different atomic weights—to discern the signature of different sources of iron.

Iron in ash from fossil fuel burning or other human activities is known to be isotopically lighter than the iron in airborne dust. This dust, carried on the wind from desert regions, is a primary natural source of iron in the world’s oceans.

The researchers also assessed how easily the iron in the samples dissolved in seawater. Iron resulting from human activities is known to be more soluble than natural iron from desert dust.

Iron in air samples from regions influenced by a well-known plume of dust from the Sahara Desert has an isotopic fingerprint and solubility similar to that of the Earth’s crust, the researchers found. All that is as expected.

But air samples collected near North America and Europe appear to contain two different fractions of iron: one similar to the iron derived from desert dust, and one that is lighter and more soluble. The researchers suggest that this second fraction is likely to be the result of human activities. Based on the time of year the samples were collected, they say, it probably reflects burning of fossil fuels.

At least half and possibly close to all the soluble iron in European and North American air masses derives from human activities, they calculated. This means that the iron available to phytoplankton in some open-ocean regions of the North Atlantic could already be mainly anthropogenic.

A comparison between existing models of dust deposition on the oceans and the analysis of the new samples suggests that these models have been overestimating the solubility of dust-derived iron and underestimating the amount of anthropogenic iron reaching the oceans.

It’s not yet clear exactly how much iron from human activities is entering the ocean, or how it might be affecting phytoplankton growth. Still, the results are a good reminder, as we contemplate multiple forms of geoengineering, that human activities often come with unexpected consequences.

Source: Conway T.M. et al. “Tracing and constraining anthropogenic aerosol iron fluxes to the North Atlantic Ocean using iron isotopes.” Nature Communications 2019.

Ocean acidification ‘could have consequences for millions’


Ocean acidification could have serious consequences for the millions of people globally whose lives depend on coastal protection, fisheries and aquaculture, a new publication suggests.

Writing in Emerging Topics in Life Sciences, scientists say that only significant cuts in fossil fuel emissions will prevent the changes already evident in areas with projected future carbon dioxide levels becoming more widespread.

They also call for a binding international agreement that builds on the United Nations Sustainable Development Goals to minimise and address the impacts of ocean acidification.

The article was written by Jason Hall-Spencer, Professor of Marine Biology at the University of Plymouth, and Plymouth graduate Dr Ben Harvey, now Assistant Professor at the University of Tsukuba’s Shimoda Marine Research Center.

They and other collaborators have published several studies over the past decade that show the threats posed by ocean acidification in terms of habitat degradation and a loss of biodiversity.

These have centred around the coast of Japan, where they demonstrated ocean acidification is having a major impact on marine life, and in the Mediterranean where they showed it was having a negative impact on wild fish.

Both regions have volcanic CO2 seeps, where the escaping gas dissolves into the sea water and creates conditions similar to that expected to occur worldwide in the coming years.

Their new publication provides a synthesis of the likely effects of ocean acidification on ecosystem properties, functions and services and is based on laboratory experiments and observations along natural gradients in CO2.

It says that studies at CO2 seeps worldwide have shown that reefs made by organisms with shells or skeletons, such oysters or corals, are sensitive to ocean acidification and that degraded reefs provide less coastal protection and less habitat for commercially important fish and shellfish.

This amplifies the risks to marine goods and services from climate change causing shifts to seaweed dominance, habitat degradation and a loss of biodiversity in the tropics, the sub-tropics and on temperate coasts.

Dr Harvey, who graduated from the BSc (Hons) Ocean Science programme in 2008, said: “We are releasing around 1 million tons of carbon dioxide per hour into the Earth’s atmosphere. About 25% of this gas is taken up by the ocean where it reacts with seawater to form a weak acid, causing surface ocean pH to fall by around 0.002 units per year. The chemistry of this rapid change in surface waters is understood, yet there is uncertainty about its effects on society which is what we are trying to overcome in this study.”

Professor Hall-Spencer, the publication’s lead author, added said: “The Paris Agreement on climate change was welcome. But it does not mention ocean acidification, nor the fact that this rapid change in surface ocean chemistry undermines the social, economic and environmental pillars of sustainable development. The time is ripe for a ‘Paris Agreement for the oceans’, with the specific target to minimise and address the impacts of ocean acidification, including through enhanced scientific cooperation at all levels.”