3297. California's Crashing Kelp Forest

By Science Daily, October 21, 2019

Kelp forests are home to many sea species

First the sea stars wasted to nothing. Then the purple urchins took over, eating and eating until the bull kelp forests were gone. The red abalone starved. Their fishery closed. Red sea urchins starved. Their fishery collapsed. And the ocean kept warming.

It sounds like an ecological horror movie, but this scenario actually happened between 2013 and 2017. Its lasting impacts continue to affect northern California's coast today, with another marine heatwave forecast for this winter.

In a study published today in the journal Scientific Reports, scientists from the University of California, Davis, and the California Department of Fish and Wildlife use two decades of kelp ecosystem monitoring data to chronicle the catastrophic shift in 2014 from a robust bull kelp forest to a barren of purple sea urchins. Similar impacts are being observed in kelp forests from Baja California to Alaska.

Uncharted Territory

The study shows how bull kelp deforestation triggered the closure of a $44 million recreational abalone fishery and the collapse of the north coast commercial red sea urchin fishery.

More than 90 percent of bull kelp and 96 percent of red abalone were lost along 217 miles of northern California coastline within just a few years. Meanwhile, purple sea urchin populations exploded 60-fold between 2014 and 2015.

"We're in the 20th year of this monitoring program, and we can confidently say, this is uncharted territory that we're in," said lead author Laura Rogers-Bennett, an environmental scientist with UC Davis Karen C. Drayer Wildlife Health Center and California Department of Fish and Wildlife operating out of the UC Davis Bodega Marine Laboratory. "We've never seen purple sea urchins at these densities before. This paper really shows what it takes in terms of multiple stressors to crash a bull kelp forest."

The Perfect Storm

The bull kelp ecosystem surveys reveal the timing and magnitude of a series of events -- what the study authors call a "perfect storm" -- that led to the unprecedented decline of the kelp forest and the animals, plants and ecological benefits it supports:

• 2013: Sea star wasting disease killed mass numbers of sea stars, a purple sea urchin predator.
• 2014-2017: A marine heatwave and El Nino event warmed the nearshore ocean.
• 2015: Purple sea urchin populations exploded.
• 2017: Mass mortalities of red abalone led to that fishery's closure in 2018 to the present.

'They're Eating Absolutely Everything'

Purple sea urchins are native to California's coast, but typically at low densities.

"What we're seeing now are millions and millions of purple sea urchins, and they're eating absolutely everything," said Rogers-Bennett. "They can eat through all the anemones, the sponge, all the kelp, the fleshy red algae. They're even eating through calcified alga and sand."

Bull kelp are one of the fastest-growing plants on Earth, capable of growing two feet in just a day. If cooler water temperatures return, kelp could likely regrow, the study said. But with ravenous purple sea urchin teeth constantly scraping the bottom of the sea floor, the kelp cannot catch a break.

Urchins are edible. Their fleshy insides -- specifically, their gonads -- turn up on sushi rolls as uni. So perhaps a purple sea urchin harvest is in order? Not so fast. With so much competition from their brethren, the insides of these urchins are nearly empty. They are starving.

Urchin Ranching and a Glimmer of Hope

In what could be a glimmer of hope for bull kelp forests, UC Davis researchers are working with Bay Area shellfish company Urchinomics to explore the possibility of removing purple urchins from their sea floor barrens and fattening them up for market -- in short, urchin ranching.

If the resulting product gives kelp beds a chance to recover, dining on purple urchin could go beyond "sustainable seafood" to become restorative. Rogers-Bennett and UC Davis Bodega Marine Laboratory Director Gary Cherr will begin trials this fall to see if urchin ranching could be a viable strategy.

Other strategies are outlined in the Sonoma-Mendocino Bull Kelp Recovery Plan, released last June by the Greater Farallones Association and CDFW. It includes measures such as creating a kelp oasis to preserve seed stock and repopulate bull kelp when conditions are conducive to restoration.

"There are too many purple urchins, and the kelp forest is in giant trouble," said Rogers-Bennett. "There are all kinds of problems associated with that. But we are working now on some of the potential solutions."

Meanwhile, this study illustrates the vulnerability of ecosystems and communities to climate-driven collapses.

The study was coauthored by Cynthia Catton, an environmental scientist with the CDFW and research associate of UC Davis Bodega Marine Laboratory at the time of the study.

3170. Oceans Are Getting Louder, Posing Potential Threats to Marine Life

By Jim Robbins, The New York Times, January 22, 2019

A container ship crossing under the Lions Gate Bridge in Vancouver. Increasing traffic and the threat of seismic blasts for offshore drilling exploration are dangerous to marine life, scientists warn.CreditCreditAlana Paterson for The New York Times

Slow-moving, hulking ships crisscross miles of ocean in a lawn mower pattern, wielding an array of 12 to 48 air guns blasting pressurized air repeatedly into the depths of the ocean.

The sound waves hit the sea floor, penetrating miles into it, and bounce back to the surface, where they are picked up by hydrophones. The acoustic patterns form a three-dimensional map of where oil and gas most likely lie.

The seismic air guns probably produce the loudest noise that humans use regularly underwater, and it is about to become far louder in the Atlantic. As part of the Trump administration’s plans to allow offshore drilling for gas and oil exploration, five companies have been given permits to carry out seismic mapping with the air guns all along the Eastern Seaboard, from Central Florida to the Northeast, for the first time in three decades. The surveys haven’t started yet in the Atlantic, but now that the ban on offshore drilling has been lifted, companies can be granted access to explore regions along the Gulf of Mexico and the Pacific.

And air guns are now the most common method companies use to map the ocean floor.

“They fire approximately every 10 seconds around the clock for months at a time,” said Douglas Nowacek, a professor of marine conservation technology at Duke University. "They have been detected 4,000 kilometers away. These are huge, huge impacts.”

The prospect of incessant underwater sonic tests is the latest example cited by environmentalists and others of the growing problem of ocean noise, spawning lawsuits against some industries and governments as well as spurring more research into the potential dangers for marine life.

Some scientists say the noises from air guns, ship sonar and general tanker traffic can cause the gradual or even outright death of sea creatures, from the giants to the tiniest — whales, dolphins, fish, squid, octopuses and even plankton. Other effects include impairing animals’ hearing, brain hemorrhaging and the drowning out of communication sounds important for survival, experts say.

So great is the growing din in the world’s oceans that experts fear it is fundamentally disrupting the marine ecosystem, diminishing populations of some species as the noise levels disturb feeding, reproduction and social behavior.

A 2017 study, for example, found that a loud blast, softer than the sound of a seismic air gun, killed nearly two-thirds of the zooplankton in three-quarters of a mile on either side. Tiny organisms at the bottom of the food chain, zooplankton provide a food source for everything from great whales to shrimp. Krill, a tiny crustacean vital to whales and other animals, were especially hard hit, according to one study.

“Researchers saw a complete absence of life around the air gun,” said Michael Jasny, director of marine mammal protection for the Natural Resources Defense Council, one of several environmental groups suing the federal government in an effort to stop the seismic surveys.

Measuring the sounds of commerce

Each seismic shot from the air guns is estimated to reach up to 260 underwater decibels, equal to about 200 decibels in the atmosphere. Container ships, another noisemaker on the seas, make sounds up to 190 decibels — the equivalent of 130 decibels in the atmosphere. (The launch of a space shuttle, by contrast, reaches about 160 decibels for those nearby.)

Every 10 decibels is an order of magnitude. An explosion of 200 decibels, then, is 10 times more intense than the sound of a container ship. Because water is much denser than air, sound travels underwater about four times faster and much farther than above the sea’s surface.

“At any one time, there are 20, 30 or 40 seismic surveys going on around the world,” for oil and gas exploration, as well as for geological research, Dr. Nowacek said.

All told in the first year of the newly approved exploration, more than five million of these huge explosions would occur all along the United States’ eastern coastline.

Christopher Clark, a senior researcher in the bioacoustics program at the Cornell Lab of Ornithology, who has studied whale communication for 40 years, described the noise as a “living hell” for undersea life, which is exquisitely tuned to sound. 

A coalition of environmental groups has filed suit against the National Marine Fisheries Service, a division of the National Oceanic and Atmospheric Administration, claiming the agency is violating several federal laws protecting wildlife, including the Endangered Species Act, by allowing the blasts. And governors from 10 states have protested the offshore drilling decision and are seeking to join the legal action.

Harming or injuring marine mammals is forbidden under the Marine Mammal Protection Act. In November, NOAA issued five authorizations allowing seismic exploration companies to “incidentally, but not intentionally, harass marine mammals.” Because of the government shutdown, other government action to begin testing has been postponed until at least March 1.

The companies involved in the exploration disagree sharply with the claims of harm. “More than 50 years of extensive surveying and scientific research indicate that the risk of direct physical injury to marine mammals is extremely low,” Gail Adams-Jackson, vice president of communications for the International Association of Geophysical Contractors, said in a statement. She contended that the groups’ efforts are solely aimed at stopping offshore exploration and development.

The companies and NOAA Fisheries said that the effects on marine life could be kept to a minimum by careful monitoring and mitigation, which would involve acoustic monitoring to detect mammal vocalizations and shutting down exploration when sensitive species like the endangered North Atlantic right whales are observed.

There are no more than 400 to 500 of the migratory right whales, which can grow up to 60 feet long, and calve and nurse their young from North Carolina to Florida. Right whales are already emaciated and stressed by a warmer ocean — they live in the Gulf of Maine, which has warmed considerably more than other bodies of water. Reproduction has been drastically reduced. And the seismic noise can mask ship sounds, resulting in collisions, another leading danger for the whales.

“We require strong protections for North American right whales in areas where they are expected to be present, including all designated habitat,” Benjamin Laws, a NOAA biologist said, defending the issuance of the permits.

Carrying sound across the ocean

Cavitation, the noise from the synchronous collapse of bubbles created by a ship’s propeller, as well as the rumble of ship engines, poses an ever bigger problem to marine life. And shipping noise could double by 2030.

Years of constant blasts could be extremely harmful, others argue, and not just for right whales. Because of the way sound reverberates in the ocean, the noise can be unrelenting.

“Prolonged chronic stress of any kind is bad, because it shunts resources away from reproduction,” Dr. Nowacek said. “It presses your adrenal glands to produce adrenaline and stress hormones, causes weight loss and immunosuppression.”

In a landmark study, when ship traffic greatly decreased after the events of Sept. 11, 2001, researchers noted a significant drop in stress hormones in the feces of right whales in the 

Bay of Fundy in Canada, the first evidence that ship noise can cause chronic stress in whales.

Moreover, acoustic communication is primary in the marine ecosystem, where visibility is so limited. Many whale species are highly intelligent, social beings and communicate in the clicks, moaning, singing and calling of their own languages. Some whales, and orcas (the largest in the dolphin family despite their killer whale designation), hunt prey through echolocation, a kind of natural sonar.

“Sound can travel enormous distances very fast and whales have evolved to take advantage of that,” said Dr. Clark, who has listened to whales near Ireland from coastal Virginia. “They can hear storms a thousand miles away.”

Aside from the seismic noise, compounded sounds from container ships to navy sonar are posing a problem for marine life. As the number of ships moving around the world has increased significantlyin recent years, cavitation, the noise from the synchronous collapse of bubbles created by a ship’s propeller, as well as the rumble of ship engines, poses a bigger and bigger problem. A recent study found that shipping noise could double by 2030.

Noise masks whale expressions between families, which can affect orientation, feeding, care of young, detection of prey and even increase aggression. Already 80 percent of communications of some species of whales is masked by noise, according to models assessed by a team of biologists.

“It’s ripping the communications system apart,” Dr. Clark said. “And every aspect of their lives is dependent on sound, including finding food.”

About 20,000 known species of fish are able to hear, and some 800 species are known to make sounds of their own to hunt, mate, navigate and communicate. One fish, the plainfish midshipman, for example, sings to the females to mate and defends nests with barking sounds.

Other studies show that beaked whales are extremely sensitive to noise, and in frantic efforts to escape seismic air guns or navy sonar they have been forced to change their dive patterns to the surface. Some have died from decompression sickness.

Loud noises can also affect behavior and even ecosystems by altering where species go. In 2008 in Canada’s Baffin Bay, seismic testing is believed to have delayed the southward migration of narwhals — the whales with the long spiral tusk — until it was too late and they became trapped in sea ice. More than 1,000 died.

The blasting can take a particular toll on a part of the body in invertebrates called the statocyst. In octopuses, squid, lobsters and other invertebrates, the organ is responsible for orientation and balance. Damaged, it disorients the creatures and makes them vulnerable to predators.

Still, while research has expanded in the last decade, much is difficult to pinpoint and sometimes impossible to study. “You can’t study a whale’s hearing,” said Lindy Weilgart, a researcher at Dalhousie University in Nova Scotia and the author of an analysis of 115 studies, released in 2018.

The exposure of mammals to such noise has been likened to living in a permanent construction zone. “Sometimes listening on the headphones gives you a headache within 10 minutes,” Molly Patterson, a researcher who studies underwater sound, said in the 2016 documentary “Sonic Sea.” “You have to take the headphones off, you have to turn the volume down. The whales can’t turn the volume down.”

One way many have escaped the cacophony is by heading to the Arctic. But as polar ice melts, and seismic exploration and ship traffic there increase, it is no longer the refuge it once was.

Ocean noise can also have economic repercussions: Research in Norway shows that commercial fishermen return to the dock with 40 to 80 percent fewer fish when exploration is underway nearby.

Regulations on underwater noise are few and far between and experts are searching for solutions. The United Nations recently held a weeklong symposium on noise pollution and marine life.

Voluntary efforts to turn down the volume are having an effect: The Port of Vancouver started the ECHO (Enhancing Cetacean Habitat and Observation) Program, asking mariners to reduce noise by having ships slow down and fix cavitation on the propellers. 

At the same time, though, if the Trans Mountain pipeline is built from the tar sands of Alberta to a port near Vancouver, as planned, tanker traffic in the Salish Sea is expected to increase by seven times. Marine biologists say that would exacerbate the difficulties the region’s endangered orcas already face in finding prey.

Scientists and environmentalists are urging that more research be conducted, to learn much more about the effects of sound and ship traffic on the creatures of the sea.

“The effects on marine mammals are felt across an extraordinarily large scale,” Mr. Jasny, the marine mammal protection director, said. “And loud noise has an effect on species across the food web.”

3067. More Than 77 Percent of Earth's Land Has Been Modified By Human Industry

By Livia Albeck-Ripka, The New York Times, October 31, 2018

         Sunset on the Tapajós River, deep in the Amazon rain forest. 

         Credit: Meridith Kohut for The New York Times

MELBOURNE, Australia — Scientists are warning that if human beings continue to mine the world’s wildernesses for resources and convert them into cities and farms at the pace of the previous century, the planet’s few remaining wild places could disappear in decades.

Today, more than 77 percent of land on earth, excluding Antarctica, has been modified by human industry, according to a study published Wednesday in the journal Nature, up from just 15 percent a century ago.

The study, led by researchers from the University of Queensland in Australia and the Wildlife Conservation Society in New York, paints the first global picture of the threat to the world’s remaining wildernesses — and the image is bleak.

“We’re on a threshold where whole systems could collapse and the consequences of that would be catastrophic,” said James R. Allan, one of the study’s authors.

In the study, Mr. Allan and his colleagues urged the participants of a United Nations conference on biological diversity, scheduled for next month in Egypt, to protect all of the world’s remaining wilderness areas.

“We cannot afford to lose more,” he said. “We must save it in its entirety.”

The parts of the world most in need of protecting are in some of the largest and most powerful nations, the study found. More than 70 percent of wilderness areas can be found in Russia, Canada, Australia, the United States and Brazil.

Wilderness, the study’s authors said, is defined as an area not subject to direct human use.

These areas are the only places on earth that have natural levels of biodiversity, and can continue to sustain plant and animal species on an evolutionary time scale.

Moreover, these spots often act as the world’s lungs, storing carbon dioxide that would otherwise be released into the atmosphere.

“Wild areas provide a lot of life support systems for the planet. We’d lose those benefits and those ecosystems services, and the cost of having to replace that would be immense,” Mr. Allan said.

In 2016, the scientists mapped the world’s terrestrial wildernesses. This year, they did the same for the world’s oceans.

More of the oceans have been affected by human industry — including oil exploration, shipping and commercial fishing — than have the world’s land mass, the study found.

According to the study, “87 percent of the ocean has been modified by the direct effects of human activities.”

“This astonishing expansion of the aggressive human footprint is happening everywhere,” said William Laurance, a professor of environmental science at James Cook University in Cairns, Australia, who was not involved in the study.

Dr. Laurance said that while he “wholeheartedly” agreed with the researchers’ message to policy experts, even more aggressive action was needed to stop global resource extraction and industrial expansion.

He warned that developing countries like Brazil and China are eager to catch up with more industrialized nations. Each step those countries take has a compounding effect on the environment: Developing mines also means building roads and refineries.

Healthy ecosystems are crucial in their own right for biodiversity and mitigating climate change, but more importantly, said the researchers, they are home for hundreds of millions of indigenous people, who rely on the wilderness to survive and thrive.

3061. Oceans Are Warming Faster Than Predicated

by Kendra Pierre-Louis, The New York Times, October 31, 2018

How do you take the ocean’s temperature?

The question might sound like the prelude to a children’s joke. But for climate scientists, the answer has serious consequences.

Climate change is rapidly warming the world’s oceans, killing off aquatic organisms — like coral reefs and kelp forests — that anchor entire ecosystems. The warmer waters also cause sea levels to rise and make extreme weather events like hurricanes more destructive.

If scientists can more accurately measure the speed at which oceans are warming, they can better predict the future effects of climate change. And a study published Wednesday in the journal Nature suggests that oceans are warming far faster than the estimates laid out by the Intergovernmental Panel on Climate Change, the global organization for climate data.

The study, led by Laure Resplandy, a biogeochemical oceanographer at Princeton University, found that between 1991 and 2016 the oceans warmed an average of 60 percent more per year than the panel’s official estimates.

In October, the panel released a major report predicting that some of the worst effects of climate change, including coastal flooding, food shortages and a mass die-off of coral reefs, could come to pass as soon as 2040 if human greenhouse gas emissions continue at current levels. The I.P.C.C. report showed that scientists may have been underestimating the severity of the world’s present climate trajectory.

The new ocean temperature estimates, if proven accurate, could be another indication that the global warming of the past few decades has exceeded conservative estimates and has been more closely in line with scientists’ worst-case scenarios.

The researchers used a new approach that derived ocean temperatures by measuring the levels of carbon dioxide and oxygen in the atmosphere.

Those gases dissolve in ocean waters, but the amount the ocean can hold depends on its temperature. “As the ocean has been warming, it’s basically pushing out oxygen and carbon dioxide,” said David Nicholson, an associate scientist at the Woods Hole Oceanographic Institution who was not involved in the study.

As Dr. Resplandy put it: “If you leave a Coke outside in the sun, it’s going to warm and it’s going to lose the gas. It’s a little bit the same idea.”

Scientists normally measure ocean temperatures using thermometers, but stitching together a global temperature record requires thermometers around the globe. Global temperature records were spotty before 2007, when an international consortium began a program, known as Argo, creating an international network of ocean-temperature-measuring instruments.

But a group from Scripps Institution of Oceanography had been taking careful measurements of atmospheric carbon dioxide since 1991, for unrelated reasons. Dr. Resplandy and her team used that data set for this study.

Dr. Nicholson said the study was an example of how collecting data now can have unexpected benefits later. “It kind of supports the importance of collecting these long-term time series even if it isn’t apparent at the start what the outcome will be,” he said.

Scientists already know that the world’s oceans absorb 90 percent of the excess heat trapped on Earth by human greenhouse gas emissions. In its recent report, the I.P.C.C. used one of the lower available estimates of how much the oceans have warmed. Dr. Resplandy and her team found that the upper estimate is more likely what is happening.

“Their estimates overlap with previous estimates, but it’s aligned with some of the higher estimates,” Dr. Nicholson said. “It’s not like completely changing our understanding of what the ocean might be taking up — it’s a new type of measurement that’s weighing in toward the higher end of that.”

There are some caveats. This is a novel approach, and it is unclear if it will hold up to further scrutiny. Kevin E. Trenberth, a senior scientist in the Climate Analysis Section at the National Center for Atmospheric Research, noted that the methodology works best over long periods of time but does not detail what happens year to year.

Still, Dr. Trenberth’s own research found that the I.P.C.C.’s measurements for observed ocean heat were too low. “This is a new complementary method, and the results are quite compatible with our estimates for the most part,” he wrote in an email.

Dr. Resplandy said her work did not upend the I.P.C.C. report’s warnings that humanity has only a couple of decades to ward off some of climate change’s most catastrophic effects.

“It doesn’t change the results,” she said. “What it does is that it makes it harder to get there.”

2977. The Last of the Ocean Wilderness

By Kendall Jones and James Watson, Scientific American, Jully 26, 2018

The ocean covers more than 70 percent of our planet, an area of nearly 140 million square miles. It is so immense that explorers once thought there was no way to cross it. Once our ships were advanced enough to do so, naturalists then thought it impossible for humans to ever exhaust fisheries or drive marine species to extinction.

How we have proved them wrong.

Commercial fishing now covers an area four times that of agriculture and much of this has been completely unsustainable. We have depleted 90 percent of important species. Large fish have been harvested so heavily that they have been virtually wiped out in many places. Indeed, studying coral reefs today has been compared to trying to understand the Serengeti by studying termites and locusts while ignoring the wildebeest and lions.

But surely, given that humans don’t live on the ocean and we need specialized ships to go far beyond the coast, there must still be immense areas that are untouched.

That is incorrect. In a study just published in Current Biology, we used fine-scale global data on 19 human stressors to the ocean—including commercial shipping, sediment runoff, and several types of fishing—to show that Earth’s “marine wilderness” is dwindling. Just 13 percent of the ocean remains as wilderness and in coastal regions, where human activities are most intense, there is almost no wilderness left at all. Of the roughly 21 million square miles of marine wilderness remaining, almost all is found in the Arctic and Antarctic, or around remote Pacific island nations with low populations.

These marine wilderness areas are home to unparalleled levels of marine life, sustaining large predators and high levels of genetic diversity. Their lack of human impacts can also make them highly resilient to rising sea temperatures and coral bleaching—stressors that cannot be halted without globally coordinated efforts to reduce emissions.

In an era of widespread marine biodiversity loss, wilderness areas also act like a window into the past, revealing what the ocean looked like before overfishing and pollution took their toll. This is crucial information for marine conservation. If we are to restore degraded areas to their former state, we need to know what to aim for.

Despite being irreplaceable and increasingly threatened, most wilderness remains unprotected. This means it could be lost at any time, as improvements in technology allow us to fish deeper and ship further than ever before. Thanks to a warming climate, even places that were once safe due to year-round ice cover are now open to fishing and shipping.

This lack of protection is largely due to international environmental policies failing to recognize the unique values of wilderness, instead focusing on saving at-risk ecosystems and avoiding extinctions. This is like a government using its entire health budget on emergency heart surgery, without pre-emptive policies encouraging exercise to decrease the risk of heart attacks occurring in the first place.

If Earth’s marine biodiversity is to be preserved in perpetuity, it is time for conservation to focus not only on the emergency room but also on preventative health measures.

This paper comes with a plea. As we develop international conservation agreements, it is crucial that we recognize the unique values of wilderness and sets targets for its retention.

Without such targets, wilderness areas will likely be lost forever—something President Lyndon B. Johnson urged us to avoid when he signed the American Wilderness Act in 1964. “If future generations are to remember us with gratitude rather than contempt,” observed Johnson, “we must leave them something more than the miracles of technology. We must leave them a glimpse of the world as it was in the beginning.”

2883. Gulf Stream Disruptions Can Set Off Deeper Ecological Crisis

By Damian Carrington, The Guardian, April 13, 2018

Serious disruption to the Gulf Stream ocean currents that are crucial in controlling global climate must be avoided “at all costs”, senior scientists have warned. The alert follows the revelation this week that the system is at its weakest ever recorded.

Past collapses of the giant network have seen some of the most extreme impacts in climate history, with western Europe particularly vulnerable to a descent into freezing winters. A significantly weakened system is also likely to cause more severe storms in Europe, faster sea level rise on the east coast of the US and increasing drought in the Sahel in Africa.

The new research worries scientists because of the huge impact global warming has already had on the currents and the unpredictability of a future “tipping point”.

The currents that bring warm Atlantic water northwards towards the pole, where they cool, sink and return southwards, is the most significant control on northern hemisphere climate outside the atmosphere. But the system, formally called the Atlantic Meridional Overturning Circulation (Amoc), has weakened by 15% since 1950, thanks to melting Greenland ice and ocean warming making seawater less dense and more buoyant.

This represents a massive slowdown – equivalent to halting all the world’s rivers three times over, or stopping the greatest river, the Amazon, 15 times. Such weakening has not been seen in at least the last 1,600 years, which is as far back as researchers have analysed so far. Furthermore, the new analyses show the weakening is accelerating.

“From the study of past climate, we know changes in the Amoc have been some of the most abrupt and impactful events in the history of climate,” said Prof Stefan Rahmstorf, at the Potsdam Institute for Climate Impact Research in Germany and one of the world’s leading oceanographers, who led some of the new research. During the last Ice Age, winter temperatures changed by up to 10C within three years in some places.

“We are dealing with a system that in some aspects is highly non-linear, so fiddling with it is very dangerous, because you may well trigger some surprises,” he said. “I wish I knew where this critical tipping point is, but that is unfortunately just what we don’t know. We should avoid disrupting the Amoc at all costs. It is one more reason why we should stop global warming as soon as possible.”

Oceanographer Peter Spooner, at University College London, shares the concern: “The extent of the changes we have discovered comes as a surprise to many, including myself, and points to significant changes in the future.”

A collapse in the Amoc would mean far less heat reaching western Europe and plunge the region into very severe winters, the kind of scenario depicted in an extreme fashion in the movie The Day After Tomorrow. A widespread collapse of deep-sea ecosystems has also been seen in the past.

But as the Amoc weakens, it might actually increase summer heatwaves. That is because it takes time for the cooling of the northern waters to also cause cooling over the adjacent lands. However, the cooler waters affect the atmosphere in a way that helps warm air to flood into Europe from the south, a situation already seen in 2015.

Gulf Stream current at its weakest in 1,600 years, studies show

 

Read more

Other new research this week showed that Greenland’s massive ice cap is melting at the fastest rate for at least 450 years. This influx will continue to weaken the Amoc into the future until human-caused climate change is halted, but scientists do not not know how fast the weakening will be or when it reaches the point of collapse.

“Many people have tried to check that with computer models,” said Rahmstorf. “But they differ a lot because it depends on a very subtle balance of density – that is temperature and salinity distribution in the ocean. We are not able to model this with any confidence right now.”

“We are hoping to somehow make some headway, but I have been in this area for more than 20 years now and we still don’t understand why the models differ so much in the sensitivity of the Amoc,” he said.

However, Rahmstorf said the international climate deal agreed in 2015 offers some hope if its ambition is increased and achieved: “If we can keep the temperature rise to well below 2C as agreed in the Paris agreement, I think we run a small risk of crossing this collapse tipping point.”