Permafrost—the ground that stays frozen for two or more consecutive years—is a ticking time bomb of climate change. Some 24 percent of Northern Hemisphere land is permafrost. That's 9 million square miles (23 million square kilometers) found mostly in Siberia, the Tibetan Plateau, Alaska, the Canadian Arctic, and other higher mountain regions.
Unfortunately, thawing permafrost releases massive amounts of methane and/or carbon dioxide. The question is whether that would happen over the course of decades or over a century or more. This short video from the Yale Climate Forum explains the current scientific thinking on just how close we might be to the lethal tipping point.
Meanwhile this 90-second permafrost primer from the Climate Desk explains exactly we want this northern freezer to remain frozen.
The map below shows land-based permafrost in the Northern Hemisphere. It also shows the subsea permafrost that underlies the continental shelves of the Arctic Ocean.
We really really don't want permafrost to melt since its emissions have the potential to dwarf our own. As the Yale Climate Forum video says, we have the theoretical ability to control our carbon emissions but none whatsoever to stop a permafrost tipping point once it's reached.
I'm strapped into my backward-facing seat on a COD, or "carrier onboard delivery" plane, the US Navy workhorse that ferries people, supplies, and mail to and from its aircraft carriers at sea. I cinch the four-point harness holding me in place. Then I cinch it some more. When it's as tight as it can go, an aircrewman walks by and yanks it so hard it squeezes the breath out of me. The hatch closes. Steam rises from the floor. Shit. I've watched the YouTube videos. I know what's coming. Takeoff, a 30-minute flight, then landing on the USS Nimitz, decks pitching, plane wings waggling, tailhook dangling from the underside of the aircraft to catch one of four arresting cables stretched across the flight deck. Since it's not hard to miss them all, the pilot will gun the engines at landing to enable an immediate relaunch. Which means that if he succeeds at trapping a cable we'll decelerate from 180 nautical miles per hour to zero in about one second.
To get to the Nimitz, 100 miles off Honolulu, our turboprop is flying a 50-50 blend of biofuel and standard JP-5 shipboard aviation fuel. The biofuel is made from algae plus waste cooking oil. This makes us part of history, my aircrewman says, players in what the Navy calls the Great Green Fleet demonstration of July 2012. It's paired with a three-year, $510 million energy reform effort in conjunction with the departments of Agriculture and Energy as part of a larger push to change the way the US military sails, flies, marches, and thinks. "As a nation and as a Navy and Marine Corps, we simply rely too much on a finite and depleting stock of fossil fuels that will most likely continue to rise in cost over the next decades," announced Navy Secretary Ray Mabus at the launch of the program back in 2009. "This creates an obvious vulnerability to our energy security and to our national security and to our future on this planet."
The Navy has set five ambitious goals to reduce energy consumption, decrease reliance on foreign oil, and significantly increase the use of alternative energy. Part of one target is to demonstrate a Great Green Fleet by 2012, and that's what's sailing this July day in Hawaii's cobalt-blue waters: a carrier strike group comprising an aircraft carrier, two guided-missile destroyers, a guided-missile cruiser, and an oiler. All are running at least partially on alternatives to fossil fuels: the Nimitz on nuclear power, the other ships on that biofuel-diesel blend. The 71 aircraft aboard—Super Hornets, Hornets, Prowlers, Growlers, Hawkeyes, Greyhounds, Knighthawks, and Seahawks—are burning the same cocktail as my COD. All of today's biofuels are drop-in replacements for marine diesel or aviation fuel and are designed to run without any changes to the existing hardware of ships or planes. "No [nation] can afford to reengineer their navies to accept a different kind of fuel," Vice Adm. Philip Cullom, deputy chief of naval operations for fleet readiness and logistics, tells me.
The Great Green Fleet is debuting at the 2012 RIMPAC (Rim of the Pacific) exercise, the largest ever international maritime war games, engaging 40 surface ships, six submarines, more than 200 aircraft, and 25,000 personnel from 22 nations. For the first time Russian ships are playing alongside US ships, and naval personnel from India are attending. Many fleets here are sharpening their focus on alternative fuels and working to assure the formulations are codeveloped with their allies. "We've had dialogue with the Australians, the French, the British, other European nations, and many others in the Pacific," and they all want to take "the petroleum off-ramp," Cullom tells me. "We don't want to run out of fuel."
You can't live off the land at sea, which is why the Navy has always looked far into the future to fuel its supply lines; the job description of admirals requires them to assess risk and solve intractable problems that stymie the rest of us. Peak oil, foreign oil, greenhouse emissions, climate change? Just another bunch of enemies. So when the Department of Defense set a goal to meet 25 percent of its energy needs with renewables by 2025, the Navy found itself fighting on familiar ground. Four times in history it has overhauled old transportation paradigms—from sail to coal to gasoline to diesel to nuclear—carrying commercial shipping with it in the process. "We are a better Navy and a better Marine Corps for innovation," Mabus says. "We have led the world in the adoption of new energy strategies in the past. This is our legacy."
It goes beyond supply lines. Rising sea levels lapping at naval bases? A melting and increasingly militarized Arctic? The Navy is tackling problems that freeze Congress solid. What it learns, what it implements, and how it adapts and innovates will drive market changes that could alter the course of the world.
A USS Nimitz boatswain tests biofuel (top left) for use by F-18s and other fighters (bottom), as sailors aboard the oiler Henry J. Kaiser transfer biofuel to the Nimitz. From top left: Devin Wray/US Navy; Chris Bartlett/US Navy; Eva-Marie Ramsaran/US Navy
But not without a fight. Six weeks before RIMPAC 2012, Republicans and some coal- and gas-state Democrats tried to scuttle Mabus' Green Fleet by barring the Pentagon from buying alternative fuels that cost more per gallon than petroleum-based fuels—the biofuel blend cost more than $15 a gallon—unless the more expensive alternative fuels come from other fossil fuels, like liquefied coal. This tricky logic made sense to Sen. James Inhofe (R-Okla.)—"[The Pentagon] should not be wasting time perpetrating President Obama's global warming fantasies or his ongoing war on affordable energy"—even though seven years earlier Inhofe helped secure a $10 million taxpayer fund to test renewable military fuels, more than half of which went to a company in his home state. Sen. John McCain (R-Ariz.) agreed, calling the purchase of biofuels "a terrible misplacement of priorities" and adding, "I don't believe it's the job of the Navy to be involved in building…new technologies." Mabus, who'd already bought the biofuels for the RIMPAC demo, fired back: "If we didn't pay a little bit more for new technologies, the Navy would never have bought a nuclear submarine, which still costs four to five times more than a conventional submarine."
En route to the Nimitz I've managed to snag a seat next to one of only two windows in the COD's dark cabin. Through the porthole I watch our transect over Pearl Harbor, the USS Arizona Memorial, and the sunken and rusting remains of much of the 1941 Pacific fleet. Beyond Pearl we climb over the Pacific Ocean, at 60.1 million square miles nearly half of Earth's total ocean area. That's a lot of territory over which to maintain maritime supremacy, while guarding the far-flung energy supplies needed to do it. Some 75 percent of the world's fuel travels by sea, with 20 percent passing through vulnerable choke points like the Strait of Hormuz and the Gulf of Aden, many guarded by US forces. Partly in defense of those lines, the Department of Defense burns more than 12 million gallons of oil a day. About a third of the DOD's fix goes to float the Navy, the world's largest, with a battle fleet tonnage exceeding the next 13 biggest navies combined.
Admirals are required to solve intractable problems that stymie the rest of us. Peak oil, climate change? Just another bunch of enemies.
Out over the ocean my turboprop hums merrily along on its biofuel blend, and so do I, until I catch my first glimpse of the Nimitz out the window—a toy miniature in a turbulent bathtub. Suddenly 1,092 feet of flight deck wedged into a ninth the space allotted a commercial landing strip seems insanely small acreage. "Go, go, go!" shout two aircrewmen, their backs to me, waving their hands in the air. This is the signal to prepare for the controlled crash of a carrier landing. We jam our heads into backrests, cross arms over our chests, hook hands into harnesses, and wait. It's an unnerving interlude, all noise dampened by the cranial I'm wearing, a helmet with built-in headphones clamped so tight my jawbone aches. Goggles down, I await what I can't see. A minute drags by. Ferociously. Another. Inflatable rafts twitch in overhead cargo nets. Then the sounds of a mass pileup on a steel interstate. Legs whiplash in the air. An unidentified flying object clips my head. It feels exactly like a tragedy at 180 nautical miles an hour—only nothing breaks, burns, or drowns at the end of it. And now here I am, on an aircraft carrier cruising at 30 knots of speed, safe and sound.
It's the Navy, so there's history. The Great Green Fleet was named after the Great White Fleet launched by President Theodore Roosevelt in 1907: four squadrons of 16 battleships painted bright white and manned by 14,000 sailors and Marines on a 43,000-mile cruise around the world. It was the first ever armada of coal-powered steam battleships built entirely of steel—the product of years of government subsidies paying three times the market rate to develop a fledgling American steel industry. When Congress moved to blockade the fleet's around-the-world funding, Roosevelt snarled at them to "try and get it back." So the fleet sailed to 20 ports on six continents over 14 months, boldly going where no US military had gone before and announcing the debut of the United States as a player on the World Ocean.
Illustration: Frank Stockton
Even then the fight over a newfangled Navy was old. For a time in the 19th century it proved so psychologically difficult to get away from sail that hybrid naval ships sported steam funnels alongside acres of snowy white canvas. Naysayers swore the Navy was giving up reliable propulsion for dangerous and infernal machines. The great 19th-century naval strategist Alfred Thayer Mahan wrote: "Sails were very expensive articles…but they were less costly than coal. Steam therefore was accepted at the first only as an accessory, for emergencies." Acting on the principles Mahan laid out in The Influence of Sea Power Upon History—a seminal book in naval strategy—the United States methodically and expensively procured ports and territories around the world specifically for use as Navy coaling stations: Guam, Guantanamo Bay, Hawaii, Puerto Rico. Yet by the time the Great White Fleet sailed home again in 1909, the coal era was over and the Navy was converting yet again, this time to oil-burning steamships. It took a lot of oil to drive a steamship, and the realization that oil wasn't going to last forever dawned far earlier in the military than among civilians. To keep the Navy afloat as long as possible, Congress passed the Pickett Act of 1910, commandeering lands in California and Wyoming, and later in Alaska, as Naval Petroleum Reserves, some of which ultimately ranked among the highest-producing oil and gas fields in the country.
The same year the Great White Fleet sailed home, 24-year-old Ensign Chester Nimitz, the man destined to be the namesake of the nuclear-powered USS Nimitz, took command of an early submarine, the USS Plunger. It was a crap assignment; young officers wanted battleships, the sexy beasts of the Navy. But Nimitz was in disgrace for having run a ship aground in the Philippines. Derisively, he called his sub "a cross between a Jules Verne fantasy and a humpbacked whale." Yet he took the job seriously and began to lobby for an undersea fleet that ran more safely and efficiently on upstart diesel engines, in contrast to the gasoline-powered Plunger. By 1911 he had successfully skippered another energy transformation, overseeing the development of the first diesel submarine, the USS Skipjack, followed by the first diesel surface ship, the USS Maumee (an engineering task that cost him a finger). Thirty-five years later, as chief of naval operations, Nimitz changed the fleet's course once again when he championed Capt. Hyman Rickover's fiercely contested bid (Rickover's opponents reportedly exiled him to an office in an abandoned women's bathroom) to establish a nuclear-powered Navy.
"Every single time there were naysayers," Secretary Mabus has said. "And every single time those naysayers have been wrong."
It's Not Just a Job, It's a Venture!
Advanced biofuels now cost $4.55 per gallon to make. But the Energy Department projects that will fall to $2.32 by 2017, in part due to the Pentagon's early R&D investments.
The Navy, USDA, and the DOE are each spending $170 million on private-sector companies building biofuel refineries. Combined with $3.4 billion of existing private capital, this investment will lead to an estimated 26 new refineries by 2015. Another $53 billion in public-private investment is anticipated by 2022.
Military demand is helping to shape the early market and scale the advanced biofuel industry, which could help commercial aviation and other industries expand their use. This is not unlike how the Pentagon helped develop radar, GPS, and microchips last century:
Mabus has touched down aboard the Nimitz for the Great Green Fleet demo in a biofueled Seahawk helicopter. Wearing his flight helmet rakishly askew, looking more the politician than the former sailor, he's piped aboard with a time-honored bosun's whistle before passing through a hatch freshly stenciled with the Navy Energy Security logo, a blue and green wave. Maneuvers get under way on the flight deck where F-18s—today called "Green Hornets," with their nose cones striped green—are taking off at 60-second intervals. The entire ship, all 97,000 tons of it, shudders from the muscle of 67,000-pound warbirds shot into the air from steam catapults. Water for the catapults comes from the Nimitz's four distilling units, which make 400,000 gallons of freshwater daily, mostly to cool the twin nuclear power plants that allow the Nimitz to sail the seas for 25 years between uranium fill-ups. In the skies above, in perfect formation flybys, jet fighters buddy-fuel each other through a hose-and-drogue system. Off our bow, while all three ships steam at 13 knots, the oiler USS Henry J. Kaiser refuels the cruiser USS Princeton, off-loading the last of today's 900,000 gallons of 50-50 biofuel blend—the largest ever purchase of alternative fuel by the US government.
"We're seeing the Navy once again leading in the type of fuel we use and how we procure it," Mabus tells an all-hands assembly in the vast interior space of a hangar bay on the Nimitz. "Today shows we can reduce our dependency on foreign oil." The crew is jammed shoulder to shoulder: sailors in marine camouflage or "blueberries," Marines in woodland camouflage, aircrew in jumpsuits, deck crew in bold-colored turtlenecks that signal at a glance their jobs on the floating war port. It's so orderly and polite, what I imagine a small-town political rally of the 1950s to be, complete with stage bunting, an American flag the size of Kansas, and testy microphones. Except there's a giant ocean heaving by outside the bay door, advanced electronic aircraft parked in the wings, a cluster of admirals wearing Green Fleet caps on the stage (of the hats, McCain griped a week later: "I do not believe this is a prudent use of defense funds"), plus a handful of reporters, a few looking seasick. Today's demo is a milestone in Mabus' energy plan. But it's also a day for the sailors, one pilot tells me, since the media presence here will raise awareness among the rank and file better than anything the Navy itself says about the seriousness of its green purpose.
"You have the senior Navy leadership here today," crows Mabus, as the chief of naval operations, Adm. Jonathan Greenert, takes the stage to praise the crew of the cruiser USS Chafee. "What I saw today was theory of practice," Greenert says. "We didn't have some scientist come down into the engine room and say, 'One day you'll see this.' You hear it today and see it on gauges." He's talking about the technologies developed to further stretch whatever fuel the Navy procures: low-tech add-ons like stern flaps to reduce ships' drag and increase fuel efficiency; high-tech plug-ins like energy dashboards with Prius-type feedback on fuel consumption; energy savers like LED lighting; plus your basic turn-off-the-lights mindset. "If we deploy these energy efficiencies fleetwide," Mabus says, "we can save up to a million barrels of oil a year. And with what we're paying, about $150 a barrel, that's $150 million the Navy can save a year."
The three-spined stickleback is a regulator of carbon dioxide emissions in its ecosystem:Piet Spaans (Viridiflavus) via Wikimedia Commons:
Top predators do more than regulate prey populations (think wolves and deer). They also regulate carbon dioxide emissions. At least they do in freshwater ecosystems—where if you take away the top predators CO2 emissions rise a staggering 93 percent.
This according to a new paper in the latest Nature Geoscience that holds ramifications for a lot more than marshes. "Predators are disappearing from our ecosystems at alarming rates because of hunting and fishing pressure and because of human induced changes to their habitats," said lead author Trisha Atwood, at the University of British Columbia.
I wrote in an earlier post here on research showing how the loss of biodiversity (itself often a function of the loss of top predators) likely alters CO2 dynamics and other issues of global change as much as greenhouse gases.
The stonefly (Hesperoperla pacifica) whose presence helps keep CO2 emissions in check: Lynette S. / Lynette Schimming via Flickr
Food web theory posits that predators influence the exchange of CO2 between ecosystems and the atmosphere by altering processes like decomposition and primary production (a function of the numbers and diversity of plants).
To test that theory, the researchers experimented on three-tier food chains in experimental ponds, streams, and bromeliads in Canada and Costa Rica by removing or adding predators. Specifically by adding or removing three-spined stickleback fish (Gasterosteusaculeatus) and the invertebrate predators stoneflies (Hesperoperlapacifica) and damselflies (Mecistogastermodesta). When all the predators were removed the ecosystems emitted a whopping 93 percent more carbon dioxide to the atmosphere.
"We knew that predators shaped ecosystems by affecting the abundance of other plants and animals," says Atwood, "but now we know their impact extends all the way down to the biogeochemical level."
From the paper:
We monitored carbon dioxide fluxes along with prey and primary producer biomass. We found substantially reduced carbon dioxide emissions in the presence of predators in all systems, despite differences in predator type, hydrology, climatic region, ecological zone and level of in situ primary production. We also observed lower amounts of prey biomass and higher amounts of algal and detrital biomass in the presence of predators. We conclude that predators have the potential to markedly influence carbon dioxide dynamics in freshwater systems.
Trisha B. Atwood, Edd Hammill, Hamish S. Greig, Pavel Kratina, Jonathan B. Shurin, Diane S. Srivastava, John S. Richardson. Predator-induced reduction of freshwater carbon dioxide emissions. Nature Geoscience (2013). DOI:10.1038/ngeo1734
A team of leading polar bear ecologists called for nations to make plans now for dealing with ongoing—and soon to be critical—threats to the survival of polar bears. The biggest problem for this iconic Arctic species is the mindblowingly fast disappearance of sea ice. Their paper appears in Conservation Letters.
For instance, last month (January 2013) the average coverage of sea ice in the Arctic Ocean was 409,000 square miles (1.06 million square kilometers) below the 1979 to 2000 January average. That's the sixth-lowest January extent in the satellite record, says the National Snow & Ice Data Center. Plus 2012 saw the lowest ever summer coverage of sea ice in the Arctic.
The 19 polar bear populations identified by the IUCN: Andrew E. Derocher, et al, Conservation Letters (2013). DOI: 10.1111/conl.12009
It's not going to be easy to mitigate these challenges, the authors warn. There are 19 populations of polar bears worldwide. Some—like the Western Hudson Bay (WH, in the map above) bears and the Davis Strait (DS) bears—experience complete sea ice melt in summer that forces them onto land where they've got nothing to eat and can only burn through their own fat until the ocean refreezes.
For other populations—the Chukchi Sea (CS), Laptev Sea (LS), and Barents Sea (BS)—many bears remain on drifting pack ice and multiyear ice year round. The problem is that a lot of that pack ice is now retreating far beyond the continental shelf where ocean productivity is higher and polar bear prey more numerous. Meanwhile multiyear ice is disappearing rapidly throughout almost all the Arctic.
Here's what we know happens to bears forced ashore for too long in summer, or kept far offshore on multiyear ice:
declines in body condition
declines in body size
declines in reproductive rates
declines in survival rates
declines in population size
declines in sea ice denning habitat
altered movements and distribution
How bad will it get? In an earlier paper one author predicted the extinction of polar bears in two thirds of their range by 2050. That's because low ice years will increase as long as greenhouse-gas-induced warming continues—until almost all years will be bad for polar bears. For example:
Adult male mortality from starvation is predicted to increase to 28-48 percent in any year when the fasting period is 30 days longer than in recent years.
The possible effects on other age and sex classes have not been modeled but are predicted to be more severe.
Some years will continue to be better for polar bears and others poorer, even as the frequency of poor years increases until all are poor years.
The first occurrences of exceptionally poor years are likely to present a near-term critical challenge to polar bear conservation.
The authors write:
When superimposed over the long-term declining trend, annual variability in sea ice makes it increasingly likely that we will soon see a year where sea ice availability for some polar bear populations is below thresholds for vital-rates. Malnutrition at previously unobserved scales may result in catastrophic population declines and numerous management challenges.
If you have the stomach for it, there's a desperately tragic video of a polar bear mother and her two cubs dying of starvation here. Be forewarned: this is graphic and ghastly. But it's also a sign of what's happening now and what's to come for many many more bears in the future. Knowledge of these kinds of events was one of the reasons this paper was written, lead author, and author of Polar Bears: A Complete Guide to their Biology and Behavior,Andrew Derocher told me.
It's not just about bears either. Starving bears forced ashore are already a threat to local communities and that's only likely to get worse in the near future. The authors write:
The most intensive program for dealing with human-bear interactions, the Polar Bear Alert program in Churchill, Manitoba, Canada, includes extensive hazing, relocation, and temporary housing of bears to mitigate conflict during the ice-free period. That program is expensive and may not be easily applied in small northern communities with limited resources. Nonetheless, we encourage alternatives to killing problem bears, which is a common outcome in northern communities. The Churchill program was established before the effects of climate change were recognized and it is unclear whether it will remain adequate as warming continues. Bears temporarily held in captivity are not currently fed so the cost of temporary holding will increase when the ice-free period extends beyond the fasting capacity of captive bears. Less-expensive options such as reducing attractants and securing storage of food should be included along with plans for increased deterrent capabilities. Training and equipping community polar bear monitors, along with extensive public education and inter-jurisdictional agreements, should be planned to help assure human safety.
Projections of cumulative months per decade where optimal polar bear habitat will be either lost (red) or gained (blue) from 2001–2010 to 2041–2050. Insets show average annual cumulative area of optimal habitat (right y-axis, line plot) for four 10-year periods in the 21st century (x-axis midpoints), and their associated percent. Larger version here: USGS
Polar bears are still hunted throughout the Arctic except in Norway and Russia. "Existing harvest management methods are inadequate for declining populations that, by definition, have no sustainable harvest."
Feeding some bears might become necessary to keep people safe. "Diversionary feeding could be a viable short-term tool to draw bears away from settlements or industrial facilities." But possible negatives include: "the potential for disease and parasite transmission as well as human-wildlife conflicts may increase as other species such as Arctic fox, wolves, and grizzly bears are drawn into diversionary feeding locations."
Feeding might also be needed to keep bears alive in areas where they might not otherwise survive. [How sad is that?]
Some bears might need to be sent to high-quality zoos for captive breeding.
Some bears might need to be euthanized if they've starved beyond rehabilitation.
Considering the global attention paid to polar bears, managers will be forced to respond to sudden changes in environmental conditions that negatively affect polar bears. We believe that managers and policy makers who have anticipated the effects, consulted with stakeholders, defined conservation objectives, created enabling legislation, and considered possible management actions will be most able to effectively respond to large-scale negative changes.
Andrew Derocher told me: "One thing we try to make clear is that we don't necessarily recommend any of these options but lay them out for consideration and discussion. Further, we don't view these desperate measures as a replacement for dealing with greenhouse gasses. If we don't deal with climate change we won't have any polar bear habitat left."
Andrew E. Derocher, Jon Aars, Steven C. Amstrup, Amy Cutting, Nick J. Lunn, Péter K. Molnár, Martyn E. Obbard, Ian Stirling, Gregory W. Thiemann, Dag Vongraven, Øystein Wiig, Geoffrey York. Rapid ecosystem change and polar bear conservation. Conservation Letters (2013). DOI:10.1111/conl.12009
The ozone hole—the thinning of ozone in the lower stratosphere above Antarctica—has changed the way that waters in the Southern Ocean mix. And that has the potential to change how much CO2 the ocean sequesters from the atmosphere. Hence the course of global climate change. This according to a new paper in Science.
"This may sound entirely academic, but believe me, it's not," said lead author Darryn Waugh at Johns Hopkins' Krieger School of Arts and Sciences. "This matters because the southern oceans play an important role in the uptake of heat and carbon dioxide, so any changes in southern ocean circulation have the potential to change the global climate."
Map of local rates of sea level rise due to ocean heating below 4000m (colors and black numbers) for deep ocean basins. Also included is the rate from 1000-4000m warming (magenta) for the Southern Ocean (south of magenta line): via NOAA PMEL
The Southern Ocean has warmed at roughly twice the rate of the global mean ocean over the past few decades (even in its deep waters, map above), with some 40 percent of the anthropogenic carbon in the oceans entering south of 40°S. The authors write:
Southern ocean ventilation is driven primarily by the [prevailing] westerly winds, which have strengthened and shifted poleward over recent decades, primarily as a consequence of Antarctic stratospheric ozone depletion. Modeling studies suggest that this has caused changes in the ocean's overturning circulation and carbon uptake.
Thermohaline circulation (aka the "ocean conveyer") showing overturning circulation (aka deep water formation): Avsa via Wikimedia Commons
The overturning circulation, as I've written before (here and here and here), plays a big part in global climate. The places where the overturning circulation (also known as deep water formation) occur—just a few spots in the high latitudes—are being closely monitored for changes.
For the research reported in this paper, the authors used water samples collected in the Southern Ocean in the early 1990s and resampled again in the the middle and late 2000s. They measured chlorofluorocarbon-12, or CFC-12. That's the ozone-killing stuff that was first produced commercially in the 1930s for use in aerosols, refrigerants, and air conditioners, and which grew rapidly in the atmosphere until the 1990s when it was phased out by the Montreal Protocol. It's been useful to oceanographers ever since as a tracer for measuring water movements over time.
Comparing CFCs in the 1990s versus 2000s samples, the researchers were able to infer changes in how rapidly surface waters have mixed into the depths. They knew that concentrations of CFCs at the ocean surface increased in tandem with those in the atmosphere. So they were able to surmise that the higher the concentration of CFC-12 deeper in the ocean, the more recently those waters were at the surface.
What they found was younger than expected waters in the subtropics and older than expected waters further south. These findings correlate to observed intensification of surface westerly winds driven primarily by the Antarctic ozone hole. Which suggests that dwindling ozone in the stratosphere is the primary cause of the observed changes in ocean circulation.
As stratospheric ozone recovers, the circulation may recover too. But there are other factors at work here. The authors conclude:
As stratospheric ozone recovers over the next 40 to 60 years, the recent trend of intensifying summer westerly winds may slow or reverse. However, continued increases in greenhouse gases will likely lead to strengthened westerlies during other seasons. The integrated impact of these trends in Southern Hemisphere westerlies on the ocean's ventilation and uptake of heat and anthropogenic carbon is an open question.
We don't hear so much about the ozone hole as we did in the 1990s. But that doesn't mean it's going away anytime soon. The video (above) by the American Museum of Natural History animates projections for a slow recovery.
And this series of images (above) show projections of what might have become of global stratospheric ozone if we hadn't curbed our emissions through the Montreal Protocol. Dark blue indicates zero ozone.
The paper:
Darryn W. Waugh, Francois Primeau, Tim DeVries, Mark Holzer. Recent Changes in the Ventilation of the Southern Oceans. Science (2013). DOI:10.1126/science.1225411
