"Relatively low cost" plan would cool the Earth's poles by 2 °C
New research suggests that cooling the poles by 2 °C (3.6 °F), and re-freezing the Arctic and Antarctic, is "feasible at relatively low cost with conventional technologies," using Stratospheric Aerosol Injection (SAI) of heat-reflective particles focused on the poles. The side effects could be nasty, and the politics near-impossible, but the plan offers a way to slow, or reverse the catastrophic sea level rise projected as polar ice collapses.
SAI is an enormously controversial idea inspired by the cooling effects that tend to follow large volcanic eruptions. These natural events eject vast amounts of dust, ash, and often sulfur dioxide into the air. The first two create a shade effect that causes a short-lived cooling effect for a couple of hours, but sulfur dioxide tends to rise high into the stratosphere, where it combines with water molecules to create sulfuric acid particles, and remains for up to three years, reflecting solar radiation away and causing a long-lasting surface cooling effect.
So the idea behind SAI is to load up high-altitude aircraft with sulfur dioxide, and fly around spraying it into the atmosphere at high altitudes, mimicking the cooling effect of a volcano. So far, so good. Mind you, the way that sulfuric acid eventually leaves the atmosphere is by combining into larger and larger droplets that eventually become heavy enough to fall down to earth as acid rain, which is, as you'd imagine, not great for plant life, fish or animals. And all sulfur oxides are nasty to breathe in, harming the lungs and causing asthma and bronchitis if inhaled regularly.
To date, most SAI research and modeling has focused on spreading these aerosol deployments all over the globe. But there's a growing number of scientists starting to look into just doing it at the North and South Poles. The Arctic and Antarctic are feeling the effects of climate change far worse than the rest of the world at this stage; they're warming several times faster than the global average, causing colossal ice structures to collapse and melt. Every climate model factors in the resulting rise in sea levels, which will have catastrophic effects all over the world.
To state the obvious, no scientist wants to fill the air with sulfur, drench the last remaining polar bears and penguins in acid rain, or give carbon emitters any excuses not to clean up their act. But faced with our current trajectory, on which summer sea ice in the Arctic will more or less disappear by 2050 or earlier, humanity finds itself between a rock and a hard place. All options need to be on the table, evaluated, and to some extent ready to go early enough to make a difference.
So research into SAI is progressing quickly, and concentrating it at the poles – an approach referred to as subpolar deployment – may deliver better returns for significantly less money and acid rain than a global model. Prior research has indicated that spring and early summer is likely the most effective season to do it, and that only doing this at one pole could have asymmetrical effects on global weather, so it's probably prudent to target both, with a fleet of planes that travels with the seasons.
A new study from a fairly broad range of contributors digs into what a bipolar SAI program targeted at "refreezing" the Arctic and Antarctic might look like, what it'll cost, and where the equipment and technology gaps might be.
The study proposes a nominal target of cooling the North and South Poles by 2 °C (3.6 °F), noting that Arctic temperatures have already risen by more than 3 °C (5.4 °F) over the last 50 years. It proposes that the aerosol injections be made at the 60th parallels, roughly the latitudes of Oslo, Helsinki, Homer, Alaska and Magadan, Siberia in the Northern Hemisphere, and level with the southern tip of Patagonia in the Southern Hemisphere. At these latitudes, it's possible to get the job done cheaper, since the troposphere sits at a lower altitude and your aircraft don't have to fly so high. This study chooses an altitude of 13 km (42,600 ft). The particles released would drift slowly toward the poles, concentrating their effects.
To achieve a 2 °C result, the plan would inject 6.7 teragrams (6.7 billion kg/14.8 billion lb) of sulfur dioxide per year into each pole, calling for an eye-watering total of 13.4 teragrams (29.5 billion lb) of material annually.
The study goes on to look at logistics, finding that existing aircraft can't carry enough payload to a sufficient height to get the job done. The closest we've currently got are military air-to-air refueling aircraft, but these can't reach the target altitudes without significantly reducing their payloads. The McDonnell Douglas KC-10 Extender, for example, could get up into the spray zone carrying some 128,801 lb (58,400 kg) of payload, but that's just 22% of the payload it's designed to carry, so you'd be carrying a lot of excess weight on every flight.
The study proposes instead a purpose-built stratosprayer called the SAIL-43K, a downgraded version of an aircraft previously specified to fly higher SAI missions closer to the equator. This machine would carry 167,971 lb (76,190 kg) of payload each mission, but its takeoff weight would be some 77,000 lb (35,000 kg) lighter than the KC-10.
To hit the cooling target, this project would need 125 purpose-built SAIL-43Ks, flying a total of 1,458 missions per day during the four-month injection period at each pole. These planes would take off, climb for 30 minutes, vent their entire load of sulfur dioxide within two minutes, then come back down over the following 30 minutes, and spend the next hour loading up again and refueling for the next mission.
In the Northern Hemisphere, there are plenty of airfields suitable for these kinds of operations; virtually the whole 60th parallel falls on land. In the south, things get a bit more fraught as there are really only a few airfields in Southern Patagonia with appropriate runways. These sit at latitudes closer to 54°, but the team calculates they'll get better results just venting the sulfur dioxide at that latitude than flying some 490 nautical miles south to hit 60°.
These airports would need to be upgraded to handle a total of 110 operations per hour, or a little more than the world's busiest current airport – this will be an enormous undertaking in the Southern Hemisphere, since there are so few airfields to start with in Patagonia. This huge infrastructure job would likely take about as long as developing and manufacturing 125 aircraft – about 15 years after making a decision to go ahead with the plan. This, in itself, is hardly a quick or complicated part of the process, and would require some degree of global agreement on a plan that would disproportionately affect people living in the latitudes in question.
In terms of money, the "relatively low cost" of this project would be around US$11 billion a year (2022 dollars), says the team. This might sound like a lot, but it's about a third of the price of a global SAI effort with the same cooling target, and the researchers note that "relative to other possible strategies by which to combat either the impacts or causes of climate change, SAI remains extraordinarily inexpensive."
While calibrated to drop polar temperatures by 2 °C and to begin re-freezing sea ice at the poles, this project will have a number of unwanted side-effects. The researchers note that the sulfur compounds added to the stratosphere may impact ozone concentrations through a number of different effects, and may thus slow or reverse the recovery of the Antarctic ozone hole. It notes that the effects of teragrams of sulfur dioxide and the associated acid rain deposits are risky both to humans and to the wider ecosystem, requiring lots more research. And it expects some stratospheric heating as well.
Furthermore, the planes themselves can only operate by burning jet fuel, using today's technologies. This annoying fact, plus the emissions involved in building out all the required infrastructure on the ground, plus the emissions involved in preparing sulfur dioxide, mean that a polar SAI program would have a pretty damn hefty carbon footprint of its own, although this would only represent a "marginal" increase to overall aviation sector emissions.
Still, the researchers conclude that "while it has yet to be established that the physical or societal impacts of any SAI program would prove to be net positive, it seems clear that a program focused on substantially cooling the world's polar and subpolar regions would be logistically feasible. This could arrest and likely reverse the melting of sea ice, land ice, and permafrost in the most vulnerable regions of the Earth's cryosphere. This in turn would substantially slow sea level rise globally."
So, short answer: yes, we can re-freeze the poles, while minimizing the risk to the bulk of humanity and agriculture. But we'd need the entire world to agree that sea level rise is a worse outcome than the effects of a massive SAI program, especially for the estimated 1% of the population that lives in the areas where the effects will be concentrated.
"There is widespread and sensible trepidation about deploying aerosols to cool the planet," says Wake Smith, lead author of the new study, in a press release. "But if the risk/benefit equation were to pay off anywhere, it would be at the poles. Game changing though this could be in a rapidly warming world, stratospheric aerosol injections merely treat a symptom of climate change but not the underlying disease. It's aspirin, not penicillin. It's not a substitute for decarbonization."
The study is open access in the journal Environmental Research Communications.
Source: Institute of Physics via Phys.org
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It is relatively simple to determine the size of particles that more or less precisely balance light pressure from the sun against their weight. Doing so along a the line in between the sun and the earth allows one to create a de facto "Lagrange point" where instead of balancing Sun/Earth attraction precisely, one balances a residual attraction to the sun against light pressure (that is, closer to the sun than L1). Generate a shipload of light-blocking "dust" with the suitable particle size, head to that point, and scatter it to hover as a transient "curtain" between the sun and the earth. Depending on the diffusion rate away from the stable locus (likely slow) one might be able to lower the effective solar "constant" for months to years.
Personally, I think this is pretty insane, no matter how they plan to implement it. I'm not that worried about the sulfur dioxide -- volcanoes dump enough of that into the atmosphere to affect global weather for years periodically whether or not we like it, and they might be able to use e.g. nitrous oxide instead that would fall to the ground eventually as fertilizer. The real risk is to the agricultural food chain. See "The year without a summer" (has its own wikipedia page) for a description of the consequences of the last time nature did this big time (Tambora eruption). See the list of related climate disruptions on a smaller scale at the end. A year without a summer at this point would kill a billion people and potentiate global war that might kill a billion more.
The alternative: pilotless aerostat delivery vehicles. Drone blimps lifting sulfur dioxide tanks, with hydrogen as both engine fuel and buoyancy gas. The safety concerns of flammable hydrogen vs. non-renewable helium would be irrelevant for pilotless, remotely controlled vehicles. After reaching the required height, sulfur dioxide would be dispersed from the bottom of the tank, while lifting gas would be compressed by compressors into the top of the tank (separated by a membrane to prevent mixing). The compression would reduce buoyancy to offset the lightening of the vehicle due to payload dispersion. After completing the process (while maintaining neutral buoyancy) the now limp blimp (I couldn't resist) would descend for another load.
Advantages: No pollution at all, pure hydrogen operation. Cheap drone operators, rather than expensive certified multi-engine airliner pilots. Much lower cost and footprint of manufacturing a blimp with a tank, as compared to a jet airliner. Minimal energy costs of reaching altitude, and potentially a higher altitude than reachable by cargo jets. Quiet, unobtrusive operation from minimal facilities rather than multiple new cargo-plane-capable airstrips. Possibility of basing the blimps on small circum-antarctic islands, such as Kerguelen, Macquarie, Bouvet, etc., rather than Patagonia, which is not only too far north, but also unfortunately in the zone of "roaring forties" winds, complicating both the missions themselves and dispersal.
Without this effect, many lakes would become anaerobic on the bottom, killing aquatic life and emitting poisonous gas into the surrounding area.
But all that is irrelevant. Most of the Antarctic ice is sitting on land, not water.
And ice melt is not the only cause for rising sea water. As water warms it expands. And the oceans are full of warming water...
Nice article Loz, but really, a cure that is worse than the targeted effect of global warming? With greater reflected solar radiation, less PV output from our existing solar cells? How is our excessive energy requirement to be met? New PV arrays? New Nuclear reactors? Is Fusion technology ready yet? Just pump more oil and mine more coal? Burn sulfur dioxide rich coal and collect the sulfer dioxide from the CO2 emissions - can that be used to seed the stratosphere? Maybe an oil company or two will buy into this, but not regular environmentalists who consider the multi-faceted effects of man-released sulfer dioxide in our already overwhelmed world.
This temperature increase, I think, will be followed by a wet winter and spring next year and generally warmer winter 2022-2023.
We have seen increased precipitation in the southwest US and elsewhere throughout the summer and early rains in California recently.