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The poles are warming much faster than the global average, causing unprecedented heat waves and accelerated melting of glaciers. Knowing how to slow down global warming has become the goal of many researchers. More recently, some have suggested that injecting aerosols (sulfur dioxide) to deflect some of the sun’s energy at very high altitude could be effective in cooling the poles. However, such an intervention in the climate brings substantially increased costs and risks to global security.
Stratospheric aerosol injection is a potential climate intervention that would aim to reduce global average surface temperatures by deflecting a very small fraction of incoming sunlight away from Earth. This injection is a controversial and unproven climate intervention that could lead to unwanted effects, and is not offered as a substitute for emissions reductions or adaptation.
However, injections of similar aerosols from large volcanic eruptions have long been known to significantly reduce surface temperatures, even at distances far from the source, as was the case after the eruption of Mount Pinatubo in 1991. There is also growing confidence that the deployment of such injections would both aeronautically feasible, so they would be extraordinarily cheap compared to other forward-looking measures to address climate change or its impacts.
However, there are practical limits to how high aerosols can be deployed in the atmosphere. Recently, a team of researchers led by Wake Smith of Yale University evaluated the safety and cost-effectiveness of deployment at an altitude of 25 km, which would be most effective, but also the altitude at which costs and risks increase. Their study is published in the journal Environmental Research Communications.
Conclusions after a series of extensive studies
Following a 2018 study that shed light on the technologies through which solar geoengineering could be performed, this new work directly answers a question posed by the National Academies of Sciences, Engineering, and Medicine in a March 2021 landmark study that recognized the need for further research into the viability of aerosol deposition well above 20 km altitude. Indeed, previous studies have noted that deployment of stratospheric aerosols at 25 km would be more efficient than at 20 km, leading climate modelers to routinely include such high deployments in their studies.
According to a article published on IOP Publishingadding to this research, Wake Smith, lead author of the study, states: There is a ceiling in the sky above which traditional aircraft cannot operate, and 25 km altitude is well above that limit. “. It should be noted that transport aircraft and military jets regularly fly at an altitude of almost 10 km, while 20 km is the domain of spy planes and high-flying drones. It is easy to understand that planning hundreds of thousands of annual flights for the deployment of solar geoengineering at heights inaccessible even to elite spy planes have to overcome many obstacles.
Under the plan outlined in their paper, the authors explain, a fleet of 125 military air tankers would release a cloud of microscopic sulfur dioxide particles at an altitude of 13 km and at latitudes of 60 degrees north and south – roughly between Anchorage and the southern tip of Patagonia. These aerosols would drift slowly towards the poles and slightly shade the surface below.
Specifically, particulate injections (13 million tons needed) would be done seasonally during the long days of the local spring and early summer. The same fleet of jets could serve both hemispheres.
However, existing military tankers such as the aging KC-135 and A330 MMRT do not have sufficient payloads at the required altitudes, while newly designed high-altitude tankers would prove much more efficient. The study’s authors estimate that a fleet of about 125 such aircraft could carry enough payloads to cool the polar regions by 2°C per year, bringing them closer to their pre-industrial average temperatures.
The cost is estimated at $11 billion a year, which is less than a third of the cost of cooling the entire planet by the same amount of 2°C and a tiny fraction of the cost of achieving net zero emissions.
Wake Smith warns that the plan would address an important symptom of climate change, but not its cause. Introduced by supplement to the original article: It’s aspirin, not penicillin. It is not a substitute for decarbonisation […]. Our findings are expected to change the way climate intervention models are operated globally and show that practical limits must be considered with radiative efficiency when designing solar geoengineering programs. “.
This plan is debated among scientists. After all, in an interview given to SkyNewsthe lead author estimated that about 175,000 flights of high-flying spy planes and drones each year would be needed to actually slow ice melt and global warming.
These jets would themselves release large amounts of carbon dioxide into the atmosphere, bringing greenhouse gases to the heights where their presence is most damaging to the climate. Wake Smith points out: There is widespread and valid concern about the deployment of aerosols to cool the planet, but if the risk-benefit equation were to pay off anywhere, it would be at the poles. “.
However, cooling at the poles would provide direct protection for only a small part of the planet, although mid-latitudes would also experience some reduction in temperature.
Despite these objections, the authors argue that since less than 1% of the world’s human population lives in the target deployment areas, a polar deployment would pose far less direct risk to most of humanity than a global program. In other words, the global advantages outweigh the local disadvantages. Wake Smith concludes: Any deliberate turning of the global thermostat would be in the common interest of all humanity. “.
Finally, the current study is only a preliminary step toward understanding the costs, benefits, and risks associated with high-latitude climate intervention. This gives further reason to believe that such tools could prove useful both in preserving the cryosphere near the poles and in slowing global sea-level rise.