The poles are warming up much faster than the global average, inducing unprecedented heat waves and the accelerated melting of glaciers. Knowing how to slow down global warming has become the quest of many researchers. Recently, some of them believe that injections of aerosols (sulphur dioxide) to deflect part of the solar energy, at very high altitude, could be effective in cooling the poles. But such climate intervention comes with substantially increased costs and risks to global security.
Stratospheric aerosol injection is a prospective 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 untested climate intervention that could lead to undesirable impacts, 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. It There is also growing confidence that deploying these injections would be both aeronautically feasible and extraordinarily inexpensive, relative to other forward-looking measures to combat climate change or its impacts.
Nevertheless, there are practical limits to the height at which aerosols can be deployed in the atmosphere. Recently, a team of researchers led by Wake Smith of Yale University, assessed the safety and cost-effectiveness of deploying at an altitude of 25 km, which would be most effective, but also the altitude for which the costs and risks are increased. Their study is published in the journal Environmental Research Communications.
Conclusions after a series of large-scale studies
Indeed, following a 2018 study that clarified the technologies through which it would be possible to undertake solar geoengineering, this new work directly answers a question posed by the National Academy of Sciences, Engineering and of Medicine in a landmark March 2021 study, which recognized the need for further research into the viability of aerosol deposition well above 20 km altitude. Indeed, previous studies have noted that the deployment of stratospheric aerosols at an altitude of 25 km would be more efficient than at 20 km, leading climate modelers to commonly incorporate such high deployments into their studies.
According to a article published on IOP Publishingappendix to this research, Wake Smith, the lead author of the study, states: There is a ceiling in the sky above which traditional aircraft cannot operate, and 25km is an altitude well above that limit. “. It should be noted that airliners and military jets regularly sail 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 solar geoengineering deployment flights at altitudes inaccessible even to elite spy planes must overcome many obstacles.
Under the plan laid out in their work, the authors explain that a fleet of 125 military aerial tankers would release a cloud of microscopic particles of sulphur dioxide 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 slowly drift poleward, slightly shading the surface below.
Concretely, the injections of particles (13 million tonnes needed) would be carried out seasonally during the long days of local spring and early summer. The same fleet of jets could serve both hemispheres.
Nevertheless, pre-existing military tankers such as the aging KC-135 and A330 MMRT do not have enough payload at the required altitudes, while newly designed high-altitude tankers would prove much more efficient. The study authors estimate that the fleet of around 125 such aircraft could carry enough payload to cool the poleward regions by 2°C per year, bringing them back close to their average pre-industrial temperatures.
The costs are estimated at $11 billion per year, less than a third of the cost of cooling the entire planet by the same magnitude of 2°C and a tiny fraction of the cost to achieve net zero emissions.
Wake Smith warns that the plan would address an important symptom of climate change, but not the cause. He states in a complement to the original article: It’s aspirin, not penicillin. It is not a substitute for decarbonization […]. Our finding is expected to change the way climate intervention models are run globally and show that practical limits must be weighed against radiative efficiency in the design of solar geoengineering programs. ».
Climate controversy
This plan is debated among scientists. Indeed, in an interview given to SkyNewsthe lead author felt that to cause a real slowdown in melting ice and global warming, it would take around 175,000 flights of high-flying spy planes and drones each year.
However, these jets would themselves release large amounts of carbon dioxide into the atmosphere, causing the greenhouse gas effects at altitudes where their presence is most harmful to the climate. Wake Smith points out: There is widespread and reasonable apprehension about deploying aerosols to cool the planet, but if the risk/benefit equation were to pay off anywhere, it would be at the poles. ».
However, the cooling at the poles would only provide direct protection for a small fraction 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 targeted deployment areas, a polar deployment would pose far less direct risk to the bulk of humanity than a program global. In other words, the global advantages outweigh the local disadvantages. Wake Smith concludes: Any intentional rotation of the global thermostat would be of common interest to all humanity. ».
Finally, the current study is only a preliminary step towards understanding the costs, benefits and risks of undertaking climate intervention at high latitudes. 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.