Radical new solutions

Climatologists have proposed a radical method of combating global warming: seasonal spraying of aerosol over the polar regions of the planet. The aerosol layer, in their opinion, partially shields radiation from the Sun and can thereby stop the melting of ice on the polar caps, where the effects of global warming are most noticeable today. At the current level of technology, it is in principle possible to achieve cooling of the poles by 2°C, that is, to bring their average temperature to pre-industrial levels.

Why is this necessary?

The Earth’s poles are warming several times faster compared to the change in the average planetary temperature. This is already leading to record-breaking heat waves that scientists are recording in the Arctic and Antarctic. According to climatologists, temperatures at the poles have increased by 3°C over the past fifty years. Since the Earth’s polar regions contain a lot of ice, its accelerated melting and the disappearance of glaciers at high latitudes could lead to a significant rise in global sea level — more than can be inferred from calculations that take into account only the trend in the average planetary temperature.

Climatologists have developed the concept of intervention in the climate system, which may become relevant in the foreseeable future if climate change begins to seriously affect the quality of life. The increase in temperature in the polar regions is proposed to be slowed down by spraying microscopic aerosol particles at high altitudes at latitudes from 60 degrees in the northern and southern hemispheres (60 ° N — this is exactly the position of St. Petersburg). The aerosol will be sprayed at high altitudes of the order of 15 kilometers — this is higher than the ceiling of conventional passenger aircraft. In this case, the particles will slowly drift toward the poles, and their clouds will partially cover the surface, protecting it from solar radiation and reducing the heating of the polar caps. Of course, such an intervention may raise many objections and fears that its impact on the climate system will be much more unpredictable than in theory.

How does it work?

Aerosol intervention projects for climate control are not new. Such ideas are well known. Typically, such futuristic technologies offer aerosol injection, one way or another affecting the entire surface of the planet. They also bear the common name SAI, or stratospheric aerosol injection. The peculiarity of the new project is that it is proposed to influence only the polar regions of the Earth, where an increase in temperature can cause much more trouble (the same melting of glaciers). You can learn more about the concept in an article published September 16, 2022, in Environmental Research Communications.

SAI is a concept that raises more questions than it answers. Its creators were inspired by a natural phenomenon: the cooling effect of the Earth as a result of massive volcanic eruptions. Such phenomena are well studied in the geological past of the Earth. As a result of eruptions, a huge amount of dust, ash, and gases are released into the atmosphere. Sulfur dioxide is often found among the gases. Dust and ash work for a short time, blocking the sunlight. The time frame of their impact is literally a few hours, maybe days, but in any case, the intervals are too short by geological standards. But sulfur oxide vapor rises high, to the level of the stratosphere, where it is adsorbed on water droplets. The result is sulfuric acid, which hangs in the atmosphere for years (up to three years, according to climatologists and geologists). This aerosol blanket blocks sunlight and creates a longer-term cooling effect on the planet’s surface. Accordingly, the main idea of all projects within SAI is to do the same, but artificially.

Particle injection is proposed to be performed seasonally: in each hemisphere, these will be days in spring or early summer, when the effect of solar radiation on snow and ice cover is maximum. Thus, it will be possible to use the same fleet of aircraft that will handle the northern hemisphere in March-June and the southern hemisphere in September-December. As an aerosol material, different options can be explored in more detail. Several groups of researchers working on climate intervention with SAI technology have so far suggested using sulfur dioxide SO2 as a first option. It oxidizes to sulfuric acid H2SO4, an effective radiation shielding agent, and after a month in the stratosphere, it coagulates to form a supercooled liquid aerosol. It is clear that the proposal to spray sulfuric acid in the air from the point of view of the scientific community is so-so (some SAI projects generally propose to spray sulfuric acid directly, without exchanging it for sulfur dioxide). But remember that this proposal comes from observations of the Earth’s climate system and its natural regulators in the form of volcanoes. It is possible that in the future if the idea comes to implementation, some other substance will be offered for aerosolization, which raises fewer questions.

The task could, in principle, be handled by existing air assets, in particular tanker aircraft for refueling in the air like the KC-135 and A330 MRTT (Multi-Role Tanker Transport) models from Airbus. But these aircraft have too little potential at such altitudes, so further modifications are likely to be required to be able to work at high altitudes. The authors propose a modification of an aircraft specially designed for such a project. They called this variant SAIL-43K. Here 43K denotes the height (43,000 feet, that is, approximately 15 km) at which the aerosol is to be sprayed into the stratosphere. SAIL stands for Stratospheric Aerosol Injection Lofter — a conceptual line of aircraft with an optimal ratio of maximum lift height and payload, which could solve the problems of stratospheric aerosol injection in climate control projects. It is assumed that an air fleet of 125 such tankers will be able to lift into the air and spray the necessary amount of aerosol to cool regions above 60° latitude by 2 °C per year.

If such results can be achieved, this will return the polar regions to indicators close to the pre-industrial era. The cost of such an event will be about 11 billion dollars per year. This is about a third of the budget that conventional projects for cooling the Earth by the same 2°C per year are estimated at. In addition, such an amount is a very small part of the funds that a radical reduction in carbon emissions from the planet will cost.

The drawbacks

But stratospheric aerosol injection is no cure for global climate change. It will treat the symptoms of such changes, not the phenomenon itself. In other words, it will act like aspirin, not like penicillin, and will not replace the need to address the causes of such a change — for example, carbon emissions into the atmosphere.

The cooling of the poles can protect only a small part of the planet from the most unpleasant consequences of climate change, although the inhabitants of the middle latitudes will also feel some decrease in the average temperature. Currently, about 1% of the world’s population lives on the territory where it is proposed to deploy an “aerosol shield”, so the potential risk if “something goes wrong” will be much less than in the usually proposed global projects. Probably, in the near future, no one will rush to build an air fleet that will spray sulfuric acid in the latitudes of St. Petersburg and Patagonia. This study is only the first step in understanding the risks, benefits, and costs of such climate intervention projects, even in the stratosphere above the deserted polar regions. Climatologists fear that if warming continues at the same pace as now, then by 2050, summer ice in the polar regions in the Arctic will practically disappear. In this case, humanity will be on the verge of unpleasant events, when it will have to choose between bad and worst scenarios. Therefore, it is good to have calculations in reserve for various options of action before the onset of such times and also to have a rough idea of what, if necessary, can be done with all this.