Recently, a document from Australia’s Breakthrough – National Centre for Climate Restoration warned that climate change models are operating on estimates that are too conservative, and that by 2050 “the scale of destruction is beyond our capacity to model, with a high likelihood of human civilization coming to an end”. With such chilling predictions, certain media are beginning to adopt the expression “climate crisis” in order to emphasize that we are immersed in a race against time to avoid catastrophe. And in this race, every idea is worthy of study, even the most audacious: cooling the Earth by reducing the solar radiation that passes through the atmosphere on a planetary scale.
For decades, geoengineering against climate change has been present on the blackboards of the experts. In its most basic form, the idea is to eliminate greenhouse gases from the Earth’s atmosphere, for example by sequestering CO2 under the ground. However, a second variant pursues a more ambitious goal: shielding the Earth from solar radiation to compensate for global warming, akin to placing an umbrella over the planet.
Obviously, such a radical proposal requires extensive and in-depth studies to ensure that the artificial modification of the climate does not in itself produce disastrous consequences. Therefore, climate engineering has been a controversial discipline since its inception. Although in conferences held throughout this decade scientists have agreed to defend research into geoengineering, there are still serious doubts about which approaches deserve more detailed study.
The most concrete idea being studied today is to disperse aerosols of particles in the atmosphere to reduce the insolation of the Earth’s surface. In terms of the nature of such particles, various proposals have been suggested, such as seawater droplets, ice crystals or even alumina and diamond dust.
The solution that has attracted the most interest in recent years is the dispersion of sulphate aerosols, a process that aims to mimic the effect of large volcanic eruptions. In the past, these natural phenomena have altered the global climate temporarily; the most famous case is the “year without summer” of 1816, due mainly to the eruption of the Tambora volcano in Indonesia.
However, critics of the proposal have serious misgivings. Experts suggest that the procedure could dangerously alter global rainfall patterns and damage the ozone layer due to the sulphuric acid formed. In 2018, a study published in Nature analysed the natural experiments of past volcanic eruptions to determine their effects on agriculture. And while a reduction in warming would relieve thermal stress in crops, the results showed that the decrease in sunlight would negatively affect plant growth.
In 1991, the Pinatubo eruption in the Philippines injected some 20 million tons of sulphur dioxide into the atmosphere, reducing sunlight by 2.5% and reducing global temperature by half a degree Celsius. Studying the global production of wheat, rice, corn and soybeans in 105 countries between 1979 and 2009, along with satellite observation of the aerosols dispersed by the eruption and in the context of global climate models, the researchers found that cooling did not result in increased yields.
“Our paper found that, for agricultural productivity, the potential benefits of solar geoengineering from reducing temperatures would be offset by damages from reductions in sunlight,” the study’s lead author, Jonathan Proctor, from the University of California at Berkeley, told OpenMind. “So on net there would be no benefit to agriculture.” Proctor also adds that other sectors of the economy could be affected. The problem is that it is still unknown in what sense: “They could potentially benefit substantially or be substantially damaged, we just don’t know.”
However, Proctor considers that his results don’t mean that solar geoengineering should be completely ruled out, but rather that we should evaluate the available options with extreme caution. “Optimising the radiative properties of particles used might be able to mitigate sunlight-mediated damages,” he says. This optimisation is the goal of scientists such as David Keith, a physicist at Harvard University and one of the most visible proponents of solar radiation management. According to Keith, “some of the problems identified in earlier studies where solar geo-engineering offset all warming are examples of the old adage that the dose makes the poison.”
Keith’s proposal does not seek to compensate for global warming in its entirety, but only to halve the increase in temperature due to greenhouse gases. Calculations by Keith and his collaborators show that this formula would avoid drastic changes in temperatures and rainfall, moderating the intensity of tropical cyclones by 85% and limiting the possible negative effects to less than 0.4% of the earth’s surface, precisely in places that have suffered less from the scourge of climate change. According to the lead author of this study, Peter Irvine, the result is “a large reduction in climate risk overall without significantly greater risks to any region.”
From computer models to the real world
Soon these predictions may begin to be confirmed. Keith is one of those responsible for the Stratospheric Controlled Perturbation Experiment (SCoPEx), which is planned for this year but still has no definite date. SCoPEx will use a balloon equipped with propellers to disperse aerosols in a sector of the sky 1 kilometre long by 100 metres in diameter, at a height of 20 kilometres and for at least 24 hours. Particles of a material that does not damage the ozone layer will be used: calcium carbonate, the same material that forms limestone, shells and eggshells, and which is also used as a digestive antacid. The instruments located on the balloon will measure changes in atmospheric chemistry and sunlight scattering.
If SCoPEx proceeds as planned, perhaps this year we will see solar geoengineering begin to move from computer models and laboratory tests to the real world, albeit on a prudently miniscule scale. And while the controversy over these proposals will remain very much alive, there are many experts for whom it is no longer possible not to speak of solar geoengineering. In the words of the director of SCoPEx, atmospheric scientist Frank Keutsch, “we should never choose ignorance over knowledge.”