With the signing of the Paris Agreement in April 2016, practically the entire globe committed itself to the fight against climate change. But even if the 195 parties that signed the milestone deal fulfill their pledges, the world may dramatically fail to reach its targets. Many suggest that the global temperature will climb by more than two degrees Celsius, despite all political efforts. More pessimistic forecasts warn that it could even rise by up to five degrees.
In the face of such potentially horrific scenarios, politics, economics and research have stopped talking only about reducing emissions and promoting green energy. Increasingly a second strategy is coming into focus: the development of technological measures that can directly intervene in the earth’s geochemical cycles. Known as geoengineering, this approach is not about combating the causes of global warming, but rather aims to mitigate the effects of climate change by actively redesigning the planet.
Geoengineering can fall into two categories. Solar radiation management techniques reflect sunlight back into space or increase Earth’s reflectivity. Such measures cool the planet but do not reduce carbon dioxide in the atmosphere. Common strategies include shooting reflective aerosol particles into the stratosphere or brightening marine clouds by injecting them with sea salt.
Secondly, Carbon dioxide removal includes efforts to reduce carbon dioxide from the atmosphere through fertilizing the ocean with iron to spur the growth of phytoplankton that absorb CO2, adding minerals to the sea to increase carbon storage, growing forests to sequester carbon or capturing carbon dioxide directly from the air. Another strategy involves seeding cirrus clouds, which trap heat, to make them disperse more quickly.
Solar radiation management seeks to recreate the natural cooling that occurred after Mt. Pinatubo erupted in 1991. Back then, the 1,486 meter volcano shot twenty million metric tons of sulfur dioxide into the stratosphere. This reflected sunlight cooled Earth by about 0.5° C for over a year.
Physicist David Keith and his group at Harvard University are among those researching stratospheric aerosol injection. They maintain that the rate of global average warming could be halved relatively quickly (within years) using just a quarter of the sulfates released by Mt. Pinatubo. If deployed alongside emission reduction strategies, it could keep temperatures below 1.5° C and reduce extreme rainfall, at a cost of between $1 billion to $10 billion a year.
However, it is not just the financial costs that loom large when it comes to geoengineering. While solar radiation management has the potential to reduce global warming and mitigate some damaging impacts of climate change, it also comes with many risks. It would do nothing to stop ocean acidification, and once begun, could not be stopped without unleashing rapid and dangerous global warming. Climate models show that it could alter global precipitation patterns and set off droughts in Africa and Asia, jeopardizing the food supply of billions. Sulfate aerosols would damage the ozone layer, exposing us to more cancer-causing ultraviolet radiation. They could also disrupt ecosystems, increase air pollution, reduce solar electricity generation, and interfere with satellite remote sensing.
Similarly, unpredictable side effects would be unleashed by the geoengineering method of brightening marine clouds by injecting sea salt for clouds, meaning they would reflect some sunlight back into space. This process could only be used on about 10 percent of the planet where the right kinds of clouds are present. But, the fact is, clouds remain the least understood components of the climate system so manipulating them with the necessary precision would be tricky. If widely implemented, it could alter climate and weather patterns.
What about the other approach to geoengineering, removing carbon dioxide from the globe’s atmosphere? Would that be safer and more feasible? The answer is no, not really. No matter how modern and pioneering some of the methods may sound, they are always associated with risk and effort. Take, for example, one popular proposal in geoengineering circles – fertilizing the ocean with iron particles in order to stimulate the growth of plant plankton, which, in turn, would consume carbon dioxide through photosynthesis.
It would indeed be possible to bind CO2 from the atmosphere but how would the ocean currents, salinity and stratification of the water change as a result of the artificial interventions? Such questions are typically ignored by the advocates of geoengineering. So far, there are no firm answers, but only small field studies, such as those in Canada and India, the results of which cannot be used to predict ecological consequences of implementation on a broad scale.
Meanwhile, afforestation, the planting of trees to increase carbon storage, would require vast amounts of land and would alter its productivity. Enhanced weathering entails spreading minerals on land or in the ocean to absorb carbon dioxide; it would consume large amounts of energy to mine, crush and transport the materials.
Less dangerous, but also less promising, are the experiments that deal with the direct extraction of carbon dioxide from the air. The first commercial facility to attempt this opened this spring in Switzerland, near Zurich. The plant captures carbon dioxide from the air, binds it to filters, then removes the carbon dioxide and uses it to grow crops or manufacture fuel. Another pilot project in Iceland stores the captured carbon dioxide underground in basalt. But to remove just one percent of global carbon dioxide emissions each year would likely require 250,000 direct-air capture plants.
A large survey was published in 2014 in Nature magazine, comparing afforestation, artificial ocean upwelling, ocean iron fertilization, ocean alkalization (a form of enhanced weathering) and solar radiation management. It found that even with continuous and large-scale implementation, all methods were “relatively ineffective,” reducing warming by eight percent or less. It also highlighted potentially severe side effects and said they could not be stopped without triggering rapid climate change.
Meanwhile, David Keith and his colleagues are planning an experiment using stratospheric aerosols next autumn in Tucson, Arizona. They will launch a balloon 20 kilometers into the atmosphere to release up to one kilo of aerosols, then measure the changes in the air mass. The scientists will use calcium carbonate, a mineral dust that will not damage ozone. Although they have tested the material in the lab, Keith acknowledges that introducing it into the atmosphere could have unintended consequences.
Practical problems, technical unknowns, unpredictable climate consequences and the latest findings, suggest that geoengineering is far from an automatic cure for global climate issues. Moreover, it could pose new problems and raise moral and political issues. What if geoengineering were actually successful? Would the fight against the root causes of climate change suffer? What types of international governance would be needed? And what counties would be able to afford these costly methods? These questions remain unanswered and should make us think.