We can counter the warming impact of greenhouse gas emissions by firing particulate matter into the stratosphere, to reflect some of the sun’s rays back into space.
Fact:
This idea, known as ‘solar geoengineering’, seeks to emulate the impact of large volcanic eruptions like that of Mount Pinatubo in 1991, which cooled the atmosphere by 0.6°C for about 15 months. The scheme has the advantage of being cheap and feasible, but the disadvantage of being potentially very dangerous.
Unfortunately, putting sulfate aerosols into the stratosphere will not precisely offset our CO2 emissions, as the two processes impact the Earth in different ways. The former blocks the entry of heat, while the latter blocks its escape. This means that while the Earth’s temperature would indeed cool if we bombarded the stratosphere with aerosols, that cooling would not be spread evenly across the globe. It is entirely possible that the polar regions would become hotter rather than cooler, and that the polar ice caps would melt at a faster rate rather than a slower one. This, in turn, would reduce the level of albedo on the planet, increasing solar radiation rather than reducing it. The simple fact is, we don’t know what the overall effect would be if we started experimenting with the planet this way.
Another problem is that eventually all of the particulate matter sent into the stratosphere would return to Earth, creating acid rain. This problem was deemed so severe in the 1970s that laws were passed to stop industries from polluting this way. Acid rain is dangerous to lakes, rivers and people’s health. It is also damaging to the ozone layer.
Then there is the problem of politics. Who decides how much particulate matter is put into the stratosphere, and what happens if a rogue state decides to ‘go it alone’? It is difficult to get agreement among nations on any issue, let alone one as important and difficult as this.
Finally, there is the question of what to do if we make a mistake. If, for example, we were to put too much particulate matter into the stratosphere, there is simply no way to get it down until it descends of its own accord – and we don’t know how long that would take. In the meantime, the impact on the climate could be catastrophic.