Reasons Against Geoengineering

Alan Robock, a volcanologist and climatologist from Rutgers University has made a list of reasons to not embark on this kind of geoengineering. Here is the list of some of the major ones:

Effects on regional climates. Following large volcanic eruptions like Mt. Pinatubo, climate scientists noted changes in precipitation leading to droughts and problems in food production. Most climate modelers studying this problem agree that these kinds of regional changes would be impossible to avoid and impossible to control.
Continued ocean acidification. Blocking sunlight in this way may limit the rise in temperature, but it would not address the problem of ocean acidification. A large fraction of the excess CO₂ added to the atmosphere by burning fossil fuels is absorbed by the oceans, and this increases the acidity of the oceans, endangering the entire marine ecosystem. This problem would continue if we only blocked the sunlight.
Ozone depletion. The sulfate additions to the stratosphere would promote the kinds of chemical reactions that destroy ozone, and ozone is a critically important part of our atmosphere in the sense that it blocks harmful UV radiation from reaching the Earth’s surface.
Effects on plants. The scattering of light caused by the aerosols may create more diffuse light that is beneficial to plants, but the reduced total amount of sunlight could be detrimental — the balance of these effects is not well understood.
More acid rain. The sulfate aerosols combine with atmospheric water vapor to form tiny droplets of sulfuric acid, which eventually fall out of the sky and land on the Earth’s surface. The global average increase in acid precipitation may not be alarming, but it is likely that there will be some regions that are noticeably impacted.
Effects on cirrus clouds. The injected aerosols are likely to affect the formation of high cirrus clouds, which can impact the energy balance and thus temperature of the Earth, but this is not well-understood at present — we don’t know whether this would increase or decrease cirrus clouds.
Whitening of the sky. The sulfate aerosols would make our sky more white than blue, which we might get used to after a while, but it would be unsettling to most people in the short term. We would, however, get much more vibrant sunsets.
Less sun for solar power. Reducing the amount of sunlight reaching the surface will necessarily reduce the amount of solar energy we can harvest — not a good thing.
Rapid warming if stopped. If we were to decide that this was a bad idea and stopped, a dramatic, potentially catastrophic warming would ensue (as shown in the model results above). This assumes that we continued to raise CO₂ concentrations in the atmosphere.
Human error. This is always a reality in any human endeavor, and an error in a system such as this could have serious consequences for billions of people.
Undermining sustainability efforts. Any geoengineering scheme is problematic in the sense that it lets us off the hook and just delays the inevitable transition to a more sustainable energy system. We will definitely run out of fossil fuels and the longer we wait to transition to a system based on renewable energy, the harder it will be.
Who is in control? Who has the power over the global temperature? This is a huge problem — it cannot be left to one nation, or one group of nations to make the decisions that will affect all of the people on Earth. Altering the climate this way will clearly create some winners and some losers. Island nations threatened with complete submergence in the future will want as much cooling as possible. The US and China and much of Europe will also want a lot of cooling to combat the rising sea levels that will force the relocation of major cities. But the Russians may want even more warming. So, who decides?
Unintended consequences. Even instance in which humans have undertaken to modify the environment, a whole host of unintended consequences arise. Our world is complex enough, with so many interconnections, that it is impossible for us to foresee all of the consequences of our actions, even with the best of intentions. As just one example of this, the first people to discover the usefulness of fossil fuels did not foresee the potential for global environmental harm.

Nevertheless, the fact remains that this mode of geoengineering would work — we could cool the planet, and the cost would be relatively small. So, perhaps it is something we should carefully study and consider in the event of unexpectedly severe climate damages — a parachute to be deployed only when the plane is going down!