If It Ain't Broke, Don't Fix It

The concept of geo-engineering--of deliberately altering the planet's climate to temper the effects of global warming--has been much on my mind lately. There are many different techniques for geo-engineering that have been proposed. Some of these include fertilizing the ocean with iron particles to encourage the growth of algae, using chemicals sprayed from airplanes to deflect sunlight and cool the earth, capturing carbon dioxide and turning it to stone, and launching giant mirrors into space to shade the earth.
On the surface, these seem like the ideal solution to the problems presented by climate change. They can be--at least theoretically--accomplished using existing technology, and have been demonstrated in sub-scale experiments to significantly impact greenhouse gas concentrations. So what, then, is the catch? The problem with a lot of geo-engineering scenarios is that while they do indeed decrease the average global temperature and reduce the amount of atmospheric carbon dioxide, they cannot be tailored to suit specific ecosystems.
For example, one plan to remove carbon dioxide from the air is to release iron particles into the ocean, triggering the growth of large amounts of microscopic algae (single-celled plantlike organisms). As the algae photosynthesize, they would absorb carbon dioxide from the air and replace it with oxygen. The problem with this idea is that in nature, these massive concentrations of algae--called algal blooms--can produce deadly plagues known as red tides. Artificially encouraging algae to grow in order to reduce carbon dioxide could have the unintended consequence of making red tides more frequent.
Geo-engineering is a controversial concept. It should not, in my opinion, be viewed as the first and foremost solution to the environmental problems facing the world today, but at best as a last resort to fall back on if all else fails. For the time being, we should focus on preserving what is left of the world's ecosystems as they are, rather than trying to reverse the damage we have done by altering them further.

In this satellite photo, a huge algal bloom is visible off the coast of Argentina. Attempts to control greenhouse gases by fertilizing the ocean could lead to more events like this, and have potentially devastating effects for sea life.