The concept of altering the global climate of a planet to make it more suitable for human colonization is known as terraforming. The idea of terraforming is first described in science fiction in 1930 by Olaf Stapledon in his novel Last and First Men, and the term itself was coined in 1942 by writer Jack Williamson. Scientific interest in the topic began with Carl Sagan’s speculations of terraforming Venus, while planetary scientist Christopher McKay made the concept almost a household word as one of the modern leaders in thinking about terraforming Mars. Humans could make a planet more suitable for human or Earth life in many ways--some just beyond our technological horizon but others within our grasp today.
One reason to terraform a planet, such as Mars, is to increase its overall surface temperature to make the climate warmer for humans. At temperatures above freezing, human colonists would not only be more comfortable, but they could melt portions of frozen ice caps to obtain valuable drinking water. We already know how to increase surface temperatures on a terrestrial planet like Mars: add greenhouse gases to its atmosphere. Although humans today are seeing the effects of excess greenhouse gases such as carbon dioxide, more potent greenhouse gases would probably be used to rapidly convert the climate of Mars. CFC’s, or chlorofluorocarbons, are most famous for their role in ozone destruction, but they are also highly effective greenhouse gases that could provide a tremendous amount of warming if released in the atmosphere of Mars. Other strategies for warming mars may use different greenhouse gases, or may even include scattered dust as a way of helping to melt the ice caps, but most forms of terraforming begin with a similar scenario to increase global average surface temperature.
Increased surface temperatures might help humans to live more comfortably in protective enclosed shelters, but what if human colonists want to walk around and breath freely as on Earth? Various plans for successive ecosynthesis have been proposed to slowly introduce Earth life to the Martian environment once temperatures have risen and liquid water is available. Photosynthetic microorganisms would be among the first settlers to begin terraforming Mars by releasing oxygen into the atmosphere. Other microbial species would then slowly be introduced, and eventually more complex plants could be added. This process could take thousands of years and would require careful monitoring each step of the way. But if successful, this would produce a fully terraformed Mars with a breathable atmosphere capable of supporting human life.
Whether or not we can terraforming Mars is a question of technology, and it seems as if current and future technology allows for this possibility. Whether or not we should terraform Mars, or any planet for that matter, raises a different set of ethical concerns that humans are only beginning to face. If life is discovered on Mars, for example, then would it be wrong to terraform the red planet? Should we protect planetary bodies by designating them as nature reserves? Or are there any considerations as to how we should colonize and develop other planets, given what we have learned here on Earth? These questions are not easily answered, but they are critical to resolve well in advance of any actual attempts at terraforming a planet.
Perhaps the greatest indicator for the success of human space colonization is not how we treat other planets but how we treat our own. Thinking about terraforming is at least one way to put the future of our climate in perspective.