A topic that comes up often when considering the long term human exploration of Mars is the concept of Terraforming. Quite literally, terraforming describes direct intervention of human beings to modify the climate of another planet to make it more like the surface of the Earth. This makes a great deal of sense; it’s much easier to explore, build cities and carry out the daily business of living if the surface is warm, radiation levels are low, and the atmosphere is thick and breathable.
Of course the closer you start out to Earth-like conditions, the easier this process is. Terraforming Triton (a moon of Neptune) or Mercury, for instance, would be almost impossible. Even though Mars is just about the best candidate for terraforming in the solar system, it would still require an unprecedented industrial intervention and some creative solutions. Despite this, Mars is unlikely to be the first place where the human race practices terraforming. Instead, we most likely will first try terraforming the Earth itself.
This process goes by the name of geoengineering, but the goals are familiar to anyone who has ever planted and nurtured a garden. The goal is not to maintain your particular patch of ground in its pristine, primordial state, but to mould a viable mini-ecosystem of your own design. To that end gardeners routinely do things like add chemical fertilizer, spray for pests and introduce new species some of which do not even exist in the wild. If part of the garden grows poorly, it can receive special attention. If a particular plant thrives excessively and threatens to overtake the whole, it can be pruned back.
Sometimes gardening is done for pure pleasure, but other times it comes out of necessity. Removing dry overburden in forests reduces the fire hazard. Controlling the types of plants living close by can help reduce the number of pests or the ease of spread of disease. It can also be the means by which a resource is protected, such as in Japan in the late 1600s when silviculture began as a way to preserve and ration the use of different kinds of wood.
This last point brings up the subject of a closed environment. If the Japanese had had easy access to wood from abroad, they likely would have not have taken such stewardship of their own forests. Like late 17th century Japan, the Earth is itself an island in the solar system for which we need to take up environmental stewardship. Human beings have proved capable of changing the climate through our activities and we need to be careful how we wield this power.
But this doesn’t mean that the Earth, its surface and its inhabitants need to revert to some primal, wild state. Instead we need to evaluate the current state of the planet, how it is changing, and how we would like it to be. Since the costs of global warming will potentially be high, it is important to mitigate this risk. But reducing our CO2 emissions may not the only way to prevent a warming of the surface. Recently, the Copenhagen Consensus and others have begun examining the possibility of using technology on a large scale to counteract the effects of global warming. You can read their most recent report here: http://fixtheclimate.com/uploads/tx_templavoila/PP_Climate_Engineering_Pielke_v.1.0.pdf.
In this report they comment on the viability of inducing cooling changes to the Earth’s climate system, including the wide dispersal of aerosols (which can affect the amount of sunlight striking the surface both directly and as condensation nuclei for clouds) as well as capture and sequestration of carbon dioxide directly from the atmosphere. One danger here is that the Earth is a complicated system and so the feedbacks resulting from the implementation of any of these ideas is not necessarily well understood.
But this sort of positive mitigation is politically attractive and some of the ideas are very intriguing. For instance, if you were to convert CO2 from the atmosphere into biofuel for a vehicle by using a process powered by a renewable source such as solar energy, such a vehicle would be carbon-neutral.
Either way, given that we are on the cusp of having the technological power to geoengineer the Earth, it is up to us to use this power wisely. As we know from Easter Island's example, island systems can be delicate. But we shouldn't shy away from using it and from creating the world we want to have instead of just recreating what has come before.
Further Reading: “Collapse: How Societies Choose to Fail or Succeed” by Jared Diamond has a great account of Japan siviliculture and discusses how societies who responsably take control of their environment can have good outcomes. (I should mention that “Guns, germs and steel” is also a really good read)