The paragraph below is an excerpt from Kim Stanley Robinson's article, "A Colony in the Sky," about "terraforming" Mars—that is, turning it into a planet that humans could live on

The paragraph below is an excerpt from Kim Stanley Robinson's article, "A Colony in the Sky," about "terraforming" Mars—that is, turning it into a planet that humans could live on. 

    Some people may believe that such a project is too large or slow or presumptuous for humanity to undertake. But consider our current situation on Earth. There are nearly six billion of us now, and the number may double, though we have no good idea how many of us the Earth can support. Many larger species are in danger of extinction unless we protect them from us. We have rearranged much of the land, and we have altered the atmosphere to the point where the global climate in the future will be a matter of legislation and industrial practice. In other words, we are already starting to terraform Earth by necessity to keep it livable. Given this situation, the attempt to terraform Mars does not look so outlandish. Doing it could be regarded as a valuable experiment, with Mars as a giant lab or university, in which we learn how to steward a planet's biosphere for long-term sustainability.