PHOTO: NASA/JPL/MSSS

Most ideas put forward by scientists such as McKay budget about five to 10 decades for the temperature increase. Most space scientists agree that we now have the technological capability to attempt some of these schemes; of course, the execution of any particular one on a planetary scale will be quite challenging, according to McKay.

Scientists also say that carbon dioxide and water alone will not be enough to sustain life. “A biosphere requires large amounts of carbon dioxide and water but also nitrogen,” says McKay.  “Nitrogen gas is essential for a breathable atmosphere and nitrogen is needed by life as an essential macronutrient.”

As far as scientists know, there is very little nitrogen in the Martian atmosphere and there is no data on the amount of nitrates in the Martian soil that could be converted to nitrogen. Theoretical arguments suggest lightning and meteorites should have produced nitrates on Mars that could be adequate, says McKay.

“The question of the nitrogen supply is probably the key question in terms of the feasibility of ecosynthesis on Mars,” he stresses.

Ethical questions also abound. As Clarke pointed out recently, “Whether we should embark on such a venture should be decided very carefully, and future Martian inhabitants must be allowed to have their say.”

Many who have thought about the topic view it from an anthropocentric view. Anthropocentrism puts human interests foremost.

In a 2002 article in Environmental Law Reporter on the ethics of terraforming, Robert D. Pinson wrote, “The most applicable environmental ethic to terraforming Mars is anthropocentrism. It puts our interests at the forefront while still ensuring the existence of all life. It seems obvious that we should give ourselves the highest level of intrinsic worth since we are the ones placing the value. Life, of course, has the ultimate intrinsic worth, but we are a part of that life. It is in our best interest to preserve and expand life. What better way than by changing a planet that is currently unable to sustain life into one that can.”

And of course there is the business of getting to Mars and back safely, while sustaining the crew through the long multiyear trip. Unmanned missions like Phoenix are technologically possible today because we do not need to worry about transporting a big payload. There are ideas for manned missions that involve getting to Mars with the aid of nuclear rockets, but a lot of work remains to be done before we can send humans there.

“We cannot, of course, begin terraforming today, but we can research and plan the future,” Pinson had said in 2002. That sentiment, if anything, has gotten stronger.

“Given the situation here on Earth, I think it prudent that we try to colonize Mars,” Pinson told IEEE Spectrum recently. “Since the evidence for water on Mars is becoming stronger and stronger, I really believe we should make an effort to get over there and investigate further.”