There is an advantage on Mars - it's already 100 percent nothing. We could try 1000 different species of plant, mold, lichens, or whatever. Anything that becomes self sustaining would be step in the right direction. The biggest problems on Mars are the temperature and the atmosphere, and I have no idea what can be done about those. Well I do, but they're such massive engineering projects as to be impractical.

Futurologist says: build glass domes. On Earth, it is very much in the realm of practicability and costs so little that it might surprise you. On Mars, the biggest costs are transport across outer space and industry bootstrapping.

http://marshallbrain.com/mars.htm esp. chapter 7

One thought I had is this: Put superconducting cables around the planet at say 20-30deg north and south. Apply a huge current to provide a magnetic field to protect the atmosphere so that is may come back over time. We did the rough calculation and came up with something like 1 million Amp-Turns to get a decent planetary field but that seemed low to me and we never rechecked our work.

Well we know how to deal with a desert - don't overfarm, don't deforest, and if that's already happened, build walls and protected national parks. It's just that it's too little, too late, and restoring a forest + the damage done by lost land and productivity from desert growth far outweights the money earned by overfarming / deforestation. Short-term gains with long-term cost.

terraforming is pure scifi, the least hospitable place on earth is vastly more hospitable than the best place on mars, even after almost every conceivable planet scale disaster. Pretty much every technique that could be used to make mars more hospitable could be used on earth instead. We dont have to spend 20 million dollars a kilogram to get there either.

Its part of a futurist escapist fantasy where we have somewhere safe to go when we ruin the earth, so why worry about it right?

The way to develop technologies that will save the earth's environment is to go to space or other worlds where there are no NIMBYs or reactionary fanatics or existing corporate kleptocracies, develop them to maturity, and then redeploy on the mother planet. Commercial fusion power, for instance, will probably always remain 'thirty years from now' as long as the unholy alliance of fossil fuel incumbents and so-called 'Greens' continues.

I like to add here: why don't we try a colony on the top of Mt Everest first? It is so much easier than going to Mars, what with (some) air and water already there. But otherwise pretty comparable. And no rockets needed.