You certainly can grow things up north, but the main problem is that while this sort of thing will expand the northern limits of arable land, that won't come close to compensating for the much more productive land further south that will suffer desertification.
That's a point that many miss. Not all land is equally productive. On some land you can get a high yield with minimal effort. On other land it takes all kinds of effort and chemicals. Unfortunately between urban sprawl and global warming we are losing the former. I've only seen one or two new subdivisions built on boulders or bedrock. I've seen hundreds tearing up rich fields prime for farming. That's not land we can get back. The best use of that land is for growing food.
In addition to the soil, there are factors like light and microclimate. The best farm land was scoped out before the 1900's and if we pave it over, it is gone.
Rick Falkvinge of the Swedish Pirate Party has a good summary of the attempt to ban porn as well as a call to action. Apparently getting e-mail through to the parliamentarians is not as straight forward as one might wish. Christian EngstrÃm, MEP, also of the Swedish Pirate Party has a good analysis of the attempted ban. Basically it's a grab at control and censorship under another guise.
"And of course this analysis overlooks the most reliable way of rigging an election, and one that is most certainly practiced here: hand-picking the electorate. Who appointed those cardinals in the first place, eh? "
That can be done on a large scale, too. It's known as gerrymandering and is done by both parties. It's especially common for congressional districts. If you look at the national map, you see all kinds of bizarre shapes designed to give one party or the other a majority. They don't follow any natural or geographic boundaries. You end up with all kinds of loops, horseshoes, dumbells, and other weird shapes. The composition of congress would be quite different if the districts were restrcited to existing counties or a plain grid.
Men of lofty genius when they are doing the least work are most active. -- Leonardo da Vinci