There was an excellent article recently authored by Michael Mehaffy from Better Cities & Towns which I wanted to share with everyone.
Here is the link: http://bit.ly/1iFpVKP
He makes several great points, here are a few of them:
One, it is not just density, but the efficient placement of people and their activities, that is important. A dense downtown, far away from a dense bedroom community, may actually be worse, from a carbon point of view, than a less dense mix of the two.
Two, research shows that the benefits of density are not linear, but taper off as density increases. In other words, there is an optimum density, above which the negative effects of density start to increase over the positive ones. That "sweet spot" seems to be in the neighborhood of about 50 people per acre. And many cities around the world achieve this density without tall buildings, and while creating a very appealing, livable environment (e.g., Paris and London, as well as the aforementioned parts of New York, Vancouver et al.).
We would not argue that tall buildings are never appropriate. However, an evidence-based approach would caution us to put the burden of proof on the proponents, not the opponents, of tall buildings, to prove their overriding benefits in a given situation.