Greenroofs in city's are the answer to cooling down.

I've been thinking this for a while, especially after looking out from several Toronto high rises and seeing the many bare flat roofs that are dying to be greened!! There's a good article in NewScientist confirming that this infact makes a huge difference, as does greening walls...
I wonder what Toronto will be like in a few years time with all the new glass condo's in place...