The headline on the Treehugger post is: "
Paris to Plant 80,000 Square Yards of Green Roofs and Rooftop Gardens by 2020
That converts to 16.528 acres, which might could provide food for maybe, oh I don't know, 100? gai Parisiennes?
(To give them their due, the actual article doesn't talk about food, but insulation. But this is a prime example of how to lie with statistics; of course if they'd used square feet the figure would be even more impressive.)