Steven Levy goes inside Apple's Nevada data center for Wired.

Apple is either really taking this seriously, or they really want us to believe that they are. I believe they are serious.

Here’s that story: Apple is close to its goal of powering all its facilities 100 percent by renewable energy. Its corporate campuses and data centers are now at 94 percent renewable and rising. (In 2010 it was 35 percent.) The next step is to extend the efforts to its retail stores.
In this accounting, Apple does not include the manufacturing, transport, and use of its actual products, which accounts for 98 percent of its carbon footprint. Still, its accomplishment on facilities, particularly data centers, is significant.

Wow. 35 percent to 94 percent in less than 4 years. That's pretty impressive. But, the second paragraph provides the real context. They've only just scratched the surface. Apple has only started to tackle the first 2 percent of its carbon footprint. And make no mistake, its carbon footprint is huge. When you sell over 225 million iOS devices per year and still growing, that's a lot of carbon.