You've heard about the cloud, right? This blog comes to you from the cloud. The cloud is where the bank keeps your money. YouTube, Gmail, Twitter and iTunes live in the cloud. So does a record of all my runs in 2011. The cloud, in essence, is the millions of data centers where information and software are stored and can be accessed by gazillions of computers.

Unfortunately, the cloud is creating problems for the planet.

Which bring us to Facebook and its coal problem. By some accounts, Facebook is the world's most visited website. Greenpeace, as a result, has made Facebook the target of a campaign called Unfriend Coal, which has its own Facebook pages (of course!) with more than 700,000 fans. Facebook recently opened a big new data center in Prineville, Oregon, where electricity is generated mostly from burning coal. Greenpeace is asking the social media giant to power its services with renewable energy instead of coal and nuclear power.

In response, Facebook -- like the rest of the IT industry -- mostly talks about efficiency. The Prineville data center is super efficient, by all accounts. What's more, to its credit, Facebook is sharing much of what it has learned about making data centers more efficient in its Open Compute project.

The trouble is, efficiency is a necessary, but insufficient response to the threat of climate change.

Or as Daniel Kessler, a Greenpeace campaigner, told me: "It's solving for half the equation."