There’s enough bad news around, so let’s warm our hands on the cosy glow of Greenpeace and Facebook, finally making up with a kiss under the mistletoe.  After a year of Greenpace campaigning for Facebook to “unfriend coal”, and Facebook shrugging the demand off, the two bodies have relented and issued a joint statement in favour of clean energy.

Greenpeace has been complaining that Facebook is using “dirty” coal-fired electricity for its Prineville data center in Oregon, while Facebook has argued that it is is using that electricity as efficiently as possible, while helping others to do the same through the information it shares in its Open Compute project.

The argument had to end sometime, because Greenpeace needs Facebook. The environmental pressure group lives or dies on the supply of young, enthusiastic recruits, and Facebook is the only place it can find them. Of course, online activism is still unproven: social media is credited with some political changes (the shaky Arab Spring for instance), but the link is not clear between Facebook Likes and real action. .

Greenpeace is the most popular environmental group on Facebook, but it decided to bite the hand that feeds it when it decided that that hand was dirty. Greenpeace’s “unfriend coal” campaign won 700,000 supporters (around one percent of Facebook’s members) in a year, and is now claiming victory.

The terms of the truce are as follows. Facebook will prefer clean and renewable energy supplies in future siting decisions, and lobby energy companies to increase the supply of clean energy to Facebook’s data centers. It will research clean energy options for data centers, and its existing Open Compute energy efficiency project will continue.

Greenpeace will get behind Open Compute. As a way to campaign for utilities to share their data, it will join an existing partnership between Facebook, NRDC and Opower.

The two companies together will host discussions on energy issues, will lobby energy companies, and will promote energy efficiency amongst Facebook users.

The catalyst for all this, Facebook’s “dirty” data center in Prineville, remains open and remains coal-fired, of course. And Oregon’s cheap coal-fired electricity makes it very likely that it will be joined by other cloud players - including a rumored Apple data center.

The main driver for cloud data centers remains price-per-cycle. And as long as that is true, cloud providers will use dirty electricity when it is offered them on good terms. The only way to change that is by a lot of publicity against fossil power.

Meanwhile, as Greenpeace fires up its cloud-based campaigns against coal power, it had better keep a sceptical eye on the cloud itself. Sure, the cloud makes computing more efficient, but if it promotes new consumption of computing resources (for instance, say, Facebook’s campaigns), that actually uses energy that otherwise would not have been used.

And unless all cloud companies can really unfriend fossil fuel completely, then more computing equals more emisisons.

So, it is good to see Greenpeace and Facebook settling down before a blazing Yule log. But let’s hope they offset the emissions replant a new tree.