If the Internet were a country, it would be the fifth biggest consumer of electricity in the world, according to Greenpeace.

That’s not just the electricity you’re using in your office or home. It’s the juice being slurped up by energy-hogging data centers operated by “cloud companies,” which store and provide data over an Internet computer network.

In the case of Apple and other tech companies, the energy in question is provided by burning coal. And Greenpeace isn’t happy about it. With its "How Dirty is Your Data?" report released just in time for Earth Day, the crusading environmental organization looks at the carbon footprint of the top 10 global cloud companies: Akamai, Amazon, Apple, Facebook, Google, HP, IBM, Microsoft, Twitter, and Yahoo!

Apple uses the most coal power of these companies (54.5%), and is scheduled to open a data center in North Carolina this spring that will be powered mostly by coal and some nuclear energy, back in the spotlight after Japan’s nuclear crisis. The facility will use as much electricity as 80,000 homes. Other big coal consumers are Facebook, IBM, HP, and Twitter.

In contrast, Yahoo! and Google take pains to locate their data centers near renewable energy sources. Google in particular is investing in solar and wind energy projects.

Apple had no comment on the criticism by Greenpeace.