Computer servers in data centers account for about 2% of global energy demand, growing about 12% a year, according to Greenpeace.  The servers can suck up as much power as 50,000 average U.S. homes.

Most of what powers the cloud comes from coal and nuclear energy rather than renewable sources such as wind and solar, says Greenpeace. Clusters of data centers are emerging in places like the Midwest, where coal-powered electricity is cheap and plentiful, the group said.

Each month, electricity used to power searches on Google produces 260,000 kilograms of carbon dioxide, according to WordStream. The searches use up 3.9 million kilowatt-hours. A single spam email of the 62 trillion sent each year creates 0.3 grams of carbon dioxide.