"If IT is fundamental to the way you run the business and you want to grow the business, you need more capacity online faster," Brouillette says. "If the CIO can't do more with its data centers, he can't meet the CEO's needs."

Companies that can't squeeze enough power out of their existing data centers are stuck building new ones at a significant capital investment or outsourcing to providers like Savvis and RackSpace.

"The number of new data center builds because there's no power at the existing data center is phenomenal," says Shally Bansal Stanley, managing director of Acumen Solutions, an IT consulting firm. "You can't get power generators. They're on back order. ... We're consuming the data center utility faster than it can be created."

Some electric utilities -- particularly California's PG&E -- offer rebates to corporate customers if they improve energy efficiency. Around 20 electric utilities offer such rebates, according to Climate Savers, an IT industry group that promotes energy savings that can be gained from purchasing the most efficient desktop computers and turning them off at night.

"In order to get some of the rebates, you have to give back the excess power," Stanley says. "You have to show that you reduced it and not redeployed it. Most of our customers are redeploying it. They're optimizing it so they can use it."

The scarcity of electric power in some locations is driving up the cost, so the two go hand-in-hand in driving CIOs to go green.

"We have a customer -- a financial services institution -- that was paying $6 million a year to the electric company for a data center. The electric utility told him that over the next 12 months, that cost was going to be $2.1 million higher," Brouillette says. "Nobody is giving him that extra money. This becomes a really big problem, really fast."

3. CEOs

CEOs are under increasing pressure to use natural resources -- energy, water, land -- in a more responsible, sustainable way. Urged on by outside directors and shareholders, CEOs are expected to understand their carbon footprint and start taking steps to reduce it.

For CIOs, C-suite pressure means not only reducing the amount of electricity they consume but switching their IT operations to locations with greener sources of power. That's why more data centers are being built using hydro in the Pacific Northwest, nuclear in Chicago and geothermal in Iceland.

CEOs "have to have a sustainability strategy that meets or exceeds the expectations of customers and shareholders," says John Skinner, marketing director for eco-technology at Intel. "One of the first people the CEO turns to is the CIO, because the CEO understands that technology is an enabler of efficiency...CEOs are turning to CIOs as allies to help identify how technology -- not just computers, but air conditioning -- can improve the efficiency of the entire corporation."

European CIOs are ahead when it comes to measuring their carbon footprint and understanding the trade-offs in how their IT equipment purchases and management decisions affect this metric.