Google is notoriously secretive about its data centers (their locations, their layouts, how much electricity they use, or even how many of them there are), saying only that the company has a stated goal and of being carbon-neutral. It's believed that Google has at least three dozen dedicated data centers (although studies of IP addresses suggests there may be many more than that). Most, if not all, of the Google data centers draw power from hydroelectric or nuclear plants.
Google says that a typical search query uses an amount of energy equivalent to the release of 0.2 grams of CO2. If that's true, and if Google handles a billion queries a day, that's equivalent to a net release of 200 tons of CO2 per day. But remember, Google's data centers are not powered by coal-driven generators (they use hydro or nuclear power instead), so in essence a Google search costs nothing, in terms of carbon dioxide.
In terms of electricity, it's a different story. We're talking huge amounts of electrical power. Some estimates put Google data center power usage at 50 megawatts per data center. At the end of a year, that's 432 million kilowatt-hours of energy used, per data center. For 36 data centers, we're talking a grand total of around 15 billion kWh per year. That's roughly twice the amount of electricity consumed by all U.S. government data centers put together [ref].
Just to put it in perspective, this means Google consumes more electricity than most countries on earth. If Google were a nation, it would rank somewhere around No. 75 of 215 countries. (For electricity usage by country, see the excellent chart here, based on statistics from the CIA Factbook.)
