A lot has changed since we wrote three years ago: "Yahoo plans to go carbon neutral by the end of 2007. Part of this will be achieved through carbon offsets, including hydroelectric and sustainable agriculture projects in Brazil." Co-founder and Chief Yahoo David Filo now says, "Reducing our carbon footprint has always been a priority and we’ve decided to focus all our energy and investment on that philosophy. We will no longer purchase carbon offsets as announced in 2007. Instead, we’ll focus our resources on reducing our carbon impact while helping the rest of the industry do the same. We believe creating highly-efficient data centers will have a greater long-term, direct impact on the environment and gives us the best opportunity to play a leadership role in addressing climate change."

Another focus appears to be reducing the amount of water typically consumed by a data center. Here is Yahoo's report about its newest data center, the Lockport, NY "Chicken Coop":

The Lockport facility will have the first implementation of Yahoo!'s green data center design, called the Yahoo! Computing Coop (YCC). The best-in-class, energy-efficient design was recognized by the U.S. Department of Energy (DOE) in 2010 with a sustainability grant of $9.9 million, the largest award received from the DOE's recent Green IT grant program. The facility uses a combination of Lockport's cool climate, prevailing winds and hydropower to keep the 120-by-60-foot server buildings cool. The YCC design, dubbed the "Yahoo! Chicken Coop," mimics the long, narrow design of a chicken coop to encourage natural air flow 100 percent of the time, resulting in an annualized average of less than 1 percent of the buildings' total energy consumption being required to cool the facility. Yahoo!'s Lockport data center is among the most efficient data centers in the world, with a low power usage effectiveness1 (PUE) of 1.08, compared with the industry average of 1.922.

The Lockport data center will:

* Consume at least 40 percent less energy, and at least 95 percent less water than conventional data centers.
* Save enough energy to power more than 9,000 New York state households annually.
* Save enough energy to power approximately 300,000 CFL light bulbs for one year, running 24/7.
* Save enough energy to power approximately 1.1 million laptops for a year.
* Save more water per year than flows over the Niagara Falls for a minute straight (4 million cubic feet per minute is what the Falls flow on average).
* Save enough water in one year to provide drinking water for 200,000 people to sustain a healthy life. (Approximately 180 gallons per year per person is the average amount of drinking water over a lifetime.)

Hydropower for the data center will be supplied by NYPA, which was recognized in 2006 as one of the cleanest utilities in the United States.

Yahoo appears to be aiming for a lower PUE than any other mega-data center.