Simply “going to Iceland” is not that simple for companies like Microsoft, Amazon, Apple, Google or others Greenpeace has chosen to focus on in its efforts to persuade Internet and cloud-computing giants to power their data center infrastructure with clean energy.

That is according to James Hamilton, member of the team running Amazon Web Services, the company’s Infrastructure-as-a-Service business. The reason is simple: latency.

“Because of the cruel realities of the speed of light, companies must site data centers where their customers are,” Hamilton wrote in his Perspectives blog. “When your latency budget to serve customers is 200 milliseconds, you can’t give up three-fourths of that time budget on speed-of-light delays traveling long distances.”

Hamilton’s post was a response to an open letter from a SmartPlanet contributor to Steve Ballmer, Jeff Bezos and Tim Cook, CEOs of Microsoft, Amazon and Apple, respectively. Citing low grades Greenpeace gave the three companies in its How clean is your cloud? report, the letter calls on them to build data centers in places like Iceland, where there is plenty of low-cost renewable energy.

Iceland has an abundance of hydroelectric power, and the country’s economic-development officials have made a lot of efforts (some successful) to attract data center construction to the country.

Large Internet and cloud companies have been building massive data centers in remote areas where power is cheaper or cleaner or both.

Facebook has built a data center in Sweden, for example, powered by hydro. Google has built one in Finland.

While they will continue taking advantage of low-cost renewable energy in remote areas for certain types of workloads, Internet giants are also going to continue using data centers in metropolitan areas - where the majority of their end-users are - for latency-sensitive workloads, Hamilton writes.

Not only is power in New York City dirty, it is also expensive, and so is real estate. But, Google still spent US$1.9bn on the massive carrier hotel at 111 8^th Ave. in Manhattan, because that is where the eyeballs are.

“It’s not like companies just love paying more or using less environmentally friendly power sources for their data centers,” Hamilton writes.

“Google is in New York because it has millions of customers in New York. If it were physically possible to serve these customers from an already built, hyper efficient data center … they certainly would.”