It's probably just as well, because although Cloud companies are quick to play the card, it seems they're not always so eager to provide information to back up the claims. And as is so often the case when it comes to sustainability, it's not just a story about energy efficiency -- it's about clean energy.

What is the link between data Clouds and Sydney in the mid-1800s? The answer is one William Stanley Jevons, an Englishman and economist who in his 1865 book, The Coal Question, argued that improvements in energy efficiency tend to increase rather than decrease the consumption of resources. The idea is now known as Jervons Paradox, and is often referred to as The Rebound Effect.

Jevons spent much of his formative working life -- from 1854 to 1859 -- in Australia as an assayist with the Sydney Mint. Gold fever was in the air, and it was Jevons' job to assess the quality of the metal coming in from the goldfields. Jevons returned to England and eventually became the first Professor of Economics at University College in London. He is often credited as the founder of modern economics and he said later that many came to him during the time he spent in Australia. Fast forward 150 years to the data centre, and Jevons Paradox continues to hold; efficiency improvements around power consumption and the resulting cost efficiencies are one of the main hype points of Cloud computing. And it is the hype that has environmentalists worried.

In May 2011, released a report of some of the big Cloud companies, including Akamai, Amazon Web Services, Google, HP, IBM and Microsoft.

The idea of the Cloud energy report card was to compare the energy-related footprint of major providers and their data centres.