I became interested in Green ICT after managing a business with ~100 servers for a weather app, so I took note of this story about UK Met Office's efforts. The Met Office is doing many of the right things, but here's the ironic bottom line:

. . . despite efforts made around improving the efficiency of its IT . . . overall, the electricity used by its supercomputers and other systems is actually still going up [reports eWeek Europe].

“Our supercomputers use something like 40 to 50 percent of our entire electricity usage in the organisation at the moment – that is about to go up to 80 percent, . . . Its going up because in order to provide more accurate weather information we need more computing power. We are getting more calculations per watt but the demand for calculations far exceeds the rate at which the suppliers are able to reduce the power consumption.”

"Calculations per watt" or "Calculations per carbon-pound" are potential measures for a growing facility, but measurements based on output value are even better (e.g., widgets shipped per carbon-pound). Forecasts per carbon-pound?

More on supercomputer energy efficiency and energy-specific computing benchmarks.