By retrofitting the Empire State Building to improve energy efficiency, they were able to save a whopping $2.4 million dollars in energy costs over a year! This is equivalent to around 4,000 metric tons of carbon, which is about what you’d get from planting a 750 acre pine forest. This shows not only what can be saved by energy efficiency, but also how much energy is being wasted by many (most?) buildings on this planet. You can read more about this in the press release.