The old saying about brain power — imagine what we could do if we actually used all of it — applies to information and communication technology as well, according to a study prepared by the Boston Consulting Group.

In a U.S.-focused addendum to The Climate Group’s “SMART 2020″ report, the Boston Consulting Group (pdf) finds that smarter use of information and communication technology, or ICT, could cut the nation’s annual carbon dioxide emissions by 13 to 22 percent by 2020. That reduction could save $140 billion to $240 billion in energy and fuel costs.

Improving energy efficiency with smart building technology alone could help the U.S. reduce carbon emissions by 270 to 360 million metric tons and save $40 billion to $50 billion in energy costs.

Currently, the U.S. emits some 6 billion tons of carbon dioxide each year. Without changes in the way the country uses energy and technology, those emissions are likely to rise to 6.4 billion tons annually by 2020.

While growing use of ICT around the world is expected to cause the industry’s global carbon footprint to double by 2020, it has the potential to help other sectors reduce emissions by five times that amount, according to the “SMART 2020″ report.

How? According to the report, making the most of ICT could help standardise information on energy consumption and emissions, provide better monitoring and accounting of energy use, offer innovations for improved energy efficiency and integrate systems for more automation and lower emissions.

“PCs, mobile phones, and the Web have transformed the way we all live and do business,” said Steve Howard, CEO of The Climate Group, “Global warming and soaring energy prices mean that rethinking how every home and business uses technology to cut unnecessary costs and carbon is critical to our environment and economy. Supported by innovative government policy, ICT can unlock the clean green industrial revolution we need to tackle climate change and usher in a new era of low carbon prosperity.”