a result of lower overhead costs for office space, heat, lighting, etc. The savings are significant; the average annual energy consumption for U.S. office buildings is over 23 kilowatt hours per square foot, with heat, air conditioning and lighting accounting for 70% of all energy consumed. Other related initiatives, such as Hoteling, reduce the square footage per employee as workers reserve space only when they need it. Many types of jobs, such as sales, consulting, and field service, integrate well with this technique. Voice over IP (VoIP) reduces the telephony wiring infrastructure by sharing the existing Ethernet copper. VoIP and phone extension mobility also made hot desking more practical. Wi-Fi consume 4 to 10 times less energy than 4G. Telecommunication network devices energy indices The information and communication technologies (ICTs) energy consumption, in the US and worldwide, has been estimated respectively at 9.4% and 5.3% of the total electricity produced. The energy consumption of ICTs is today significant even when compared with other industries. Some study tried to identify the key energy indices that allow a relevant comparison between different devices (network elements). This analysis was focused on how to optimise device and network consumption for carrier telecommunication by itself. The target was to allow an immediate perception of the relationship between the network technology and the environmental effect. These studies are at the start and the gap to fill in this sector is still huge and further research will be necessary. Supercomputers The inaugural Green500 list was announced on November 15, 2007, at SC|07. As a complement to the TOP500, the unveiling of the Green500 ushered in a new era where supercomputers can be compared by performance-per-watt. As of 2019, two Japanese supercomputers topped the Green500 energy efficiency ranking with performance exceeding 16 GFLOPS/watt, and two IBM AC922 systems followed with performance exceeding 15 GFLOPS/watt. Education and certification Green computing programs Degree and postgraduate programs that provide training in a range of information technology concentrations along with sustainable strategies in an effort to educate students how to build and maintain systems while reducing its harm to the environment. The Australian National University (ANU) offers "ICT Sustainability" as part of its information technology and engineering masters programs. Athabasca University offer a similar course "Green ICT Strategies", adapted from the ANU course notes by Tom Worthington. In the UK, Leeds Beckett University offers an MSc Sustainable Computing program in both full