O2 has become the first mobile broadband provider to be recertified with the Carbon Trust Standard for its commitment to green practices.
The firm, which originally received the award in January 2009, has been recognised for successfully measuring, managing and improving carbon efficiency across its business.
Over the last two years, O2 has honed its energy efficiency strategies further to cut carbon emissions by nearly 30,000 tonnes of CO2.
Ronan Dunne, UK Chief Executive at the internet service provider, noted that the Carbon Trust Standard is "the de facto UK mark of commitment to carbon reduction".
"By retaining the [status] we've proved that by using technology to measure energy usage, connect people, and encourage new ways of working - we can make a major difference to climate change," he said.
In the five years O2's performance has been measured by the Carbon Trust Standard, the company has improved carbon efficiency by 22 per cent relative to its turnover.
Initiatives undertaken by the firm include the launch of a company-wide sustainability strategy called think Big, the development of a new low-carbon head office, a £2 million investment in 7,000 electricity smart meters, and a £750,000 investment in power quality monitoring for data centres.