CNBC is readying a series of programmes and events to push its green credentials and coverage.
The agency will run a PR campaign to bring together global CEOs, government policy makers, NGOs and academic figures to discuss key sustainability issues.
A central aspect to the campaign will be building awareness of CNBC's Energy Opportunities initiative, which consists of a series of TV news and documentaries and three international conferences.
The 12-month retainer was won following a competitive pitch.
Daljit Bhurji, MD of Diffusion, commented: 'We will be targeting online news sites, blogs, forums and LinkedIn groups to reach senior decision-makers, the green community and academia to get them to participate.'
The brief includes using social media to reach out to consumers concerned about sustainability issues, and encouraging them to visit the Energy Opportunities site.