Universal McCann currently holds the account but the organisation has issued a tender notice ahead of a statutory review of the business.
Media agencies have been invited to complete a pre-qualification questionnaire by 23 December. The contract will be awarded for an initial period of two years, with the option of extending the contract for one period of up to 24 months or two periods of up to 12 months each.
The Carbon Trust last reviewed its media in 2009 when it appointed Universal McCann to its consolidated media buying account after a pitch against Carat, Manning Gottlieb OMD and Brilliant Media.
In July, the organisation appointed TBWA\London group to handle advertising and media planning. TBWA is unaffected by the review.