AMV already handles the Department for Enviroment, Food and Rural Affair's (DEFRA) £5m climate change account, and now adds the Department for Transport's (DfT) £4m climate change business following a consolidation.
Leo Burnett, which previously handled the DfT's £4m climate change account, submitted proposals for the consolidated business along with AMV.
The two were tasked with producing an integrated campaign encouraging the public to "Act On CO2" for the DEFRA and DfT.
Defra and DfT are now considering whether to hold a pitch between roster agencies PHD and MindShare for the communcations planning brief. The COI said a decision is expected shortly.
David Watson, head of marketing at Defra, said: "Climate change is one of the biggest challenges facing us today. This is an exciting opportunity to bring a truly joined-up approach to government communications in this area."
Helen Clark, deputy head of transport publicity at the DfT, said: "DfT and Defra are already working closely together on policies to tackle climate change, so it makes sense to do the same on communications.
"We need to implement a long-term strategic plan to change public behaviour and we were impressed by AMV's vision."
Leo Burnett first picked up the climate change brief from the DfT last year and created the campaign strapline, "Act on CO2".