"At the time, there were a number of things I was disheartened about - one of which was the failure of climate change legislation.
"Through Walmart I was able to work with two million employees. To ... engage this many people in a company that actually wanted to change was a great opportunity."
During his time at Walmart, Werbach worked with individual stores to reduce their carbon footprint. Programmes ranged from store recycling systems to creating sustainable products.
Employees were also encouraged to change one aspect of their lifestyle to make it more environmentally friendly.
People would walk or bus to work instead of travelling in private vehicles. Werbach carried this initiative through to Saatchi & Saatchi.
As chief sustainability officer at Saatchi & Saatchi, Werbach's main aim is to incorporate sustainable business practices into the core business objectives of the organisation's clients.
"My definition of sustainability in the business sense is to be able to thrive in perpetuity.
"Companies can only achieve this if they adjust to the changing world and understand sustainable business practice as a core business objective."
Werbach says the increasing awareness among younger people about environmental practices is a strength in moving towards sustainable business practices.
He himself first joined Greenpeace at the age of 13 and has since been twice elected to the organisation's International Board.
"Every CEO I have talked to says their greatest asset is their people. It is the single most important thing and to be globally competitive you need to have the best, and the best talent in the world cares about whether your company is sustainable or not."