The agency is offering extra paid travel and holidays if employees choose to travel via land or sea instead of flying. The incentive is part of its new 'Climate Perks Scheme'.
The announcement follows research by Flight Free UK that one flight can double a person's carbon output for the year, and one transatlantic flight generates more CO2 emissions than the average person consuming meat or using a car for a year.
The Flight Free UK campaign wants to encourage 100,000 people to go flight-free in 2020.
Greenhouse PR chief executive Anna Guyer said: "Until now, however much people cared about the environment, flying was a carbon-heavy luxury they avoided talking about. They’ll take a reusable coffee cup, yet won’t consider the sleeper train."
"We offer extra holiday days to accommodate slower, low-carbon public transport options. So many businesses say they care about the climate emergency, but they aren’t treating it as one. I urge them to join us in offering reward schemes such as Climate Perks and help spur the flight-free movement in the UK."