You can’t manage what you can’t measure. If your conference would like to reduce its carbon footprint, in particular if it has committed to the TCS4F manifesto, then you need to estimate how much CO₂ was released in the atmosphere by holding the conference. This is a critical step to understand your environmental impact, seeing how it evolves from one year to the next, and understanding how it varies depending on location. It also allows organisers, if they wish, to buy carbon offsets to compensate the environmental cost of the event.