Air Force One is only one of the planes that will make the trip. There are the planes that carry the limos, the Secret Service, and all the support vehicles, personnel, and communications equipment.
Then there are all the emissions that come from getting Obama from the airport to where he is going, plus all of the emissions from all of the idling local vehicles tied up in the massive traffic jams that are so much a feature of a Presidential visit to a city.
Then, there was the trip to pick up the Nobel Gong while insulting just about every co-celebratory group and entity in Norway while he was there.
Planting an entire forest wouldn’t come close to the emissions involved in this.