Those 50,000 people will come from as far as Auckland, New Zealand and as near as Paris itself. If you add up all the Bangkoks, Bermudas, Cape Towns, Sydneys, Santiagos, Samoas, Jakartas, Singapores, and Stockholms in between, the average distance per traveler is about 9,000 miles, round trip.
Those people will arrive on trains, cars, but mostly airplanes. When flown at full capacity (and the airline industry being what it is, and the Paris meetings being what they are, there’s little reason to think the planes will be anything but packed), a Boeing 747 (a happy medium between private jets and bullet trains) gets about 16.5 miles per gallon of jet fuel. Between 50,000 attendees, that’s about 27 million gallons of the stuff.
When burned, every one of those 27 million gallons of jet fuel releases about 21 pounds of carbon dioxide into the atmosphere. Added up, all those planes flying to the Paris climate talks will release about 575 million pounds of CO2.