Except burning a gallon of jet fuel emits 21.1 pounds of carbon dioxide, according to the EIA. So 20,000 pounds of jet fuel emits 211 (short) tons of CO2. Summers' number is too high by a factor of 1400.
It seems he only cited Obama's jet fuel consumption, and no one else's. The juxtaposition of the two numbers seems to indicate they're related, but they're not.
Wired says the Paris conference will emit 300,000 tons of CO2, which isn't that much really -- it's what just 18,000 Americans emit in a year -- or as Wired puts it,
"...22 seconds of global CO2 emissions. Add in two weeks of hotels, taxis, espressos, pastries, and wine toasts, and you can probably tack on another half second or so."There is probably some double counting there, since the people are the conference aren't taking taxis at home, or eating pastries at home, or drinking wine at home. But the flying definitely counts extra.
Would it have been better off if everyone stayed home? No -- conferences are valuable, and Web coverage of them seems ever more available. The IPCC conference is more valuable than most, and worth some emissions. The solution to climate change isn't -- and will never be -- living in tents. It's generating the energy we need in ways that do not emit carbon.