Electricity production is the biggest chunk of greenhouse emissions, accounting for 29% while transportation accounts for 21% [0]. Within transportation, emissions from airplanes only account for 9%. Extrapolating, airplanes are then calculated to be responsible for about 1.89%. On the other hand, emissions from vehicles and trucks emit 17.4%.

Applying Pareto's rule, we're better off focusing our efforts on decreasing emissions on electricity production and vehicles.

[0] https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emis...