I make this commitment to stop flying, until we reduce our present carbon emissions to zero by 2030 or sooner, or unless airlines change their carbon based fuels to a completely renewable source. For the present moment I do not believe that alternative biological fuels can be that alternative for two reasons. First, that we must reduce our emissions quickly. Second, that we cannot use plants that presently are carbon sinks, or improve the soil, or take the place of food.
— Helen Hutchison