Air travel is a source of emissions that no one really has a good answer for. Scientists in China may be close though with a process that uses plant waste to create aviation fuel which could lead to the deduction in CO2 from planes.
The researchers are looking into a biofuel that is produced from agriculture and lumber waste. It relies on cellulose and is renewable (an inexpensive, which is nice). The resulting fuel is more efficient which can make flights more efficient.
At this time, the fuel has only been created in a library environment but the researchers are hopeful that it can be produced at scale but they do need to get past the hurdles of parts of the process that are not environmentally friendly.