In 2018 Global CO2 emissions were 31.7 gigatonnes. Aviation's contribution to this was around 859 million tonnnes of CO2 (2.7%)
The OCED in 2011 estimated 2050 global emissions to be between 28 - 49 Gt CO2 per annum in the best and worst case scenarios respectively. ICAO's fuel burn estimates for the air transport industry in 2050 range from 730 Mt to 1.434 Bt of fuel the equivalent of 2,3 - 4,5 Gt CO2 per year, making it responsible for between 5% and 16 % of global emissions in the best and worst case scenarios.
If current crude oil production levels are sustained, by 2050 the aviation sector could take up between 16% and 32% of all crude oil production. Currently around 6% of oil is converted to Jet Kerosene. such a change in the scale of production will require significant investment.
Bio-fuels or sustainable aviation fuels (SAF) have savings on CO2 emissions produced compared to burning jet fuel, typically somewhere between 20% to 80%. Global bio-fuel production is increasing as alternatives to fossil fuels are sought.
However, SAF at present cannot replace all fuel use as jet fuel has essential lubricant and cooling properties, meaning they must be mixed with conventional jet fuel for safety. This problem may be overcome in the future with new technology, but it means even when using SAF at least 50% of emissions still coming from jet fuel.
Bio-fuels also have other non CO2 benefits. NASA carried out tests on Alternative Fuel
Effects on Contrails and Cruise Emissions which showed a significant decrease in soot emission when
using SAF of between 50%-70%
The Committee on Climate Change cautiously estimate SAF use at 10% by 2050. However, ICAO is heavily reliant on SAF to meet Carbon Neutral Growth (CNG) aspirations.