Methane, CH4

A serious concern that IPCC has raised over the years is the potential for a severe feedback event to occur with the release of methane from regions of permafrost, or from hydrates from the seabed of the oceans. 

A study on alternative fuel use found an interesting effect that shows that all news is not bad news... however, the overall situation suggests that we are heading towards challenges.

"Given the predicted growth of aviation and the recent developments of alternative aviation fuels, quantifying methane (CH4) and nitrous oxide (N2O) emission ratios for various aircraft engines and fuels can help constrain projected impacts of aviation on the Earth’s radiative balance. Fuel-based emission indices for CH4 and N2O were quantified from CFM56–2C1 engines aboard the NASA DC-8 aircraft during the first Alternative Aviation Fuel Experiment (AAFEX-I) in 2009. The measurements of JP-8 fuel combustion products indicate that at low thrust engine states (idle and taxi, or 4% and 7% maximum rated thrusts, respectively) the engines emit both CH4 and N2O at a mean ±1σ rate of 170 ± 160 mg CH4 (kg Fuel)−1 and 110 ± 50 mg N2O (kg Fuel)−1, respectively. At higher thrust levels corresponding to greater fuel flow and higher engine temperatures, CH4concentrations in engine exhaust were lower than ambient concentrations. Average emission indices for JP-8 fuel combusted at engine thrusts between 30% and 100% of maximum rating were −54 ± 33 mg CH4 (kg Fuel)−1 and 32 ± 18 mg N2O (kg Fuel)−1, where the negative sign indicates consumption of atmospheric CH4 in the engine. Emission factors for the synthetic Fischer–Tropsch fuels were statistically indistinguishable from those for JP-8." [1]

Reference: 

[1] Aircraft Emissions of Methane and Nitrous Oxide during the Alternative Aviation Fuel Experiment (Gregory W. Santoni, Ben H. Lee, Ezra C. Wood, Scott C. Herndon, Richard C. Miake-Lye, Steven C. Wofsy, J. Barry McManus, David D. Nelson, and Mark S. Zahniser); Environmental Science & Technology 2011 45 (16), 7075-7082DOI: 10.1021/es200897h