As Earth Week reminded us recently, the quest to find a sustainable alternative to fossil fuel is becoming more urgent.

While the earliest aircraft piston engines were powered by gasoline, Jet A-1/Jet A kerosene has been used by the air transport industry since the 1950s.

A global jet fuel distribution system has also evolved to annually supply 85 billion gallons of the stuff to 3,500 airports and 13,000 aircraft worldwide.

The properties of Jet A-1 and current fuel formulations have implications for every part of the aviation industry from engine design to distribution. For a new fuel to enter the picture, it has to be a “drop-in” replacement, have favorable economics, not create competition with world food supplies, and have a better emissions profile than existing jet fuel. A tall order.

The drivers behind the quest for alternative fuels are partially a response to the long-term projections of unsustainable Jet A-1/ Jet A consumption – particularly as most of the future demand will come from developing countries.

The April ruling by the U.S. EPA on six greenhouse gases (GHG) as health hazards is just the latest signal that airlines will have to count their emissions.

The search for alternative fuels has been around for a long time. Hydrogen as a fuel for jet engines was tested as early as the 1930s. Pratt and Whitney’s 304 jet engine used liquid hydrogen in 1957. Fischer-Tropsch (FT) synthesis emerged from research in the 1920s in Germany. Microalgae were proposed as biofuels in the early 1950s at MIT.

However, with innovation, timing is everything – and perhaps the time for alternative jet fuels has finally arrived.

The big attraction of FT synfuels is their “drop-in” quality, requiring no change to engines or infrastructure. So FT synfuel is a step towards solving the supply problem, although perhaps not the GHG problem.

Biodiesel is the conversion of vegetable oils or animal fats into an alternative to petroleum-based diesel. A process of combining the oils and fats with methanol converts them into fatty acid methyl esters or FAME. FAME has properties similar to diesel but is not a “drop in”.

Liquid hydrogen and methane have a high-energy content and are compatible with gas turbine engines. They are almost ideal in terms of low GHG emissions, but their low density requires completely new aircraft fuel systems design, larger aircraft and a new distribution infrastructure.

So while there is potential for hydrogen applications in power generation and road transport, the consensus is that use in commercial aviation is several decades away.

Meanwhile, biofuels derived from biomass can be converted to jet fuels by extracting natural oils and using hydroprocessing to covert into aviation fuels without the FT reaction. First generation biofuels such as ethanol, corn and soybeans had the problem of competing for land with food production and encouraging deforestation - as well as not meeting specifications for Jet A-1.

Second generation biofuels such as Jatropha, babassu, switchgrass and halophytes (plants that root in salt water) present opportunities to grow a multitude of bio-fuels but without impact on food crops or deforestation. An additional advantage of these plants is that they absorb CO2 emissions as they grow.

However, the big challenge for second generation biofuels is the low yield per hectare. One estimate suggests twice the area of France would be required to produce today’s jet fuel requirements.

Boeing, Airbus, Shell and many others have now embraced algae, often referred to as a third generation biofuel. Without leaves or stalks, it is a very efficient energy source; uses much less land area and has a low carbon footprint. It also yields 15 times as much oil as second generation biofuels and has the added benefit of being a carbon sink.

The FAA considers the use of algae-based biofuels to be feasible in eight to 10 years. Boeing estimates that algae could produce all the world’s jet fuels in an area the size of Belgium. So good news for France.

Energy is deeply rooted in our economic, social and political psyche. New technologies are creating a surfeit of possibilities, but in the end, these have to be rooted in reality. How much change the existing energy infrastructure will be willing to sustain has to do with the degree of global urgency on energy security and climate change.

Al Gore said in An Inconvenient Truth that old habits and new technology yield unpredictable consequences. In the long term, alternative fuels will be matched with new engines and infrastructure and develop new habits.

In the immediate future, the challenge is to find a new fuel that fits well with our old habits.

Dr. Paul Forster is the Adjunct Professor, Hong Kong University Business School of Science & Technology and a member of the HongKong Climate Change Business Forum. His current focus includes carbon management in the logistics industry.