As I oversee many TENS of tonnes of kerosene being oumped in to the few aeroplanes that I servive each day, I often stand to contemplate how many THOUSANDS of times this amount are being pumped as I stand ther and watch.
Make no mistake that at that rate the reserves of fuel certainly have an end.
There are many alternative fuels getting around, but the long and short of it is that there is no replacement for Kero because the amount of usable energy per kilogram of usable fuel in kero has no alternative.
Natural gas for example produces less energy per kilogram than kero. It's not a replacement. Neither is bio diesel which has or waste vegetable oil, which have a similar energy-weight density - because there's simply not enough of the stuff - it's harder to get than oil where theres a demand.
Oil companies have been pumping sea water down end of life wells for years to extend their life.
Ethanol comes nowhere near petrol let alone kero.
Fuel Cells run on hydrogen. The problem is that Hydrogen is one of the most environmentally destructive fuels available because it is uncontainable as the smallest element, and it redily migrates to the upper atmosphere as the lightest atom, where it happily combines with Ozone. Don't believe the fuel cell propoganda - they are hiding the ozone problem. Nothing can contain Hidrogen.
The simple fact is after kero is depleted - aviation is gone. The industry is hiding that.
Why?
Most businesses don't need to prove profitibility beyond five years to get finance.
Simple.