Is it inevitable that environmental constraints will lead to a reduction in air travel?

Iy’s not inevitable; air travel is too heavily subsidised and to convenient to be pegged back until it is made to bear its full costs.

I like Kerry Green’s idea but the costs of so many tunnels makes the idea impractical. Or does it?

The desire for fast, convenient transportation is forcing the aviation industry as a whole to look for alternative fuels as well as alternative power devices. There will be at least one, if not multiple solutions. The biggest obstacle is the government and the airline companies themselves.

Your article and comments are interesting and well thought out. At this time when people aspire to be able to travel un-hindered to anywhere in the World the use of air transport systems (aircraft) will continue. The only constraint as I see it is the costs associated with the fuels needed to provide the propulsion system for such travel.

Until recently the fact that this fuel is available at huge subsidies to the air transport industry has not been an issue: it now is and it needs addressing. Whilst fuels specifically used for air transport may only consume 12% (I think?) of all the fuels used in transportation it is none the less a large proportion.

We must consider the fact that the aspiring Nations of China and India now rising to become super-economic powers with a population that equally aspires to have access to the same consumerist items as seen in the EU and the USA and the likes it must be a concern for Us All across the World for the consequences. If the aspiring Middle Classes in China and India continue to view what they see in the EU/USA as the model for them then within 20 years I can see there being at least 600 million cars in China and a similar number in India. That must be of greater concern to this debate than to curtail or restrict air transport. It is equally important to note that in this development for personalised transport that the people will not be happy with the locally produced cars but rather the up-market vehicles and in that regards those that consume even more fuel per kilometre.

I suggest the issue must be look at personal transportation first as the effects will be more pronounceable.

Whilst we have seen amazing developments in the reduction of liquid fuel use per kilometre of cars and vans during the past decade this has been out-weighed by the growth in use of same. This is a paradox of issues that has to be addressed. The move to so-called Hybrid drive vehicles that use both liquid fuels and electricity (derived from battery storage) although lauded as a suitable way forwards does not seem to have had much of an impact and I fear will not do so until the prices of these vehicles is brought down drastically. Likewise the development of the Electrically-Driven vehicle is also likely to be stymied because of limitations in range (there is no potential for any personalised piece of transport that has a range of barely 100 kilometres before needing a full re-charge that can take as long as 8 hours! (when the liquid fuel driven vehicles that use Petrol/Gasoline or Diesel can go 550 kilometres on a single tank!) And when the source of power is made from Fossil Fuels like Coal Oil and Natural Gas (do not be hood-winked, yes Natural Gas is also a Fossil Fuel!) Those who suggest this hypothesis are living in cloud-cuckoo land!

No, unfortunately, we have become so used to having vehicles that can be driven these distances with a single recharge of fuel and until we find a convenient alternative to a 60 litre tank of liquid fuel we will be using personalised transport like this well into the 2040s. We will therefore need to concentrate on developing alternative Non-Food based Liquid Fuels (ethanol or Butanol) made from Biomass sources such as the Second Generation (LIgno-Cellulose) based sources we are currently bringing to the fore in the UK (South Milford Yorkshire) Holland (Hardenberg) the Mediterranean Basin (Malta and Israel) Vietnam and the USA (Kentucky etc.) and Canada being promoted by Genesyst or in the Macro-Algae developments by Applied Biofuels Limited (to convert Sequestered Carbon Dioxide) to be used as well as those to make the Biofuels Ethanol or Butanol and the higher order fuels currently being investigated to replace JP-4 and the likes for Aircraft Fuels using similar Genesyst technology. I am at a loss to understand why the industry that is seeking to make the Dry Renewable Energies should be looking at the Water-Laden or Oil Based Biomass materials when there are plenty of alternatives available for this in Photo-Voltaic (P-V) Cells (particularly the Thin-Film technologies using those using Paint-On Films) or in Wind Energy or in Hot Rocks and Sea-Energy and Hydro-Electric systems in conjunction with the Nuclear Powered Reactors that use Fissile Materials that are from the selection of elements that have Short Half-Life Radioactive Decay Periods of Months and Years rather than the 10,000 years or longer from the Transuranic series that were developed in the first instance to make Nuclear Weapons.

There is an opportunity here worth considering and the questions opened up in this article is much wider than the original. As Engineers we should be thinking more Ethically about what we do and I hope that this response does this.

It is only by moving towards a more sustainable reach in Renewable Fuels will we be able to look at the Dry Energies more effectively.

in reply to Kerry Green and Hugh Putt. Tubes above ground would be much cheaper and work just as well