Air flight has a huge negative impact on the problem of global warming and carbon emissions. While the primary greenhouse gas emission from powered aircraft in flight is carbon dioxide, other emissions may include nitric oxide and nitrogen dioxide, sulfur oxides, carbon monoxide (which bonds with oxygen to become carbon dioxide), incompletely burned hydrocarbons, tetra-ethyl lead, and hydroxyl. Alternative flight technologies are being developed; some are even influenced by the designs of the past.
One alternative to flight is the airship (also known as dirigibles or aerostats). These lighter-than-air aircraft fly by having a large envelope (balloon) filled with a lifting gas, most often helium. The most well known airship is the ill-fated Hindenburg which was filled with the flammable lifting gas, hydrogen (due to the limited supply of helium). Airships can be propelled and steered and one of the most well-known modern airship is the Goodyear Blimp.
Unfortunately, there is a sustainability problem with most airships: they use a non-renewable resource of helium gas. Although helium is readily abundant in the atmosphere there is currently not a practical method way of recovering it so modern use of helium is derived from underground stores commonly associated with natural gas stores. Just like fossil fuels, once the helium reserve is used up it will take millions of years to replenish.
Robert Richardson, professor of physics at Cornell University in Ithaca, New York, believes that party balloons filled with helium are too cheap because of the government’s subsidy of helium. He believes they should really cost around $100 each to reflect the scarcity of helium gas.
On the plus side, the use of helium does not have any of the other nasty emissions associated with fossil fuels so using helium will not contribute to global warming.
Some modern airships run on other lifting gasses including hot air (as is used by a hot air balloon), hydrogen (but this is highly flammable), steam (heat-resistant material is needed), ammonia (a toxic gas), methane (highly flammable), goal gas (poisonous and polluting), neon (rare and expensive), nitrogen (only 3% lighter than air).
Given all the tradeoffs of these lifting gasses the most sustainable and environmentally friendly method to lift an airship is the use of hot air or a hybrid of hot air and another lifting gas. A well-known example of this hybrid technology is the Rozière Balloon originally built in 1785. This type of balloon has separate chambers for a non-heated lifting gas as well as hot air. The advantage of a Rozière is that it allows some control of buoyancy with much less use of fuel and it can sustain long flight times, up to several days or even weeks.
Newer technologies for airships are being constantly developed. Just recently, a small company Zero2infinity announced their design of the Bloon, a 400 foot diameter balloon that will carry tourists 22 miles into the upper atmosphere where they can have a near-space experience for several hours before they return to the earth. The company has tested unmanned versions of the design and hopes to be fully operational by 2013.