Though I have argued that jet flights are the one application that cannot be easily substituted out using electricity, we are not out of options.
Jet Fuel can be synthesized from natural gas, coal, biofuels or a number of other more esoteric processes.
It's likely, however, that the expense of flights will be higher than they are today because of a combination of demand and limited availability of jet-fuel compared to todays near ubiquity of the fuel.
Nevertheless, it's unlikely that jet-flights will disappear entirely because
1. We can still do it due to the ability to provide jet-fuel through alternative pathways
2. There are applications that require jets such as high-speed transatlantic (or transpacific) journeys where traveling by ship won't cut it.
In other land based use-cases, as stated elsewhere we could substitute regular rail, buses or personal electric vehicles. In applications that required fast transit times, at least in Europe and Asia there are high-speed rail links.
In any case, the coal-to-liquids application has just been demonstrated on a trial basis by SASOL of South Africa as below:
"Lanseria, Johannesburg – Sasol, the world’s leading producer of synthetic fuels from coal and natural gas, today flew the world’s first passenger aircraft exclusively using the company’s own-developed and internationally approved fully synthetic jet fuel.
The fuel, produced by Sasol’s proprietary Coal to Liquids (CTL) process, is the world’s only fully synthetic jet fuel to have received international approval as a commercial aviation turbine fuel.
Sanctioned by the global aviation fuel specification authorities the jet fuel is the first fully synthetic fuel to be approved for use in commercial airliners. This marks a significant development in the adoption of clean burning alternate fuels for the aviation industry. The engine-out emissions of Sasol’s synthetic jet fuel, are lower than those from jet fuel derived from crude oil, due to its limited sulphur content.
The historic flights, from Lanseria Airport in Gauteng to Cape Town, kicked-off Sasol’s 60th birthday celebrations, by staging a fly-past at the opening of the Africa Aerospace and Defense (AAD) 2010 exhibition at Cape Town’s Ysterplaat Air Force Base. "
Original story is here: http://www.sasol.com/sasol_internet/frontend/navigation.jsp;jsessionid=PQSDEWYJUK0WHG5N4EZSFEQ?articleTypeID=2&articleId=28500003&navid=1&rootid=1