A global deal on airline emissions leaves a number of loopholes.
A carbon tax on airline tickets might sound like a tricky sell, but many airlines already collect a similar levy to raise funds for developing world health initiatives.
Governments and the aviation industry have welcomed new proposed aircraft emissions standards - which rather suggests that the new rules don't go far enough.
The profitability of the airline industry is fragile at best, but that doesn't mean Australia can't make room for another airline.
Aviation, which transformed travel and way of life in the 20th century, is being transformed in the 21st century and faces some difficult 21st-century problems.