From TFA:

> Rather than dramatically changing the route of a flight, the trial will mostly involve changing an aircraft's altitude by around 2,000ft.

What if there are more headwinds at that height which require increased fuel use?

	▲	bfc1890 11 hours ago \| parent [-]
		If you have any experience with the majority of airlines, you can be sure they are not planning to spend any significant amount of extra fuel on this problem. I am not a pilot, but I assume once you are at cruising altitude, small altitude changes are a rounding error