The WJEC seems to like this "market failure" stuff. In fact, I had to do a whole question on their specimen paper about carbon emissions and relate it back to economics. And I resisted the urge to spell it out, simple as simple does, that market failure was utter garbage.
Why are airline passengers not paying the "full cost of their flight" at present, one of the questions asks. They obviously want a generic "it's market failure because it doesn't take into account the external cost of pollution" answer. But that's just the start. To what extent might increasing taxes on air travel reduce carbon emissions from air travel asks the next - that's hardly economics for starters, and my answer if given free rein would be that individuals should not be forced to cough up to pay some fake scientists for dodgy theory.
In fact, on the final question asking if pollution permits were the best way to reduce CO2, I wrote, within the answer, "Since it the theory is questionable the government should not get involved", obviously in a more Orwellian-taught-to-the-test way.
I had an hour's worth of questions on that.
But the point is that we get all this "market failure" stuff, generally from lefties, who say that the market has failed to allocate resources efficiently. Says who? Those who use the market, who are willing to choose the intersection of supply and demand, certainly find it efficient - that's equilibrium for you. But who says that pollution is a failure of the market? Who says that we should distort markets to implement some crazy theory? Generally those on the authoritarian left who want the government to gain more power, to implement more legislation, etc.
Why should I be forced, by a government, to pay more because they think that we're making the world warm up? The answer's simple - I shouldn't.
What is market failure? There's no such thing. It assumes markets are perfect, and they aren't. The only way a market can "fail" is when government makes it.