Reading the curve from cheap to expensive abatement
A marginal abatement cost curve plots emissions reductions in order of increasing cost per ton. The leftmost bars are the no-regrets measures: efficiency gains, methane capture, gas plant maintenance that reduce emissions and save money. Moving right, reductions get pricier: fuel switching, industrial electrification, carbon capture. The curve's shape reveals which abatements are obvious wins and which require heavy investment or behavior change.
Using MAC curves to set climate targets
Policymakers use MAC curves to answer: at what carbon price will actors voluntarily abate? A $50/ton price will trigger all abatements up to that point on the curve; a $100/ton price unlocks more expensive options. The curve is not static: technology improvements (cheaper solar, battery storage) shift it downward over time, making future reductions cheaper. But the curve hides heterogeneity: what is cheap for a large utility may be prohibitively expensive for a small firm, so policy must account for economies of scale and distributional impacts.