Marginal abatement cost curves, which suggest the cheapest approaches to reducing carbon emissions, are out of favor in international climate finance discussions because they are not good tools to use when thinking about systemic and urgent change. On the other hand, international financing studies based on adding up the investment requirements linked to an emissions path to 1.5 degrees of warming produce historically implausible numbers and endanger existing development finance. To close the gap, we need to push the cost curve down (through technology advance) and lower the price of finance (through scalable multilateral development bank support) while protecting development finance and focusing it on where it is most needed: the poorest countries suffering the most from climate change.Marginal cost curves illustrate the costs of getting to lower emissions. The McKinsey Cost Curve (Figure 1) lines up greenhouse gas abatement technologies by their cost per ton of emissions averted.Next to the y-axis are approaches that both reduce greenhouse gas emissions and save money— things like switching to LED lighting and improving building energy efficiency. In the middle are approaches that are cheap but still slightly more expensive than existing higher-emission approaches (think nuclear power over coal power). On the right are approaches that, with today’s technologies, are very expensive per ton of greenhouse gasses abated, like carbon capture and storage.