International shipping is a major – and rapidly growing – source of greenhouse gas emissions. Agreement to apply a carbon price to shipping can both reduce emissions and raise funds for climate change adaptation and mitigation in developing countries. Two challenges loom especially large after the UN Climate Change Conference in Cancun, Mexico. First, governments must close the gap between the cuts to greenhouse gas emissions pledged so far and those needed to avoid catastrophic climate change. Second, rich country governments must mobilize the money needed to fill the Green Climate Fund (GCF) established in Cancun. Our well-being depends on the urgency with which these twin challenges are confronted. In 2011 a deal to control rising emissions from international shipping could help tackle both.