For more than two decades, the global climate change regime has been failing to produce outcomes that will genuinely confront the threat of climate change. Recent years have seen greater political will to forge a successful agreement at the 2015 Paris summit. Optimism has been particularly high since China and the US reached a bilateral deal in 2014. But it remains uncertain whether a Paris agreement will be sufficiently ambitious to avoid the worst effects of climate change. Past experience in global climate governance cautions against assuming that any agreement is a step forward. Drawing on green political theory, this paper approaches climate change as part of a wider condition of unsustainability. It defines a standard of ecological rationality for measuring the adequacy of climate agreements, and outlines the importance of strong ecological reflexivity for overcoming the weaknesses in existing global climate change governance.