Inequality, communication and the avoidance of disastrous climate change

International efforts to provide global public goods often face the challenges of coordinating national contributions and distributing costs equitably in the face of uncertainty, inequality, and free-riding incentives. In an experimental setting, we distribute endowments unequally among a group of people who can reach a fixed target sum through successive money contributions, knowing that if they fail they will lose all their remaining money with 50% probability. We find that inequality reduces the prospects of reaching the target, but that communication increases success dramatically. Successful groups tend to eliminate inequality over the course of the game, with rich players signalling willingness to redistribute early on. Our results suggest that coordinative institutions and early redistribution from richer to poorer nations may widen our window of opportunity to avoid global climate calamity. Preserving the global climate commons is one of the biggest collective action problems humanity has ever faced (1 ); evidence suggests that we have already exceeded the planet’s “safe operating space” in the climate system (2 ). Containing the rise in global mean temperature is a global public good, where the benefits of efforts to reduce emissions are shared by all, irrespective of individual contributions. Such disconnect between individual and collective interest is a prime cause of public goods under-provision (3 -7 ). Whereas public goods experiments under controlled conditions oversimplify the complexity of international climate action (8 ), they nonetheless shed light on the relative importance of factors that affect its success (9 ). Standard public good games are concerned with the creation of a collective gain (10 -15 ). Climate change, however, is about avoiding an uncertain public bad. This has been framed as a “collective-risk social dilemma” of sequential contributions to a public climate fund aimed at avoiding a probabilistic loss arising if the target is missed (16 ). Participants in this threshold public goods experiment behaved less rationally than theory predicted, often failing to avoid simulated dangerous climate change due to miscoordination in final rounds (17 ). But what will be the outcome if participants can communicate with one another? And what is the effect of inequality on effort coordination? International progress in reducing CO2 emissions has been remarkably slow, not least because of free-riding incentives, as partly captured by the threshold public goods game of loss avoidance (16 ). The core of this game, however, is a problem of coordination: players are best off when synchronizing contributions in the face of multiple equilibria (3, 18 ). The game therefore calls for communication. The latest climate agreements negotiated in Copenhagen and Cancun introduced