A novelty of the new Paris Agreement is the inclusion of a process for assessment and review of countries’ nationally determined pledges and contributions. The intent is to reveal whether similar countries are making comparable pledges, whether the totality of such pledges will achieve the global goal, and whether, over the coming years, the contributions actually made by countries will equal or exceed their pledges. The intent is also to provide an opportunity for countries to express their approval, or disapproval, of the pledges and contributions made by individual countries. Here we report the results of a lab experiment on the effects of such a process in a game in which players choose a group target, declare their individual pledges, and then make voluntary contributions to supply a public good. Our results show that a review process is more likely to affect targets and pledges than actual contributions. Even when a review process increases average contributions, the effect is relatively small. As the window for achieving the 2 °C goal will close soon, our results suggest that, rather than merely implement the Paris Agreement, negotiators should begin now to develop complementary approaches to limiting emissions, including the adoption of agreements that are designed differently than the one adopted in Paris.