Die Dis cus si on Pape rs die nen einer mög lichst schnel len Ver brei tung von neue ren For schungs arbei ten des ZEW. Die Bei trä ge lie gen in allei ni ger Ver ant wor tung der Auto ren und stel len nicht not wen di ger wei se die Mei nung des ZEW dar.Dis cus si on Papers are inten ded to make results of ZEW research prompt ly avai la ble to other eco no mists in order to encou ra ge dis cus si on and sug gesti ons for revi si ons. The aut hors are sole ly respon si ble for the con tents which do not neces sa ri ly repre sent the opi ni on of the ZEW. Abstract: From a current perspective the Paris Agreement is not sufficient to limit the global mean temperature below 2°C above pre-industrial level as intended. The Agreement stipulates that parties review, compare and ratchet up efforts to combat climate change over time. Within this process, commitments heavily depend on what has been already achieved and this status-quo reflects an important reference point serving either as commitment advice or potential threat. We present an experimental study that is specifically designed to incorporate the effect of a status-quo via pre-existing contribution levels under endowment heterogeneity in a game in which participants make voluntary contributions to a public good. Our participants are sampled from the United Nations Youth Associations Network, representing participants from 51 countries. Members from developed and developing countries take decisions against the background of different initial levels of endowments and pre-existing contributions. Our analysis indicates that starting with ambitious pre-existing contribution levels can foster aggregate mitigation levels. Falling behind this status-quo contribution levels by reducing the public good appears to be a strong behavioral barrier. These observations might provide support for the basic structure of the Paris Agreement with Nationally Determined Contributions and the possibility to adjust them, even if a downward revision of national targets may not be precluded.Keywords: Paris Agreement; Nationally Determined Contributions; Ratched-up mechanism; International public goods; Online experiment JEL classification: H41; C91; F53; Q58 Acknowledgements: Special thanks to the United Nations Youth Associations Network (UN-YANET) and in particular Tjalke Weber and Anna-Katharina Deininger for their support in conducting this experiment. We also thank seminar and conferences audiences in Athens, Bremen, Kassel, Kiel, and Münster for constructive and very helpful comments. This project was made possible through funding from the Leibniz Association (funding code SAW-2014-ZMT-1 317).