  Properly coordinating cooperation is relevant for resolving public good
problems such as clean energy and environmental protection. However, little is
known about how individuals can coordinate themselves for a certain level of
cooperation in large populations of strangers. In a typical situation, a
consensus-building process hardly succeeds due to lack of face and standing.
The evolution of cooperation in this type of situation is studied using
threshold public good games in which cooperation prevails when it is initially
sufficient, or otherwise, it perishes. While punishment is a powerful tool to
shape human behaviours, institutional punishment is often too costly to start
with only a few contributors, which is another coordination problem. Here we
show that whatever the initial conditions, reward funds based on voluntary
contribution can evolve. The voluntary reward paves the way for effectively
overcoming the coordination problem and efficiently transforms freeloaders to
cooperators with a perceived small risk of collective failure.
