The warm-glow of giving is one mechanism proposed to account for high levels of human cooperation. However, little is known about how warm-glow can be harnessed to sustain long-term cooperation to benefit wider society (vaccinations, blood donation). We argue that the power of warm-glow to sustain long-term cooperation cools offs over time but can be warmed-up with a simple intervention message. We test, and confirm this prediction, in a field-based experiment (n = 5,821) comparing warm-glow versus positive affect messages to predict long-term cooperation (blood donation) and confirm our findings in a subsequent implementation study comparing donation attendance in a 3 year pre-implementation period, prior to the warm-glow message being sent to all 1st time donors in Australia (Ns = 90,317, 93,430 & 89,606) to a 2 year post-implementation period (Ns = 81,766 & 88,551). Exogenously manipulated warm-glow can encourage long-term cooperation that benefits society. Wider societal implications are discussed.