Despite the overwhelming evidence for global warming and recommendations to respond to the climate challenges, the implementation of pro-environmental behavior (PEB) remains difficult for many individuals. One key notion in this context is that the reconfiguration of behavior generally requires cognitive effort. In a preregistered study entailing both laboratory and online samples we tested in how far participants are willing to invest cognitive effort for a pro-environmental cause (eco reward) and how this differs from cognitive effort for personal outcomes (own reward). Both eco and own reward led to response speeding and reduction of interference compared to no reward trials in a cognitive control task. However, the speeding effect was significantly smaller for eco reward trials, resonating with the notion that pro-environmental outcomes have a lower motivational value than personal ones – despite equal probability and magnitude of the associated monetary incentive. While present in the full sample, this difference was most pronounced in the online sample, which might reflect a weaker contribution of social desirability in this context. By singling out cognitive effort and the inherent costs thereof (rather than temporal and/or financial costs), the current paradigm can be used to test which factors and interventions might increase or decrease the willingness to allocate cognitive resources towards pro-environmental goals – which is key for initiating and also maintaining behavioral change.