As by‐products, emissions follow economic fluctuations. Ignoring this fact in environmental policies can lead to unexpected emissions fluctuations and an increase in intervention costs. Using a real business cycle model, we compare two policies: a fixed tax policy where the price is constant over time and a variable tax regime where the tax rate is set at the beginning of each period. We find that while both programs result in lower emissions, a variable tax regime is preferable since first, it can ensure that the maximum welfare is always achieved, and second, it is more effective in stabilising emissions.