this way low initial rates can foster political acceptance and give stakeholders time to adjust while increases over time guarantee stable revenue and maintain environmental effectiveness if uncertainty about the predictability and longevity of a tax rate emerges investors may regard the risk of lowcarbon energyefficient or pollutionreducing investments to be too high at the same time incentivising private investment requires additional measures to minimize risk and create stable investment frameworks that guarantee or at least increase the probability of a safe return such measures can include lowcost loans for private investors accelerated depreciation preferential interest rates or for renewable energy longterm power purchase agreements cottrell fortier and schlegelmilch