Depending on the penetration level and the scenario considered, wind and solar technologies allows for a 30-60% reduction of C02 emissions in the short term. This reduction on carbon emissions, however, is not always confirmed in the long term. Introducing renewables into an electricity system whose baseload technology emits C02, such as coal, will definitively reduce the C02 emissions from the electricity sector in both the short and the long term. However, this will not hold when the baseload technology displaced by renewables does not emit C02, as is the case for nuclear energy. In this case instead, the electricity produced by fossil-fuelled technologies tends to increase, and C02 emissions will be generally higher than in the reference scenario without renewables. In other words, nuclear energy is more efficient than variable renewable energy in limiting C02 emissions as it will not induce a shift towards carbon-intensive peak-load technologies.