(on average) than during production. For electric cars, emissions caused during operation depend on energy sources used to produce electricity and thus vary a lot geographically. Studies suggest that when taking into account both production and operation, electric cars would cause more emissions in economies where production of electricity is not clean, e.g., it is mostly coal based. For this reason, some studies found that driving electric cars is less environmentally damaging in western US states than in eastern ones, where less electricity is produced using cleaner sources. Similarly, in countries like India, Australia or China, where large portion of electricity is produced by using coal, driving electric vehicles would cause larger environmental damage than driving petrol vehicles. When justifying use of electric cars over petrol cars, these kinds of studies do not provide sufficiently clear results. Environmental impact is calculated based on fuel mix used to produce electricity that powers electric cars. However, when a gas vehicle is replaced by an equivalent electric vehicle, additional power must be installed in electrical grid. This additional capacity would normally not be based on the same ratios of energy sources ("clean" versus fossil fuels) than the current capacity. Only when additional electricity production capacity installed to switch from petrol to electric vehicles would predominantly consist of clean sources, switch to electric vehicles could reduce environmental damage. Another common problem in methodology used in comparative studies is that it only focuses on specific kinds of environmental impact. While some studies focus only on emission of gas pollutants over life cycle or only on greenhouse gas emissions such as CO2, comparison should also account for other environmental impacts such as pollutants released otherwise during production and operation or ingredients that can not be effectively recycled. Examples include use of lighter high performing metals, lithium batteries and more rare metals in electric cars, which all have high environmental impact. A study that also looked at factors other than energy consumption and carbon emissions has suggested that there is no such thing as an environmentally friendly car. The use of vehicles with increased fuel efficiency is usually considered positive in the short term but criticism of any hydrocarbon-based personal transport remains. The Jevons paradox suggests that energy efficiency programs are often counter-productive, even increasing energy consumption in the long run. Many environmental researchers believe that sustainable transport may require a move away from hydrocarbon fuels and