ABSTRACT
Society has reached high levels of development during the last century. This progress, however, has been achieved at the expense of extensive consumption of natural resources, such as petroleum, natural gas and coal. These fossil fuel resources took millions of years to be formed, and they are currently being consumed at a rate that is orders of magnitude higher than their natural regeneration cycle, making them non-renewable sources of energy. The most recent data available for world energy consumption indicate that society still remains highly dependent on fossil fuels at the present time. For example in 2008, fossil fuels supplied 85% of the total energy consumed in the US, [1] and almost 80% of the energy produced in the European Union. [2] These fossil fuel resources are used to provide energy for various sectors of society (i.e., residential, commercial, indus-
trial, transportation and electrical power), among which the transportation sector is the largest and fastest growing energy sector, responsible for almost one third of the total energy consumed in the world. Moreover, a large fraction of the energy for the transportation sector (96%) is currently derived from petroleum. [3]
Three important issues are associated with the large-scale utilization of fossil fuels: availability, global warming and uneven geographic distribution of reserves. Fossil fuels are fi nite and, as indicated above, their current consumption rate is higher than their corresponding regeneration rate, leading inevitably to depletion. Projections for the near future indicate that world energy consumption will increase by 35% over the next 20 years to meet the growing demand of industrialized countries and the rapid development of emerging economies, [4] and world demand for petroleum will raise by 30%, reaching 111 millions of barrels per day in 2035. [5] Taking into account these forecasts and current data of proven reserves, it has been estimated that oil, natural gas and coal will be depleted within the next 40, 60 and 120 years, respectively. [6] In the case of petroleum, many researchers predict a more dramatic situation and estimate that the global production of oil will reach a maximum in the year 2020 and decay thereafter. [7]
Global warming is, possibly, the most dramatic and known collateral effect produced by the massive utilization of fossil fuels. [8] Fossil fuels are transformed into energy by means of combustion reactions, leading to net emissions of CO2, a strong greenhouse gas, into the atmosphere. Accordingly, the extraction of fossil fuels for energy production has allowed a large part of the carbon stored in the earth for millions of years to be released in just a few decades.
