ABSTRACT
Human contributions include increased levels of carbon dioxide (CO2) and other greenhouse gases (GHG) in the Earth’s atmosphere. One of the
most significant ways people contribute to greenhouse gases is by burning fossil fuels (oil, coal, natural gas). Each year, we release about 7 billion tonnes (t) of ancient stored carbon (1 tC = 3.66 tCO2 equivalent) into the atmosphere by burning fossil fuels. [7, 8] It is estimated that natural processes can only absorb about half of that amount. Most of the burning occurs in running automobiles, in heating homes, powering factories, and in generating electricity. The clearing of land contributes as well. When trees are cut down in the context of deforestation, they are no longer available to absorb CO2 from the atmosphere, and as they decay or burn, they actually release CO2. Many scientists estimate that global carbon emissions need to be reduced by ~70%, a figure consistent with the goal of limiting the global average temperature increase to 2 °C (relative to pre-industrial levels), if the world is to avoid dangerous climactic changes. [7, 9]
The 20th century has been an era of petroleum that has provided humanity with a wide range of fuels and chemicals that have influenced most aspects of human life. About 90% of fossil oil is used in the production of energy (power, heat, and transport fuels), while ~10% is used to produce chemicals and materials. [10] In 2008, the total world energy consumption was ~5×1020 J with 78% derived from fossil fuels, 2.8% from nuclear power, 13% from traditional biomass, used primarily for cooking and heating, 3.2% from hydro-
power, 1.4% from biomass/solar/geothermal hot water/heating, 0.6% from biofuels, and 0.7% from wind/solar/biomass power generation, i.e. 19% from renewables (Figure 1.2). [11] Global renewable energy capacity grew at rates of 10-60% annually for many technologies during the five-year period from the end of 2004 through 2009.
