Fossil fuels are the accumulated remains of prehistoric plant and animal bodies that decompose undisturbed over millions of years to form hydrocarbon deposits. Once they are used they cannot be replaced for tens of thousands of years, hence they are a non-renewable energy source. These deposits may be coal, oil, petroleum or natural gas, which can be used as fuel for electricity, cars and other activities.
Fossil fuels in the United States alone make up 90% of the country’s total greenhouse gas emissions.
Fossil fuels are currently the world’s primary sources of energy, with petroleum providing 36.8%, coal 26.6% and natural gas 22.9% of energy production globally. This amounts to a 86% share for fossil fuels as a primary energy source. Non-fossil sources, are less carbon-intensive sources of energy. However these technologies, such as hydroelectric, nuclear, geothermal, solar, tide, wind and biofuels, currently provide just 14% our energy.
Composed of plant and animal matter, fossil fuels are very high in carbon. This means that when they are burnt for fuel, they release that carbon into the atmosphere and contribute to the greenhouse effect. The IPCC states that fossil fuel use is the primary contributor to increased CO2 levels, with deforestation providing another significant but smaller contribution.
Rising populations in many developing countries, and unsustainable consumption patterns in developed countries is placing increased pressure on demand for fossil fuels. As a result, we are depleting non-renewable fossil fuel deposits and burning pumping vast quantities of greenhouse gases into the atmosphere, contributing to global warming.
Significantly, developing countries are increasing their use of fossil fuels as a source of cheap electricity. For instance China is reportedly building two new coal plants per week on average, and already consumes far more coal than the United States.
Nevertheless, today’s economically developed countries have also contributed greatly to global warming from burning fossil fuels that. Reduction of CO2 emissions from fossil fuels needs to occur in both developed and developing countries. In addition, developed nations need to facilitate the financing, transfer, and deployment of renewable energy technologies to developing economies.
 Osman Chughtai and David Shannon, ‘Fossil Fuels’, University of Michigan,
 Hegerl, G.C., F. W. Zwiers, et. al., 2007: ‘Understanding and Attributing Climate Change’. In: ‘Climate Change 2007: The Physical Science Basis’. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, at. al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA,http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9.html