The degree to which we use energy has far-reaching consequences. For example, the simple act of driving to work uses fuel that is ultimately tied to both international conflict and global climate change. The success of modern civilization is fundamentally linked to our ability to harness energy, primarily in the form of fossil fuels like oil, coal, and natural gas. As shown in Figure 1, in 2008 the world consumed about 500 quadrillion—a million billion—British Thermal Units (Btu) of energy, 85% of which came from burning fossil fuels (for reference, a gallon of gasoline provides about 125,000 Btu [2]). But what’s all the buzz about fossil fuels anyway? Why aren’t they a sustainable option?

Figure 1. Historical and projected World Energy Consumption by Fuel Type, in units of quadrillion Btu [1]. Liquids (blue line) consist of petroleum and petroleum derivatives.

Fossil fuels are carbon-based materials found in the Earth’s subsurface, formed from decomposing plant and animal remains over the span of millions of years [3]. They are attractive as energy sources primarily because they can be transported with relative ease and the energy delivered is highly concentrated.

However, there are major drawbacks to using fossil fuels for primary energy. First, fossil fuels are limited in supply. If we run out of fossil fuels without a backup plan, our energy demands will be unmet. We’re not sure how much fossil fuels we have left, but we can estimate the quantity of proven reserves—the amount of fossil fuels that would currently be profitable to extract [4]. There are approximately 1,471 billion barrels of proven oil reserves [1]. In 2011 the world consumed an average of 89 million barrels of oil per day [5]. At this rate the oil reserves will last us for only 45 years. We can do a similar calculation for natural gas and coal: at our current consumption rates, natural gas will last us around 62 years and coal will last us around 130 years [1,6]. We’ve often heard the argument that estimates of proven reserves for oil and natural gas tend to increase; this is because improvements in extraction technology and increasing demands change the definition of what is profitable to extract [4]. Nonetheless, the point remains that fossil fuel resources are finite and, based on the calculations above, will not allow human societies to flourish for timespans longer than 50-200 years.

A second drawback to relying on fossil fuels is that approximately 42% of the world’s oil is produced by nations in the Organization of Petroleum Exporting Countries (OPEC), and nearly half of that comes from Saudi Arabia, Iran, and Iraq [7]. There are significant national security concerns related to depending upon and financially supporting these politically volatile nations, some of which have links to terrorist networks.

Fossil fuel use is also unsustainable for our health and the safety of the environment. For example, emissions from coal-fired power plants include particulate matter and mercury, and are responsible for respiratory illness and premature death especially in vulnerable populations like children and the elderly [8]. In the United States, coal-fired power plants are responsible for 40% of annual mercury emissions and 76% of acid gas emissions; it is estimated that 13,000 deaths per year are due to particulate pollution [9]. Due to the Clean Air Act, the United States has instated more measures to regulate pollutants than developing countries. Poor regulations pose a serious public health problem for countries like China, where over 70% of energy needs are met by burning coal [10]. Unfortunately, coal plant emissions are not just local, meaning that longer-lived pollutants like fine particulate matter, mercury, and cancer-causing chemicals get transported from countries with poorer air quality standards to other areas of the globe [9]. Further, coal has a considerable hidden cost associated with economic, health, and environmental impacts. It is estimated that the combined cost of mining, transportation, processing, and combustion to the United States alone can range from 300 billion to over 500 billion dollars annually [11]. In other words, we pay a high price for coal in the form of health care costs and higher taxes but coal appears cheap only because the price is not directly on our electricity bills. If we account for these hidden costs, coal-generated electricity is three times more expensive than what we pay directly and suddenly renewable sources of electricity are economically competitive with coal [11]. (For more details on how the true cost of coal is calculated, check out the interactive guide at

Human fossil fuel use is also contributing to global climate change: burning fossil fuels produces the greenhouse gas carbon dioxide as a byproduct. There is increasing evidence that the carbon dioxide produced from burning ancient fuels is accumulating in the atmosphere faster than the land and oceans can take it up. In 2008 alone, the world emitted 30.2 billion metric tons of carbon dioxide from burning fossil fuels. With increases in population and improvements in living standards worldwide, energy-related carbon dioxide emissions are projected to increase by more than 40% of 2008 levels over the next 30 years [1]. This puts the welfare of future human societies at risk because carbon dioxide accumulation in the atmosphere is associated with sea level rise, the melting of glaciers and sea ice, and increases in the frequency of heat waves, droughts, and extreme weather events [12].

These facts paint a grim picture, so what are the alternatives to fossil fuels? While we cannot change the basic need for energy to power our lives, we can continue to develop technology to change where that energy comes from. Fossil fuels took millions of years to form, and it will take that much time for them to be replenished. Yet, our need for energy is immediate. From national and energy security perspectives, it will be important to increase domestic fossil fuel production in the short term, but this still does not address the issues relating to finite supplies, air quality, and human-caused climate change. Instead of continuing to rely upon them in the long term, domestic fossil fuels can be used in the short-term to bolster renewable energy technologies until these technologies are dependable enough to stand on their own.

Sustainable energy, harnessed from renewable resources like the sun, wind, water, and crops, is responsible for meeting only 10% of the world’s energy demands (Fig. 1). What’s fascinating is that in one year, usable but unharnessed sun and wind resources produce 50 times more energy than the world currently consumes [13]. But if there is so much energy around us, why is it so hard for us to shift to sustainable energy sources? As of now, renewable energy technologies are not optimally designed or economically profitable partially because few financial resources are being channeled into their development. That said, all technologies that humans enjoy today (including cars, telephones and electricity!) were once in a stage too young to be considered reliable or profitable for the mass market. However, continued investments gave researchers the resources and opportunities to develop these technologies and maximize performance and functionality. There will never be a magic solution that eliminates all the negative consequences of our energy demands, but we can make educated choices about using and developing energy sources that significantly reduce the social and environmental impacts of our energy use.

Archana Dayalu is an Atmospheric Chemistry graduate student in the Department of Earth and Planetary Sciences.


[1] United States Energy Information Administration. (2011). “International Energy Outlook”

[2] United States Energy Information Administration. (2012). “Annual Energy Review 2011”

[3] United States Department of Energy. “How Fossil Fuels were Formed” (April 24, 2012)

[4] Conger, C. “How much Fossil Fuel is in the Earth?”, Discovery News (September 24, 2012)

[5] International Energy Agency. “Oil Market Report 2012”

[6] United States Central Intelligence Agency World Factbook. “Natural Gas – Proved Reserves” (2011)

[7] United States Energy Information Administration. “2011 World Oil Production”

[8] United States Environmental Protection Agency. “Particulate Matter & Health” (June 15, 2012)

[9] American Lung Association. “Toxic Air: Time to Clean Up Coal-fired Power Plants” (March 8, 2011)

[10] United States Energy Information Administration. “Country Analysis Brief: China”

[11] Harvard School of Public Health. “Explore the True Costs of Coal: The Measureable, Economic, and Qualitative Cost of Coal” (July 1, 2012)

[12] “IPCC, 2007: Summary for Policymakers”, 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, Qin, D, Manning, M, Chen, Z, Marquis, M, Averyt, KB,  Tignor, M, and Miller, HL (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

[13] Jacobson, M, and Delucchi, M. “A Path to Sustainable Energy by 2030”, Scientific American (November 2009)