The purpose of this lesson is for you to review key concepts from Lesson 4 (Energy In-Depth) in EM SC 240N. I strongly encourage you to at least browse through Lesson 4 [1] of EM SC 240N, though that is not required.
By the end of this lesson, you should be able to:
To Read | Lesson 4 Online Content | You're here! |
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To Do |
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If you have any general course questions, please post them to our HAVE A QUESTION discussion forum located under the Discussions tab in Canvas. I will check that discussion forum regularly to respond as appropriate. While you are there, feel free to post your own responses and comments if you are able to help out a classmate. If you have a question but would like to remain anonymous to the other students, email me through Canvas.
If you have something related to the material that you'd like to share, feel free to post to the Coffee Shop forum, also under the Discussions tab in Canvas.
Okay, now let's tie this all together. Modern society is inextricably tied to the availability of energy, as we explored in Lesson 1. We just went through more than two full lessons outlining a lot of reasons to be concerned about the sustainability of modern society, in terms of the 3E's of sustainability and otherwise. Putting these two broad concepts together begs the question: What is sustainable energy?
At the risk of sounding glib, the short answer is that there is no short answer. You will probably not be surprised to know that there is no single or even "correct" answer, that is to say, an answer that everyone can agree with. This has a lot to do with the fact that a singular definition of sustainability remains elusive, but in addition to that there is a lot of uncertainty with regards to both the long- and short-term impacts of energy use, and even how much energy (non-renewable in particular) is left to harvest. I want to be clear that the analysis that follows is not meant to answer the question once and for all, but to help frame some of the key considerations to make when answering the question. As you'll see, I've divided the analysis into sections for a number of energy sources, and subsections that provide information regarding supply, feasibility, and sustainability impacts.
One last thing you should consider prior to reading through this lesson: No matter what mixture of energy sources/technologies that we decide to use, we cannot continue to emit CO2 like we are for long. As detailed in the previous lesson, the reality of anthropogenic climate change and its negative impacts have near universal agreement among experts. You may have read about a United Nations study in 2018 that asserted that humanity will likely need to cut global emissions by 40% - 50% by 2030 (that's really not long from now!) and would need to be 100% carbon neutral by 2050 in order to prevent the worst impacts of climate change (here is an NPR summary [2] and here is the official "Summary for Policymakers" [3] from the UN). In case you were wondering, global emissions have only increased since the start of the Industrial Revolution (see below). In addition, a report authored by 13 federal agencies [4] in the U.S. found that consequences for the U.S. will be dire if emissions are not significantly reduced. This report was particularly notable because it was released by the Trump Administration, which is no friend to climate regulation. (It was only released because it is mandated by Congress, and was immediately downplayed by the Administration, but still.)
Please keep this in mind as you read through these summaries. There is near consensus that humans must significantly reduce net emissions to near zero by mid-century, or we face a very dire future. No energy solution should be considered sustainable in the long term if it emits any carbon dioxide unless carbon reduction technologies are sufficient to offset these emissions. Right now, it is much cheaper to not emit in the first place than to capture and store them.
As you can see in the chart above from the EIA, there is a range of estimates of how much coal is available, each having a varying level of accuracy. Feel free to review the coal page [9] in EM SC 240N for an explanation of these, but the quantity that is most commonly used to indicate "how much is left" is estimated recoverable reserves. The estimated recoverable reserves [10] are the portion of the demonstrated reserve base that can be realistically recovered, taking into consideration restrictions (e.g., "property rights, land use conflicts, and physical and environmental restrictions"). Consider it a very good scientific estimate of how much we can mine in the foreseeable future. The demonstrated reserve base [11] also includes coal that could conceivably be mined commercially, but other issues (e.g., technological and political) make it unrealistic.
So how much coal is left?
There are many benefits to living in the United States, but having easy to understand energy units is not one of them. We use a mixture of Imperial and English units, with the system usually referred to as U.S. Customary units. Most of the rest of the world uses metric units, which are also considered SI units (Systéme international d'unités). Got all that? Good. (Here is an explanation [12] of how convoluted the non-metric units are if you are so inclined.)
Coal in the U.S. is usually measured in tons, which is a unit I'm sure you have heard of, and likely used, before. A U.S. ton is equivalent to 2,000 pounds. However, to prevent confusion with an Imperial ton, the U.S. ton should be referred to as a short ton. A long ton, on the other hand, weighs 2,240 pounds. Finally, the metric ton, which is also known as the tonne, is equivalent to 1,000 kg, or about 2204.6 lbs. To summarize:
Credit: Encyclopaedia Britannica [13] and U.S. EIA [14]
The following are some facts about the feasibility of continued coal use:
Now the bad news: coal has a lot of negative environmental and social impacts.
Probably the most important sustainability issue with coal is that it is so carbon-intensive. It emits about twice the carbon dioxide per Btu as natural gas and is responsible for more carbon dioxide emissions than any other energy source, and the energy sector is the largest source of carbon dioxide emissions worldwide. [21] There are other concerns, according to the EIA, including mercury pollution and acid rain. While coal companies are generally very careful to replant any vegetation destroyed by mining, it can irrevocably compromise the landscape.
One possible solution to this is carbon capture and sequestration (CCS) [22], which is a process that can capture CO2 and bury it (i.e., sequester it) in underground rock formations. Under ideal circumstances, up to 90% of the carbon dioxide will turn into solid rock and thus not pose a leakage threat. (This is usually what is referred to as "clean coal" technology, though it is notable that only the carbon emissions are reduced in "clean coal" plants. Mining waste and particulates and other emissions still make this a relatively "dirty" source of energy.) While promising, there is some indication [23] that CCS might not be as effective as once hoped. It is only beginning to be demonstrated on a commercial scale [24], and some plants have had major issues [25], so the jury's still out.
In short, coal is a reliable energy source and is generally a relatively cheap source of energy as long as externalities are not included. Coal does provide good-paying blue collar jobs, and the loss of coal industries can be devastating to local towns. If externalities were to be included, the price would undoubtedly increase, especially if the social cost of carbon were included. CCS provides some hope for reducing the carbon dioxide emissions of coal use, but other significant sustainability problems will persist.
Unless you've been hiding under a rock for at least the past 10 years, you have heard about natural gas in the news. If you have heard about it, it was most likely in relation to hydraulic fracturing, or simply "fracking." This is a VERY controversial topic at the moment, and with good reason (as we'll see below). Because of this, you have to be careful where you get your information (good thing you are taking this course!). Our old friend Hank provides a pretty clear and unbiased description of fracking in the video below.
One popular misconception is that fracking has only been around since the early 2000s or so. As Hank explains, this is simply not the case. Hydraulic fracturing has been known to increase the output of gas (and oil!) wells since the mid-1900s. The main innovation that has caused the recent fracking boom is directional drilling (sometimes called horizontal drilling). Until relatively recently, oil and gas wells were generally drilled in a straight line. But directional drilling allows operators to change the direction of the drill bits so that they can trace the path of underground rock layers (which are rarely straight up and down). This allows for significantly more gas output per well and is what mainly facilitated the fracking boom.
Like coal, it is impossible to determine the amount of natural gas reserves available in the U.S. or worldwide. Most of the data you will see are based on "proved reserves," which the EIA defines as "estimated volumes of hydrocarbon resources that analysis of geologic and engineering data demonstrates with reasonable certainty are recoverable under existing economic and operating conditions." (Credit: US EIA [27]). Basically, proved reserves are a reasonable estimate of the amount of natural gas that is believed to be in the ground that can be recovered given current technology, and for a profit.
Because the proved reserves are based partially on technology, as technology has advanced - especially with fracking - the proved reserves have generally increased. This is clear in the chart below. The upward trend in available gas would seem odd to the uninitiated since it is a finite resource. But it's important to keep in mind that the chart reflects proved reserves, not the actual amount in the ground.
I'm sure you noticed the dramatic drop in proved reserves from 2011 to 2012 and 2014 to 2015. 2015 has a somewhat simple explanation. The price of natural gas dropped significantly from 2014 to 2015, which "(caused) operators to revise their reserves downward", according to the EIA [30].
In the chart above, shale gas refers to gas that is locked up in the pores of shale in underground layers, as described in the fracking video above. Tight gas refers to gas that is locked up in other formations like low-permeability sandstone. For a full explanation of the terms, see this EIA website [32].
So how much gas do we have left? The EIA provides the following analysis and explanation [33]:
At the rate of U.S. natural gas consumption in 2016 of about 27.5 Tcf per year, the United States has enough natural gas to last about 90 years. The actual number of years will depend on the amount of natural gas consumed each year, natural gas imports and exports, and additions to natural gas reserves.
Like coal, the natural gas infrastructure is well-established, including wells, pipelines, and power plants. As you saw previously, natural gas is relatively cheap. The recent boom in natural gas production has provided a lot of high-paying relatively low-skilled jobs and has generated millions of dollars in royalties for landowners. Increased use and cheaper (up front) cost of natural gas has allowed the widespread replacement of coal-fired power plants, which has resulted in natural gas increasing its share of U.S. electricity production from 18% in 2005 to 32% in 2015. During the same period, coal's share has dropped from 51% to 34%. This is a major change in just over a decade!
One major benefit of this is that it has contributed to reduced CO2 emissions that come from electricity generation in the U.S. These emissions are at their lowest level since 1993. The EIA explains that: "A shift in the electricity generation mix, with generation from natural gas and renewables displacing coal-fired power, drove the reductions in (CO2) emissions." This is a major benefit of natural gas. As indicated previously, burning natural gas results in approximately half of the emissions from an equal amount of coal energy.
But this is not the whole story regarding emissions. Remember that while natural gas emits about half of the CO2 as an equivalent amount of coal when burned, natural gas itself is about 30 times as powerful as carbon dioxide in terms of greenhouse effect impact over a 100 year period and about 80 times as powerful over a 20 year period. One result of this is that methane leaks throughout the natural gas supply chain (from the well to the end user) counteract some of the positive impacts of natural gas being a relatively clean-burning fuel.
Some other considerations regarding natural gas, mostly from this article by John Wihbey [38] include:
In short, natural gas is really a mixed bag of sustainability implications, especially with regards to hydraulic fracturing. The primary benefits from a sustainability perspective are that there is no doubt that it has reduced CO2 emissions, but to what extent natural gas leaks have counteracted that is in question; and also that it has created an economic boom, at least in the short term. There are many downsides, particularly with regards to environmental damage (water, air, land), but also with regards to quality of life for some people near wells.
In terms of feasibility, oil is so ingrained in modern society and its infrastructure is so well-established that there is no risk of not being able to integrate oil supplies into the economy and society. However, oil supply projections have a very interesting history, and like the price, projections of supply have been volatile. First of all, like natural gas, the calculation of proved reserves is subject to limitations of using current technology, economics, and known reserves, each of which can change from year to year. Like natural gas, for oil, proved reserves refer to "those quantities of petroleum which, by analysis of geological and engineering data, can be estimated with a high degree of confidence to be commercially recoverable from a given date forward, from known reservoirs and under current economic conditions" (Credit: CIA Factbook [40]). The result (again, like natural gas) is that even though oil use is increasing globally every year, there are paradoxically more proved reserves. Please note that the chart below represents global proved reserves.
How is it possible that we can continue to use more oil each year, yet the estimated remaining supplies keep increasing? The primary reason is improving technology. We have so far been able to exploit new resources as the market demands more oil. The most recent increase in proved reserves, especially in the U.S., is from shale oil that can be extracted through hydraulic fracturing (aka fracking). There has been an oil boom that has come in lock-step with the recent natural gas boom, all due to fracking. Access to additional "unconventional" reserves via tar sands in Canada has also contributed to the increase in proved reserves and supply.
Dr. James Conca provides a very good explanation of the somewhat complex workings of the global oil market in the article below. As you will see, the price of oil and the economic feasibility of technology is not as simple as supply and demand. He also throws in a nice lesson on how fossil fuels are formed for good measure. Also, if, like me, you have found yourself wondering whether oil deposits are more like a jelly donut or tiramisu, he'll help you out with that as well.
There are a few important things to point out from this article:
So, how much oil is left, and how long will it last?
There are many sustainability considerations when it comes to oil. The following are some of the sustainability benefits:
However, there are of course drawbacks, including the following:
Oil is an extremely useful resource, and it is a very important aspect of the modern economy, and by extension, society. Considering that current projections assert that we only have about 50 years of supplies left, we should probably try to maintain our resources for as long as possible, and avoid an abrupt collapse. But we also should be conscious of the sustainability impacts of its extraction and use.
Nuclear energy has been a hot-button issue for a very long time, both domestically and internationally. It provides a significant portion of the global electricity supply, as you will see in the image below.
Nuclear energy is non-renewable. Uranium is by far the most-used nuclear fuel. As with other non-renewable fuels, all of the uranium that is on earth now is all that we will ever have, and estimates can be made of the remaining recoverable resources. At current rates of consumption, we will not run out of uranium any time soon. But this depends very highly on a number of variables, including keeping consumption at current levels, technology not advancing, estimates of reserves changing, and so forth.
The World Nuclear Association (WNA), an industry association, provides a very thorough explanation of possible complicating factors [57], but they state that at current rates of consumption, the world has enough reserves to last about 90 years. The Nuclear Energy Agency (NEA [58]), like the WNA, [58]is effectively an industry group and has a wealth of expertise at its disposal. They indicate that as of 2009, the world had about a 100 year supply of uranium. So it appears that as long as the rate of use does not increase there is a little less than 100 years of nuclear fuel supplies left.
According to the World Nuclear Association, there are 454 operable reactors worldwide with a further 54 under construction [59]. The technology is well known by now, and despite the extreme danger posed by nuclear meltdowns, there have been very few major incidents. You are probably familiar with the Fukushima Daichi meltdown that happened in 2011, and perhaps heard of Chernobyl in Ukraine in 1986 (still the worst nuclear disaster to date), and maybe even Three Mile Island in the U.S. in 1978. Here is a partial list of nuclear accidents [60] in history from the Union of Concerned Scientists (UCS). But putting aside this risk at the moment, nuclear energy has shown itself to be a viable source of electricity, and likely will continue to be used for the foreseeable future. Among other things, nuclear power plants generally have a useful lifetime of around 40-60 years, so we are "locked in" until mid-century at least.
Nuclear energy is a mixed bag in terms of the question of sustainability. You may recall that nuclear is considered a carbon-free source, and since it is a proven and reliable source, it is seen by many as a good option. Note that despite being considered "carbon-free," nuclear energy results in some lifecycle emissions because of the materials used in mining, building the power plant, and so forth. (Lifecycle emissions are all the emissions generated by all processes required to make an energy source, including things like mining of materials, manufacturing of equipment, and operating equipment.) But according to the National Renewable Energy Laboratory (NREL) [61] it has approximately the same lifecycle emissions as some renewable energy sources.
Some other sustainability considerations include:
The first article below is a good example of why it pays to pay attention to citations and be well informed on a topic, in regards to finding good information sources. The article is on a website that I've never heard of before, so at first, I was suspicious of the content. However, they provide legitimate sources for the information presented, and I have enough prior knowledge to know that the arguments they put forth are legitimate. Overall, it's a good summary of some of the pros and cons of nuclear energy.
Overall, nuclear is reliable and almost carbon-free but is expensive and non-renewable. Also, because power plants are so expensive to build, once they are built they are generally used for as long as possible, as long as they are still economic. When accidents happen, they can be catastrophic, but they are extremely rare. However, the waste product from nuclear power plants is dangerous for thousands of years, and right now we have no way of safely disposing of it - it is kept in storage, usually at the power plants themselves.
The supply aspect is very straightforward for wind and solar: they are inexhaustible! As stated in Lesson 1, both of them get their energy from the sun; and if the sun stops shining, we have more important issues to deal with than not having a source of renewable electricity. The amount of solar energy that hits the earth in one hour is enough to power the world for an entire year (this is a commonly held fact, but here is one source [69]). There is no shortage of solar energy!
As for hydroelectric, though it also gets its energy from the sun, it is limited due to its dependence on the availability of flowing water. As of 2014, about 17% of the world's electricity came from hydroelectricity. According to the International Energy Agency [70], there is about 5 times as much technical potential for hydroelectric worldwide as is currently generated today. We certainly would not want to exploit all of it, given some of the environmental impacts of large hydroelectric facilities (see below), but this number does provide a frame of reference.
The feasibility is a mixed bag.
One sign that bodes well for renewables is that the cost has come down significantly in recent years.
This is all based on the levelized cost of electricity (LCOE), which was noted in the nuclear lesson. The LCOE is the amount it costs to generate each unit of energy (usually measured in $/megawatt-hour) on average over the lifetime of an electricity source. To calculate the LCOE, you take the total lifecycle costs and divide by the total electricity output over the lifetime of the source. This is of course not including externalities, which would likely make renewable energy cheaper right now, especially if the social cost of carbon were to be considered. See the chart below for details. Note that information for utility-scale vs. residential-scale solar was not made available for the U.S., but refer to this chart from Lazard [73] for global data, which also includes residential and utility-scale solar.
Plant Type | Total System LCOE ($/MWh) |
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conventional combined cycle natural gas | 48.3 |
advanced combined cycle natural gas | 48.1 |
advanced combustion turbine natural gas | 79.5 |
advanced nuclear | 90.1 |
geothermal | 43.1 |
biomass | 102.2 |
onshore wind | 48.0 |
offshore wind | 124.6 |
solar PV | 59.1 |
hydroelectric | 73.9 |
The bottom line in terms of cost is that right now, well-sited wind and utility-scale solar are the cheapest form of electricity available, other than only the least expensive natural gas power plants. (Please note that energy efficiency is cheaper than all energy sources!) Other renewable sources such as small hydroelectric, biomass, geothermal, solar thermal, and commercial-scale solar are very cost-competitive with coal and natural gas, and generally less expensive than nuclear. All of this does NOT include subsidies, by the way!
All three of these sources are carbon-free, so they are ideal with regards to anthropogenic climate change. Even after consideration of the embodied energy of these sources, the lifecycle carbon footprint is minimal for renewables, as you can see in the chart below. In terms of climate change concern, there is really no debate: these renewables are great choices.
However, there are some other considerations to make in terms of sustainability. First, large hydroelectric facilities are not very environmentally friendly. Depending on the location, there can be problems with flooding of habitats and even towns, compromising fish migration, altering stream content and temperature, impacting scenic areas, and other considerations. The articles below provide some insight into some of these potential problems. Note also that not all hydro has the same problems - by using different types of hydroelectric facilities such as run-of-river and micro-hydro [78], environmental and social impacts can be minimized.
In terms of social equity, there are a few important considerations to make. First of all, do people have access to energy, and can they afford it? This is a tricky question to answer, as it depends on a lot of factors, many of which were indicated above. Some equity and other considerations include:
One of the benefits of conventional energy generation is that the infrastructure is largely set up, at least in industrialized countries. In the U.S., for over 100 years, we have built an energy infrastructure based on large power plants and fossil-fuel based vehicles. This gives conventional energy sources an advantage in terms of providing access. That said, wind, hydro, and solar can all utilize the existing infrastructure. Hydroelectric dams provide the same service as fossil-fuel power plants, but usually on a slightly smaller scale, so they are a good fit. They also provide a very consistent stream of electricity as long as no droughts are occurring, and they can increase and decrease production pretty rapidly, unlike solar and wind.
Probably the biggest current problem with solar and wind is that they are intermittent - the sun does not always shine, and the wind does not always blow. This is a major issue because we currently do not have the storage capabilities to provide the energy on command. One common problem with wind and solar are that they are often highest in areas with low population densities. In the U.S., for example, the greatest on-shore wind resources are in the Great Plains in the Midwest, where the population density is very low.
One of the benefits of solar is that as long as there is not too much shading, many households can satisfy their energy needs using existing rooftop spaces. However, not every location is ideal for solar. The intermittency of wind and solar is also a major problem, as noted above. This will change if/as battery technology becomes more accessible, and as the grid is upgraded.
Overall, the biggest advantages of renewable energy sources are:
The main disadvantages of solar, wind, and hydro are:
The last thing I'd like to note is that the most sustainable energy is the energy that you don't use. Remember that energy efficiency is sometimes called the "fifth fuel?" That is very much applicable to these considerations. Also, as noted above, energy efficiency has been found to have a lower LCOE than any other energy source! [86] The more we can reduce our energy use while getting the same benefits from the energy service, the better off we will be.
By now you should be able to:
You have reached the end of Lesson 4! Double-check the to-do list on the Lesson 4 Overview page [87] to make sure you have completed all of the activities listed there before you begin Lesson 5.
Links
[1] https://www.e-education.psu.edu/emsc240/node/552
[2] http://www.npr.org/2018/10/08/655360909/grim-forecast-from-u-n-on-global-climate-change
[3] https://www.ipcc.ch/site/assets/uploads/sites/2/2018/07/SR15_SPM_version_stand_alone_LR.pdf
[4] http://www.nytimes.com/2018/11/23/climate/us-climate-report.html
[5] http://ourworldindata.org/co2-and-other-greenhouse-gas-emissions
[6] https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions
[7] https://creativecommons.org/licenses/by-sa/4.0/
[8] https://www.e-education.psu.edu/emsc240/sites/www.e-education.psu.edu.emsc240/files/table14.xls
[9] https://www.e-education.psu.edu/emsc240/node/531/
[10] http://www.eia.gov/coal/reserves/
[11] https://www.eia.gov/coal/annual/pdf/table15.pdf
[12] http://www.britannica.com/science/British-Imperial-System
[13] https://www.britannica.com/science/British-Imperial-System
[14] https://www.eia.gov/tools/glossary/index.php?id=Metric%20ton
[15] https://www.stlouisfed.org/on-the-economy/2017/december/coal-declining-due-economics-regulation
[16] https://www.worldenergy.org/data/resources/resource/coal/
[17] http://www.eia.gov/energyexplained/index.cfm?page=coal_environment
[18] http://www.theatlantic.com/business/archive/2015/08/coals-externalities-medical-air-quality-financial-environmental/401075/
[19] http://www.cnn.com/2013/07/13/us/u-s-mine-disasters-fast-facts/
[20] https://en.wikipedia.org/wiki/Climate_change_mitigation#/media/File:Global_Carbon_Emissions.svg
[21] https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data
[22] http://web.archive.org/web/20170125065638/https://www3.epa.gov/climatechange/ccs/
[23] http://news.mit.edu/2015/carbon-dioxide-sequestration-doubts-0120
[24] http://insideenergy.org/2016/10/11/clean-coal-fact-or-fiction/
[25] https://www.theguardian.com/environment/2018/mar/02/clean-coal-america-kemper-power-plant
[26] http://commons.wikimedia.org/wiki/File:Petroleum_drilling_onshore_system.svg
[27] https://www.eia.gov/naturalgas/crudeoilreserves/
[28] http://www.eia.gov/energyexplained/index.cfm?page=natural_gas_reserves
[29] http://www.eia.gov/dnav/ng/ng_enr_wals_a_EPG0_R21_Bcf_a.htm
[30] http://www.eia.gov/naturalgas/crudeoilreserves/
[31] https://www.e-education.psu.edu/emsc240/node/579
[32] http://www.eia.gov/energy_in_brief/article/shale_in_the_united_states.cfm
[33] http://www.eia.gov/tools/faqs/faq.php?id=58&t=8
[34] http://www.forbes.com/sites/peterdetwiler/2012/12/17/just-how-long-will-us-gas-supplies-last/
[35] https://www.e-education.psu.edu/emsc240/node/588
[36] http://www.eia.gov/todayinenergy/detail.cfm?id=26232
[37] https://www.e-education.psu.edu/emsc240/node/587
[38] http://www.yaleclimateconnections.org/2017/06/pros-and-cons-of-fracking-research-updates/
[39] http://www.forbes.com/sites/edfenergyexchange/2015/06/05/how-to-ensure-new-natural-gas-infrastructure-doesnt-lock-out-renewables/
[40] https://www.cia.gov/library/publications/the-world-factbook/rankorder/2244rank.html
[41] https://www.e-education.psu.edu/emsc240/node/578
[42] http://www.eia.gov/beta/international/data/browser/#?ord=SA&cy=2015&v=H&vo=0&so=0&io=0
[43] https://www.forbes.com/sites/jamesconca/2017/03/02/no-peak-oil-for-america-or-the-world/#1387d1cd4220
[44] https://www.bp.com/content/dam/bp/en/corporate/pdf/energy-economics/statistical-review-2017/bp-statistical-review-of-world-energy-2017-full-report.pdf
[45] https://data.bls.gov/timeseries/CES1021100001
[46] https://www.ogj.com/articles/2017/08/study-us-oil-gas-industry-supported-10-3-million-jobs-in-2015.html
[47] http://www.eia.gov/energyexplained/index.cfm?page=oil_environment
[48] http://www.economist.com/news/science-and-technology/21615488-new-technologies-are-being-used-extract-bitumen-oil-sands-steam
[49] http://www.eia.gov/dnav/pet/pet_move_impcus_a2_nus_ep00_im0_mbblpd_a.htm
[50] http://opinionator.blogs.nytimes.com/2013/02/13/avoiding-the-curse-of-the-oil-rich-nations/
[51] http://www.economist.com/news/middle-east-and-africa/21647361-broken-oil-industry-source-many-woes-crude-politics
[52] http://www.bbc.com/news/world-africa-13317174
[53] http://oilprice.com/Energy/Oil-Prices/The-Dark-Side-Of-The-Shale-Bust.html
[54] http://www.npr.org/2015/04/20/400374744/5-years-after-bp-oil-spill-effects-linger-and-recovery-is-slow
[55] https://www.e-education.psu.edu/emsc240/node/571
[56] http://www.tsp-data-portal.org/Breakdown-of-Electricity-Generation-by-Energy-Source#tspQvChart
[57] http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Uranium-Resources/Supply-of-Uranium/
[58] http://www.oecd-nea.org/
[59] http://www.world-nuclear.org/Nuclear-Basics/Global-number-of-nuclear-reactors/
[60] http://www.ucsusa.org/nuclear-power/nuclear-power-accidents/history-nuclear-accidents#.Veeuk_lViko
[61] https://www.nrel.gov/docs/fy13osti/57187.pdf
[62] http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/radwaste.html
[63] https://www.epa.gov/navajo-nation-uranium-cleanup
[64] http://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf
[65] https://understandsolar.com/pros-and-cons-of-nuclear-energy/
[66] http://www.npr.org/2016/04/07/473379564/unable-to-compete-on-price-nuclear-power-on-the-decline-in-the-u-s
[67] http://www.nytimes.com/2014/12/23/science/nuclear-carbon-free-but-not-free-of-unease-.html?_r=0
[68] http://cen.acs.org/articles/91/web/2013/04/Nuclear-Power-Prevents-Deaths-Causes.html
[69] http://www.sandia.gov/~jytsao/Solar%20FAQs.pdf
[70] http://www.iea.org/publications/freepublications/publication/hydropower_essentials.pdf
[71] http://web.stanford.edu/group/efmh/jacobson/Articles/I/JDEnPolicyPt1.pdf
[72] http://www.greens.org/s-r/60/60-09.html
[73] http://www.lazard.com/media/450784/lazards-levelized-cost-of-energy-version-120-vfinal.pdf
[74] https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf
[75] https://www.greentechmedia.com/articles/read/wind-and-solar-are-our-cheapest-electricity-generation-sources-now-what-do
[76] http://energyinnovation.org/2018/01/22/renewable-energy-levelized-cost-of-energy-already-cheaper-than-fossil-fuels-and-prices-keep-plunging/
[77] https://www.e-education.psu.edu/emsc240/node/575
[78] http://energy.gov/eere/water/types-hydropower-plants
[79] http://www.eia.gov/energyexplained/index.cfm?page=hydropower_environment
[80] http://www.nytimes.com/2011/05/20/world/asia/20gorges.html
[81] https://www.youtube.com/watch?v=5wqJ9RpYiZ8
[82] http://www.eia.gov/energyexplained/index.cfm?page=solar_environment
[83] http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/environmental-impacts-wind-power.html#.VefnMPlViko
[84] https://upload.wikimedia.org/wikipedia/commons/8/84/United_States_Wind_Resources_and_Transmission_Lines_map.jpg
[85] https://commons.wikimedia.org/wiki/File:United_States_Wind_Resources_and_Transmission_Lines_map.jpg
[86] http://aceee.org/press/2014/03/new-report-finds-energy-efficiency-a
[87] https://www.e-education.psu.edu/emsc470/811