TIL about fossil fuels


Fossil fuels -- coal, natural gas, and oil -- provide the large majority of our power in the United States and around the world. In this episode of TILclimate (Today I Learned: Climate), John Reilly of the MIT Joint Program on the Science and Policy of Global Change joins host Laur Hesse Fisher to demystify fossil fuels: what are the different kinds of fossil fuels, and how do they compare to each other? What is “fracking” and how did impact energy use and CO2 emissions in the United States? What kinds of decisions do we need to make to transition to clean energy, while providing electricity to a growing number of people?

John Reilly is a senior lecturer at the MIT Sloan School of Management and Co-Director of the MIT Joint Program on the Science and Policy of Global Change. An economist, he researches economic models that connect human activity with natural systems like the ocean, atmosphere, and vegetation.

Season two of TILclimate focuses on our global energy system, its relationship to climate change, and what our options are for keeping the lights on while creating a clean energy future. We’re partnering with the MIT Energy Initiative, which will air longer interviews with each guest to take a deeper dive into these topics.


For more episodes of TILclimate, visit: tilclimate.mit.edu

To listen to the MIT Energy Initiative podcast, visit: energy.mit.edu/podcast

For in-depth analyses on energy technologies, check out the MIT Energy’s “Future of” report series: energy.mit.edu/research-type/future-of/

For the full break-down of where U.S. gets its energy: https://www.eia.gov/energyexplained/us-energy-facts/



Produced by the MIT Environmental Solutions Initiative at the Massachusetts Institute of Technology

Laur Hesse Fisher: Hello and Welcome to TIL Climate, the show where you learn about climate change from real experts. I’m your host Laur Hesse Fisher, from the MIT Environmental Solutions Initiative, in lovely Cambridge, MA. This is the second episode in our series about energy and climate change in partnership with the MIT Energy Initiative. So if you’re just joining us, check out last week’s episode on the electric grid.

Today, we’re going to be exploring where our energy comes from in the United States. We’ll talk about the different types of fuel and how they differ in terms of their impact on climate change, and how these energy sources have changed over time.

To do this, we sat down with Dr. John Reilly.

John Reilly: [00:00:44] I'm the co-director of something called The Joint Program of Science and Policy of Global Change, and I'm a senior lecturer in the Sloan School.

Laur Hesse Fisher: [00:00:51] Dr. Reilly is an MIT economist who studies global environmental change. To begin, let’s look at what our energy makeup is today in the United States.

John Reilly: [00:01:01] we still supply 80% of our energy needs in the US with fossil energy: oil, coal, and gas. About 8% of energy needs is from nuclear, and about 11% from renewables. And if we break down that renewables further, solar and wind is only providing three percent of our current energy needs.

Laur Hesse Fisher: [00:01:20] In a future episode, we’re going to go into more detail about these fuel sources. But briefly, the term “renewables” refers to energy that’s generated by sources that won’t deplete. The wind won’t stop blowing, the sun won’t stop shining, rivers won’t stop flowing into the ocean. Conversely, fossil fuels refer to energy that’s made from dinosaurs and ancient animal and plant matter that has been pressurized under the earth’s surface for millions of years. Unlike wind and solar, we will eventually run out of fossil fuels.

To understand the current energy breakdown, it can be helpful to understand how we got where we are today.

John Reilly: [00:02:00] You can kind of go back into England, back in the pre-industrial early industrial era.

People are mostly relying on wood for heat and they completely deforested Britain and had to find something else and they dug up coal and found you could burn that. So first the world kind of moved to coal and and that was a denser form of energy.

Laur Hesse Fisher: [00:02:21] By denser energy, he means that if you burned the same amount of coal and wood, the coal would provide you with more energy.

John Reilly: [00:02:29] So this new energy source really opened up new avenues to use energy leading us to use… steam engines and other sorts of things.

Laur Hesse Fisher: [00:02:38] Without coal, it’s very possible we wouldn’t have had the kind of growth in our economy and quality of life that we’ve enjoyed for the past 150 years.

There are two other kinds of fossil fuels that are important in the modern energy equation: oil and natural gas.

John Reilly: [00:02:58] So oil starts out as crude oil. We drill it out of the ground and then it's refined into various products like gasolines. It may be diesel, it may be heating oil, it may be jet fuel so that’s oil. Liquid fuels have a lot of value in transportation because they're dense. You can fill up your tank and it lasts for a long time.

Laur Hesse Fisher: [00:03:21] Sometimes oil is used for electricity and heat, but mostly it’s used for transportation. Even though we use the word “gas” to refer to fuel for our car, it’s actually short for “gasoline” and it is made from oil and it’s a liquid. Natural gas is a completely different form of energy, though it’s often found in the ground with oil.

John Reilly: [00:03:42] So when you drilled an oil well you often got this gas. And that was kind of a problem because, gee whiz you didn't really want that, you wanted to wanted the liquid oil. So oftentimes that was just vented into the atmosphere or flared off. But eventually people said well look this stuff could be used as well. And so we began developing a collection system and a distribution system that could actually use natural gas and get it to places where it was needed rather than just waste it and vent it. And then people began discovering well, there are actually deposits that are all natural gas or mostly natural gas and so as that distribution system developed, we actually, you know started looking for gas for itself.

Laur Hesse Fisher: [00:04:21] Natural gas is piped into houses for heating and cooking, and is also burned in power plants to generate electricity.

Up until recently, coal was our cheapest fuel for electricity, because it was so abundant in the United States and the technology boom was making it easier and easier to automate coal power plants. But now, coal accounts for just 13 percent of our primary energy consumption.

And that... is because of hydraulic fracturing, better known as fracking.

John Reilly: [00:04:53] In 2007-2008 this new technological development allowed us to exploit these resources of oil and gas that otherwise were locked too tightly in rocks that we weren't able to get.

Laur Hesse Fisher: [00:05:05] Before fracking, the U.S. had to import a lot of its natural gas from elsewhere. Fracking made natural gas cheaper than coal, and this completely shifted the U.S. energy economy.

John Reilly: [00:05:17] Much of the last few decades in the United States, the concern was how dependent we were on energy imports. And so as late as around 2007, we were importing 30% of the energy we use in the country. So we were one of the biggest importers in the world.

Starting with this fracked gas explosion... I guess, maybe not the best word to use with it, in 2007-2008, gas became very cheap. And so we actually began crowding out coal production and using gas in the United States.

As of 2018, we're almost in balance. So we're only importing four percent of our energy needs. So we're close to becoming a net energy exporter. So that's completely reversed the whole story in the US.

Laur Hesse Fisher: [00:06:06] It also reversed the U.S. trend in emitting CO2. Emissions started to decline.

John Reilly: [00:06:13] Energy use in the United States has been flat since about 2007. Carbon dioxide emissions actually declined by about 12 and a half percent, and that's because not only was energy use flat but we also had the switch from coal to gas.

Laur Hesse Fisher: [00:06:29] That’s because coal emits more CO2 when burned than natural gas. Burning coal emits by far the most carbon per unit of energy used. Using natural gas in its place can cut emissions by more than half. That means we could make a huge dent in carbon emissions by switching from coal to gas. And that cues up one of the big debates that is going on among energy experts.

John Reilly: [00:06:54] Natural gas is cleaner than coal, but it still has carbon dioxide emissions. So the challenge, the debate is a bridge to a cleaner fuel or is it just a bridge to an economy heavily dependent on natural gas. And then, if we build a lot of capacity around natural gas, then all of a sudden we're locked into gas and we're not a bridge to a cleaner economy, to a clean fuel.

you know, renewables, maybe nuclear power uh, that has no CO2 em- essentially no CO2 emissions with it.

So the question becomes are we really serious about meeting the targets we have. And so if you're really pushing hard to meet them and we have to get low quickly then expanding gas capacity is investing in a bunch of stuff that's locking you in and maybe you don't want it.

So that is a huge debate amongst many people. But in poorer countries of the world, they're just trying to kind of get energy, you know, basic energy needs of people, met.

Laur Hesse Fisher: [00:07:52] Yeah, and as these countries give their people access to electricity for the first time, the big debate is, how do we power that demand?

John Reilly: [00:08:02] Unfortunately for the climate and the environment, fossil fuels still tend to be the least expensive way to produce electricity.

Even as renewable costs fall, I mean, sometimes people make the mistake of saying, "Oh look, renewable costs are coming down. They're going to be cheaper than fossil fuels." But fossil fuel cost keeps coming down too because fossil fuel companies keep finding better ways to mine coal or pull oil out of the ground. You know, the fracking boom in the United States all of a sudden found this resource which is lots of places. And so the costs have been going down rather than up.

So if you're focusing on development mainly, then that is often the fuel of choice for electricity.

So, poorer countries of the world, are they going to go through a fossil fuel phase and then produce a lot of CO2 emissions and then find out they have to move beyond that? Can we just skip it?

Laur Hesse Fisher: [00:08:57] And that’s the biggest challenge for our future: that clean, carbon-free energy technologies need to be able to compete... everywhere.

In our next set of episodes, we’re going to start talking about these clean energy technologies, their benefits and their challenges. We’ll cover renewable energy, like solar and wind; batteries and energy storage; nuclear power; energy efficiency; and the elusive nuclear fusion. We’ll also talk about carbon capture and storage.

This was our second episode of our energy and climate series. If you're eager to hear more you can check out the MIT Energy Initiative’s Future of Energy studies, where they do a deep dive into these Technologies. They also put out a podcast where you can hear more from John Riley and Professor Noelle Selin, just search for “MIT Energy podcast” or check out the links in the show notes.

We always enjoy hearing from our listeners, so send us any questions or comments you have by tweeting us @TILclimate or emailing us at TILclimate@mit.edu especially now, as we're picking topics for season 3. Today I learned climate is brought to you by the MIT Environmental Solutions initiative. Thanks to John Reilly for speaking with us and thank you for listening.


An educator guide for this episode can be found below.


Critical Thinking 

  • Hydraulic fracturing, or fracking, has been a topic of debate over the years. Why is that? Burning natural gas, which is mainly extracted through fracking, is considered to be “more environmentally friendly” than coal. But what are the environmental risks of the fracking process itself? What are the ethical implications of fracking? What communities are most likely to be immediately impacted by fracking? Why? 
  • What are the challenges of shifting away from fossil fuels and replacing them with clean energy sources? Is it mainly an issue of economics? An issue of politics? Or of technology? How do all of these areas impact the speed of and commitment to this transition in the United States?


  • Professor Reilly mentions “dense” forms of energy, which are sources that provide more energy from the same quantity of the substance. How does the energy density of coal compare to that of natural gas? What about to that of oil? And nuclear? 
  • How has the makeup of fuel sources in the U.S. evolved over the years? What trends do you notice in the use of fossil fuels and renewables? Laur Hesse Fisher mentions that U.S. CO2 emissions have been increasing. Which fuel sources emit the most emissions? The least? Do these statistics support trends in climate change mitigation? If so, how?


  • Near the end of this episode, Professor Reilly brings up the topic of how poor countries are currently focused on trying to meet the basic energy needs of their citizens. He raises the question of whether they will go through a fossil fuel phase. Do you think that these countries should skip the fossil fuel phase and move directly to clean energy? Do you think that they can? How much pressure do you think should be placed on them to skip to clean energy? How does this compare to the amount of pressure you think should be put on developed countries to move away from fossil fuels?



  • Recall Professor Reilly’s statement on the makeup of fuel sources in the U.S.: “80% fossil energy, 8% nuclear, and 11% renewables.” Pick another country in the world and compare its fuel sources with those of the U.S. How do they differ? Which uses more fossil fuels or renewables? Compare your results with the rest of the class.   

Need additional open source educational resources related to the topic of electric grids? You may find these free teaching materials from MIT OpenCourseWare (OCW) useful: 

The Physics of Energy 

Level: Undergraduate 

The course is designed for people who want to understand the fundamental laws and physical processes that govern the sources, extraction, transmission, storage, degradation, and end uses of energy. Learn about how different types of energy technologies function, with an emphasis on combustion technology. 



Fundamentals of Advanced Energy Conversion 

Level: Undergraduate

This course covers fundamentals of thermodynamics, chemistry, flow and transport processes as applied to energy systems. Topics include analysis of energy conversion in thermomechanical, thermochemical, electrochemical, and photoelectric processes in existing and future power and transportation systems, with emphasis on efficiency, environmental impact and performance. Systems utilizing fossil fuels, hydrogen, nuclear and renewable resources, over a range of sizes and scales are discussed. 


Sedimentary Geology 

Level: Undergraduate 

Survey of the important aspects of modern sediments and ancient sedimentary rocks. Emphasis is on fundamental materials, features, and processes. Textures of siliciclastic sediments and sedimentary rocks: particle size, particle shape, and particle packing. Mechanics of sediment transport. Survey of siliciclastic sedimentary rocks: sandstones, conglomerates, and shales. Carbonate sediments and sedimentary rocks; cherts; evaporites. Siliciclastic and carbonate diagenesis. Paleontology, with special reference to fossils in sedimentary rocks. Modern and ancient depositional environments. Stratigraphy. Sedimentary basins. Fossil fuels: coal, petroleum.


Internal Combustion Engines

Level: Graduate 

This course studies the fundamentals of how the design and operation of internal combustion engines affect their performance, efficiency, fuel requirements, and environmental impact. Topics include fluid flow, thermodynamics, combustion, heat transfer and friction phenomena, and fuel properties, with reference to engine power, efficiency, and emissions. Students examine the design features and operating characteristics of different types of internal combustion engines: spark-ignition, diesel, stratified-charge, and mixed-cycle engines. 


All Comments

Thank you for this excellent primer on where we are with our current energy consumption in this country. I look forward to the future episodes to get informed on some of the current status of renewable energy sources and most particularly how we are doing in improving lithium ion battery development to increase the storage of renewable energy and the expansion of this technology.