Now that we've established the scientific context for climate change and understand that its emissions that primarily drive these changes, let's take a closer look at these emissions by sector. As we work our way through this lesson, be thinking carefully about how these emissions sectors relate both to the proximate causes and driving forces of climate change we learned about last week.
By the end of this lesson, you should be able to:
This lesson will take us one week to complete. Please refer to the corresponding module in Canvas for specific assignments, deliverables, and due dates.
If you have questions, please feel free to post them to the "Have a question about the lesson?" discussion forum in Canvas. While you are there, feel free to post your own responses if you, too, are able to help a classmate.
To understand emissions sources, it's useful to categorize those emissions. One such way to do that is by sector. This lesson is going to look specifically at Energy, which is the biggest source of anthropogenic GHG emissions (by far!). More specifically, we are going to break down energy into a few subcategories: power generation, transportation, and industrial processes, as shown below. This lesson, we'll be focusing on the subset of that big almost-the-whole-piece-of-the-pie energy sector.
Energy use and consumption produce more GHG emissions than any other realm of human endeavor. A brief look at the socioeconomic drivers of energy use and consumption helps explain some of the reasons why. Current technologies for generating energy focus on GHG-intensive fossil fuels; the economic system favors producing the greatest amount of energy at the lowest cost and does not account for the environmental costs of energy production; political and legal institutions promote and protect fossil-fuel industries and typically fail to foster alternative energy sources adequately, and Western lifestyles are energy-intensive but many non-Westerners aspire to a Western lifestyle. Add to that the exponential growth of Earth’s human population and it is no wonder that GHG emissions continue to grow rapidly.
Global GHG emissions from energy use and production far outweigh emissions from other activities. The industrial processes, agriculture, land-use change and forestry, and waste management sectors together account for 37 percent of all global GHG emissions in the accompanying pie chart. However, a significant proportion of the emissions from agriculture and from land-use change and forestry involve fossil fuel consumption, so the percentage of emissions from energy is greater than the graphic implies. Consequently, far more than two thirds of all GHG emissions result from energy use and production.
In the pie chart, electricity and heat production is clearly the largest emitter of GHGs, being responsible for over one quarter of total emissions. Most of these emissions are attributable to society’s dependence on coal and secondarily on natural gas. The remaining energy categories –– manufacturing and construction, transportation, and “other” –– each contribute approximately equal proportions of the global GHG emissions.
Going beyond this particular graphic, when compiling the national GHG emissions inventory, the US breaks its energy sector emissions into three broad categories: mobile sources, stationary sources, and fugitive sources.
The stationary sources category is large and includes many activities.
There are many other important categories of GHG-producing activities:
Even so, these enterprises consume huge amounts of electricity, and most of this electricity comes from fossil fuel-powered power plants, so these categories are indirectly responsible for a very large proportion of GHG emissions.
In addition to transportation and stationary sources, fugitive CH4 emissions from coalmines and from oil and natural gas drilling sites, as well as from natural gas pipelines, were thought to be a relatively small source of GHG emissions. Recent work, however, suggests that fugitive emissions may in fact be a major source of atmospheric CH4, so this part of the energy sector is coming under increased, intense scrutiny.
The relationships among energy production, energy storage and distribution, energy marketing, and energy demand and consumption are extremely complex. Thus, trying to pin GHG emissions to any one component in this complex web is arbitrary. Indeed, calculating emissions from the energy sector is fraught with error because of this complexity. It is best to think not in terms of exact proportions of GHG emissions from any one activity or subsector, but in terms of which categories are the big players.
The world consumes massive quantities of energy, with much of that energy embodied by GHG-emitting fossil fuels.[1] This image shows primary energy consumption by world region in 2015. Together, China and the United States represent 40% of global energy consumption. This is why our cooperation to solve climate change-related challenges is so pivotal.
The next image shows a graph of global consumption by fuel type for 1990-2016. Overall consumption has almost doubled in this time period (and has more than doubled if we went back 40 years). The three fossil fuels (oil, coal, and natural gas) dominate, encompassing between 80 to 90 percent of energy consumption throughout the period. Oil provides the largest proportion of energy, but proportionally has lost ground to coal and especially natural gas (why might that be?). Coal has had an upsurge in the 21st century, especially after 2005, and may become the leading fossil fuel in the future as oil supplies drop and demand for energy increases in places such as China and India, with massive coal reserves but little oil and natural gas. Biomass and hydroelectric power grew a little. Other renewables are a trivial proportion of the global energy picture. Clearly, the grip of the GHG-producing fossil fuels on the world energy picture is strong.
The next image shows a map of per capita energy consumption across the globe. An obvious general pattern emerges: low-latitude countries have very low per capita consumption –– and therefore low per capita GHG emissions –– while mid- to high-latitude countries have high per capita consumption and emissions. (Exceptions exist. For example, Saudi Arabia has anomalously high per capita energy consumption compared to surrounding countries because it is a wealthy, oil-rich country with a low population.) On the one hand, the pattern suggests that low-latitude countries with very low per capita energy consumption and very high populations such as China, India, and Indonesia, will become significant sources of GHGs as their per capita consumption figures rise. Indeed, China, which has the world’s largest population, has rapidly rising per capita energy consumption. Combined with its focus on coal as its primary energy source, China is now the world’s largest emitter of GHGs. India is hot on China’s heels, with a rapidly expanding coal-based economy. On the other hand, the pattern also suggests global inequities because the mid- to high-latitude countries have such very high per capita energy consumption figures. Opportunities exist for these countries to reduce per capita consumption by undertaking energy efficiency measures, adopting non-GHG-producing energy types, and modifying their energy-intensive lifestyles. This contrast between the low latitudes (the global South) and the mid- to high latitudes (the global North) is at the heart of the ongoing United Nations climate negotiations.
[1] Most of the remainder of this lesson is based on figures presented in Sims, et al., 2007. Energy supply. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz, et al. (eds)], Cambridge University Press.
The next image shows CO2 emissions from fossil fuel combustion by country. In 2015, China's share was 28 percent of the world’s CO2, while the US share was 15 percent. The next closest country, India, emitted about 6 percent of the CO2. Clearly, to bring down global emissions from the energy sector, China and the US must lead the way.
The next image is a graph depicting fossil fuel-based CO2 emissions for the US, China, several other key emitters, and the aggregate rest of the world between 1970-2017. What jumps out at you?
The next image displays the GHG emissions from the various systems used to generate electricity. Clearly, coal and its close cousin lignite produce the most GHG per unit of energy produced. Fuel oil is the next most GHG-intensive generation system. Natural gas, which is often touted as the clean alternative to coal, certainly emits about half as many GHGs per unit of energy but is still extremely GHG-intensive compared to non-fossil fuel alternatives. Renewables and nuclear produce trivial quantities of GHGs compared to the three fossil fuel types –– coal, oil, and natural gas.
The final graphic in this section illustrates the fact that CO2 emissions go down as efficiency in burning fossil fuel in power generation goes up. For coal, new technologies improve efficiencies and reduce emissions –– but they are still exceptionally high compared to the alternatives. New natural gas power generation is about half as CO2-intensive as the best single-purpose coal-fired power plant. Cogeneration (also known as CHP, combined heat and power) is dual-purpose and drastically improves the efficiency of any fossil fuel power generating system, halving the efficiency of single-purpose systems.
Transportation is a fundamental activity causing climate change. The transport sector includes air, sea, rail, road, and off-road transport and depends on petroleum for 95 percent of its energy. Consequently, it produces 23 percent of the energy-based GHGs, with 75 percent of those GHGs coming from road transport. Moreover, GHG emissions from this sector are the fastest-growing of all emissions. It is imperative that society figures out ways to reduce emissions from transport ––especially road transport –– in the near future.
Transportation emissions have historically been the second-biggest sector for most countries (or other geographic scales of measurement), coming in only behind stationary energy sources. But, as the energy sector makes consistent strides in efficiency, these scales are tilting. Look at 2016 in the next image. Transportation emissions overtake emissions from electric power generation.
CO2 emissions from historical and projected energy consumption by the transportation sector in the next image shows a five-fold increase in emissions between 1970 and 2050. Emissions growth from sea transport is relatively small, whereas air and road transport increases are bigger with the highest growth rates projected for air transport. However, despite the higher growth rates, road transport still maintains the vast majority of transportation-related emissions and therefore represents the biggest opportunities for reductions.
The US EIA finds that energy-related CO2 emissions in the transportation sector will remain relatively constant after 2030 because of little change in the carbon intensity of transportation fuels (EIA Annual Energy Outlook 2017 [16]).
Projections of energy consumption (Figure 5.3) suggest that China will not be alone in its dash to institute private car ownership. Experts project that energy consumed for transport will more than double between 2000 and 2050. The strongest growth is expected to take place in the air, freight trucks, and light-duty vehicles (LDVs), which includes cars, pickup trucks, minivans, and sport utility vehicles (SUVs). That growth will be greatest in the developing countries, especially China, India, other areas of Asia, and Latin America. Note that this projection drastically underestimated the growth in China during the first decade of the millennium.
Focusing on LDVs in the next image, projections for the total stock see a doubling of LDVs in the 2020s and tripling of this vehicle type by mid-century. The least growth is projected to take place in developed countries, while robust increases are expected in developing countries. The biggest increases are projected for China, but those increases are happening now, so growth may be slower for that country later in the century.
Vehicle ownership is a function of per capita income: as income goes up, rates of car ownership increase (Figure 5.5). The wealthiest major country –– the United States –– has much higher ownership rates than any other nation. Vehicle ownership is still very high among the next richest countries, essentially Canada, western and northern Europe, Japan, Australia, and New Zealand. Next comes southern and eastern Europe and Korea, followed by other developing countries around the world.
The take-home message from this series of graphs is that global energy consumption and GHG emissions from transport are increasing rapidly and are expected to continue grow significantly in the future. The largest subsector responsible for this growth is personal vehicles, which is projected to grow strongly over the coming decades as nations and their people emerge from poverty and are able to afford ownership.
The material for this section comes from Kahn Ribeiro, S., S. Kobayashi, M. Beuthe, J. Gasca, D. Greene, D. S. Lee, Y. Muromachi, P. J. Newton, S. Plotkin, D. Sperling, R. Wit, P. J. Zhou, 2007: Transport and its infrastructure. In Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds.), Cambridge University Press, Cambridge and New York.
Given car ownership rates for the U.S., transportation emissions are a major concern in this country. Transportation is responsible for 29 percent of the nation’s emissions as demonstrated in the next image. This sector is the fastest growing, accounting for almost half (48 percent) of the net increase in U.S. emissions since 1990. This rapid growth and sizeable portion of the overall emissions profile also means that there is ample opportunity for reductions.
Let's break the US transportation sector down in more detail to get a better look at where these emissions originate:
According to the EPA [21], 95% of the world's transportation energy comes from fossil fuels. Ninety five percent! (That's higher than I expected, how about you?) This is predominantly comprised of gasoline and diesel for on-road use.
As global demand for personal transport goes up (World Economic Forum, 2016 [22]), we'll need to think creatively about how to reduce emissions while accommodating an increasingly mobile global population.
How do we handle twice as many cars worldwide in 2040 while also seeking to aggressively reduce global GHG emissions?
Reducing energy intensity and switching to low/no carbon fuel sources are just a few of the ways we might be able to achieve those goals. Check out some of the proposed solutions outlined in Project Drawdown's Transport Sector Summary [23].
The two takeaways from this graph are (1) transportation emissions have more than doubled since 1970 and are expected to continue increasing and (2) the vast majority of those emissions come from on-road sources (light duty vehicles and medium-heavy duty vehicles).
People often wonder, "But is an electric car really a better bet for the climate?" After all, we have to plug them in to charge them, and in many cases that electricity is generated with fossil fuels. And what about hybrid cars? Where do they stack up?
The video below from the Union of Concerned Scientists compares an average passenger car with a traditional internal combustion engine to that of an electric passenger car with an 84 mile range to answer this question. Take a look.
For more analysis of the charging emissions from electric vehicles, check out:
The Department of Energy offers this handy tool [27]for consumers who want to understand the relative emissions if they buy (and charge) an EV where they live based on the fuel sources for electricity in their state.
When we talk about agricultural emissions, that can mean a lot of different things as these emissions are dependent on the type of activities occurring on a farm. For our purposes for this lesson, we'll look broadly at emissions from crop production and livestock production.
It can be tricky to understand the overall role agriculture plays in global emissions because of how some of these smaller sectors are grouped together sometimes. To take a closer look, we're going to take these pieces of pie and slice them even thinner.
The graphic below demonstrates that agriculture, land use, and forestry (often called AFOLU [29]) account for about a quarter of global greenhouse gas emissions.
We'll focus our attention this week on these bigger subsector areas. And then, to keep things fun, I've included food waste in this section too. It's not technically categorized as an agricultural emissions source here, but I think in the context of our thinking about where emissions are coming from and what we can do about them, it makes sense to talk about it here (and, we're also covering waste this week - so it fits nicely with that, too).
In the following video, Penn State Professor (and METEO 469 course author) Michael Mann discusses the systemic changes we need - primarily in agriculture but also in other contexts of our emissions behaviors (remember proximate causes and driving forces?). He talks about the need for both individual and collective action and how those efforts work together. (This video is required course content and fair game for the content quiz/exam 1.)
While we spend a lot of effort thinking about the role of livestock production as agricultural emissions, crop production also plays a significant role in several ways.
The livestock we raise for meat and dairy consumption has a sizable impact on the global emissions profile.
Sometimes, the popular media likes to capitalize on the sensational nature of talking about cow burps and farts and greenhouse gas emissions (see Forbes article [40] for proof). And maybe this isn't all bad if it gets people talking (and possibly giggling) about the role our diet plays in the global climate crisis. (Did the instructor really use the word 'farts' in class? I think so...). And while that's certainly part of the puzzle, livestock-related emissions are much more complex and varied. We're going to take a look at several broad categories (as outlined by the Food and Agriculture Organization of the United Nations).
The emissions profile for livestock production varies by species. For example, if you look at this graphic below, you'll notice that almost all of the emissions associated with beef production come from enteric fermentation (the often satirized burps and farts, if you will), while chickens - not ruminant animals like cows - have no emissions from enteric fermentation and instead, their emissions are coming exclusively from manure management.
Before returning to Penn State to teach in the ESP Program, I worked as a Policy Analyst and Account Manager for a greenhouse gas offset project developer called Environmental Credit Corp. (now ClimeCo). Most of the offset projects we developed were related to manure management on hog and dairy farms. So, while all this chatter about manure this week may seem a bit unconventional or even gross to you, I guess I'm just used to knowing more about animal poop than I ever imagined I might! I thought I'd share a little bit of that experience with you here, as it relates to reducing greenhouse gas emissions from manure management practices on large-scale farming operations.
Many dairy and hog farmers use 'manure lagoons' for long-term storage of their manure. To put this bluntly, if you have a thousand (or in many cases way more than a thousand) anythings going to the bathroom every day, you need to figure out where all of that waste is going to go. For many farmers, manure lagoons offer a cost-effective and logical solution. They pump the manure into lagoons (they look like ponds, only you don't want to swim there!) and then several times a year, draw the manure out and land apply it to their fields as fertilizer. But, for the time, it's just sitting there, the manure is decomposing aerobically (with oxygen) and releasing methane directly into the atmosphere (and stinking up the neighborhood). The company I worked for partnered with USDA to offer farmers a simple alternative - covers for their manure lagoons. In the most simplistic of terms, we put tarps over these big ponds to capture the gas. In reality, it's a bit more complicated than that, and under those tarps (which are really 60 mm thick high density plastic), is a series of pipes to collect the gas. Now, the manure is decomposing anaerobically (because we took away the oxygen) and we can capture that gas.
What would we do with a bunch of captured methane? Well, there are a few options. The first, and less ideal option is simply to flare it. When it combusts, it combusts as carbon dioxide. So, there's still a greenhouse gas emission which occurs, but remember, its global warming potential is so much less than methane, there is a benefit to this. But it seems wasteful to just flare it when we can use it.
I'd like you to 'meet' Tom Butler. Tom was one of my favorite clients. He's a hog farmer in Lillington, NC and runs an 8,000 head feeder to finish operation. We covered Tom's manure lagoons in 2006 or thereabouts. Initially, we just flared the gas. But over the years, Tom has built a renewable energy empire on that hog farm, and he's now using all of his gas on-site to power his farm. How neat is that? And, lagoon covers offer some ancillary benefits worth noting, too. Think about Hurricane Dorian - do you want a hurricane's worth of rain dumping into a manure lagoon and possibly causing it to run over? No, you do not. With a covered lagoon, Tom doesn't have to worry about (increasingly more frequent) extreme weather events. Also, covered lagoons drastically reduce odor issues. I'll admit, I was nervous the first time I pulled up to Tom's farm. My husband had lived in North Carolina and assured me there was no smell quite like a hog farm. But, it actually was pretty tolerable.
Tom's a great example of a progressive farmer who is trying his best to do right by land, his animals, and the planet, and I thought it'd be nice to share this story with you, even if it is mostly about manure.
I couldn't dig up the picture, but I have a picture of me standing out on this lagoon. It's like standing on a water bed, only that's not water underneath the cover. Joking aside, Tom's crew and ours had to manage the cover very carefully - methane is highly combustible (obviously) and dangerous to work around. The life expectancy on a cover like this is 20-30 years, so Tom's still has a fair bit of life in it, and I'm excited to see what he'll do next. For perspective, this lagoon is over an acre in size.
We're choosing to look at emissions from food waste within the context of agriculture this lesson (though waste is also covered in Lesson 3), but ultimately, this is one that's hard to really pinpoint to a specific sector because it touches so many sectors. From land use, livestock, transportation, energy, and water - anytime we throw away food, we're throwing away all the embodied emissions in its production, harvest, processing, and transport to reach us. We could talk about food waste at very specific scales, but for our purposes in this lesson, we're going to think about food waste a bit more generally. It could be occurring during production, on its way to the grocery store, at the retail outlets, or in our own refrigerators (insert hand-raising emoji).
We don't hear much about food waste in the context of climate change, but it's really a sleeping giant. Take a look.
Land use and land cover change affect our overall greenhouse gas emissions profile because some types of land use do a great job of pulling carbon out of the atmosphere and storing it away while other types of land use have just the opposite effect. Understanding how are decisions related to land use fit into the overall emissions profile helps us make informed decisions.
Just how big of a factor is land use? Let's take a look.
As the FA 2019 semester began, fires raged (and continue to rage) across the Amazon. While this problem is inherently complicated and tangled up in the politics of the region, it's also one highly relevant to the human dimensions of climate change. Obviously, fires burn more in dry seasons. This region isn't particularly dry right now (compared to recent years at the same time) and yet more fires are burning. This is due at least in part to intentionally set fires to clear the land for agriculture. As we're learning in this lesson, agricultural land isn't as effective at sequestering carbon, and of course agriculture carries with it its own set of emissions. Additionally, the Amazon rainforest is one of the most biodiverse regions in the world, and while that might not feel directly connected to climate change. It's often the case that we see the human dimensions of climate change in the news throughout the course of our semester together, so I thought it was worth talking a bit specifically about the wildfires in the Amazon burning right now and how that relates to our changing climate (both cause and consequence). Here are some useful resources about the situation if you're interested (though they are not required reading for the course):
During the FA 2020 semester, we had several students enrolled in the course impacted by the fires burning across the western US.
Let's take a quick look at the emissions from our waste sector. Generally, we can break these down into four categories for direct emissions from waste:
Remember, these are just direct emissions from waste - so what you don't see captured here are the emissions from hauling waste to landfills, or collecting it from your front yard or the dumpster behind your apartment. Those are indirect emissions.
Since municipal landfills represent such an enormous piece of the waste sector pie, let's focus on what that looks like (so we can start thinking about what we might be able to do about it).
When we send our trash to the landfill, there's a fair bit of organic matter in the mix - things like food waste and yard waste. This organic matter will decompose anaerobically and release methane. Much like the lagoon covers we just talked about earlier in this lesson, there are a few options for what we can do to minimize those emissions. We can flare the gas, or the landfill can harness the gas and either use it on site or sell it back to the grid. But beyond that, we can work do divert that organic matter from ever reaching the landfill in the first place. Composting food waste and yard waste is a great place to start! Does your community offer organic waste collection or dropoff? You should check it out! Perhaps you can put your organics out for collection so even if you're not an aspiring backyard composter (I'm not), you can help keep it out of the landfill.
Take a close look at the biggest culprit of methane emissions from landfills on this bar graph from the Methane Landfill Initiative. This is 2010 data, so perhaps China is catching up to the US a bit, but for this snapshot in time, landfill emissions in the US were almost 3x that of the next closest country.
In the US, landfills over a certain size (containing 2.5 million metric tons of waste or 2.5 million cubic meters of waste) must capture their gas under Clean Air Act regulations. The EIA estimates that in 2017, about 370 landfills across the country were collecting their gas as part of this regulation (EIA, 2019 [53]). There are additional voluntary projects around the country as part of the Landfill Methane Outreach Program [54].
This lesson is devoted to understanding the emissions that drive climate change. We've broken them down by sector to try to understand how our actions result in a changing climate (we'll need to know this if we have any hope of doing something to solve it!). As you consider these emissions sectors, also think about the proximate causes [55] and driving forces [56] contributing to the emissions patterns. What do you see?
You have reached the end of Lesson 2! Double-check the lesson assignments in the corresponding lesson module in Canvas to make sure you have completed all of the tasks listed there.
Links
[1] http://cait.wri.org/
[2] https://creativecommons.org/licenses/by/4.0/
[3] http://www.wri.org/our-work/project/earthtrends-environmental-informationupdates/node/296
[4] https://www.carbonbrief.org/explained-fugitive-methane-emissions-from-natural-gas-production
[5] https://www.wri.org/blog/2013/04/close-look-fugitive-methane-emissions-natural-gas
[6] https://www.eia.gov/outlooks/ieo/pdf/0484(2017).pdf
[7] https://www.iea.org/reports/key-world-energy-statistics-2021/supply
[8] https://www.ipcc.ch/report/ar4/wg3/energy-supply/
[9] https://www.ucsusa.org/global-warming/science-and-impacts/science/each-countrys-share-of-co2.html#.W575uqinGUk
[10] http://www.flickr.com/photos/notanyron/4198850714/
[11] http://www.flickr.com/photos/notanyron/
[12] http://creativecommons.org/licenses/by-nc-sa/2.0/
[13] https://e360.yale.edu/digest/transportation-replaces-power-in-u-s-as-top-source-of-co2-emissions
[14] http://www.eia.gov/todayinenergy/detail.php?id=30712
[15] https://www.ipcc.ch/report/ar4/wg3/transport-and-its-infrastructure/
[16] https://www.eia.gov/outlooks/aeo/pdf/0383(2017).pdf
[17] https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions
[18] https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle
[19] http://www.climate.dot.gov/about/transportations-role/overview.html
[20] https://www.epa.gov/greenvehicles/fast-facts-transportation-greenhouse-gas-emissions
[21] https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data
[22] https://www.weforum.org/agenda/2016/04/the-number-of-cars-worldwide-is-set-to-double-by-2040
[23] https://www.drawdown.org/solutions/transport
[24] https://www.ipcc.ch/report/ar5/wg3/transport/
[25] https://www.forbes.com/sites/energyinnovation/2018/03/14/charging-an-electric-vehicle-is-far-cleaner-than-driving-on-gasoline-everywhere-in-america/#2d8eda6871f8
[26] https://theconversation.com/climate-explained-the-environmental-footprint-of-electric-versus-fossil-cars-124762
[27] https://afdc.energy.gov/vehicles/electric_emissions.html
[28] https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/4_Volume4/V4_01_Ch1_Introduction.pdf
[29] https://www.ipcc.ch/report/ar5/wg3/agriculture-forestry-and-other-land-use-afolu/
[30] http://www.researchgate.net/publication/331555875_Climate_change_mitigation_potential_of_agricultural_practices_supported_by_IFAD_investments_An_ex_ante_analysis
[31] https://www.cnn.com/videos/world/2019/08/09/amanpour-michael-mann-ipcc-climate-crisis.cnn
[32] https://insideclimatenews.org/news/24092018/infographic-farm-soil-carbon-cycle-climate-change-solution-agriculture
[33] https://www.usda.gov/
[34] https://blog.nature.org/science/2014/06/18/global-agriculture-land-sustainability-deforestation-foodsecurity/
[35] https://news.berkeley.edu/2012/04/02/fertilizer-use-responsible-for-increase-in-nitrous-oxide-in-atmosphere/
[36] https://www.epa.gov/ghgemissions/understanding-global-warming-potentials
[37] https://www.nature.com/articles/nclimate3158
[38] https://www.eia.gov/todayinenergy/detail.php?id=18431
[39] http://www.fao.org/3/i3437e/i3437e.pdf
[40] http://www.forbes.com/sites/samlemonick/2017/09/29/scientists-underestimated-how-bad-cow-farts-are/#4a6fbd4a78a9
[41] https://academic.oup.com/af/article/9/1/69/5173494
[42] https://butlerbioenergy.net/about
[43] https://magazine.campbell.edu/articles/power-of-rural/
[44] https://www.wri.org/blog/2016/06/4-surprising-reasons-measure-and-reduce-food-loss-and-waste
[45] https://www.arborday.org/carbon/carbon-emissions.cfm
[46] https://www.pbl.nl/en
[47] https://www.carbonbrief.org/media-reaction-amazon-fires-and-climate-change
[48] https://www.nationalgeographic.com/environment/2018/11/how-cutting-the-amazon-forest-could-affect-weather/
[49] https://www.washingtonpost.com/weather/2019/08/21/amazonian-rainforest-is-ablaze-turning-day-into-night-brazils-capital-city/?utm_campaign=Carbon%20Brief%20Daily%20Briefing&utm_medium=email&utm_source=Revue%20newsletter
[50] https://www.epa.gov/ghgreporting/ghgrp-waste#2017-subsector
[51] https://www.waste.ccacoalition.org/document/landfill-methane-reducing-emissions-advancing-recovery-and-use-opportunities-gmi
[52] https://www.globalmethane.org/
[53] https://www.eia.gov/energyexplained/biomass/landfill-gas-and-biogas.php
[54] https://www.epa.gov/lmop
[55] https://www.e-education.psu.edu/geog438w/node/630
[56] https://www.e-education.psu.edu/geog438w/node/363