(Wonkiness Alert: this post will be a bit wonky, with data being presented and science being spoken.)
Before I jump into the swirling pool of emissions data, I need to editorialize a bit. As I studied the Executive Summary of the Draft EPA document used for this post, I realized that something was not being said. I'm neither an expert on this topic nor an insider in the EPA; however, given the political climate in which this document was produced (Trump administration), I will assume a political filter was applied.
The report presents greenhouse gas emission data for the years from 1990, 2005, and 2015 through 2019. The discussions in the report focus on comparisons of emissions for 1990 and 2019, in terms of increases or decreases between those years. In every data table, the columns are labeled with years, as shown below. I wondered why the year 2005 was included and highlighted in the tables, and the reason finally struck me (I was not hurt). The United States emission reduction goals in the Paris Agreement on Climate Change are based on emissions in 2005 as the baseline year. The EPA report uses the term "climate change;" however, there is no reference (at least in the Executive Summary) to the Paris Agreement or that 2005 is the baseline year for U.S. emission reduction goals. In fact, the report does not talk about emission reduction goals.
So I have to assume, again, without knowing for sure, that the EPA scientists who wrote the report gave us a marker for looking at Paris Agreement goals. And so, in this post, I will use the 2005 data to look at how the USA is doing relative to the Paris Agreement goals. My final assumption is that, under the Biden administration, future EPA reports will not try to hide anything!
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This post is focused on greenhouse gas emissions in the United States. For context, some global data are included in this section.(1) The seven top emitter countries in 2017 are shown below. The U.S. is second, behind China.
On a per capita basis, the United States leads the world with about 19 tons of CO2 equivalent per person, followed by Russia (~15.5 tons/person), Japan (~10 tons/person) and the European Union and China (~8 tons/person each). Finally, when parsed by economic sector, as shown below, the energy sector accounts for 72% of global emissions, of which 31% is production of electricity and heat, and 15% is from transportation.
So how are we doing on climate change in this country? We all know that it is real, that it started having real impacts years ago, and that the future looks different for human societies if we don't change the trajectory. I have wondered about this myself, so I decided to do some reading. I selected one document: Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2019. U.S. Environmental Protection Agency. in Federal Register, February 12, 2021. (1) This document was out for review comments until late March, 2021. I reviewed the Executive Summary.
My goal in this post is to summarize the large amount of information in a clear and simplified way; this might or might not work.
Let's start with defining a few terms and acronyms:
- emissions inventory - identifies and quantifies the anthropogenic sources and sinks of greenhouse gases
- GHG = greenhouse gas, a gas in the atmosphere that can directly or indirectly contribute to climate change
- GWP = Global Warming Potential is a way to compare the ability of a gas to trap heat in the atmosphere relative to another gas
- MMT CO2 Eq. = million metric tons of carbon dioxide equivalent. CO2 is used as the reference gas to calculate and compare the GWP of other gases. For these calculations, the GWP of CO2 has a value of 1. The report lists more than two dozen other gases that have GWP values relative to CO2; examples are: methane (CH4) = 25, nitrous oxide (N2O = 298, and hydrofluorocarbon 23 (HFC-23) = 14,800. In other words, one unit of methane has the greenhouse gas equivalent of 25 units of carbon dioxide.
- a metric ton (MT) is 2,204.6 pounds, or 1,000 kilograms. 1 million metric tons (MMT) is 2.205 billion pounds.
- LULUCF: Land Use, Land Use Change and Forestry. These landscape categories have associated emissions and sinks of greenhouse gases. For example, a forest landscape might lock up more carbon than it emits. LULUCF includes agriculture, conversion of land from rural to urban, urban trees, forestry and other land uses.
- total emissions and net emissions: total emissions is the total of emissions from all economic sectors; net emissions is total emissions minus the amount of carbon removed, or sequestered, from the atmosphere by LULUCF.
The above might be the wonkiest part of this post!
Let's start with the big picture. Just how much GHG does the U.S. put into the atmosphere every year, and how has this changed in the past 29 years?
- In 1990, total U.S. emissions was 6,449.4 MMT CO2 Eq.; net emissions was 5,548.6 MMT CO2 Eq.
- In 2019, total U.S. emissions was 6,577.2 MMT CO2 Eq.; net emissions was 5,788.3 MMT CO2 Eq.
- Gross U.S. emissions per year increased by 2.0% between 1990 and 2019. However, gross emissions was 15.7% above 1990 levels in 2007, and generally decreased between 2007 and 2019.
- Net emissions increased by 4.3% between 1990 and 2019.
Paris Agreement Goals
The U.S. stated goal in the Agreement was a 17% reduction in carbon emissions by 2020, and a 26% to 28% reduction by 2025, compared to 2005 emissions. (Without digging into the Agreement, I assume that "carbon emissions" means GHG emissions expressed as CO2 equivalent. I also don't know if the goal is based on total or net emissions, so I will assume it is net emissions.)
The actual emissions in 2005 were: 7,432 MMT Total, and 6,644 MMT Net.
The actual emissions in 2019 were: 6,577 MMT Total, and 5,788 MMT Net
The U.S. goal for 2020 is: 6,169 MMT Total, and 5,514 MMT Net
The U.S. goal for 2025 is: 5,351 MMT Total, and 4,784 MMT Net
In 2019, the 2020 goal for total carbon emission reduction was not met*, and the net carbon emission was slightly greater than the goal (not met). (Data for 2020 are not in this report; however, the pandemic might have resulted in a greater lowering of emission due to less transportation activity in the United States.)
A few figures from the EPA report are instructive. Figure ES-3 shows changes of emissions relative to 1990 levels. Note the steady increase through 2007, followed by a bumpy but overall steady decline through 2019. (Editorial comment: the trends might be related to programs introduced and removed by the Obama (2008-2016) and Trump (2016-2019) administrations. The data might also reflect the impacts of the economic recession starting in 2008.)
I have summarized, below, some of the data from Table ES-2 in the report, showing the major sources of carbon emissions.
Table ES-2 Recent Trends in GHG Emissions and Sinks (MMT CO2 Eq):
Total Fossil Fuel combustion 1990 = 4,731.5 2019 = 4,888.5
transportation 1,469.1 1,843.2
electric power 1,820.0 1,606.0
industrial 853.8 837.6
residential 338.6 338.8
commercial 228.3 238.3
In 1990 and 2019, emissions from the transportation sector and the generation of electricity sector accounted for 69.5% and 70.6%, respectively, of total emissions from fossil fuel combustion. This is an important set of numbers to understand, as it tells us where we need to focus our attention for GHG reductions. These two sources are interrelated. The most obvious way to reduce transportation emissions is to transition from fossil fueled vehicles to electric vehicles; however, the methods of generating electricity also have to transition from a reliance on fossil fuels.
At this point, two more graphics are instructive. Figure ES-6 shows 2019 emissions from fossil fuel combustion. Combustion of petroleum accounts for most of the emissions from transportation. Combustion of coal and natural gas account for the majority of emissions for generation of electric power, with coal representing more than half. Overall, emissions are greatest from burning petroleum, followed by natural gas and then coal (see pie diagram in figure).
The next figure looks at emissions from electric power generation. Total emissions have steadily decreased since 2007 (solid black line, right axis), while the total amount of electric power has increased between 1990 and 2007, and then leveled off between 2007 and 2019. The reason total emissions have declined is two-fold: more renewable generation (e.g. wind and solar), and replacement of coal-burning with natural gas generation facilities (natural gas has lower emissions than coal).
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------------------------ -------------------------- ------------------------Different gases have different global warming potentials (GWP). For the EPA report, every gas has a carbon dioxide (CO2) equivalent. For the emission inventory, CO2 has a value of 1 GWP, methane (CH4) has a value of 25, nitrous oxide (NO2) is 298, hydrofluorocarbon 23 (HFC-23) is 14,800, and etc.
Methane (CH4) is the second largest emission gas after CO2, at 10% of all emissions. The top five sources of CH4 emissions are, from highest down, enteric fermentation, natural gas systems, landfills, manure management, and coal mines. Enteric fermentation is methane emitted by livestock (burps and farts). In 2019, enteric fermentation was 178.6 MMT CO2 eq., representing 27.1% of the CH4 total emissions, an increase of 8.4% since 1990. This increase tracks the increase in cattle populations in the U.S.
And, just in case you are wondering, as I did, about CO2 emissions from human breathing, I did a rough calculation. (2) For the population of the USA in 2021, total emissions from breathing is 84.5 MMT CO2 eq. (I did not do a calculation for human burping and farting.)
Carbon sinks. Land Use, Land Use Change and Forestry (LULUCF) are the areas where carbon is removed from the atmosphere. It is important to know that there are LULUCF emissions, as explained in the EPA report: "LULUCF emissions of CH4 and N2O are reported separately from gross emissions totals. LULUCF emissions include the CH4, and N2O emissions from Peatlands Remaining Peatlands; CH4 and N2O emissions reported for Non-CO2 Emissions from Forest Fires, Non-CO2 Emissions from Grassland Fires, and Coastal Wetlands Remaining Coastal Wetlands; CH4 emissions from Land Converted to Coastal Wetlands; and N2O emissions from Forest Soils and Settlement Soils."
LULUCF carbon stock change is how the EPA lists the removal or locking-up of GHG: "LULUCF Carbon Stock Change is the net C stock change from the following categories: Forest Land Remaining Forest Land, Land Converted to Forest Land, Cropland Remaining Cropland, Land Converted to Cropland, Grassland Remaining Grassland, Land Converted to Grassland, Wetlands Remaining Wetlands, Land Converted to Wetlands, Settlements Remaining Settlements, and Land Converted to Settlements."
LULUCF data, in MMT CO2 Eq., include:
1990 2005 2019
Emissions 7.9 16.8 23.4
Carbon stock change -908.7 -804.8 -812.4
Net -900.8 -788.0 -788.9
These data show that the capture and sequestration, or retention of GHG from release to the atmosphere is going in the wrong direction.
What's the take away? (This section is editorial.)
It is obvious from this brief summary (and I encourage you all to look at the EPA document linked in note 2, below) that the major sources of greenhouse gas emissions in the United States, 70% of the total, are the transportation and electricity generation sectors. These two sectors are inter-related; we cannot decrease one by increasing the other, we have to decrease both. As the demand for electricity increases for reasons of reducing GHG emissions (for example, more electric vehicles, new residential and commercial construction that is all electric, &c), the production of this electricity must be from non-emission methods (i.e. renewable). It does not make sense to drive an electric car that recharges with electricity generated by burning coal or natural gas.
Many Americans are doing things to reduce their "carbon footprint." Some examples are replacing incandescent light bulbs with compact fluorescent or LED bulbs, purchasing more energy efficient appliances, installing solar panels on homes, &c. These are worthwhile actions; however, based on the data above, the residential and commercial sectors are not the major sources of GHG.
We Americans need a national program, enacted into law, that will drastically change the transportation and electric generation sector emissions. The Biden administration is proposing a massive infrastructure bill that will address these issues (as well as many others). This is perhaps the most important moment in the effort to reverse the trend of climate change. It is already too late in some respects; however, a focused, concerted effort can slow the trend, improve prospects for human society in the future, and set the United States on a course that makes sense.
It appears, from my cursory review, that the U.S. has made good progress towards meeting the Paris Agreement goals. New goals for the years 2030 and beyond will be set soon, and political will is the key to success. It is unfortunate that, like so many other issues, climate change is a partisan issue. The Democrats have two years to make significant progress that demonstrates to voters that there are tangible benefits to them from the needed programs.
Remember, the planet is not in danger; human societies are in danger. The planet will be fine, no matter what we do. Will we?
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* the original post stated that the goal "was met," this statement was corrected on April 7, 2021.
NOTES:
(1) https://www.c2es.org/content/international-emissions/
