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Thanks to the COVID recession, US GHG emissions fell by 10.7% in
2020, compared with 2019, according to the US Environmental
Protection Agency (EPA), a much higher rate than in any other year
since tracking began in 1990.
US CO2-equivalent GHG net emissions totaled 5.222 billion metric
tons (mt) in 2020, compared with 5.842 billion mt the prior year
(which itself was a reduction of 1.7% from 2018).
The figures include a reduction for carbon sinks. The US is the
world's second-largest carbon emitter, behind China, which has net
GHG emissions of about 9.9 million mt/year, according to the
International Energy Agency.
The 29th annual "Inventory of US Greenhouse Gas
Emissions and Sinks" was released in draft form on 15 February
and in final form on 14 April. In the draft, the estimated
emissions were 5.216 billion mt of CO2-e.
"The sharp decline in emissions from 2019 to 2020 is largely due
to the impacts of the coronavirus pandemic on travel and economic
activity. However, the decline also reflects the combined impacts
of many long-term trends, including population, economic growth,
energy market trends, technological changes including energy
efficiency, and the carbon intensity of energy fuel choices," EPA
said.
Source: US EPA
Fossil fuel consumption
Fossil fuel consumption accounted for 92% of CO2 emissions in
2020 (4.33 billion mt), with transportation representing 36% of
that amount and electric power generation 33%.
Emissions from transportation declined by 10.7% between 2019 and
2020, and the electric power sector showed a 10.5% decrease in
emissions "due to a decrease in electricity demand of about 3.8%
and also … [the] continued shift from coal to less carbon-intensive
natural gas and renewables," EPA said.
Since 1990, EPA said CO2 emissions across the entire economy
decreased by 8.4% (397 million mt CO2-e).
Still, in 2020, emissions of CO2 represented nearly 79% of the
total GHG inventory, making it the focus of much current and proposed US regulation and funding for the energy
transition. "Historically, changes in emissions from fossil fuel
combustion have been the main factor influencing US emission
trends," EPA said.
Source: US EPA
In recent decades, coal-to-gas switching in power and improved
efficiency of passenger vehicles and trucks have been driving the
decrease in this category. "From 2005 to 2020, power sector CO2
emissions dropped 40.1% while generation remained relatively flat
(a 1.3% decrease)," EPA noted.
On the auto side, EPA proposed new rules in
August that could reduce emissions by 9.8% for cars and light-duty
trucks in model year (MY) 2023 over current rules, and an
additional 5% per year for MY 2024-2026.
Methane update
Methane emissions—which are a particular concern of US policy efforts—accounted
for 10.9% of the GHG inventory in 2020. Since 1990, they have
decreased by 16.6%. Methane's global warming impact is about 80-84
times greater than that of CO2 for the first 20 years it is in the
atmosphere, according to climate scientists.
President Joe Biden has set a goal for the US to reduce methane
emissions by 30% from 2020 to 2030, as one of the sponsors of the
Global Methane Pledge announced
in September.
EPA reported that the oil and natural gas industry reduced its
methane emissions by 37.6 million mt between 1990 and 2020, a
decrease of 15.5%. The decrease in the oil and gas sector is
largely due to improved leak controls on gas pipelines and
compressors, EPA said.
The landfill industry (67.3 million mt) and the coal mining
sector (55.3 million mt) have reduced their methane emissions to an
even greater degree over three decades, or 38% and 55%,
respectively. For landfill operators, the answer has been
installation of technology to capture and sell methane; for the
coal industry, EPA noted that the emissions reductions are related
to fewer mines in operation.
Industrial processes and product use
Industrial processes and product use (IPPU) accounted for 380
million mt of CO2-e in 2020, less than 1% higher than the 378.2
million mt in 2019. Leading the sector—and accounting for more
than 120 million mt of GHGs in 2020—were the industries of iron
and steel production, cement, and petrochemicals.
Biden launched a new series of programs on 15 February that
would help to reduce emissions from both the energy and IPPU
sectors, using the more general term "manufacturing sector" in the
announcement. These include
investments in production, storage, and use of green hydrogen;
guidance to support the carbon capture and storage industry's
growth; and government preferences for buying low-emissions steel,
concrete, and other materials.
"By helping manufacturers use clean energy, efficiency upgrades,
and other innovative technologies to reduce emissions, the
administration is supporting cleaner industry that can produce the
next generation of products and materials for a net-zero economy,"
the White House said.
Agriculture
Agricultural emissions are not declining as quickly as those of
the energy sector, and EPA reported they accounted for 595 million
mt CO2-e in 2020, or 10% of the US GHG inventory in 2020. This was
a reduction of 4.5% compared with 2019, or less than half of the
overall US rate of improvement during the year.
Methane makes up a much larger share of agriculture's GHG
inventory than it does for other sectors, about 42% in 2020, and
has become a major industry target through the installation of
hundreds of dairy digesters across the country.
Even larger is the production of nitrous oxide (N2O), which was
55% of the CO2-e inventory, due primarily to fertilizer use.
"Agricultural soils are the largest anthropogenic source of N2O
emissions in the United States, accounting for 74.3% of N2O
emissions in 2020 and 5.3% of total emissions in the United States
in 2020," EPA said. Nitrous oxide emissions have been flat since
1990, as they were only 0.1% higher in 2020 than 30 years
earlier.
Land use change
EPA reported that the land use, land-use change, and forestry
(LULUCF) sector registered CO2-e removals of 810.7 million mt in
2020. "This represents an offset of 13.6% of total greenhouse gas
emissions in 2020," EPA said, and was an increase of 50 million mt
from the prior year.
The hefty gain in 2020 in LULUCF stocks reverses the trajectory
of losing land sinks during the last few years and also over the 30
years of EPA tracking. Between 1990 and 2020, total LULUCF carbon
sequestration decreased by 9.1%, or about 81 million mt, "primarily
due to a decrease in the rate of net carbon accumulation in forests
and remaining cropland, as well as an increase in CO2 emissions
from land converted to settlements."
Flooded land was the largest source of methane emissions in 2020
from the LULUCF category, followed by forest fires, but fires were
the largest source of nitrous oxide emissions.
Additions and adjustments
For the 2020 inventory, EPA added new categories of methane and
CO2 emissions that were not included in prior inventories. It
accounted for methane leaks from residential and commercial
appliances, industrial facilities, power plants, and natural gas
fueled vehicles. The inventory also factored in fugitive CO2
emissions from coal mining, and methane, and CO2 emissions from
land converted to flooded land.
Also, the agency back-adjusted the 30 years of data for several
categories in which it has improved its methodology in the last
year. For the 2020 inventory, the following categories have been
adjusted by more than 2.5 million mt of CO2-e: methane from natural
gas waste systems; methane from manure management; CO2 from land
converted to grassland; and nitrous oxide from wastewater
treatment.
