3. Energy and climate change

Key data

(2017)

GHG emissions without LULUCF*: 6 456.7 MtCO2-eq, -12.0% since 2005 GHG emissions with LULUCF*: 5 742.6 MtCO2-eq, -13.0%% since 2005

Source: UNFCCC.

Overview

The United States (US) is pursuing a balanced approach that aims at mitigating climate change while expanding the economy.

In 2017, total greenhouse gas (GHG) emissions (excluding emissions from land use, land-use change and forestry) in the United States amounted to 6 457 million tonnes of carbon dioxide equivalent (MtCO2-eq). This was around 12% of global emissions, the second-highest share in the world after the People’s Republic of China (IPCC, 2018). Since 1990, total GHG emissions have increased by 1.3%, but since 2005, emissions have decreased by 11.5%, driven mostly by a fuel switch from coal to gas and renewables in power generation.

Energy-related emissions from combustion processes in the power and heat generation, transport, industry, households, and commercial sectors are the largest contributor to total GHG emissions. In 2017, energy-related emissions accounted for 84% of total emissions followed by the agriculture sector (8%), industrial process emissions (6%) and the waste sector (2%) (Figure 3.1). Energy-related emissions include carbon dioxide (CO2) emissions from fossil fuel combustion, but also other emissions from the energy sector such as methane leakage from natural gas systems. CO2 emissions from combustion are the focus of this chapter. Those accounted for around three-quarters of total GHG emissions in 2017.

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3. ENERGY AND CLIMATE CHANGE

CO2 is the main GHG, accounting for 82% of total GHG emissions, largely corresponding to emissions from combustion processes. Remaining GHG emissions are mainly methane and nitrous oxide (N2O), mostly from agriculture, waste management, and oil and gas production.

Figure 3.1 GHG emissions by sector, 1990-2017

Energy*

4 000

2 000

0

IEA (2019). All rights reserved.

US GHG emissions have fallen by 12% since 2005, mainly due to a decline in energy-related emissions driven by a fuel switch from coal to gas and renewables in power generation.

*Energy includes power and heat generation, commercial, households, industrial energy consumption and transport. Energy-related emissions include both CO2 emissions from combustion and other GHG emissions related to the energy sector.

Source: EPA (2018a), Inventory of Greenhouse Gas Emissions and Sinks 1990-2016, https://unfccc.int/documents/65674.

Energy-related CO2 emissions

The trend for energy-related CO2 emissions has changed multiple times in recent decades. Emissions increased until the 1990s, after which they plateaued in the early 2000s, followed by a decline in the last decade (Figure 3.2). In 2017, energy-related emissions amounted to 4 759 million tonnes of CO2 (MtCO2), a 17% reduction since the peak in 2005. Power generation accounted for 38% of energy-related emissions and transport for 36%. The rest was from industry (9%), residential (6%), commercial (5%) and other energy sectors (5%).

In the past decade, CO2 emissions have fallen across all sectors, but the biggest decrease was in power generation. From 2007 to 2017, emissions from power generation dropped by 16%, despite electricity generation remaining stable during that period. This large reduction in emissions happened through rapid growth in renewable energy sources and natural gas from the shale revolution, replacing old coal-fired power generation systems. Emissions reductions in the power sector contributed to over 70% of total reductions in energy-related emissions in the United States in the last decade. Growth in renewables and in natural gas-fired generation each accounted for roughly half of power sector emissions reductions.

Emissions have also fallen in other sectors, notably in industry, where an overall decline in energy consumption as well as fuel switching from coal to natural gas led to emissions

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3. ENERGY AND CLIMATE CHANGE

reduction of 12% between 2007 and 2017. Transport emissions have also declined in the last decade, but by a more modest 5%, and since 2012, the trend has been increasing. If continuing on the current trajectory, the transport sector will soon surpass the power sector as the largest source of CO2 emissions in the United States.

In line with the growing share of transport emissions, the largest source of energy-related CO2 emissions is oil combustion (Figure 3.3). In 2017, oil accounted for 42% of total emissions. Coal emissions have significantly fallen in recent years, and their share in total emissions fell from 38% in 2007 to 28% in 2017. This drop correlates with growth in natural gas emissions, which accounted for 30% of total emissions in 2017, up from 22% in 2007.

Figure 3.2 Energy-related CO emissions by sector, 1990-2017

IEA (2019). All rights reserved.

Emissions have fallen across all sectors in the past decade, most significantly in the power sector and less so in the transport sector.

*Other energy industries includes emissions from coal mines, oil and gas extraction, oil refineries, blast furnaces, and coke ovens.

**Industry includes CO emissions from combustion at construction and manufacturing industries.

***Commercial includes commercial and public services, agriculture/forestry and fishing. Source: IEA (2019), CO Emissions from Fuel Combustion 2019, www.iea.org/statistics/.

IEA (2019). All rights reserved.

Oil is the largest source of CO2 emissions in the United States, and its share is increasing, as transport emissions account for a growing share of the total and as coal use declines.

*Other includes emissions from non-renewable waste.

Source: IEA (2019), CO Emissions from Fuel Combustion 2019, www.iea.org/statistics/.

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CO2 drivers and carbon intensity

Total energy-related CO2 emissions in a country are driven by the growth in population, economic development and changes in the energy intensity of the economy (total primary energy supply [TPES] per gross domestic product [GDP]) and carbon intensity of energy supply (CO2/TPES).

From 1990 to 2017, US GDP per capita grew by 48% and population increased by 30%, while energy-related CO2 emissions remained relatively stable (Figure 3.4). This was achieved through a reduction in energy intensity of the economy by over 40% and a decline in carbon intensity of energy supply by 12%. During the last decade in particular, the United States has seen a decoupling between energy-related emissions and growth in the economy and population.

Figure 3.4 Energy-related CO2 emissions and main drivers in US, 1990-2017

IEA (2019). All rights reserved.

Despite large economic growth per capita, energy-related CO2 emissions are on a similar level to 1990, thanks to reduced carbon intensity of the economy.

Note: Real GDP in USD 2010 prices and at purchasing power parity (PPP).

Source: IEA (2019), CO Emissions from Fuel Combustion 2019, www.iea.org/statistics/.

Carbon intensity of the economy, measured as the ratio of CO2 emissions per unit of GDP, is used as a common indicator of whether CO2 emissions are decoupling from economic growth. In 2017, US carbon intensity was 0.27 kilogrammes of energy-related CO2 (kgCO2) per USD,1 the seventh-highest among the 30 International Energy Agency (IEA) member countries and 16% above the IEA average (Figure 3.5). However, this reflects already significant improvement over the previous decade: US carbon intensity fell by 28% from 2007, more than the average reduction across IEA countries (Figure 3.6).

1 United States dollars in 2010 real values and at PPP.

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Figure 3.5 CO2 intensity (energy-related emissions) in IEA member countries, 2017

IEA (2019). All rights reserved.

The US economy has the seventh-highest CO intensity among IEA member countries.

Source: IEA (2019), CO Emissions from Fuel Combustion 2019, www.iea.org/statistics/.

2

IEA (2019). All rights reserved.

US CO intensity has declined faster than the IEA average, but remains at a higher level.

Source: IEA (2019), CO Emissions from Fuel Combustion 2019, www.iea.org/statistics/.

2

Lower carbon intensity in electricity generation has been a main driver of the recent decline in overall carbon intensity in the US economy. Substitution of coal-fired generation with less carbon-intensive natural gas-fired generation – enabled by rising domestic shale gas production – and growth in renewables have been the main contributing factors (Figure 3.7). Although nuclear power remains the dominant source of low-carbon electricity generation, growth in solar and wind power has significantly contributed to a decline in carbon intensity of electricity generation. Between 2007 and 2017, the share of fossil fuels in electricity generation declined from 72% to 63%, while the share of renewables in the sector increased from 8% to 17%.

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