U.S. and Global Carbon Intensity Trends

President Barak Obama proudly announced to the public that “the United States has reduced [its] total carbon pollution more than any other nation on Earth”[1] over the past eight years. In fact, the US lowered its emissions by 690 MMTCO2 between 2004 and 2012; the only close competitor is the EU which reduced its emissions by 530 MMTCO2 in that time span. Though absolute emissions are an easily identifiable metric for progress towards climate change goals, there are several other metrics and the US is a global leader according to many of them.

Relative emissions – how much carbon a nation produces today compared to a previous time period – are also insightful. For example, the Kyoto Protocol called for 2012 greenhouse gas emissions (not just CO2) to reach a global average 5% lower than 1990 levels.[2] In terms of carbon emissions, the US – which signed, but not ratified the Protocol – is the closer to reaching that goal than any other major economy outside of the EU. Of the major economies represented in Figure 1, the US is the only nation not to have ratified the Kyoto Protocol.[3]

Figure 1. Carbon dioxide emissions relative to 1990 levels for major economies.

Source: British Petroleum, “Statistical Review of World Energy 2013: Historical Data Workbook,” June, 2013.

However, both absolute and relative emissions fall short of clearly articulating progress towards climate change goals. For example, the world’s total carbon emissions still rose by close to 5900 MMTCO2 between 2004 and 2012 in spite of the US and EU improvements. Further, some reductions occurred in response to economic downturn. “Creating jobs and leading to a cleaner, safer planet” were the accolades the President gave to his all-of-the-above energy strategy, so a more helpful metric would attempt to decouple carbon emissions from economic conditions.[4]

What comes closer to supporting President Obama’s claim of, and provides a more exemplary metric for, progress towards climate change goals is quantifying the energy system’s reliance on carbon – that is, how much carbon is emitted for a given amount of energy produced (kgC/GJ). This is sometimes referred to as carbon intensity.

In the eight year period referenced by the President, the US decreased its reliance on carbon-intense fuels by about 5% – the second best improvement during that time period with Canada improving the most. (See Table 1.) Canada underwent fuel transitions while increasing its total energy consumption; this helped improve its carbon intensity more than the EU and the US which experienced fuel transition, but also consumed less energy in 2012 than in 2004.

The US’s carbon intensity has declined since 1965; its 10.9% improvement is slightly less than the world average of 11.4%. So, even as the world increased its carbon emissions, it decreased its reliance on carbon-intense fuels. This is indicative of progress towards climate change goals because, as the trend continues, the US and other nations could completely divest themselves of carbon-intense fuels, thus producing only carbon-free energy.


Table 1. Notable carbon emitting countries and their improvements in CO2 emission metrics. (Positive numbers represent desirable changes/reductions; negative numbers represent undesirable changes/increases.)

Emissions in MtC02

% Change in kg/GJ

2004

2012

2004-2012

1965-2012

China

5102.0

9208.1

3.21

9.58

US

6472.4

5786.1

4.94

10.88

EU

4503.3

3977.5

4.59

28.66

India

1116.3

1823.2

-0.03

5.25

Russia

1604.4

1704.3

0.67

23.85*

Japan

1394.6

1409.0

-11.30

1.64

South Korea

591.2

763.7

-1.88

23.50

Canada

628.7

619.6

5.44

20.21

Saudi Arabia

409.7

615.3

0.40

9.17

Iran

423.4

608.3

2.69

5.03

Brazil

369.7

500.5

1.49

23.56

South Africa

417.9

446.1

0.41

5.06

Australia

370.6

392.2

2.99

6.31

Ukraine

343.8

321.7

-2.73

20.33*

World

28602.7

34466.1

-0.54

11.40

* Calculated using an estimated based on carbon intensity of the Soviet Union as a hole in 1965.

Source: British Petroleum, “Statistical Review of World Energy 2013: Historical Data Workbook,” June, 2013.

As seen in Table 1, progress towards reducing the US energy system’s reliance on carbon has spanned administrations from both sides of the aisle, and pre-dates President Nixon’s call for energy independence in 1974. In fact, the International Panel on Climate Change (IPCC) has noted that although improvements in carbon intensity develop “comparatively slow, at the rate of 0.3% per year, the trend has persisted throughout the past two centuries.”[5] Instead of being driven by policy, “the overall tendency toward lower carbon intensities results from the continuous replacement of fuels with high carbon content by those with low carbon content,” says the IPCC.[6] This fuel transition referenced by the IPCC is the emergence of coal to replace wood, oil rising to replace coal, natural gas rising to take market share away from oil, and so forth. (See Figure 2.) Each new fuel source emits less carbon than the one before it – an unintended side effect for the at least the first century and a half of fuel transitions.

Figure 2. Long-term transitions in the US’s primary energy fuel supply.

Source: Data compiled from British Petroleum, “Statistical Review of World Energy 2013: Historical Data Workbook,” United Nations, “World energy supplies 1950 – 1974,” 1976, United Nations, “Proceedings of the International Conference on the Peaceful Uses of Atomic Energy,” Vol. 1, 1956, and Vaclav Smil, “Energy Transitions: History, Requirements, Prospects,” Santa Barbara: Praeger, 2010.

As President Obama continues to tout his all-of-the-above plan and push forward with his Climate Action Plan, it begs to be compared to the long-term trends cited by the IPCC and others. If fuel substitution can be expected to continue reductions in the energy system’s reliance on carbon, then it not only solidifies carbon intensity as the primary metric for marking progress toward climate change, but could also predict the fuel(s) of the future to better inform today’s R&D investment strategies for the US and other nations.



[1] Barack Obama, “ 2014 State of the Union Address,” Washington, DC, January 28, 2014. Available at:  http://www.whitehouse.gov/the-press-office/2014/01/28/president-barack-obamas-state-union-address.

[2] United Nations, “Kyoto Protocol to the United Nations Framework Convention on Climate Change,” 1998.   Available at: https://unfccc.int/kyoto_protocol/items/2830.php.

[3] Canada signed the Protocol in 1998, ratified it in 2002, but withdrew in December of 2012.

[4] Obama, “2014 State of the Union Address.”

[5] International Panel on Climate Change, Nebojsa Nakicenovic and Rob Swart ed., “Emissions Scenarios,”  Cambridge: Cambridge University Press, 2000.

[6] IPCC, 2000.

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