To answer this question we need a source of U.S. emission data. The U.S. Department of Energy (DOE's) just released its 2004 annual report on U.S. greenhouse gas (GHG) emissions (downloadable
here). While a year behind, DOE's annual emissions reports are a treasure trove of information. Although data-rich and rather dry, the report allows us to answer the question posed above, and to assemble an interesting picture of GHG emissions trends in the United States. It also provides some insights into the challenges facing the United States in reducing GHG emissions. I've tried to paint such a picture below:
U.S. emissions in 2004 were 7.1 billion tons of CO2e (CO2 equivalent, a common metric for the six gases in the inventory), an increase of 2% from 2003, and 16% from 1990.
- This works out to almost 25 tons of CO2e per person.
- The totals do not account for net land-use based sequestration, which totaled more than 1 billion tons in 1990. But because sequestration fell to 828 million tons in 2003, the net increase in U.S. emissions since 1990 is actually closer to 20%.
Carbon dioxide accounted for 84% of this CO2e total. Methane was the next largest contributor (9%). Nitrous oxide accounted for 5%, and HFCs, PFCs, and SF6 emissions totaled a mere 2%.
Overall carbon dioxide emissions grew by almost 2% from 2003 (reflecting rapid economic growth), and have grown by more than 19% since 1990.
- Energy-based carbon dioxide emissions have grown 18% since 1990 (reflecting 20+ percent gains in residential, commercial, and transport sectors). Industrial emissions, however, are up only 2% (due to shifts away from coal-based industries, and toward less energy-intensive manufacturing sectors).
- If looked at separately, electricity-based emissions are up by 28% since 1990. Natural gas emissions from power generation are up by 67% since 1990; coal-fired emissions are up 25%.
- Electricity production accounts for 39% of total energy-based carbon dioxide emissions (up from 36% in 1990). Coal-fired emissions still account for 82% of electricity-based emissions (down from 84% in 1990). And the carbon intensity of electricity is down only 1% since 1990!
Methane emissions were up almost 1% from 2003, but are down 11% since 1990.
- Landfill emissions were down 27%, and coal-mining emissions were down more than 30%.
- Conversely, methane emissions from domestic livestock are up 26% (due to larger production facilities).
Nitrous oxide emissions are up almost 6% from 2003, and 5% since 1990.
- Energy-related nitrous oxide emissions are up 25% since 1990, as are waste management emissions. Industrial emissions, however, are down more than 50%. Agricultural emissions are up just 6%.
HFCs, PFCs, and SF6 emissions are up 10% from 2003, and 77% since 1990.
- HFCs are up 246% since 1990 (given their role as CFC replacements). PFCs, however, are down 67% since 1990, and SF6 are down 50%. It should be noted that while emissions associated with HFC replacements for CFCs are included in the report, CFC emissions are not (CFCs are being phased out under the Montreal Protocol, and are often omitted from GHG inventories). So actual net U.S. emissions are somewhat overstated in the report.
These data show that GHG emissions trends vary dramatically sector to sector. Emissions in some "low-hanging fruit" sectors, such as landfill and coalmine methane, and PFCs and SF6, have decreased dramatically. But with carbon dioxide at 84% of the U.S. emissions footprint, with energy-based emissions growing solidly, and with the carbon intensity of electricity actually increasing over time, it's going to take a concerted effort to turn U.S. emissions around.
So what was the President's target? To reduce the emissions intensity of the U.S. economy (as measured by CO2e per unit of Gross Domestic Product) by 18% during the period 2002-2012. Quite a few factors tend to reduce the emissions intensity of the economy, including rapid economic growth, high energy prices, and the ongoing shift away from a manufacturing economy. At the time, the DOE was projecting a "business as usual" intensity reduction of about 14% between 2002-2012. Today, U.S. emissions intensity is already down by some 5% since 2002. So the President looks to be in good shape in terms of his intensity reduction commitment.
I know of no evidence, however, to suggest that policy interventions are significantly contributing to the declining emissions intensity, and the DOE's report makes no such assertion. Moreover, a falling emissions intensity doesn't change the fact that actual U.S. emissions continue to grow significantly, that 2005 was the hottest year on record, if
only by a bit, or that the last nine years have been the
warmest years on record. And while the U.S. emissions intensity is likely to continue to fall, there's nothing to suggest that any of these other trends is likely to change either.
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Dr. Mark C. Trexler has more than 25 years of energy and environmental experience, and has focused on global climate change since joining the World Resources Institute in 1988. He is now president of Trexler Climate + Energy Services, which provides strategic, market, and project services to clients around the world.
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