Thoughts on an Immediate Freeze on Carbon Dioxide Emissions

September 25th, 2006

Posted by: Roger Pielke, Jr.

Last week I discussed Al Gore’s call for an “immediate freeze” on U.S. carbon dioxide emissions. I dismissed this as being in the realm of fantasy, but the notion of freezing U.S. carbon dioxide emissions motivated me to investigate the issue a bit further. The following data and analyses report what I’ve learned.

Data on projected carbon dioxide emissions is available from the U.S. Energy Information Agency (EIA) here (xls). It is presented in tons of carbon dioxide so it needs to be converted to tons of carbon (divide by 3.664). In 2006 the U.S. is projected to emit 1.63 gigatons of carbon (GtC). This is projected to increase to 2.21 GtC by 2030. EIA projections go to 2030, so that is what I use below.

What accounts for this increase? There are two important factors. One is the projected increase in U.S. population and the other is the projected increase in per capita emissions. I gathered data on projected population increases from the U.S. Census here (xls) and data on projected per capita carbon dioxide emissions here (pdf). I also gathered data on projected immigration from the Congressional Budget Office here (pdf) (note that in the calculations below I use the Social Security Administration’s Intermediate projections). These various data allow the projections to be disaggregated. Here is what I found.

U.S. Carbon Dioxide Emissions 2007-2030

Projected population growth accounts for 64% of the increased U.S. carbon emissions.

Of this growth 40.5% comes from births in the U.S. and 23.5% comes from immigration (i.e., 40.5 + 23.5 = 64).

The remaining 36% comes from an increase in the per capita production of carbon dioxide which EIA estimates to increase by 11% by 2030. (Note that the per capita increase is not included in the above estimates of the effects of population growth. If included they raise the values by about 2.9% — 43.4% — and 1.1% — 24.6% — respectively).

How much carbon emissions are we talking about under an immediate U.S. freeze?

The accumulated U.S. emissions in excess of its 2006 value 2007-2030 equal 7.0 GtC. What would it mean to global carbon emissions if the United States were in fact frozen at their 2006 levels? In 2030 accumulated global emissions would be 228 GtC versus 235 GtC (world data here in xls).

But let’s go further, what if the United States were to become immediately carbon neutral starting in 2007? Through 2030 accumulated global carbon emissions would then be 189.0 GtC. In 2030 global emissions would be 9.72 GtC, or about equivalent to what the world is projected to see with the U.S. under business-as-usual in 2018.

What to conclude from all of this? Here are a few things:

1. The majority of increasing emissions in the United States comes from its population growth. About 37% of this increase (i.e., 23.5/64) is due to emissions from immigration. It is not inaccurate to say that through immigration the United States is “offsetting” the emissions from other parts of the world to some degree, since their net emissions will decrease to to emigration. But it is also true that most (if not all) immigrants are coming to the U.S. from countries with far lower per capita emissions, so there is a net increase in global emissions from immigration to the U.S. Of course, the factors which lead the U.S. to such high emissions in the first place are what drive much of the motivation for immigration. Will policy makers talk of stopping immigration as a climate policy? I doubt it, but it is interesting to consider.

2. Per capita increases in carbon emissions, at 11% by 2030 seem quite small and in principle could be relatively easily addressed through improvements in efficiency. Transfer and adoption of many European practices to the U.S. would I think be more than sufficient to meet an 11% goal.

3. An immediate freeze of U.S. carbon dioxide emissions, even if possible, would have exceedingly little effect on the overall challenge of reducing global carbon emissions. It would reduce the accumulated global total by 2030 by about 3% and delay any projected effects of climate change by about 6 months.

4. If we go to the extreme and assume that the U.S. becomes carbon neutral in 2007, this would have a clearly discernible effect on accumulated emissions but really wouldn’t much change the overall challenge of reducing global carbon emissions. If the U.S. were carbon neutral starting in 2007 then it would reduce the accumulated global total by 2030 by about 20% and delay any of the projected effects of climate change by about 12 years. The relative importance of the U.S. as a contributor of to carbon dioxide emissions is projected to decrease from 21.9% of global annual emissions in 2006 to 18.6% in 2030.

All of the projections above from EIA, Census, SSA, and CBO are made in the face of considerable uncertainties. For example, this recent paper (in PDF and peer-reviewed journal version) suggests that, under some scenarios, demographic factors may in fact lead to a decrease in U.S. per capita emissions as the population ages.

Whatever the future holds, it is clear from this data that while the United States is the largest contributor to carbon dioxide emissions, it nonetheless produces a small share of total global emissions. Given that the majority of its emissions come from its growing population, this places the U.S. at a disadvantage with countries with slower rates of population growth when emissions reductions are accounted on a national basis (discussed here). A continued discussion of climate policy in terms of nations seems to be more divisive than anything else from the standpoint of policy development. Politically, however, the focus on the U.S. does serve a function in both domestic and international politics and in my view goes far beyond the issues related to climate change.

7 Responses to “Thoughts on an Immediate Freeze on Carbon Dioxide Emissions”

  1. LDilling Says:

    I think the reason for the original framing is that the U.S. produces 25% of the world’s emissions (not exactly a “small” share) for only having 5% of the world’s population. So the original framing of the emissions problem was one of per capita equity– how much CO2 should one person be allowed to emit– and many feel that the U.S. exceeds its “share”. What this framing omits of course is that the U.S. GDP is also quite large, one figure I saw for 2002 said about 32% of the world’s economy. Since the U.S. GDP is tied to energy use and 85% of energy in the U.S. comes from fossil fuel (although energy intensity is improving steadily), emissions are accordingly higher than other countries. This doesn’t answer what emissions “should be” for one person, but is a second dimension to the numbers. A per nation focus or per person focus does obscure these other aspects. As far as population policy or immigration being discussed as climate policy, the Sierra club does have a focus on population as a topic:
    Population and affluence are always key variables in modeling of future scenarios of emissions. However, I think population growth, immigration and any discussion of limits are such hot-button topics that they are unlikely to be a key feature of a climate policy. Much easier to talk about and tackle energy efficiency and renewable energy.

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  3. Roger Pielke, Jr. Says:

    Hi Lisa!

    Thanks for weighing in!. The point is that efforts to motivate energy efficiency and renewable energy via international cooperation are inextricably tied to issues of population so long as we talk about climate policy at the level of nations. If we separate these issues when we talk about climate policy we are missing a big pary of the policy and political picture.


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  5. kevin v Says:

    My take home message from the numbers is that Jevons’ Paradox is alive and well and will continue to be a factor in trying to reduce emissions. You show an expected 11% increase in per capita usage (and I’m sure that’s based on previous trends which have also been steadily upward) which is exactly counter to what we’d expect — that is, we’d expect that as our economy grows more efficient, the amount of energy to produce each dollar of GDP diminishes, so we should be using *less* energy per captia, not more. The fact that per captia emissions increase instead of decrease even in the face of increasing efficiency of usage points to a very real challenge in cutting emissions. It says to me that if we’re planning on relying solely on market mechanisms to adjust energy prices and bring down per-capita emissions we’d better be thinking more critically.

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  7. Joseph O'Sullivan Says:

    The continued discussion of individual nation’s climate policy is unfortunately divisive.

    But, I think one issue about the US joining the efforts to reduce CO2 is the US’s historic role in environmental regulation, particularly pollution control regulation.

    Before recent changes in political leadership, the US was been a leader and innovator in these areas. With more cooperation maybe better solutions will be found.

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  9. D. F. Linton Says:

    This post provides an economist’s view of GDP and energy usage.

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  11. winston Says:

    There may be a price for the US to do something about reducing its per capita emissions but you don’t say what the value might be, Roger. If the US still has ambitions to lead the world on something worthwhile then I should think it must in fact opt to lead, mustn’t it?

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  13. Steve Hemphill Says:

    As far as “then I should think it must in fact opt to lead” you apparently missed that U.S. CO2 emissions increased only 2.1% from 2000 to 2005 while EU 15 emissions increased *twice* that.

    I wonder what the ratios are for *real* pollution?