28 May 2010

Misrepresentation of the IPCC CO2 Emission Scenarios

In a correspondence in Nature Geoscience a group of scholars (Manning et al. 2010) take issue with claims made by the Global Carbon Project that has fed into oft-repeated claims that global emissions are increasing above the highest of IPCC scenarios. For instance, in 2008 the GCP issued a press release that claimed:
Emissions growth for 2000-2007 was above even the most fossil fuel intensive scenario of the Intergovernmental Panel on Climate Change (SRES-IPCC).
This perspective has been echoed by activists, such as Joe Romm, who wrote the following in Nature Reports Climate Change:
Carbon emissions from the global consumption of fossil fuels are currently above 8 GtC per year and rising faster than the most pessimistic economic model considered by the IPCC
The problem with such statements is that they are wrong. (To defend GCP a bit, their presentation has become a bit more nuanced in more recent years, but still not quite correct.) Manning et al. explain the problem that they seek to correct:
Fossil fuel CO2 emissions have increased significantly. However, contrary to some statements in recent publications1–3, current emissions are not higher than covered in the climate change scenarios used by the last two Intergovernmental Panel on Climate Change (IPCC) assessments4,5. And although emissions were recently near the top of the range that has been covered6, the changes in atmospheric CO2 concentration follow long-term average emissions rather than short-term variations.
The problem lies in a technical distinction between scenario averages (the mean across a family of scenarios) and scenario markers (a representative scenario from a family). Manning et al. expalin:
We therefore take issue with the comparison8,9 of the estimated evolution of industrial CO2 emissions since 1990 with subgroup averages of the SRES scenarios, rather than with the illustrative scenarios. These comparisons can be misleading over the next few decades because the upper boundary of the range covered by subgroup average emissions is significantly lower than the upper boundary of the range of illustrative scenarios. As a result, the comparisons with subgroup averages have led others1–3,10 to incorrectly conclude that current emissions are higher than the values used in climate change projections. This may be spreading into general reviews of climate change science11,12, causing a growing inconsistency between the modelling work that has been done for the IPCC and its broader interpretation.
The figure at the top of this post is from the Manning et al. paper.

Interestingly, I wrote an email to the GCP in November, 2007 as part of a discussion on this exact issue, making essentially the same points. Here are some excerpts from what I sent to GCP:
The IPCC SRES has 40 scenarios from four "families" of emissions. The emissions profiles for fossil fuel and industry for these 40 are provided here:


Looking across the 40 SRES scenario projections for 2010 fossil fuel and industry CO2 emissions shows a range of 7.25 to 10.32 GtC, equating to annual growth rates of .05% to 3.95% per year. If the 2000-2006 observed growth rate is 3.3% per year wouldn't this suggest that figure 7 in the November 15 GCP_CarbonCycleUpdate is fairly misleading, and in fact incorrect when it states:
"Current emissions are tracking above the most intense fossil fuel emission scenario established by the IPCC Special Report on Emissions Scenarios-SRES (2000)"?
For its part the IPCC SRES report notes, "The wide ranges of energy and industry-related CO2 emissions in the SRES scenarios reflect the fact that the "best" or the "most likely" quantifications are nearly impossible to identify." Would it not be accurate to say instead that current emissions remain within the envelope of estimates provided by the IPCC in 2000, but in the top 12.5% of scenarios (there are 5 of 40 at a growth rate of 3.3%/year and higher for 2000-2010)? . . .

I think that taking either the marker or the average of the SRES scenario families is far less robust than simply presenting the envelope of projections in the entire 40 scenarios. The IPCC itself urges great caution in aggregating scenarios, and goes to great length to advise that there is no basis for assign probabilities to any of them (hence, no basis for averaging).

So I would urge some greater caution in how you present the recent trends than I observe in your powerpoint. They are surprising and very significant, but they are not outside the IPCC SRES envelope (though perhaps outside your own simpliifcation of that envelope). Your message is far too important to risk being caught up in such a silly point.
The fact that emissions have been running at the top half of the SRES range, and above most of the marker scenarios is troubling enough, for reasons that we explained in Nature in 2008 (Pielke et al. 2008, PDF). There is no need to misrepresent the science to claim that things are worse than we thought. The are already worse than we thought without the misrepresentation.

Kudos to Manning et al. for helping to set the record straight.


  1. Emissions are tracking below the A1B scenario and above the others, including the 'end of times' A1F1 scenario.

    So 'Glass Half Empty' Romm is technically correct, current emissions are tracking above the 'worst' case scenario.

    Current emissions are tracking below the 'middle of the road' A1B scenario.

    Of course complicating all of this is that the mix of CO2 emissions, energy vs durable goods, impacts the long term outlook.

    Concrete and steel production emit quite a bit of CO2.

    1 pound of cement results in approximately 1 pound of CO2 emissions.(if coal is used as the primary energy source)

    In 2007 China consumed 1.3 Gigatons of cement, almost all of it domestically. The US consumed 100 million tons of cement in comparison.

    Personally I see no reason to assume that long term Chinese cement consumption will remain at 3 times the US per capita cement production.

    Cement production by country

  2. -1-Harrywr2

    Thanks for this, as usual.

    Romm cites the GCP, which presented an average of the scenarios (not the figure shown above from Manning et al.). Romm also references "model" not "scenario" underscoring his error ;-)

  3. Welcome Roger,


    Another interesting tidbit.

    Per capita residential housing in China has gone from 3.6 sq meters in 1978 to 22-28 sq meters in 2008.

    I had been looking for China's 'missing coal', they don't have the generating capacity to burn more then 1 1/2 billion tons/yr, but they are going thru close to 3 billion a year.

    A good sized chunk of the 'missing coal' is in the cement and steel to build housing.
    The IPCC A1 storyline
    "a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and rapid introduction of new and more efficient technologies."

    Sounds like what is going on in China and India.
    Rapid economic growth takes a lot of concrete and steel.

  4. Prof Pier Vellinga did the same in Holland in his inaugural speech "Hoogtij in de delta" .


  5. "There is no need to misrepresent the science to claim that things are worse than we thought. The are already worse than we thought without the misrepresentation."

    What is meant by "worse" and who are the "we?"

    Over at WUWT Willis Eschenbach has a post about misrepresenting sea ice, appears similar to the misrepresenting of CO2 in this post. He tries to track down the source. See: http://wattsupwiththat.com/2010/05/28/wheres-the-ice-for-my-drink/#more-20010

    He writes:

    "And with all of that publicity, with all those news reports, with all that discussion and debate … as near as I can determine, despite Reuters saying it was published a month ago, the study has never been published anywhere.

    Not only that, but nobody seems to have noticed that the study has never been published."

    If the Cryosphere Today graph of Global Sea Ice is accurate, what is meant by "worse" in the context of the alarmist quote above?

  6. Roger. Surely you mean things are better than we thought. Despite emissions being greater, global temperatures have fallen. According to the highly respected Dr Phil Jones of East Anglia.

    C - Do you agree that from January 2002 to the present there has been statistically significant global cooling?

    No. This period is even shorter than 1995-2009. The trend this time is negative (-0.12C per decade), but this trend is not statistically significant.


  7. Warmer is better for people and other living things. Absent some scientific evidence of a tipping point, what is the downside from some warming?

    What is "worse"?

    Whole lot of speculative assuming goin' on.

  8. "The IPCC itself urges great caution in aggregating scenarios, and goes to great length to advise that there is no basis for assign probabilities to any of them (hence, no basis for averaging)."

    If there is "no basis" for assigning probabilities to any of the emissions scenarios, this means that the future emissions are completely unpredictable. This essentially substitutes irrationality for science; it essentially says that science is incapable of predicting future emissions.

    It's exactly like the "Limits to Growth" series of books (/frauds), wherein the authors produce a set of scenarios without estimating probabilities of occurrence, thus rendering the whole exercise completely unfalsifiable.

    It's great for scaring people, but it's not science.

  9. A long evidence-based approach and response doesn't do it.

    A more appropiate and snappier response would have been, "at least I have nuts, which is more that can be said about you!"