MER vs PPP is a lot like the “hockey stick”…a bunch of argument that is basically irrelevant.

The IPCC and virtually the entire economics profession are so far wrong in their projections of economic growth in the 21st century, that the differences between MER and PPP analyses pale in comparison.

The IPCC TAR has a median projected world GDP per capita in 2100 of approximately $45,000, and a maximum of $129,000 (in 1990 dollars). The actual value will be approximately $8,000,000 (in year 1990 dollars):

http://markbahner.typepad.com/random_thoughts/2004/09/second_thoughts.html

http://markbahner.typepad.com/random_thoughts/2004/10/3rd_thoughts_on.html

http://www.longbets.org/194

Since the IPCC’s projected GDP per capita in 2100 is off by approximately a factor of 200, it’s not worth spending much time arguing PPP versus MER.

(a) climate reconstructions of the past 1000 years or so in general;

(b) the reconstructions by Mann et al.
(1998 in “Nature” and 1999 in “Geophysical Research Letters”).

The confusion between the two subjects might be inevitable during the
preparation and immediately after the publication of the IPCC WG1 2001
report, because then Mann et al.’s seemed to be the only well-documented
reconstruction of global mean temperature.

But, since then results of many more studies has appeared, and
debates on the two things should be distinguished now.
It seems that some people intentionally use the term “hockey stick” to
perpetuate the confusion and to deflect public attention from the
reconstructions other than those of Mann et al.
I do not think that Dr. Pielke had such intention, and from the
context I can guess that he meant (a). But, as far as I know,
the most well-known debate was about validity of (b).
Thus I think that the unqualified use of the term “hockey stick debate”
has an unintended effect to prolong the confusion.

[Disclosure:
As one of translators of Spencer Weart's "Discovery of Global Warming"
which includes the graph of Mann et al. (1999) as one of the few graphs
in the book with the word "hockey stick curve" in the caption,
I myself might have contributed to propagate the confusion in Japan.
Though the book was published in 2003 (and in Japanese in 2005),
it contains a perspective as viewed in 2001, and it was difficult
for me to add an appropriate note as the translator. That was one of
the reasons I began watching both Prometheus and RealClimate.]

**

I think that the answer to the Dr. Pielke’s main question is
dependent on another issue about how to frame climate policy
which he often emphasizes (typically, in the article here titled
“What is climate change?” on 22 December 2004).
As long as we base on the qualified definition of “Climate Change”
adopted by UNFCCC, and as long as not all stakeholders are
confident about projection of future climate based on theories
and numerical models, we cannot avoid the path of detection and
attribution. Then, the question what the climate was like in
the past millenium and how well we know it comes central, even
though it still seems to be one of weakest parts of climate science.
As long as UNFCCC is as it is, it seems inevitable for some people
who has opinions about climate policy to say something about
climate reconstruction.

Even without such external forcing, scientists will continue scientific
debates about validity of one study or another, but they will
be detached from policy discussion.

But, on the other hand, it is difficult imagine how to frame
climate policy instead of the way that UNFCCC currently adopts.

One direction is, as Dr. Pielke wrote in “Adaptation and Climate”
on 2 March 2005, focus on adaptation or resilience.
No matter what brings them, climate change and variation will
certainly occur some time, and it is better for the humans to be
less vulnerable to them.

Another thing is, as he discucces recently in “Cart or Horse?”
on 19 May 2005, the issue of “mitigation of excessive greenhouse
warming” may be subordinate to energy policy.
I agree with the general direction of the suggestion,
though I am not sure about particular things.
(I understand that the discussion there is mainly oriented to
the national policy of the United States.
As a foreigner I do not want to participate in the discussion itself
but to international implications of it.)

I do not mean that climate change due to greenhouse gases is irrevalent.
But I mean that it can be considered less grave than year-to-year
variation of climate on one hand, and than the issue of limits of
energy resources (as a physical scientist I would like to call it
“low-entropy resources” but it may be too pedantic.) on the other hand.
I do not think that any “climate policy” concerning anthropogenic
greenhouse effect is viable without simultaneously considering
so-called energy policy.

But, as I guess, international agreement about energy policy is
much more difficult than what has been done about climate policy,
even though the result of the latter until now may be tiny.
I think that we need to restrict growth of energy needs, and that
it implies de-construction of the concepts of “economic growth”
and “development”. (We must distinguish “good developments” and
“bad developments” from a new viewpoint, I mean.)
Also, if we include nuclear power as an option, the issue
of proliferation of nuclear weapons will enter together, and,
in some sense, all the military issues will also be connected.
I am afraid that to frame the issue as primarily energy policy
(internationally, I mean) will be equivalent to postpone any effective
decision practically forever.
On the other hand, framing climate policy stand-alone seems futile.
It seems that we have a real dilemma.

Kooiti Masuda
In Yokohama (sometimes in Fujisawa), Japan

“IPCC scenarios did include PPP-based scenarios, which Mr. Castles and Mr. Henderson have conveniently ignored.”

If we look at the detailed part of the IPCC response (no cost at http://crga.atmos.uiuc.edu/publications/ipcc-sres-revisited.pdf
pp 5 near the top

“Both measurements of GDP are provided in the underlying report and in particular in Appendix VII for all MESSAGE scenarios (see also in SRES, 2000: Figure 3-1; Section 3.3.1, Box 3-1, Figure 3-12, and Table 4-19). The writing team decided not to report both measures of GDP throughout the SRES report in order not to generate confusion about growth rates and other scenario indicators that include GDP especially in comparison with the literature that almost exclusively reports GDP in MER, and which the SRES writing team had the mandate to review.”

Holltsmark and Alfsen have an interesting comment on PPP vs MER, basically that the latter overstates economic growth, but that at the same time (and for the same reasons) it would overstate the growth of emissions.
http://stephenschneider.stanford.edu/Publications/PDF_Papers/HoltsmarkAlfsen.sub170204.pdf

http://sciencepolicy.colorado.edu/prometheus/archives/risk_uncertainty/000088reducing_uncertainty.html

I am aware of that response. The essence of the comment remains. That paper you refer to and subsequent statements from the IPCC suggest that the IPCC don’t really know what they are talking about with respect to PPPs and MERs.

A potted version of the counter can be found in the Economist http://www.economist.com/printedition/PrinterFriendly.cfm?Story_ID=2189568

I have also seen a paper by some people from Statistics Norway that suggests that the IPCC made an error in using MER but that, because of an offsetting assumption the net result is that the emissions scenarios are little affected (http://stephenschneider.stanford.edu/Publications/PDF_Papers/HoltsmarkAlfsen.sub170204.pdf.) I can’t comment on this paper in more depth but the relevant point is still that the IPCC doesn’t understand the difference between PPP exchange rates and MERs. That is, they are not experts in statistics and economics and that if they are ‘correct’, it is by chance not design.

http://www.ingentaconnect.com/content/mscp/ene/2003/00000014/F0020002/art00005

The abstract rather captures the tone:

“The response is:

• The IPCC SRES reviews existing literature, most of which is MER based, including that from the World Bank, IEA and USDoE.

• Scenarios of GDP growth are typically expressed as MER (the preferred measure for GDP growth, as opposed to PPP which is a preferred measure for assessing differences in economic welfare).

• IPCC scenarios did include PPP-based scenarios, which Mr. Castles and Mr. Henderson have conveniently ignored.

• Contrary to what Mr. Castles and Mr. Henderson claim, IPCC scenarios are consistent with historical data, including that from 1990 to 2000, and with the most recent near term (up to 2020) projections of other agencies.

• Long-term emissions are based on multiple, interdependent driving forces, and not just economic growth. Mr. Castles and Mr. Henderson need to look beyond GDP.

• The IPCC scenarios provided information for only four world regions, and not for specific countries. Mr. Castles’ and Mr. Henderson’s critique is not of IPCC scenarios but of ongoing unpublished work in progress that is not part of SRES.

We therefore show that Mr. Castles and Mr. Henderson have focused on constructing a “problem” that does not exist. SRES scenarios are sound and the IPCC has responded seriously and conscientiously.”

Ah: does the visual have intrinsic value as a metric, thus having value for decision-making? Got it. The next step being how do we make data compelling for decision-makers.

I say data alone is insufficient to compel those without expertise. Non-contextualized data is like asking whether a particular phone number tells you something about the person answering the phone. Even bell curves need labels on the axes, but there is usually accompanying explanatory text to contextualize the graphic.

I see you were trying to bookend the debate to frame your (before now unannounced) paper. Certainly, as John states above (and folks like Lindzen allude to when stating we can’t forecast in the future) the socioeconomic component is understudied. Hence the need for adaptive management and scenario analysis. Whether humans can utilize this approach is, as you infer from your paper above, rather problematic.

We simply don’t manage ourselves well enough to plan for this situation. “Herding cats” comes to mind.

Best,

D

Pielke, Jr., R. A., 2005 (in press). Misdefining Climate Change: Consequences for Science and Action, Environmental Science and Policy.
http://sciencepolicy.colorado.edu/admin/publication_files/resourse-479-2004.10.pdf

The hockey stick supports a conclusion that the effect of man on global temperature is large. This seems to go further than your comment above that it is cause for concern. This comes from a conclusion that previous natural variability was small and, thus, current variability can all be attributed to man. This directly leads to conclusions about (b) how we evaluate options on climate change. (I do not see that anything can affect (a) the options available to us they always remain the same although our consideration of them varies).

Beyond that, the ‘hockey stick’ has a much more limited role to play – if man-made contributions to the atmosphere are solely accountable for the recent increase (the blade) then that leads to conclusions about the strength of responses we might generate if we reverse or reduce these and, thus, the efficacy of attempts to do so. But it does not illuminate the cost of doing so or the benefits from doing so – just the global temperature that might result.

The discussion about the costs and benefits is primarily an economic discussion. At best the hockey stick can inform one part of the evaluation – the effect of any policies to restrict CO2 output on global temperatures.

And now the distracting part of the hockey stick. The evaluation of costs and benefits is one aspect of the politics of climate change that seems to be poorly studied (but not poorly pronounced on). The discussion on climate change to date is primarily conducted by people who specialise in the physical sciences but not the social sciences.

One example of this is the contre temps between Castles/Henderson and the IPCC. Castles and Henerson suggested that the IPCC was straying outside its area of expertise in generating economic forecasts that were used as inputs to their climate models – and had made some errors in doing so. They have consequently called for greater input from statistical and economic agencies in formulating and evaluating policies on climate change.

To sum up, a scientific conclusion on the effect of man on global temperatures should not lead to any policy conclusions absent a thorough evaluation of the costs and benefits of doing so. (But the scientific conclusion will obviously inform that evaluation.) To do that economists or similar social scientists need to be involved in policy formulation to a much greater extent that seems to have been the case so far.

Risbey et al. [Clim. Res. 16:61,2000] and Risbey and Kandlikar [Bull. Amer. Met. Soc. 83:1317, 2002] report many and diverse types of evidence which various experts find variously persuasive in answering the question of whether climate change has been detected. One of the four main evidences of detection reported by experts to Risbey and Kanlikar was the 20th-century global mean temperature trend. I stress that this means the contrast in recent global mean trend with the relatively flat trend portrayed throughout the hockey stick shaft period.

Loehle [Ecological Modelling 171:433, 2004; and Energy & Environment 15:1, 2004] discusses Risbey et al’s work in this regard, and points out that multiproxy approaches like Mann et al’s inherently tend to smear variability out of the record, even though the long term trend may be correct.

The question of whether climate change has or has not been detected, I think has clear policy relevance. Your (a) and (b) categories seem to relegate determination of need for policy change to someone other than “policymakers”. I strenuously disagree, if that is the case. If the science is clear that a need for change is warranted, then scientists should be able to communicate this to the policymakers.

The hockey stick scandal has important implications in this regard. That IPCC used the Mann et al. graph in a promotional way is as clear a fact as can be. The policymakers should hear scientists’ explanation for why the hockey stick was so embraced. It will help the policymakers understand what IPCC reports represent. One notion that I think policymakers will not find reassuring is that IPCC relies so much on initial peer review by journals like Science and Nature.

Refs:

* Loehle, Craig 2004a: Climate change:
detection and attribution of trends from long-term geologic data”,
Ecological Modelling 171:433, 2004

* Loehle, Craig 2004b: Using
Historical Climate Data to Evaluate Climate Trends: Issues of Statistical Inference. Energy & Environment 15(1):1-10, 2004

* Risbey, James, Milind Kandlikar, and David Karoly 2000: A Protocol to Articulate and Quantify Uncertainties in Climate Change Detection and Attribution. Climate Research 16 (1), 61-78. pdf — http://www.maths.monash.edu.au/~ris/publications/daproto.pdf

* Risbey, James, and Milind Kandlikar 2002: Expert Assessment of Uncertainties in Detection and Attribution of Climate Change. Bull. Amer. Met. Soc., 83 (9), 1317-1326. pdf — http://www.maths.monash.edu.au/~ris/publications/daexpert.pdf