A constant-rate (i.e. straight-line) extrapolation of global warming from the 20th to the 21st century, as in the brief’s Figure 2, is a favorite technique of one of the authors, Pat Michaels. This technique gives 21st century warming at the low end of the spectrum of possibilities resulting from the different model-input scenarios. It is one possible future, but it’s never been clear to me (or to anyone else I know besides Pat) why the other possibilities — all of which involve more global warming — should be ignored.
Pat argues that it is the general tendency of climate models when forced with exponentially increasing CO2 concentrations (as were the models used in Dr. Covey’s CMIP project) to produce a nearly linear temperature rise into the future. He argues that CO2 concentrations have been increasing at a marginally exponential rate, just at a rate that is only about 1/2 the 1%/year rate. Thus, he continues, the observed rate of warming, according to model projections, should be linear, with a slope somewhat less than the slope produced by feeding the models 1%/yr. And the observations tell him that this is exactly the case. The observed warming rate during the past several decades has indeed been constant at about 0.18C/dec–just as models indicate that it should be. And since models typically maintain a linear warming rate into the future (under exponentially increasing CO2 concentrations), Pat maintains the observed warming rate into the future–and projects a warming of about 1.8C by 2100. This does NOT mean that he doesn’t think that the CO2 concentration in the atmosphere will stop increasing, just the opposite–he assumes it will continue to exponentially increase as it has been.
I hope that this clarifies Pat’s argument, so that others besides Pat, understand it. You all may not agree with it, but it is really not that difficult to understand. This is the scenario that he believe is the most likely, and thus the one that he focuses on.
to some degree supported by the fossil fuel industry since 1992
[Response: Hmmm…. Well, Michaels has been using this argument for almost two decades. If it had much validity, one would presumably have expected him to have been predicting 0.18 C/dec the whole time. Only that isn’t the case. The earliest use of the argument that I can find has him predicting 0.10 C/dec, then 0.13 C/dec (1999) then later 0.15 deg/C and now 0.18 deg/C. To anyone else, that would imply that simple linear extrapolation probably doesn’t have much predictive power. – gavin]
Wish the Court could have read these responses. That last sentence is important, the one wondering whether all but the lowest GW scenario should be ignored.
Folk wisdom teaches us “to hope for the best, and expect [& try to avert] the worst.”
And I still get this niggling feeling that we aren’t talking enough about the worst of the worst possibilities, bec it’s less probable and/or science isn’t really up to snuff yet about all that could possibly go wrong….since the system is so extremely complex.
Throw into the equation militant humans who go on the warpath if their material base is a bit threatened, and the worse possible scenario is probably beyond our wildest imaginations.
So why are the powers-that-be so adamently opposed to lowering C02 emissions a bit. If they’re so opposed to lowering the small amount indicated in the case, then that indicates they don’t want any action taken against this problem at all, but to just wait & see whether the worse of the worse actually happens. Like some fascination with watching disasters, some death wish for the world.
I read the Native Alaskan brief. I hope the SC justices also did so.
Comment by Lynn Vincentnathan — 7 Dec 2006 @ 4:49 PM
Re #1. Hmmm, Gavin. Good point! A quick check of Pat’s The Satanic Gases (2000) show that he projected a rate of 0.13C/decade from CO2 rise alone based upon the argument that I outlined above. I think since that time, I have convinced him that most unadulterated GHG warming began after the PDO shift in 1977, and thus 1977 should be the starting point in his temperature analysis of the impacts of rising GHGs. If you use 1977 as a starting point, you get around 0.18C/decade. In The Satanic Gases (and probably in any writing prior to that) he used the trend during the prior 30 years, which included temperature data, which in my view, was still part of the cooling (or steady) period prior to the PDO shift and when the GHG warming clearly began to manifest itself.
If you mention one person’s sources of income, you should mention everybodies, including you own.
Government or NGO funding does not necessarily come without strings and could be used as a ‘label’ of bias. Self-censorship, or going with the crowd – be it the prevailing left, right or green ideology – may also be involved. Scientists are human and believers….You do yourself no favour at all by harping back to fossil fuel funding.
Most fossil fuel people here now love carbon taxes, regulations for they increasingly improve profits, reduce risks or involve subsidies to investors. We need to replace fossil fuels in a hurry, here in Europe, and this has little to do with climate but a lot – in public rhetoric -with the ‘global warming ‘ threat. The real reasons are more complex.
Comment by Sonja Christiansen — 8 Dec 2006 @ 12:07 PM
[Response: Repeated (and repetitive) cut and pastes from politicised sources are not useful. If you have something you want to say, say it. – gavin]
“Most fossil fuel people here now love carbon taxes, regulations for they increasingly improve profits, reduce risks or involve subsidies to investors. We need to replace fossil fuels in a hurry, here in Europe, and this has little to do with climate but a lot – in public rhetoric -with the ‘global warming ‘ threat. The real reasons are more complex.”
I don’t get the sense that fossil fuel “people” in the US are supportive of a carbon tax. Europe on the other hand has had a heavy carbon tax (i.e., gasoline tax) for decades, for reasons that are not particularly complex. Europe has little oil or other fossil fuel supplies appropriate for fueling cars and trucks and has to buy it on the world market using hard currency.
As an economic necessity in the post-WWII years they put in large gasoline taxes to limit use of oil and encourage car/truck makers to produce fuel efficient vehicles. They also have robust public transportation, including electric trains and urban light rail that can be powered by domestic coal and nuclear fuels. Europe has also been a leader in prototyping renewable energy and, in the case of wind power, implementing it on a large scale. France’s move to nuclear power for their electrical power production is part of the same paradigm.
RE the low end projections of CO2 & warming. Are these totally problem-free? Are not these also worth avoiding, if we can? And we don’t hear much about the possible scenarios after 200 years, 500 years, etc. We’d probably still eventually reach very harmful levels, only slower.
So here’s an idea. Why not end this experiment on planet earth, drastically reduce our GHG emissions (since we can do so profitably anyway), and never really find out which scenario was the most accurate? If the ego needs feeding, I’d even be willing to say, well, it seems you low guys may have perhaps been right. But just as long as we all stop this global warming experiment now.
Comment by Lynn Vincentnathan — 8 Dec 2006 @ 5:22 PM
How do the rest of us make comments to the Supreme Court on this issue?
Re #8: “How do the rest of us make comments to the Supreme Court on this issue?”
It is now too late for this particular case for any further comment, the briefs have all been filed and the arguments heard.
In general, however, anyone can submit an amicus curiae (friend of the court) brief for a case on the Supreme Court docket before the relevant deadline.
The Supreme Court is very particular about the format and timing, and there are procedural hoops to go through, so most are filed by counsel who are familiar with the details. The Court frowns on briefs that do not directly address the issues presented by the case in a way that presents new information not already part of the record. E.g. Rule 37 of the Supreme Court (about the filing of amicus briefs) begins:
“1. An amicus curiae brief that brings to the attention
of the Court relevant matter not already brought to
its attention by the parties may be of considerable
help to the Court. An amicus curiae brief that does not
serve this purpose burdens the Court, and its filing is
Pat argues that it is the general tendency of climate models when forced with exponentially increasing CO2 concentrations (as were the models used in Dr. Covey’s CMIP project) to produce a nearly linear temperature rise into the future.
Figure 2 in the brief compares the CMIP 1% experiments (see for instance fig. 9.3 in IPCC TAR ) with global temperature data after 1975. – This comparison is both misleading and problematic.
The CMIP results show how a number of models warm up relative to their control state as CO2 increases by 1% per year. This change in radiative forcing is described as “idealized” by the CMIP group. The purpose of the experiment was to compare model responses, the goal was not climate prediction. After 80 years of intergration the range of warming obtained in the models is ~ 1.2 – 3.7 degrees, with most models falling somewhere in the 1.5 – 2.5 range. The average is about 2 degrees.
Figure 2 in the brief overlays the CMIP results with data showing the increse in global temperature from 1975 and also shows a linear fit through the data. This linear fit implies a warming of about 1.3 degrees over the eighty year period.
It is a bit surprising to see actual data superimposed on a graph from the idealized 1% CMIP experiment (where the x-axis is “Model Years” and starts at zero and goes to 80). For the real data one can ask: why is 1975 year zero?
The answer can be seen in footnote 10 (bottom p. 12 of the brief) where they say
The increases [in CO2] in the previous three decades (ending in 2004) have been .49, .42, and .43% per year, respectively.
Thus, the reason that 1975 is year zero is simply that the brief authors are considering real world “experiment” where CO2 was increased by 0.42 – 0.49% per year from 1975. There is also an assumption of linearity, such as the claim made by Chip here above and on p. 11 of the brief that
…the models respond quite linearly to changes in atmospheric carbon dioxide with respect to percent (i.e., a 1% change in concentration per year produces roughly twice as much warming as 0.5%).
Now, based on this it is clear that figure 2 in the brief is really comparing two different CO2 forcing histories: In the CMIP history we have a 1% CO2 increase per year and 2 degrees warming over 80 years, in the “real world” history we have 0.42 to 0.49% increase in CO2 per year and extrapolated to 80 years we get roughly 1.3 degrees warming.
But wait a minute, if the brief authors are correct and a “1% change in concentration per year produces roughly twice as much warming as 0.5%” then we should expect the CMIP models to yield 1 degree warming (over eighty years) with 0.5% CO2 increase per year. This is already less than the brief authors get with 0.42 to 0.49%.
Using the average of the annual CO2 growth rates given in the brief (0.42, 0.43 and 0.49) and the linearity argument then it follows that under 0.5% growth per year the real world extrapolation would have given about 1.46 degrees over a period of eighty years, which is far more than CMIP.
In short, the linearity argument and the annual CO2 rates of increase cited by the authors imply that the CMIP models have a reponse that is too low.
This is why the comparison is misleading. The x axis is wrong. They should be looking at warming rate per percent increase in CO2 rather than Model Year.
But of course, rather than showing that the models are overestimating the warming, this would indicate that they might be underestimating, turning the brief on its head. “Contra-contrairians” might argue that this shows that actual climate predictions in the IPCC TAR (see for instance summary figure 9.14) were to moderate ;-)
Now, the comparison is also problematic. First there is an obvious problem with this somewhat haphazard mix of idealized model experiment results and real world data. Second, the relavant forcing is equivalent CO2, so the 0.42 – 0.49% increase per year is to low. Third, to fit global temperatures to CO2 over a period of 30 years and and use a linear trend to extrapolate for the next 50 years is asking for trouble. For one thing, the fit neglects lags in the system (such as those resulting from ocean heat uptake) and it also neglects changes in albedo and other radiative factors.
To summarize: Figure 2 in the brief makes a dubious comparison between the results from idealized model experiments and real world data. If this comparison is taken seriously and the CO2 growth rate taken into account, it implies that the real world is more sensitive to CO2 increase than the models in the experiment. However, the comparison is problematic so one need not worry. As the comparison forms the core of the arguments in the brief it follows that its conclusions need not be taken seriously.