Guest Post by Willis Eschenbach
I wrote my first computer program in 1963. It was an implementation of the Sieve of Erastosthenes, used to find prime numbers. I haven’t stopped programming since then. So I am intimately acquainted with the innards of computers, computer programs, and computer models, both iterative and otherwise.
And those who read my writing know that I don’t have much use for the suite of IPCC computer climate models as a way to predict the future evolution of the global climate. I think they are Tinkertoy™ exercises in parameter tuning.
So it may come as a surprise that there is a model out there that I wouldn’t say I trusted, that would be far too strong. But I would say that it certainly bears watching, because it’s the best of the models. It bears scant similarity to any of the IPCC models. In its current incarnation, it has the lovely name of GATOR-GCMOM.
It came up recently in a Discover magazine article entitled “White Roofs May Actually Add to Global Warming”. Go figure, huh? Figure 1 shows what painting roofs white was supposed to do for the climate.
Figure 1. How it was supposed to work … but didn’t. Ah, well. So much for the White Roof Project.
When I read the Discover story, I wasn’t surprised to find that the model that produced such a counterintuitive result was the same GATOR-GCMOM, whose development I’ve been following and speaking favorably of for over a decade. It’s the work of a brilliant man named Mark Jacobson at Stanford University. It started small, as a local or regional model to trace the paths of pollutants around point sources. In its current form it includes literally dozens and dozens of chemical, atmospheric, and oceanic processes which are not represented in any other climate model on the planet. It uses a variety of ingenious ways to do things to reduce computational overhead. A full list of the differences from IPCC models and a discussion of the development of the GATOR model is here (PDF).
So why does the GATOR-GCMOM model say that painting the roofs white will heat the planet?
The Discover article says:
The model found that more white roofs means less surface heat in cities (which is obvious enough to anyone who’s sat in a car with a black interior in the sun). Lower local temperature means less water evaporates and rises up to eventually form clouds, says lead author and Stanford University researcher Mark Jacobson. The decrease in clouds allows more sunlight to reach the Earth’s surface, leading to higher temperatures overall.
So, clouds once again affect the climate in an unexpected way. I’m shocked. The article also states:
The model also predicts that much of the light reflected by rooftops will eventually be absorbed by dark carbon soot and particulates that are especially prevalent in the air above urban areas. This could limit local cooling and cause warming elsewhere as the particles drift away.
This shows an unexpected (but reasonable) interaction between two factors, reflected sunlight and black carbon particles in the air.
Why would I think that Jacobson’s model might be showing something near reality in this question, when I am generally scornful of the IPCC models? Several reasons:
1. The time frame of the analysis is short, he’s not futzing around with 100 year fantasy forecasts.
2. Both outcomes, once examined, make sense. Changes in clouds, and in atmospheric heating from sunlight hitting black carbon, certainly would affect the outcome, the physics is well established.
3. The GATOR model started small, modeling local conditions, many years ago and built gradually outwards from there. From the start, it was frequently compared to reality and tested and refined. It wasn’t conceived of as a global model like many climate models. So it was continually being tested on how accurately it could represent the temporal evolution a host of local conditions around cities and bays, studying pollution plumes and their changes over time, comparing them to observations … a host of real-world testing unlike anything that any of the IPCC models have undergone. Then, over about twenty years, it has been slowly expanded to be a global model.
4. I may be wrong, but I cannot find any indication of tunable parameters anywhere. Seems like there must be some somewhere, but for the most part it’s truly physics and chemistry based, unlike IPCC models.
5. It uses a nesting grid scheme which allows for a variety of grid-size resolutions as needed. This lets some areas be intensively sampled (say around a city) while a larger area of the ocean might need far fewer samples.
6. It handles chemistry at a very detailed level, involving hundreds of chemical compounds in both the ocean and the atmosphere. Other climate models don’t even touch chemistry except perhaps in the simplest ways.
7. The result was counterintuitive, but still demonstrable. A model that only shows us what we already know is not that useful. This one showed us something we didn’t know.
Anyhow, for me the takeaway message is CLIMATE ISN’T LINEAR. The IPCC paradigm is, change the forcing and the temperature has to change proportionally.
But in this case, not only is the temperature response not proportional. It’s not even in the right direction. Kinda deals the whole “temperature change equals forcing change times climate sensitivity” idea a body blow …
So that’s all the reasons why I find this result quite plausible. It’s the best model on the planet, and it is uniquely qualified to look at this particular question. If Jacobson were to start using the model for hundred year runs looking for trends, that would be a big question mark for me, I don’t think any model can do that.
But for this kind of analysis? It does what the best of models can do—it points at things in front of our eyes which we might not have noticed. Doesn’t prove anything, the output of a computer model is never evidence … but it certainly teaches us something, which is much more valuable. It teaches us that in a complex system like the climate, a simple, totally obvious cause and effect relationship may not work out anything like that. As in this case, where something that obviously, logically, and unquestionably will cool the earth … may just end up warming it.
Anyhow, that’s the latest news from the land of Settled Science, where all temperatures are unshakably tied to forcings …
Regards to everyone,
w.
Geof Sherrington,
the air does not absorb much visible solar. The reflected energy from the white roof would NOT significantly warm the air. The decrease in IR from the roofs would more than balance the increase in visible radiation and cause a decrease in the air temp. Higher up where you have aerosols and clouds to absorb more of the reflected visible it may balance or be warmer. I’ll tentatively agree with the model this time!!
The whole debate seems pointless. Guess what? many commercial roofs are already employ a reflective coating. Heat accelerates decay of the roofing material and reduces its service lifetime, increasing maintenance costs. Commercial roofs need to be re-coated every 15-20 years in any case. Residential roofs in the US typically employ shingles rated between 10 and 25 years; I suspect 15 years is probably about average (the 25 year shingles cost significantly more). We don’t need a Dept. of Energy initiative to paint roofs — they will all be redone sometime in the next 20 years anyway. And the people paying the bills will make decisions on material and color which are locally optimal (as best they can determine). If people believe lighter colored roofs will lower energy costs, they will use them (local homeowner associations permiting).
Given time, roof color will converge toward the optimal balance of cost, esthetics, and function. Let’s see: if we assume that will take 20 years at 3mm sea level rise per year, that means the oceans will rise another 6 cm before we get this roof radiation thing under control. Which is, ummm, approximately exactly the same as it would rise if we spent however many Billion$ to paint all the roofs white this year.
I don’t think in this matter we should pay any attention to what any model shows.
ferd berple says: October 21, 2011 at 7:47 am
The is the number one key factor in making a model that might actually produce meaningful results. …..
fb – your explanation to Willis’ post was informative, thank you.
And reitererated in another post above Stephen Brown @ur momisugly 4.56pm provided a link to
http://www.bishop-hill.net/blog/2011/10/20/best-paper-out.html#comments
In climatology the standard progression is:
1) Policy changes
2) Publicity
3) Scientific publication
…
And possibly at a later date, if the computer is large enough, proof (though this step is optional)
Oct 20, 2011 at 9:20 PM | ZT
Perhaps ZT could have added to 1) establish regulatory and legislative change.
dlb says: October 21, 2011 at 3:42 am
Do cities produce more convective cloud than nearby areas?
Given that the majority of cities are established on a coast (?) http://www.tyndall.ac.uk/cities-and-coasts-publications that is an interesting question I hope someone answers.
Like Y2K, could it be like the lead (paint and then atmospheric) or asbestos debacles?
For the home handy man (or woman) where the (25yr) warranty on roofing material has expired. Or not! http://www.heritage.nsw.gov.au/docs/maintenance4-1_corrugated.pdf and information on roof painting, including a reasonable overview of the variety of roofing material in NZ/Aus http://www.resene.co.nz/homeown/h2pyhome/Painting_Roofs.pdf
Also publication ‘Walls and Roofs in South Africa’ (and 25 degrees in Africa) provide an overview of the town planning and architectural industry (and energy). http://www.mediainafrica.co.za/
I notice that on high convective summer afternoons when we get the popcorn variety thunderstorms that they often spawn from whatever major roadways happen to be in a loosely parallel direction of low level wind, (also where you see some birds like hawks riding thermals right up to the base of rapidly forming clouds several thousands of feet up). But, just like a pot of water about to boil, even though the first bubble will generally start at the hottest spot, the whole pot is going to boil no matter where the first bubble formed.
Of course we all know that painting the roofs is merely an academic discussion here, for two simple reasons:
[1] :: Many roofs (speaking about asphalt tiles here, not clay, stone, wood) are NEITHER black nor white already. For the past 3 or 4 decades our roofs have always been what I would call gray with black speckling, which I see everywhere. So we kinda split the difference in this argument long ago. I have seen darker shades and lighter shades but the majority seems to be in between white and black already. So why did this nitwit Chu even bring this subject up?
[2] :: Painting anything is a love-hate affair. This goes double for outdoor things. This goes quadruple (or probably octuple) for roofs and all items in direct sunshine, alternating between freezing and boiling, wet and dry. There is no place more extreme than a roof. Painting them is a losing proposition, there is no chance for success. But let’s say against all logic you do it anyway. Well the paint comes from somewhere, usually the lowest bidder. So a really great question is: how do Chinese paint particles running off into the groundwater factor into AGW eco-zealotry?
A Swedish scientist observed that the tragedy of climate science was that meteorology began during the coldest decades of the last 10,000 years. That implicit “normal” has biased everything.
Global warming? I should bleedin’ hope so, and thank all the gods for it. It’s been a huge boon and relief from the horrors of the LIA. Long may it continue!
[Changed “3” to “1”, which is what I think you intended. If not I’ll change it back. ~dbs, mod.]
There’s been a massive real-world experiment in reflective roofs, in a high-sunlight locale. In Spain, much of one province, Almeria, has been given over to greenhouses — and the glass and plastic etc. reflect brilliantly. Result: a drop of 0.3°C in average temperature per decade.
http://geographyfieldwork.com/images/Climate/AlmeriaGreenhouses.jpg
philip Bradley says:
October 21, 2011 at 12:47 am
It takes a pretty shallow thinker to accept this and other glib assumptions of Jacobson’s GATOR model. “Somewhat
scepticalskeptical” (fixed that for ya) is a somewhat reasonable position to take. Exceedingly skeptical would be the most reasonable.As with all other climate models these are hypotheses stated in computer lanugages rather than human language. The translation to computer language does nothing to improve or test the hypotheses. All it does is grease the wheels that produce hypothetical predictions. Like any other hypotheses these predictions must be tested in some fashion. So one might reasonably ask how it is that Jacobson’s model predictions are tested?
And just as a side note for Willis, it is NOT well established that black carbon in the atmosphere causes heating. You’re conflating that with black carbon on the ground, particularly on snow or ice. In the atmosphere it is generally believed the greater effect is surface cooling because it blocks sunlight from reaching the surface. The notion that it would “move” urban heat to other areas because the particles would heat up from sunlight reflected off white rooftops then drift elsewhere is asinine. The heat capacity of soot particles is essentially zero.
Dave Springer says:
October 23, 2011 at 12:01 am
Two things, Dave.
First, the heat capacity of a typical soot particle is undoubtedly greater than that of a molecule of carbon dioxide simply because it weighs more … perhaps you’d care to comment on that in light of your claim that the heat capacity of soot is zero.
Second, you haven’t thought the carbon question all the way through. Black carbon in the air is warming with respect to reflected sunlight, you are conflating that with incoming sunlight. It is different from the case with incoming sunlight because if the reflected sunlight misses the black carbon, it most likely goes on to space. If it hits the black carbon, it stays in the system, which inevitably must lead to warming.
w.
Brian H says:
October 22, 2011 at 6:01 pm
The Almeira temperature record is here. Please point to the “drop of 0.3C in average temperature per decade”.
I ask because there’s not enough data there to say anything at all about the Almeira temperature, much less identify a 0.3°C change. Where did you get that number from?
w.
The fundamental problem with all computer models is that computers can not represent numbers exactly and they can not preform even basic arithmetic functions like additions and subtraction completely accurately because of how numbers are represented. Most of the time these minuscule inaccuracies can be ignored, but when you keep iterating these functions over the datum 10’s or 100’s of thousands of times on thousands of data points, there is no such thing as minuscule inaccuracies.
Willis;
I’m just parroting the article:
http://geographyfieldwork.com/AlmeriaClimateChange.htm
So actually the total impact is greater, 0.3 + ~0.7 increase elsewhere, or 1.0°C/decade:
Brian H says:
October 24, 2011 at 7:56 pm (Edit)
Thanks, Brian. The original paper is here. They appear to have used data from the INM, the Spanish Met office. Unfortunately, they haven’t archived the data they used, so no way to tell if it’s valid.
w.