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.
Willis,
If you keep coming to sensible conclusions and ideas such as this, you will become a target of displeasure to those on the AGW side, keep your a@se covered.
Heh. Interfere with the H2O cycles at your peril! Evaporation and recondensation are the big dogs; they bite hard.
Lower local temperature means less water evaporates and rises up to eventually form clouds
This may be true in some locations, but urban evaporation (from rainfall) is low anyway (storm drains).
But I am sure its not true in other locations such as mediterranean climates where a cloud free sky is the norm during the summer.
Then there is the Urban Irrigation Effect, which significantly raises near ground humidity during the summer in places like Perth. Where most people run sprinklers several times a week to water their gardens.
This near ground humidity rarely results in clouds. It seems you need quite a deep column of humid air to create convection clouds.
While the model sounds interesting, I’m somewhat sceptical of the quoted conclusion above.
“But in this case, not only is the temperature response not proportional. It’s not even in the right direction.”
Balderdash! I have actual experimental results refuting this so-called model (and just in time for the next climate conference!). I’m still writing the press release for my not-yet-peer-reviewed not-yet-written paper, so I can’t reveal the details yet, but I will say that my experimental method involves two glass cookie jars…please keep this info confidential.
This is good.
Hmm, if we wanted to increase global temperatures I wouldn’t suggest painting everything white.
But I wouldn’t suggest pumping greenhouse gases either.
I would suggest putting soot in glaciers and ice in general.
And I would suggest way of absorbing more solar energy- since we don’t want to absorb energy on roofs reflecting the energy or painting white would be fine- not the issue.
Probably simplest way would put salt lakes on the Sahara desert such bodies of water would absorb a lot of energy and evaporation carry the energy elsewhere. And to be useful mine the salt [let a few lakes dry up and rotate to different lakes] and also plant crops in area also.
I wonder if he explicitly models CO2. Might an increase in atmospheric CO2 concentration speed warming and evaporation in the am and then increase cloud cover and/or precipitation in the pm, for a net reduction in earth surface temperature?
The major effect of white roofs is to reduce demand for air-conditioning and so reducing power demand. The direct effect on climate will be small.
The feedbacks you get so excited about here are the sort you would dismiss as third order effects if they were in the other direction.
If there was enough aerosol in the atmosphere to absorb “much” of reflected sunlight, there would be enough to absorb “much” of the incoming sunlight. Certainly this effect is real, and slightly reduces the efficiency of white roofs, but probably by no more than a little dirt on the roof reducing the albedo.
The cloud argument is equally trivial. Cities only take up a small proportion of the earth’s surface – any change in albedo in cities can only have a minimal on the overall formation of clouds.
Climate change is a long term phenomena – how are you going to predict how the climate will have changed in a hundred years without running the models for a hundred years. If you want to argue that that cannot be done, then you have to accept that uncertainly about the effects on climate are large. Doubt may be the product of the so-called sceptics, but uncertainly is not their friend.
So what we wind up with after painting all the roofs is a broken thermostat™.
Or maybe not. Because the reduction of clouds which inconveniently caused more warming, will eventually evaporate more water and create those clouds and cooling rain later, thereby kicking the thermostat on again. My mind is spinning.
All in all, I would say that your famous thermostat hypothesis is perfectly safe and very hard to dispute. I’m not sure that any amount of tinkering can really break it’s functionality.
But about those white roofs. It is not like the bulk of humanity and their humble abodes lie at low latitudes in deserts. The idea was hogwash all along because so many people do not want or need sunlight reflecting roofs. They might want them for 8 hours a day for 3 months of the year. Perhaps in the future they’ll have computerized auto-polarizing White in summer, Black in Winter. But that ratio in a year would still be like a minimum of 75% of the time black anyway. Does anyone even go outside anymore?
Yep, pie-in-the-sky insanity. It is a lot like light bulbs. There is a definite place for both incandescents and the alternatives (or white and black roofs). Yet someone always has the chutzpah to attempt to make a blanket decision for *everyone*. The correct answer in both situations is to use the color roof (and type of light bulb) that bests suits your specific circumstance.
And those politicians and scientists that attempt such single solution mandates must be scorned, fired and more.
Once you’ve said, “don’t trust it”, you have said it all. Just don’t trust it –don’t even trust that you are “learning something” from it.
Mark, with whom I went to high school, is 100-percent on the AGW bandwagon and — not infrequently — holding the reins. See his work on “CO2 domes” — http://pubs.acs.org/doi/full/10.1021/es903018m — in which he specifically indicates that CO2 is lethal (with some wiggle words, just in case).
The idea of painting houses white also fails for anyone not in the tropics….
If painting the roof while lowers the temperature of the house (ignoring for a moment what it does to the area), it will be a bit cooler in the summer, but also cooler in the winter…thus for many people who dont have a/c (ie most people outside of North America…), but do have heating (pretty much everyone), the net result will be more heating needed. Thus pumping more heat out in the winter, and requiring more of those evil CO2 producing power plants.
For me, in the UK, we need the heating on from October to April. All the time.
Whereas the number of days that A/C would be usful is maybe 2 weeks in the year
Do cities produce more convective cloud than nearby areas? If observations show this then the model may have some relevance. Otherwise it is just more of the same modelling masturbation.
richardjamestelford says: October 21, 2011 at 1:30 am re white paint reduces load on air conditioning.
Must be 2 years ago I disagreed with the thesis that painting the town white would make it cooler. One main reason is that hot air reflected from a white roof top is the very air that gets sucked into the feed of the adjacent air conditioner, requiring a higher power input. Another factor is that the heat reflected by the white can still find its way between buildings and heat their sides instead of their tops.
The main way a town gets cooler if painted with white roofs is by relocation of energy by some (unstated) mechanism away from the town for dissipation in to the air of less dense populations.
As I’ve written n times, you can’t analyse effects like this with intuition and a simple static mind game. Gather all of the relevant numbers and crunch them in an interactive dynamic program for so long as they stay valid.
I live in a rural area, and have noticed that over the winter, there do tend to be clouds over the two nearby “cities”, such as they are, when the sky is otherwise clear. Never thought about it much though, except that I thought they were more proof of UHI as these clouds often show convection when there is very little convection, if any, anywhere else in the winter months.
Funny too that in the summer months, you may see large flocks of buzzards circling lazily on “thermals” to gain altitude over airports and mall parking lots. I wonder where these are in the models?
“For me, in the UK we need the heating on from October to April. ”
As general rule maybe have white roof if average temperature is 15 C.
So southern Spain or similar warm climate. Or say, if get average solar energy more than 5 kW/h per square meter.
So places like UK, Germany, most of France, Seattle, or New York it doesn’t make much sense for thermal reasons.
Willis
You’ve been both noticed and promoted!
See the comment at Oct 21, 2011 at 12:09 AM | Unregistered Commenter sHx in His Grace’s blog here:- http://www.bishop-hill.net/blog/2011/10/20/best-paper-out.html#comments
I’m dubious of that. When I look at a daytime sat image I can easily see the difference between lighter colored city areas and darker forest areas such as my back yard where the afternoon temperature can be 10F lower than Boston in the summer. On Santorini all the building are white and you can easily see them from space so ‘much’ does not appear to be absorbed.
I’m not sure that I agree that painting a roof white will cause the world to warm, but there are several folks here who have argued that they need a black roof in the winter for warmth. You guys are forgetting that things radiate away energy at the same rate that they absorb energy. We paint wood stoves black for a reason. A black roof that is hotter than its surroundings will radiate energy away, just as a black roof will absorb energy from direct sunlight. In the winter, there is less sunlight than there is darkness, so a black roof will tend to cool the home more than a white roof will.
On the lines of “white roofs, less clouds” I’d like to add that the burning of fossil fuels has water as one of the emissions. All of the cars, all of the people breathing, all of the bath, shower, dishwashing, car washing, irrigation, etc. that goes on in a city, as well as the extra soot that darkens the streets, walls, and air around a city will make the effects of the roofs smaller. I believe there is enough hot water vapor in inhabited areas that we will still have plenty of clouds.
The advantage of a lighter colored roof, that occurs to me, is lower energy bills. There’s no reason for us to decide that better, more efficient use of energy is a bad thing, regardless of it’s use to combat CO2 caused Global Warming. For the record, I don’t think CO2 is warming the planet. In fact, I think we’re just rebounding from the LIA, right before our plunge into the next glaciation period, but what do I know?
This could limit local cooling and cause warming elsewhere as the particles drift away.
… but this doesn’t change the aggregate total global energy; it merely reduces a local “hot spot.”
Good thing the California Air Resources board decided that mandating reflective paints in cars was not cost effective (“banning” black cars was the common theme when it was proposed). Too bad they don’t apply the same cost/benefit analysis to their cap and trade.
Willis, I’m a bit jealous. You probably got to use old Eratosthenes’ old computer after he was done with it. I started in 1966 myself.
Your reasons for liking some features of this model smell good to me as well.
I dropped my subscription to Discover a few years ago after they featured an article by Laurie David. Prior to that, I would have characterized the content of the magazine as “Lukewarm,” meaning while they supported the belief that AGW was real, they weren’t alarmist or strident about it.
Willis,
Does the GATOR model calculate an estimate of climate sensitivity (ie. degrees K warming per doubling of CO2 concentrations)?
If so, I’d be curious to know how their estimate compares to others?
Dave:
Take two identical houses of identical roof temperatures in the dark but with one black and one white then yes I agree that the black one would cool the house quicker. But that is an over-simplified initial condition that won’t occur on a sunny winter day. The black roof collects heat during the day and the white one collects none. Ignoring the fact that the warmer black roof is also conducting heat to the air in my attic thus reducing delta T across the insulation below it, when the sun goes down my black roof is warmer than your white roof. The black one is radiating both ways part of which is warming me and my house below for part of the day and then into the night. The white roof stored no heat so it just stays bone cold day and night. At some point in the middle of the night the white roof would eventually be retaining more heat but I think testing is the only way to determine which color roof actually offers a net heat advantage over 24 hours.
(Now you have me thinking about snow and ice damning, thanks a bunch!)
Mike M says:
October 21, 2011 at 7:45 am
Dave:
In the winter, there is less sunlight than there is darkness, so a black roof will tend to cool the home more than a white roof will.
Take two identical houses of identical roof temperatures in the dark but with one black and one white then yes I agree that the black one would cool the house quicker. But that is an over-simplified initial condition that won’t occur on a sunny winter day. The black roof collects heat during the day and the white one collects none. Ignoring the fact that the warmer black roof is also conducting heat to the air in my attic thus reducing delta T across the insulation below it, when the sun goes down my black roof is warmer than your white roof.
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Mike, I agree that during the hot daylight hours, the black roof will be warmer than the white roof. It will also cool off much faster. At the point where the roof cools past the temperature of the insulated interior, the heat transfer begins to the outside.
If the temp outside is cooler than inside, the temperature flow will be outward, regardless of the color of the roof, right? Heat only flows in one direction; from hot to cold. So, even if the white roof does not warm as much as the black roof during the day, a warm attic will attempt to warm the cold air outside it, hampered only by the insolation and the speed of the heat transfer properties of the surface of the material. As I remember it, the heat transfer is governed by a) surface area, b) color (for radiation) and c) thermal conductivity for convection. The air touching the roof will cool it by convection, and the difference between the temperature of the roof and the sky will cool it by radiation. Surface area would remain the same between the roofs.
Correct me if I’ve got these factors wrong. So, unless the sun warms your roof to hotter than the inside temperatures, deltaT is always going to be outward. I think most of the temperature is going to be transfered via convection. If the air is cooler than the interior, the warmer roof tiles will warm the air faster than it will the interior of the roof. Also, with longer cooling periods than warming periods, the roof will lose heat to convection AND radiation for something like 16 hours a day, and lose to convection but gain through radiation only half of that time. Depending on the strength of the solar radiation in your part of the world, the daylight hours will have a weaker or stronger effect on the temperature of the tiles and the heat transfer.
I still maintain that a black roof will lose more energy during cold weather than a white roof.