There are many claiming to be "climate scientists". What does it mean to be a scientist? I think it is agreed that it takes more than a college degree, lab coat, and computer to be a real scientist. Science requires experimental controls - something not found in the statistics about an open system with confounding variables. There is no doubt that increasing the opacity of the air by the added CO2 causes an increase in global temperature. There is also no doubt that changes in solar radiation changes global temperature. The question is if the amount of increase contributed by man's emissions of CO 2 is significant compared to changes due to the sum of the confounding variables (see list below).
In real science, everything that can possibly be done to eliminate confounding causes are eliminated. The earth's atmosphere is an open system - no one knows with any certainty the amount of materials emitted by the earth or even additions from outer space. An open system is one where we can not control for confounding variables.
Statistics often provides a scientist a good idea
for a hypothesis, but
statistical correlations do not prove cause and
effect. A meaningful correlation has to be more than just two variables
trending in the same direction. News reports
about science often confuse correlation with cause and effect. The news
media acts as if 'correlation' is proof of
causality, to the confusion of the lay public. There is especially much
muddled thinking in climate news reporting
where we are talking about a simple trend with many confounding
Collected statistics are the epidemiological part of science. Its
proper use in science is to suggest an experiment. Only controlled
experiments can show an 'arrow of causation'. In a controlled
experiment, only one variable is changed at a time. There is a 50:50
chance that two variables that are trending in one direction will
correlate. ( consider CO2 and the temperature above ). If CO2
went up and down and temperature did the same with a slight phase shift
it would have greater meaning.
Humidity has changed in the same time frame. Is it due to unprecedented use of irrigation or and effect of warming? Once again, we need to remember that a correlation in the data does not show an arrow of causation or even dependency.
For something to be considered a scientific fact, it must be testable with the scientific method.
1. Observe some aspect of the universe. ( correlations belong here )
2. Invent a tentative explanation, called a hypothesis, that is consistent with what you have observed.
3. Use the hypothesis to make predictions.
4. Test those predictions by experiments or further observations and modify the hypothesis in the light of your results.
5. Repeat steps 3 and 4 until there are no discrepancies between theory and experiment and/or observation.
Real science is humble. Many things are unknowable. It is a human tendency to not to accept the idea that some things are beyond our reach of knowing, but there are things we can't know, no matter how much money is poured into research.
Step 4 of the scientific method requires an experiment. An experiment requires a control. What are the controls in climate science?
Real science publications archive and make available to the public all the input data of papers along with all computer code used to generate any output. Reputable publication have peer reviewers that are given complete access to the complete data so they can review, audit, and look for problems. Reputable publications have reviewers that are not coworkers of the authors. This is not the norm for what is being passed off as 'climate science' - see Disclosure and due diligence It is common sense to disregard any papers that have closed data, methods that can not be independently verified.
Climate science is often reported as if a 'run' of a computer model is an experiment (it is not!). A computer model can not discriminate theories into true and false because it is not measuring reality. (Such models may give one an idea where to experiment, but to claim they "prove" anything is pure fiction and should lead one to discount the source. At best you can use a computer model to disprove a theory.)
Computer models were used to convince the SEC to remove regulations that led to the current (Oct 2008) economic melt down. From a NY times article:
A lone voice of dissent in
the 2004 proceeding came from a software consultant from Valparaiso,
Ind., who said the
computer models run by the firms which the regulators would
be relying on could not anticipate moments of severe
With the stroke of a pen, capital requirements are removed! the consultant, Leonard D. Bole, wrote to the commission on Jan. 22, 2004. ...
The public needs to recognize that just because something is modeled on a computer - it need not represent reality, and the result of erroneous public policy are not with out great cost.
Computer models are sometimes used to simulate electronic circuits for engineers - in an electronics circuit (which is a closed system) - these computer models sometimes predict behavior quite different from the real circuit. If such a models adjusted until the results give the expected result, it is often to the folly of the engineer. The proof of such a circuit must wait until a real circuit is built: reality must be tested, not a model. (Common electronic circuits can be modeled quite well, and these models are of practical use, yet these models still can mislead engineers at times. Be aware that circuit models, besides being a closed system, are several magnitudes less in complexity and size compared to the simplest climate models.)
Freeman Dyson, professor of physics at the Institute for Advanced Study, in Princeton has this to say about the computer models:"... I have studied the climate models and I know what they can do. The models solve the equations of fluid dynamics, and they do a very good job of describing the fluid motions of the atmosphere and the oceans. They do a very poor job of describing the clouds, the dust, the chemistry and the biology of fields and farms and forests. They do not begin to describe the real world that we live in. The real world is muddy and messy and full of things that we do not yet understand. It is much easier for a scientist to sit in an air-conditioned building and run computer models, than to put on winter clothes and measure what is really happening outside in the swamps and the clouds. That is why the climate model experts end up believing their own models." The full text of the above quote is worth a read.
Four of the six points above have serious problemsI remember reading a news article when I was in 5th or 6th grade by "scientists" that predicted that we were going into a new ice age because of man made pollution. Here is a later one. I thought it was true and worried about it for years. I followed every global climate article I got my hands on, until I realized they didn't have any way to truly support the claims they were making. Some of these same people are in the global warming business now.
Supporters of global warming will say, "I've known of hundreds of scientists with diverse political backgrounds (from all over the world) who have come to the same conclusion", but taking polls on the opinion of people whose income is tied to the existence of a problem is not science. A poll of PC (Politically Correct) scientists from the year 1400 would have put the earth rather than the sun at the center of our solar system. While there are quite a few PC scientists today claiming to "know" that man is causing global warming, there are other scientists that honestly and humbly disagree.
A politically popular opinion doesn't make
it correct. No poll
of scientists has anything to do with science.
Science is not a democratic process!
Supporters will further say, "Many of these scientists are established, world-renowned, tenured professors who do research in numerous areas and whose jobs are certainly not dependent on the existence of global warming".
But let us consider the peers of Copernicus; did their being "established, world-renowned, tenured professors" make them right? Would publication of balanced humble papers without dire conclusions effect the issuance of research grants? This link may be over hyped, but his detractors can only rebut with ad hominem attacks as he points out the difference between a scientific forecast and forecasts by scientists.
Richard Feynman was a physicist, who was not only closely associated with QED (Quantum Electro Dynamics), but also wrote about the scientific method and scientific rigor. I first ask you to read his bit about cargo cult science. Pay close attention for the part about the oil drop numbers - and realize that it applies here.
When a hypothesis fails to explain the given data, it follows that it must be abandoned. Non of the models I've read about can explain the lack of elevated temperatures at higher elevation. (As of 2006 there is now some hand waving about the ozone hole causing stratospheric cooling).
Feynman also became a bit of an artist on the side. This is important because drawing depends more on being a good honest observer than on talent. If you draw a picture and notice that the chin isn't where it belongs, it is easier to overlook after one starts inking over the pencil lines. What makes art truly art, is the discrepancies between reality and the art. It tells us as much about the artist as it does the subject. The way slight distortions are adjusted and blended in. Being a real scientist means we have to bend over backwards in order to find our human induced distortions of the object we are trying to draw conclusions about. This takes honesty and courage to report all warts and wrinkles in the subject AND the observer.
I am told that, "... meteorologists I know that are skeptical about global warming are weather forecasters (not researchers) and have little expertise in the science of climate change -- their jobs do not require it." Well if changing weather isn't climate change what is it? Meteorologists are trained to look at numbers trends and graphs and form conclusions about the probability of future events. They know that seeing patterns in data can be the playground of fools (are there any fool-proof computer programs that accurately predict the stock market?) More importantly, a meteorologist's experience will have taught them to be very careful about making claims about the future with limited data. Perhaps this experience has given them a better feel for what is knowable than the global climate researchers? The "science of climate change" was quite wrong when they were predicting a "new Ice age". Real science requires something that is beyond the combinations of a bunch of estimates plugged into human choice tainted computer models.
I truly wish Richard Feynman was alive to day to comment on the scientific vigor in global warming. Research can often look like science, yet fail to be real science in the end. Where is the "whats bad about it" part in the AGW papers? Why? Could it be that the AGW rhetoric is not real science?
The idea that because CO2 has gone up and surface temperatures have also gone up means nothing. It is a correlation only in the sense that both variables are headed in the same direction. The odds of this being the case are 50% A similar correlation exists between CO2 and breast cancer. There is no cyclic variable in the global warming studies. (If we include proxy measurements, ice core samples - they have CO2 lagging temperature not leading) If CO2 had gone up and down 4 times and ground temperature had followed - that could be interesting, but would only start to mean something after 10 to 100 cycles. If CO2 had gone up and down several times and global temperatures had followed there would be a meaningful correlation, yet that would still fail to show cause and effect - (they both could be caused by a third factor).
We've been told that "The atmospheric levels of CO2 have risen 30% since the Industrial Revolution (~1780) and 18% since1959". Yes,CO2 has increased slightly, and there is input from man, but even that can not be shown conclusively. In an open system it is entirely possible that other variations of natural CO2 sources and sinks may be more responsible. There could be natural sources and sinks of CO2 that have not been identified. In an open system, there is no control of other variables, thus what we can know is quite limited.
One of the biggest confounding issues is that of man caused changes in humidity. Almost the entire flow of the Colorado river now goes across the content by air, rather than flowing into the Gulf of California as it did 100 years ago1. Water vapor is also a green house gas - it differs from CO2 in an important way in that it is limited to the lower part of the atmosphere - if it goes higher it condenses, dumping heat in the upper atmosphere. If the temperature is higher, water vapor rises higher and pumps heat to a higher altitude thus forming a negative feed back system that should tend to stabilize temperatures. On the other hand, water vapor is a potent 'green house' gas that blocks the heat flow from the earths surface even better than CO 2. Further complications are due to the fact that the altitude of condensation are effected by dust and even cosmic rays. Much of the water used in irrigation evaporates and only stays in the air for a number of days before being rained out - yet this rain evaporates again continuing the elevated humidity and the heat that is pumped to the upper atmosphere is a climatic effect..On the other hand, CO2 stays in the atmosphere much longer, but once it is removed from the atmosphere tends to stays out. Water vapor in the form of clouds blocks the warming of the earths surface by the sun. Temperature can effect humidity and humidity can effect temperature. This total process is played out in the clouds, something that is not at all well modeled at this time.
Water vapor accounts for about 70% of the greenhouse effect with carbon dioxide somewhere between 4.2% and 8.4%. Water vapor, a potent green house gas, averages 25,000ppm of the lower atmosphere compared to CO2 which is only about 360 ppm. The Atmospheric CO2 change is only about +60 ppm. Realize that we are talking about a change in CO2 from 0.030% to 0.036% or a 0.006% change as a percentage of the atmosphere. The global warmers don't use these numbers instead 'warmers' say it increased 30% (for maximum rhetorical effect?). Over the same periods specific humidity has increased several percent and could be a change of 25,000ppm to 26,250ppm or 2.5% to 2.6% or a 0.1% change. This change in water vapor (probably due to irrigation) is about 16 times larger than the change in CO2 near the ground. (remember in the stratosphere is possibly cooling and has very little water vapor). see:
Both CO2 and water vapor have similar emissivityso that any change in greenhouse effect due to CO2 would be swamped by changes in water vapor. One could also speculate that this explains the change in global temperatures at lower altitudes with out effecting the upper atmosphere. But lets not draw conclusions based on speculations.Here is a quote from Reid Bryson, Emeritus Professor and founding chairman of the University of Wisconsin Department of Meteorology (now the Department of Oceanic and Atmospheric Sciences)
"Well let me give you one fact first. In the first 30 feet of the atmosphere, on the average, outward radiation from the Earth, which is what CO2 is supposed to affect, how much [of the reflected energy] is absorbed by water vapor? In the first 30 feet, 80 percent, okay? ...: And how much is absorbed by carbon dioxide? Eight hundredths of one percent. One one-thousandth as important as water vapor. You can go outside and spit and have the same effect as doubling carbon dioxide."
If (and I mean IF) man is causing climate change it seems possible it is due to irrigation - not CO2. (Would banning irrigation be a popular political movement?)The computer models appear to assume a constant relative humidity which would artificially generate higher temperature predictions
Atmospheric CO2 may have a slight effect, but there is no proof that man's contribution as a source of CO2 (ESTIMATED at about 4% of all sources) is the reason temperature is slowly trending upward. It is entirely possible that CO2 is going up due to natural variations more than mans contribution - probably not - but the point is that even this is not a scientific fact.(BTW I think we should be taxing oil imports (in place of income taxes) for other reasons.)
One other detail - the ice core data shows that increases in CO2 follow warming periods - instead of proceeding them. This is expected, because sea water holds less CO2 as it warms and absorbs more as it cools (a established testable fact!).
Low altitude warming has not been established as anything historically out of the ordinary. The data just isn't there to do this. At this time and into the foreseeable future it is unknowable. Being unknowable is the heart of the problem of calling climate speculations,"climate science".
The great computer models used to predict the dire consequences don't really accurately model clouds, and for good reasons. Clouds are extremely complicated to simulate. Water vapor tends to condense into water droplets at nucleation sites . These sites can be a spec of dust, but are also caused by cosmic rays, neutrinos, and even agitation of air. Cosmic rays are not constant, they vary with solar storms and the position of solar storms on the sun. (solar weather forecasts exist!) These nucleation sites cause non-linear and chaotic effects. The lack of real cloud simulations in the model reduces this to a political campaign - one that is misleading the public about what is known and knowable.
Henrik Svensmark, a weather scientist at the Danish National Space Centre, believes that the planet is experiencing a natural period of low cloud cover due to fewer cosmic rays entering the atmosphere. But is this a truth? How can he know any better than the warmers? Looking at system with numerous confounding variables greatly limits what is knowable. Once again, I hope people will realize that true wisdom is knowing what we don't know. A paper showing a link between gamma rays and climate Gamma_Rays_and_Climate.pdf
At this time, it is hard to see that adequate peer review is being practiced in several of the journals involved and there is no excuse for not making data sets available in this day of computers and the Internet.The lack of disclaimers about computer-models vs experiments also degrades the credibility of these papers. The public does not understand that all computer models have fudges in them to get convergence. The public does not know that there are compromises in resolution in space and time in these models due to practical concerns. and Here I quote Dan Hughes:
"The AOLGCM codes are known to not be capable of attaining calculated results that are independent of the sizes of the discrete increments used in the numerical integration of the model equations. So far as I can determine, there is no attempt at all to demonstrate that the numerical solutions converge to the solutions of the continuous equations."
"A nice little loophole has been created, whether implicitly or explicitly I don't know. The scientific journals associated with the climate-change community will accept papers for publication the basis of which are calculations by computer software that has not been peer-reviewed. So, AOLGCM-based papers get peer-reviewed and published and then cited in the IPCC reports. This is not correct because it bypasses the independent verification and replication processes of the scientific method."
This is not science.
One bright spot is that NASA's Hanson recently gave Steve McIntyre credit for pointing out a small error from combining different sets of ground station data (that slightly lowered the US warming numbers) at around Y2K.McIntyre pointed to the error in spite of not being giving access to all of the data and software used.
The key to separating scientific knowledge from beliefs that science can be demonstrated. We may never have good enough error bands on the data about global temperature data; thus it is something that is just not knowable. Opinions on things unknowable are called beliefs. Because of the inapplicability of the scientific method when dealing with open systems, opinions on global warming are beliefs akin to a sort of religious view and not scientific fact. (this applies equally to folks that say warming is disproved).
"Climate science" as reported in the press is not really science. In real sciences the scientists first job is to prove himself wrong - that is to list the numerous way that the results my be in error and how the conclusions are limited. No forthright "bending over backwards" efforts are made by the global warming proponents. Instead, there are efforts to state things in emotional terms and a disturbing pattern of data errors and omissions. When claims are made dealing with an open system using correlations of data without knowable error bands, it fails to be science. There is no way to separate out the increased use of irrigation and the resulting increase of low altitude water vapor (very much a green house gas). Could changes of global low altitude humidity be a plausible competing theory? The correlation of temperature and variations of solar output is ignored.
Open systems, like the stock market are the subject of randomness - and much has been written about the "black swan" effect and the inability of professional stock pickers to come out ahead of amateurs in the long term. To infer a long term trend in what appears to be mostly noise - or randomness is a game of chance at best. All that can possibly be determined are floors of probability in an open system, and even those don't mean that much if one considers "black swan" effects.
I fail to see even an estimate of the amount of error of natural emissions of CO2 prominently displayed in the bandied documentation. Using real science, means you figure the answer and then you do the hard part of calculating the minimum, maximum, and probable errors. It is not possible in this case to even have hard numbers on CO2 venting - thus we are again not looking at science, but only estimates and speculation. Attaching numbers to speculation does not elevate it to science.
We are told that, "Carbon dioxide is measured
directly at Mauna Loa in
Hawaii", but it is really just a much better
estimate of just one place and not really a direct measurement (There
is no pipe to install a calibrate-able flow
meter.) How much CO2 is emitted from underseas
vents? To what accuracy is it known?
Satellite data is extremely important, as it is the best data available and has no micro-climate artifacts. The satellite data is the only data that comes close to measuring anything that could be called global temperature and not effected by micro-climate and would be most difficult to fudge. According to the MSU/NASA UAH data, the atmosphere as a whole seems to be cooling or warming slightly depending on what level of the atmosphere you look at. The data below is the best >>> GLOBAL <<< data we have. Ground stations of various designs and distributions, or combined bucket types and engine intake ship data can not come close to this NOAA satellite data.
But do you know what I see in that data? (And I'm really good at looking at statistics) - Not much that is significant -- mostly some noise - noise that is much higher than any trend. You could pick selected start and end points to show either cooling or warming. There is obviously no hokey-stick. Some indirect temperature trends track with solar output with a fairly good correlation. Will the new solar activity change solar output and cause more warming? What are you willing to bet on it? I wouldn't, as I am rather certain that we don't know.
One more reason to take the above graph data seriously - it comes from real scientists who share their data and lean over backwards to show possible errors. This is what real science looks like.
To claim as a "fact" something from a trend who's amplitude (and direction) can be changed by changing end points due to the noise involved not science; it is politics.
Turns out there are lots of problems that the satellite is free from -
Examples of improperly sited ground stations:
http://www.norcalblogs.com/watts/images/incinerator.jpg Quincy, CA at the CalTrans office, they measured temperature right next to a trash incinerator.
http://www.norcalblogs.com/watts/images/chimney.jpg Mt. Hamiltion, CA east of San Jose, where the Mt Hamilton astronomical observatory sits, they measured temperature on the roof of a building AND next to a chimney!
There are similar problems with historical water temperature with changes from types of buckets and then on to engine intakes.
The point is that the artifacts in these data sources is larger than the trends claimed and produce the uncertainty (we really don't know).
Everyone has an agenda at some level. I am assuming
that you, the
reader, are not influenced by the popularity of the
idea of global warming and you have really looked at the raw data
yourself and made sure that no one was hand picking
start and endpoints of data sets and that non of these people worried
(even subconsciously) that if they failed to show
the right result they would fail to get new funding.
Let me illustrate: QED (Quantum Electro Dynamics) is real science. The theory was put in place and then controlled experiments were run against it in closed systems - the theory wasn't changed every time someone came out with a new test. This is what real science is about.
With global warming you have a computer model of the largest physical system on earth, that has several uncontrolled inputs with huge error bands that can interact in non linear ways. The model is simplified in many ways because of the limits of computer power. You have emotional humans that decide on just what compromises to make - and these choices can greatly skew the results. Just the sheer number of terms makes the output dubious at best - reminiscent of the drake equation.
There is a famous saying in physics:``Give me four parameters and I can fit an elephant. Give me five and I can wag its tail''
(The source of the above quote?? Variants of the
statement have been attributed to C.F. Gauss, Niels Bohr, Lord
Kelvin, Enrico Fermi.)
When one considers that these models may have parameters that number in the tens to hundreds and are only growing in size, the possibility of generating meaningful global climate computer models is a fantasy.
I worry that there is a pattern of tweaked data and hyperbolic press releases related to this subject. If this is a real phenomenon, so much political polarizing of the issue will prevent any unified action.Were the errors reported in "Energy and Environment" 11/03 the result of fudging the numbers? I hope not, but they very well could have been from a subconscious hope. (The actions of the journals involved is an embarrassment to science) A scientist's first job is to prove himself wrong. That isn't the way much climate research is approached.
Sadly, http://www.climateaudit.org/ has convincingly illuminated something that looks a lot like probably fudged data - omitted data, tampered data and more.
The much hyped report from the EPA was made by people who's income depends on the continued belief of a CO2 caused warming trend. What do people who do not depend on there being a "global warming" problem say? The meteorologists I've met (that don't have a political or economic ax-to-grind), say that the only thing they have seen that is close to a proved theory is that global temperature tracks solar output. As scientists, they should be careful to wait a few more solar cycles before even taking that to heart.
The EPA's reference even lists a 1996 Nature article that used a data set with fudged endpoints.
To make these claims without real science behind it also raises a moral problem, as the unintended consequences may be harsh on the poor people of non developed countries. If CO2 could be shown to cause some global warming, will a carbon ban kill more or less people than the potential perceived problem? If food becomes more expensive with carbon taxes, there will be starvation of the poorest in the world.
The release of emails confirmed my suspicion that some of the
loudest proponents were purposely cooking the science. That they
have been "dishonest" with the public does not change what is
knowable. Real scientists don't "hide declines" in their data.
Tom Wigley of NCAR: “Mike, the Figure you sent is very deceptive … there have been a number of dishonest presentations of model results by individual authors and by IPCC …”
Phil Jones: “Basic problem is that all models are wrong – not got enough middle and low level clouds. …what he [Zwiers] has done comes to a different conclusion than Caspar and Gene! I reckon this can be saved by careful wording.”
Phil Jones: "I’ve been told that IPCC is above national FOI Acts. One way to cover yourself and all those working on AR5 would be to delete all e-mails at the end of the process. Any work we have done in the past is done on the back of the research grants we get – and has to be well hidden. I’ve discussed this with the main funder (U.S. Department of Energy) in the past and they are happy about not releasing the original station data."Michael Mann: “… the important thing is to make sure they’re [the skeptics are] lo[o]sing the PR battle. That’s what the site [RealClimate.org] is about.”
John Mitchell: "Is the PCA [principal components analysis] approach robust? Are the results statistically significant? It seems to me that in the case of MBH [one of the key hockey stick articles authored by Mann, Raymond S. Bradley, and Malcolm K. Hughes] the answer in each is no"
Raymond Bradley re: Mann and Jonespaper, stating: “I’m sure you agree–the Mann/Jones GRL [Geophysical Research Letters] paper was truly pathetic and should never have been published. I don’t want to be associated with that 2000 year “reconstruction.”
G.H. Cook: “I am afraid that Mike [Mann] is defending something that increasingly can not be defended. He is investing too much personal stuff in this and not letting the science move ahead.”
Peter Thorne of the U.K. Met Office: “I also think the science is being manipulated to put a political spin on it which for all our sakes might not be too clever in the long run.”
More emails - I leave it to the reader to decide if these are scientists or charlatins.
I do not gloat over the emails - I am quite saddened - the damage done to the term science
is not trivial. The emails reveal a closed off circle that has
succumb to a variety of cognitive biases and are more concered with PR
than doing good science.
when applied to AGW would suggest that we should stop producing CO2
just in case the theory might turn out to be provable and true - to
prevent possible harm. The only problem is we know that increasing the cost of
energy costs lives. There is also the problem that the precautionary-principle, when applied to itself, forbids the precautionary principle!
[2013-07] The above bit about the precautionary-principle seems to have this page quoted in it's entirety with out citing it's source in university course material. Hard as it might be for some of these sophisticated scolars to imagine, but doing things 'just-in-case' can have really bad effects. Argumentum ad ignorantiam is a falacy. Unintended consequences of governmental precationary actions are well documented and common. Long papers of frantic hadwaving (using probabilities without error bands) does not change this.
Back when punch cards ran the world, they called it dynamic programing, You would vary all the coefficients of an equation via nested loops until the equation would produce the data with some amount of accuracy. It is a useful tool to help tease out hypotheses from data.
Once it works on past history and predicts the set of data it is tempting to think it means something. To really test it, you have to run it and make predictions to be tested with experiment. If the prediction is complex (ie. wave forms) and matches we can assign a confidence. Of course if all we have is a trend - there is only a 50:50 chance that it means anything. The idea that once it predicts the past it will also predict the future is just wrong. If on the other hand, they froze the computer model and collected data over several solar cycles and then ran the model, - over several such runs, we could start to attach a probability of the model's output being predictive.
a = 0.28
e = 0.87
Obviously does not have an A/e of 1.
It is also important to note that painting the inside of screens can also make a difference.
Other emissivities of interest:
Wood - planed oak 0.90
Dry soil 0.92
Wet soil 0.95
Brick - common 0.93
Aluminum Polished sheet (I would guess aluminum foil would be similar) 0.05
Emissivity changes with temperature a bit. These numbers are from Infrared System Engineering by Richard Hudson JR.
Two things to keep clear when thinking about emissivity, it is commonly under stood that emissivity = absorptance. This is just not true for solar radiation. (Comes close for some materials, but not for others. Polished aluminum has an a/e of over 14!)
Also, the darkness of a color is not a good judge. I quote from Hudson's fine book:
"We must resist the temptation to estimate the emissivity of a material on the basis of its visual appearance. A good illustration of this point is furnished by snow "
White Paint a = 0.28 e = 0.87 a/e
Sherwin Williams (A8W11)
Concrete a = 0.60 e = 0.88 a/e =.68
Aluminum foil a = 0.15 e = 0.05 a/e = 3.00 (aluminum foil get very hot in the sun for this reason)
Asphalt a = 0.9 e = 0.95 a/e =0.95 (not sure I believe this number?)
So the best selection of a surface for a screen would be a low e value combined with a/e close to 1. The understanding of emissivity was not so good when the standards for screens was developed - during the space program it became critical to have craft with an a/e close to 1 and low emissivity so as to not cook or freeze the electronics.
It is important to note that solar radiation at the earths surface is not black body radiation!The confounding issues I've come across are :
Religion provides the means for the ignorant to declare with absolute certainty that they know the unknowable.
True wisdom is knowing how little we know for certain
"Believe those who are seeking the truth; doubt those who find it." Andre Gide:
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. --Galileo Galileo
I was gratified to be able to answer promptly, and I did. I said I didn't know. -- Mark Twain
Inconsistent Truth(C)2003-2013 Karl Schmidt