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Empirical evidence that humans are causing global warming

What the science says...

Select a level... Basic Intermediate

Less energy is escaping to space: Carbon dioxide (CO2) acts like a blanket; adding more CO2 makes the 'blanket' thicker, and humans are adding more CO2 all the time.

Climate Myth...

There's no empirical evidence

"There is no actual evidence that carbon dioxide emissions are causing global warming. Note that computer models are just concatenations of calculations you could do on a hand-held calculator, so they are theoretical and cannot be part of any evidence." (David Evans)

The proof that man-made CO2 is causing global warming is like the chain of evidence in a court case. CO2 keeps the Earth warmer than it would be without it. Humans are adding CO2 to the atmosphere, mainly by burning fossil fuels. And there is empirical evidence that the rising temperatures are being caused by the increased CO2.

The Earth is wrapped in an invisible blanket

It is the Earth’s atmosphere that makes most life possible. To understand this, we can look at the moon. On the surface, the moon’s temperature during daytime can reach 100°C (212°F). At night, it can plunge to minus 173°C, or -279.4°F. In comparison, the coldest temperature on Earth was recorded in Antarctica: −89.2°C (−128.6°F). According to the WMO, the hottest was 56.7°C (134°F), measured on 10 July 1913 at Greenland Ranch (Death Valley).

Man could not survive in the temperatures on the moon, even if there was air to breathe. Humans, plants and animals can’t tolerate the extremes of temperature on Earth unless they evolve special ways to deal with the heat or the cold. Nearly all life on Earth lives in areas that are more hospitable, where temperatures are far less extreme.

Yet the Earth and the moon are virtually the same distance from the sun, so why do we experience much less heat and cold than the moon? The answer is because of our atmosphere. The moon doesn’t have one, so it is exposed to the full strength of energy coming from the sun. At night, temperatures plunge because there is no atmosphere to keep the heat in, as there is on Earth.

The laws of physics tell us that without the atmosphere, the Earth would be approximately 33°C (59.4°F) cooler than it actually is.

This would make most of the surface uninhabitable for humans. Agriculture as we know it would be more or less impossible if the average temperature was −18 °C. In other words, it would be freezing cold even at the height of summer.

The reason that the Earth is warm enough to sustain life is because of greenhouse gases in the atmosphere. These gases act like a blanket, keeping the Earth warm by preventing some of the sun’s energy being re-radiated into space. The effect is exactly the same as wrapping yourself in a blanket – it reduces heat loss from your body and keeps you warm.

If we add more greenhouse gases to the atmosphere, the effect is like wrapping yourself in a thicker blanket: even less heat is lost. So how can we tell what effect CO2 is having on temperatures, and if the increase in atmospheric CO2 is really making the planet warmer?

One way of measuring the effect of CO2 is by using satellites to compare how much energy is arriving from the sun, and how much is leaving the Earth. What scientists have seen over the last few decades is a gradual decrease in the amount of energy being re-radiated back into space. In the same period, the amount of energy arriving from the sun has not changed very much at all. This is the first piece of evidence: more energy is remaining in the atmosphere.

 

Total Earth Heat Content from Church et al. (2011)

What can keep the energy in the atmosphere? The answer is greenhouse gases. Science has known about the effect of certain gases for over a century. They ‘capture’ energy, and then emit it in random directions. The primary greenhouse gases – carbon dioxide (CO2), methane (CH4), water vapour, nitrous oxide and ozone – comprise around 1% of the air.

This tiny amount has a very powerful effect, keeping the planet 33°C (59.4°F) warmer than it would be without them. (The main components of the atmosphere – nitrogen and oxygen – are not greenhouse gases, because they are virtually unaffected by long-wave, or infrared, radiation). This is the second piece of evidence: a provable mechanism by which energy can be trapped in the atmosphere.

For our next piece of evidence, we must look at the amount of CO2 in the air. We know from bubbles of air trapped in ice cores that before the industrial revolution, the amount of CO2 in the air was approximately 280 parts per million (ppm). In June 2013, the NOAA Earth System Research Laboratory in Hawaii announced that, for the first time in thousands of years, the amount of CO2 in the air had gone up to 400ppm. That information gives us the next piece of evidence; CO2 has increased by nearly 43% in the last 150 years.

 

Atmospheric CO2 levels (Green is Law Dome ice core, Blue is Mauna Loa, Hawaii) and Cumulative CO2 emissions (DOE Data Explorer). While atmospheric CO2 levels are usually expressed in parts per million, here they are displayed as the amount of CO2 residing in the atmosphere in gigatonnes. CO2 emissions includes fossil fuel emissions, cement production and emissions from gas flaring.

The Smoking Gun

The final piece of evidence is ‘the smoking gun’, the proof that CO2 is causing the increases in temperature. CO2 traps energy at very specific wavelengths, while other greenhouse gases trap different wavelengths.  In physics, these wavelengths can be measured using a technique called spectroscopy. Here’s an example:

Spectrum of the greenhouse radiation measured at the surface. Greenhouse effect from water vapor is filtered out, showing the contributions of other greenhouse gases (Evans 2006).

The graph shows different wavelengths of energy, measured at the Earth’s surface. Among the spikes you can see energy being radiated back to Earth by ozone (O3), methane (CH4), and nitrous oxide (N20). But the spike for CO2 on the left dwarfs all the other greenhouse gases, and tells us something very important: most of the energy being trapped in the atmosphere corresponds exactly to the wavelength of energy captured by CO2.

Summing Up

Like a detective story, first you need a victim, in this case the planet Earth: more energy is remaining in the atmosphere.

Then you need a method, and ask how the energy could be made to remain. For that, you need a provable mechanism by which energy can be trapped in the atmosphere, and greenhouse gases provide that mechanism.

Next, you need a ‘motive’. Why has this happened? Because CO2 has increased by nearly 50% in the last 150 years and the increase is from burning fossil fuels.

And finally, the smoking gun, the evidence that proves ‘whodunit’: energy being trapped in the atmosphere corresponds exactly to the wavelengths of energy captured by CO2.

The last point is what places CO2 at the scene of the crime. The investigation by science builds up empirical evidence that proves, step by step, that man-made carbon dioxide is causing the Earth to warm up.

Basic rebuttal written by GPWayne

Addendum: the opening paragraph was added on 24th October 2013 in response to a criticism by Graeme, a participant on the Coursera Climate Literacy course. He pointed out that the rebuttal did not make explicit that it was man-made CO2 causing the warming, which the new paragraph makes clear. The statement "...and humans are adding more CO2 all the time" was also added to the 'what the science says section. 


Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 12 July 2015 by MichaelK. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

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Comments 126 to 150 out of 417:

  1. #123 KR at 07:49 AM on 22 August, 2010 do you think that in other wavelengths the top of atmosphere (TOA) emissivity has increased? Yes. Note that the measured TOA emissivity has decreased at all observed wavelengths in that graph. In the graph, yes. Not in reality. As I have already told you, the offset in the graph is arbitrary. TOA radiative imbalance, as measured by satellites, have some 6 W/m2 uncertainty. Can you produce evidence to that effect? If not, I can't take your comment seriously. You can't produce evidence to the contrary either. The 0.9 W/m2 radiative imbalance at TOA is only assumed, never measured. In order to be taken seriously you have to be able to tell assumptions and facts apart in the first place.
  2. #124 KR at 07:52 AM on 22 August, 2010 Delamere et al 2000 is an interesting paper. But they fail to show actual data for TOA emissions. Of course they don't do that. It is about modeling, not measurement. But they do provide some hints regarding why these quantities are not measured properly yet.
  3. KR, In particular, "Trapped radiation will only serve to slow the radiative cooling exhibited by black body radiation" is completely insensible - random words that don't mean anything to me. Thank you. I believe I can make it clear. If an object is radiating at 390 Watts/m^2 (m^2 is meters squared) and a GHG absorbs some of it and sends back 2 Watts, then the rate of cooling via Radiation has dropped to 388 Watts/m^2. Since a Watt is a joule/second, then the most obvious choice of words to me was to say that it 'slowed'. Keeping in mind that radiation travels at the speed of light, any IR trapped by CO2 is in effect trapped at the surface since it's frequency at the surface is every 1/150,000,000 seconds if trapped at 1 meter or 1/15,000 seconds if trapped at 10,000 meters. Temperature changes over such short time periods and so little energy can, for practical purposes, be seen as not changing. To describe the 'trapped' energy when it is away from the surface requires one to predict it's location within the atmosphere which is highly variable and since everyone is so concerned with it's contribution to surface temps, that is the obvious choice again. So, if you consider the 'trapped' energy as stuck at the surface, or better yet, when you are measuring it it is at the surface, then in practical terms you have reduced the radiation rate by 2 Watts. Now consider that a cubic meter of water at 15 C (average Sea Surface Temp) contains about 1.2 Billion joules, a reduction in cooling of 2 Watts is a 12 hour reduction of 86,400 Watts. Sound like a lot? Consider it takes a 4.1 Million joule increase to raise that 1 cubic meter of water 1 C. However, the radiative resistance does not impede Convection or Evaporation (where available), in fact, since a slight increase in Temperature will be observed at the surface, the Convection rate will increase accordingly. Better?
  4. theendisfar - as in our previous conversation, I refer you to Trenberth et al 2009. The measured energy leaving the surface of the Earth run to 396 W/m^2 IR [pyrometers and FTIR spectrometers], 78 W/m^2 latent heat (evaporation) [from global precipitation and energy required to evaporate that much water], and ~24 W/m^2 convection [various estimates, but primarily what's left over]. Measured, repeatable (and frequently repeated) numbers. Unless you have measurements to the contrary, convection is 1/3 the energy of latent heat, and 1/16th the energy of IR, not the dominant effect you claim. And of course it has zero effect at the top of the atmosphere, where radiation is the only energy exchange with space. Next objection to the greenhouse effect?
  5. KR, So it's not so much gibberish in that it can't be clarified, it was gibberish because of a lack of understanding and trust of the source. This is relevant because if what I have stated is accurate, cannot be falsified, then one of the understandings must be wrong. Barring someone able to falsify the understanding I have, I hold it to be accurate. And of course it has zero effect at the top of the atmosphere, where radiation is the only energy exchange with space. This is good, we agree. Convection stops at the Tropopause. Where the Earth was able to cool via Conduction, Convection, and Radiation starting at the surface, it lost Conduction with only a small amount of altitude, and then it loses Convection at the Tropopause. A transfer of energy means that energy has traveled over distance. To say that conduction plays no or little part in cooling the Earth's surface because Radiation is the only ultimate escape is nonsense. To say the same of Convection is equally nonsense. I took a look at Trenberth et al, is this what you're getting your info from? Imagine for a moment I had "provided a review of past estimates", and "performed a number of radiative computations", and "values constrained by", and ""but adjusted to an estimated imbalance", and "Revised estimates", and "radiation is adjusted", and "by making modest changes" in the short understanding I posted above. It opens far more questions than it would have answered. Again, just because convection only moves energy to the Tropopause does not mean it is not the primary transport of energy from the surface to it. Just because Conduction only moves energy from the surface to the immediate atmosphere above it, does not mean it is not the primary transport of energy to it. Any issues with #129? Make sense?
  6. KR, Clarification. This is relevant because if what I have stated is accurate, cannot be falsified, then one of the understandings must be wrong. 'Understandings' meaning, energy can be added to a system by slowing, trapping, what have you, the radiation rate through whatever mechanism you like, GHE, enhanced GHE, super enhanced, etc versus the 1st and 2nd Laws are kept intact. The Sun is the only source of energy that adds energy to the Earth's system. Well, Star light (entire spectrum) does too if you want to get picky. This is why I brought up the back pressure that would occur if you slowed the rate of cooling by reducing the radiation rate (speed of light) and instead had to use Convection, several dozen meters per second max. The 2nd Law clearly shows that if you reduce the rate of one means of energy transfer, it will automatically increase the rate of another means if available. Again, for clarification, convection only moves the energy to the top of the Troposphere where radiation becomes the only means to transfer energy and it again reaches the speed of light. What I'm saying is that the atmosphere itself can easily absorb the extra 2 Watts from CO2 trapping via increased convection rate and by the elasticity of the atmosphere itself. The altitude of the troposphere is much higher at the equator than the poles far a reason.
  7. Theendisfar, the energy trapped in the atmosphere by GHGs ends up in the form of heat, by those GHG molecules banging into other molecules. Convection merely helps speed that distribution, not reduce that total amount of energy. The total heat of the system increases.
  8. theendisfar - You object to Trenberths measurements because they're complicated? That is what you're saying in that post! Imagine the following conversation about some science conclusion: "How did you measure your data for X?" "I used a mass spectrometer." "Ooo - that's complicated. And that opens more questions than it answers!" "Then I suggest you try disproving mass spectroscopy - good luck, come back when you have something valid to say." The various uncertainties in the Trenberth energy budget measures are on the scale of the total convective energy exchange - it's that small a portion of the energies (~18-20W/m^2, listed as "sensible heat"). IR from the ground (and back IR from the atmosphere) was first clearly measured in the 1950's, and has been repeatedly measured since then with a variety of instruments: ~396W/m^2. So: when you've disproved FTIR and pyrometers, and come up with different estimates for global precipitation and energy of vaporization of water - then we can talk about your new (and measured) energy budget. Insisting, in the face of actual measurements, that your personal world view is overridingly true (in this case that convection is the major portion of energy exchange) is a Common Sense logical error. It reflects a lack of domain specific experience.
  9. theendisfar, you agreed that: 1. The Sun is the only input of energy to the Earth system (combined atmosphere, land, ocean). 2. CO2 traps some of that input energy. 3. Radiation is the only way for that input energy to escape the Earth system (combined atmosphere, land, ocean). Then surely you must agree that the total energy in the Earth system (combined atmosphere, land, ocean) increases as a result of the CO2 trapping energy. I'm talking about the total, regardless of where or how it is distributed within that system. Do you agree? Please give a simple, short, answer directly to that specific question.
    Response: Empirical evidence of point 2 is in the post at the top of this page, in the section "CO2 Traps Heat." Empirical evidence for the conclusion is in the section "The Planet is Accumulating Heat."
  10. Tom, the energy trapped in the atmosphere by GHGs ends up in the form of heat, by those GHG molecules banging into other molecules. Energy is never actually trapped anywhere. We disagree on how the energy at the surface it transfered to the atmosphere. You say radiation being absorbed by GHG and then collisions with N2 and O2 molecules, I say via conduction at the surface and slightly, very slightly, by radiation absorption and then conduction to immediate surroundings. Convection merely helps speed that distribution, not reduce that total amount of energy. Have I stated otherwise? The total heat of the system increases. I believe I see the disconnect now that I quickly looked at #134. If you'll take a detailed look at 107-110, 128, last part of 130, and last paragraph of 131 it will help prepare you for my response to #134. Please take a moment to refute 107-110. You must understand that the journey of the energy within the system is just as important as to how much is incoming and how much s outgoing. Regions of the Earth's atmosphere are different temperatures, not only because of the input and outgoing energy, but because of the Transport mediums of available for the flow of energy. Your top of atmosphere reasoning (radiation only means of escape) has no explanation as to why the Troposphere averages 15 C at the surface and -54 C at the Tropopause (which is highly variable, altitude, from equator to poles).
  11. The Global Energy budgets are worse than bunkum because, 1) - The viewpoint used in IR budgets is simply wrong for what they try to depict and describe. At best the viewpoint used is misleading, but more likely the view is partial and inaccurate, being an instant and 2D view of a 24 hour and 3D planet. 2) - They completely misrepresent the real heat movements, depicting a ludicrous and physically impossible scene where radiation losses and movements dominate conduction, convection, and latent heat movements within the atmosphere. 3) - They hide / misrepresent the individual and comparative sizes (volumes) of the various energy flows. 4) - They do not take into account the temperature and the effects of the relative temperature differences of the energy flows. An agreed model of the atmosphere has to be arrived at for any meaningful debate to take place.If not agreed there will be nothing but endless nit-picking and confusion of units.All are agreed on units of time and the Earth's divisions and the location of 0deg Longitude.Something the same has to be done with respect to providing the layman with a reasonable working model of the Earth's atmosphere.The whole subject lacks definition.
  12. theendisfar at 03:48 AM, I enjoy following this exchange. It provides an exercise in lateral thinking which is probably lost on those who only think logically, which the inhabitants here predominately do. Just looking for a clarification, when TOA is being discussed, what point in the atmosphere is actually being considered the TOA?
  13. KR, That is what you're saying in that post! Absolutely not! What I'm saying is that the link you provided was an abstract that didn't even attempt to hide that it was a bunch of number crunching. Had I sent a similar link to you, I would have expected you, a skeptic of my position, to first note all the subjective terms and data massaging. Perhaps you would not have objected to such obvious areas of question, and instead you would have objected to the source's organizational affiliations, or font, or hair color or something. Beats me. But I don't need to rely on someone else's understanding when I have one myself. One that has not been falsified. Surprising given all the 'experts' here. What you sent me was not complicated, it didn't actually state anything once you added up all the estimates, computations, constraints, adjusted estimates, revised estimates, and modest changes. That's how AGW is most often explained. I say most often just to keep the possibility that someone can actually explain it in a way that a learned skeptical person could test themselves. Seriously, if I had sent you an abstract that had all that in the heading, you would not have laughed and said nice try buddy? Simply amazing. The fact that not one person here can refute my understanding is quite telling. Nice try gentlemen, but sorry; revising estimates, then adjusting them, adding constraints, and making modest changes + "AGW is real" ain't gonna cut it.
  14. theendisfar, you wrote "You must understand that the journey of the energy within the system is just as important as to how much is incoming and how much s outgoing." You're not addressing my simple, direct question. The journey of the energy within the system is irrelevant to the bottom line of how much energy is coming in to the entire Earth system (atmosphere, land, ocean) as radiation from the Sun, minus how much energy is going out of that same system as radiation to outer space. Empirical evidence summarized at the top of this page tells us that the "in" energy is greater than the "out" energy. The unavoidable consequence is that energy accumulates inside the system. The distribution of that energy, and even its form (e.g., sensible heat versus latent heat) is irrelevant to that accumulation that results from that imbalance of in versus out. Do you agree with that? Simple question.
  15. johnd, Glad someone is :) It frustrating as heck debating people who only rely on and offer other people's work, but can't find any flaws with your understanding. If they can't refute plain English how can I reliably think they have any understanding of the works they're offering? So it goes, I suppose. Just looking for a clarification, when TOA is being discussed, what point in the atmosphere is actually being considered the TOA? Beats me, but I will offer it plays little role in surface or even tropospheric temps with regards to any radiation that is 'trapped' in the system. As long as it is outside the Stratosphere, that is. Why/how would it? Curious, did you get a chance to ponder 107-110?
  16. Tom, The answer cannot be answered so simply because we do not agree. I can use simple terms, but the farther we are from having the same understanding, the more simple steps will have to be described. #139 has given me a better understanding of your understanding, so after I go out and enjoy some of this beautiful day, I will try to bring our understandings together from my end. Thanks for doing the same from your side. The distribution of that energy, and even its form (e.g., sensible heat versus latent heat) is irrelevant to that accumulation that results from that imbalance of in versus out. Do you agree with that? Not a chance, and I believe that I can accurately describe my position, but later :)
  17. theendisfar at 03:48 AM on 23 August, 2010 ”Energy is never actually trapped anywhere” Of course it is. Obviously one needs to be specific about what one means in any particular case. However it’s a dull “argument” that attempts to negate truism by semantic quibbling. The fact that the earth has a biosphere that is conducive to higher lifeforms, not to mention our entire way of life, is due to trapping energy; e.g.: - the energy of solar photons of visible wavelengths/energies is trapped in photosynthetic reactions, converted to free energy in ion gradients across cell membranes, and chemical bond energies in the form of (initially) generic carbohydrate (CH2O)n. It’s the trapping of solar energy that drives life processes. - Our societies are largely fuelled by the trapped energies of solar photons, sequestered for eons in the form of chemical energy, and released by controlled oxidation. - Our earth is around 33 oC warmer that it would be as a blackbody emitter with an earth-like albedo bathed in the solar flux in the absence of an atmosphere. The enhanced warmth is due to the trapping of solar energy by atmospheric greenhouse gases. More energy is retained in the earth system in the presence of greenhouse gases than would be there without them (around 33 oC's worth of surface temperature). Call it something else if you like but you can't negate a reality with semantic "arguments"! It’s obvious what “trapped energy” means in these real world contexts.
  18. theendisfar, if more money goes into your bank account than goes out of it, then money accumulates in your bank account. Whether that money is distributed across your checking, saving, and money market subaccounts within that bank account is irrelevant to the fact that the total bank account amount increases. Do you agree with that?
  19. theendisfar at 04:28 AM, I look at things from a different perspective. Whilst we live immediately on the surface within the atmosphere, the main sources and sinks for heat already within the system are the oceans and the land. H2O in it's various forms plays the primary role in trying to constantly maintain thermal equilibrium because all sources and sinks are not equal. This is what we know as weather. Solar radiation is the primary source of heat and before it can heat the atmosphere it must first intersect the planets immediate surface before it undergoes any transformation. For this reason I believe that any changes begins with any variations on the amount of solar radiation that intersects with the earths surface. The output of the sun may vary, or conditions in the atmosphere between the sun and the surface may vary causing changes in the amount of solar energy that arrives, and where it arrives. Clouds are what I believe to be the major factor that drives that. The main problems with making a case for clouds is that there is little historical data available, and the understanding of the processes involved in the formation of clouds is low. This makes such discussions difficult, CO2 is a much simpler concept for the average punter to grasp, as you mentioned the thinking has already been done by others, so clouds are mostly consigned to the too hard basket.
  20. Chris wrote:- "The enhanced warmth is due to the trapping of solar energy by atmospheric greenhouse gases. More energy is retained in the earth system in the presence of greenhouse gases than would be there without them (around 33 oC's worth of surface temperature)." Surely gravity gives rise to an increase in temp at the surface.P1/T1=P2/T2? Take out "greenhouse gases" and leave just N2 and O2. Would it make much difference? I don't think so.Sorry but the idea that the 33degC difference is due to 0.03-0.04%"greenhouse gases", I just don't get.....and neither does 90% of the folk I've talked to who have made an effort to understand this so-called "science".
  21. #145: "Surely gravity gives rise to an increase in temp at the surface.P1/T1=P2/T2?" What does gravity have to do with that? "leave just N2 and O2. Would it make much difference? I don't think so." It would be interesting to hear you substantiate this opinion, in more depth than 'I don't think so'. Perhaps you should have a look at Dr. Roy Spenser's backyard experiment verifying that atmospheric greenhouse gas does indeed warm the surface. Talk about empirical evidence! And from a noted skeptic, no less.
  22. Muoncounter says:- "What does gravity have to do with that?" at TOA T=0degC,P=near 0. at surface, T=15degC,P=15lbs/squ in Why the increase in P at the surface? Gravity? The "I don't think so" means that I have formed an opinion on the matter which I have expressed here for either refutation or retention, dependent on the quality of replies. For that is the raison d'etre of this website, I think.
  23. AWol, theendisfar - you might find the recent Science of Doom postings on The Hoover Incident and Heat Transfer Basics and Non-Radiative Atmospheres useful primers. They discuss what would happen if we didn't have greenhouse gases in the atmosphere.
  24. AWoL, only the action of increasing pressure of a given quantity of gas increases the temperature. Once the gas is at that new pressure, the temperature does not increase any more. Pump up a bicycle tube quickly and you can feel the tube get warmer from the air being compressed from one atmosphere (outside the tube and pump) to greater than that (inside the tube). But let the tube sit undisturbed for awhile and it (and the compressed air inside it) will exchange energy with the surrounding air until the tube once again is at the same temperature as its surroundings. It does not continue getting hotter, nor remain hot by replacing its lost energy, merely by virtue of being at high pressure. Air in the Earth's atmosphere does get compressed when gravity drags it down, and so it does heat. But eventually that same air rises and so loses that heat it acquired. Averaged over the atmosphere, across time, the net effect on total atmospheric temperature is zero.
  25. #147: "Why the increase in P at the surface? Gravity?" Ah, so the temperature at the surface is merely due to the weight of the atmosphere. Then it follows that gravity causes increased temperature. In classical mechanics, gravity is a force and forces can only increase temperature (a statistical measure of kinetic energy) when work is done. Yes, falling objects gain kinetic energy. So you must believe that all atmospheric gas fell from outer space to the surface of the earth? "I have formed an opinion on the matter which I have expressed here for either refutation or retention," And yet this opinion remains unsubstantiated. The quality of the replies here is excellent (and quite patient). Interestingly, I last heard the same 'I dont think so' opinion over at a competing website, W..T?

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