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SkS Analogy 9 - The greenhouse effect is a stack of blankets

Posted on 29 June 2017 by Evan

Tag Line

The greenhouse effect is like a stack of blankets on a winter night.

Elevator Statements

  1. More blankets = more warmth: The greenhouse effect is like blankets warming the Earth. If it is -18°C (0°F) in your bedroom, you need a few blankets to keep yourself warm. More blankets = more warming. Too many blankets and you sweat. So the point is that the greenhouse effect is a good thing, up to a point.
  2. More blankets means warmer inside, cooler outside: With an increasing number of blankets, the temperature above the blankets gets cooler, because more energy is trapped below the blankets. With increasing greenhouse gases (GHGs) in Earth’s atmosphere, the upper atmosphere gets progressively cooler, because more energy is trapped in the lower layers of the atmosphere. This is one way that scientists know that the recent warming is due to greenhouse gases and not due to increasing solar output. In the sleeping analogy, if you turned up the temperature in the room, it would get warmer both above and below the blankets. If the recent warming was due to a hotter sun, then both the upper and lower atmosphere would warm. But the upper atmosphere is getting colder, just as the top of the outer blanket covering you gets colder when you add more blankets but leave the room temperature the same. See the SkS article "Is the CO2 effect saturated?"
  3. It is not the rate at which you put blankets on, but the total number of blankets that determines your final warmth. CO2 emission rates don’t affect the final temperature due to global warming, except that if we slow the emission rates it buys us more time. It is the total CO2 emitted that determines the final temperature we will reach, just like it is only the total number of blankets over you that matters, and not the rate at which you put them on.1 Note: the emission rates are important for determining how rapidly the climate changes and increased emission rates will make it more difficult for animals and humans to adapt to the increased warming. But just like when filling a bathtub, to keep the bathtub from overflowing (i.e., keeping global warming to under 2°C), it is not the rate at which the bathtub is filled that matters, but the total amount of water put into the tub. Carbon budgets refer to the total amount of CO2 we can emit before we exceed a dangerous level of warming, just as a blanket budget represents the total number of blankets we can tolerate before we start to sweat and overheat. Some skeptics refer to a time about 100's of millions of years ago, during the late Ordovician when CO2 levels were higher, but earth was the same temperature as now, or cooler. They point to this time to imply that CO2 levels do not correlate to temperature. But during the Ordovician the sun was cooler (like a colder bedroom), so that the colder bedroom combined with more blankets = similar temperature as today. If you turn down the heat in your room, you need an extra blanket or two. Thus, with a colder room, your blanket budget is higher.

Climate Science

On the topic of the blanket budget, assuming that we warm 3°C for every doubling of CO2 (this is the average climate sensitivity used by the IPCC [Intergovernmental Panel on Climate Change]), this corresponds to the following temperature increase for given CO2 atmospheric concentrations. Each of these atmospheric concentrations roughly corresponds to a particular CO2 budget.
•    350 ppm CO2 = 1°C warming
•    445 ppm CO2 = 2°C warming (2°C is the target agreed to by the Paris Agreement)
•    560 ppm CO2 = 3°C warming
•    700 ppm CO2 = 4°C warming (considered by many Climate Scientists to be unbearable)
We are currently at about 406 ppm, increasing at about 2 ppm/year. This means that at the current emission rates we will have reached our budget for 2°C by the year 2035 and crossed into really dangerous territory. This is why Climate Scientists are saying that there is no time to waste for cutting our carbon emissions.

The budgets used by the IPCC  are based on scenarios more complex than the simple math above, but IPCC budget estimates also often assume that we will be able to suck CO2 out of the air and bury it in the ground … at some time in the future. My simple estimate uses a climate sensitivity of 3°C/doubling of CO2, and assumes that we will not be successful at sucking CO2 out of the atmosphere and storing it underground. After all, to bring CO2 concentrations down means that we have to suck all of the CO2 emitted in a given year + an extra amount. Is that feasible? Great if we succeed, but at current emission rates we will be at our budget limit by 2035, and the planet will be warming while we are trying to bring these massive negative emissions technologies online. A good read on the subject is Kevin Anderson, or if you can watch him as well.

1. The rapid rates of increase in emissions we are seeing will create huge difficulties in adaptation, but simply slowing rates of growth will not be enough. What counts is total emissions load in the atmosphere that we eventually get to, as this will drive up temperatures for millenia, because the Earth's system will take considerable time to re-absorb CO2.

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Comments 1 to 20:

  1. The analogy was doing well up until point 3, the rate of putting on blankets and the Ordovician goes a little far; it's complicated. The rate matters especially with relation to the carbon cycle and weathering. Blankets are not added continuously, and there is no blanket cycle with blankets dissolving. Not to mention positive feedbacks under those blankets!

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  2. Yeah I think paragraphs one and two are excellent. The basic blanket analogy is just so good, simple and clear. I have just recently purchased some thick curtains, and I'm surprised just what a difference those make to temperatures, especially noticeable when I wake up in the mornings.

    Paragraph three sends a slightly mixed message. The total number of blankets is crucial of course, but the rate is very  important in relation to carbon cycles.

    The rate is also important because adpatation becomes harder if rates of change are rapid. It's also just too easy for people to say total quantities will be far in the future, and not our problem. Both rates and total numbers are equally important arent they?

    I agree about the late Ordivocean. This is sceptics cherry picking a period that suits their perspective, and its doubly frustrating because they seem unable or unwilling to grasp the totally plausible explanation you documented. In fact past climate history is very complicated and sometime superficially inconsistent with theory, but only a combination of various factors like solar changes along with greenhouse gases and other geological factors seem to explain everything, including the apparent inconsistencies and oddities. It appears to have been a complex evolving sort of system interracting in numerous ways. 

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  3. "Some skeptics refer to a time about 600 million years ago, during the late Ordovician..."

    My understanding is that the Ordovician era was from approximately 488 million to 444 million years ago. :-)

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  4. Those wishing to dismiss current high levels of atmospheric CO2 by comparing them to earlier periods of high levels of atmospheric CO2 need to keep up with current research:

    "The evolution of Earth’s climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere.

    Here we show that the slow ∼50 Wm−2 increase in TSI over the last ∼420 million years (an increase of ∼9 Wm−2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO2. This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth’s long-term habitability.

    Humanity’s fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene (50 million years ago).

    If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years."

    Foster et al 2017 - Future climate forcing potentially without precedent in the last 420 million years

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  5. Commenters 1-4, I get your message about the rate. I realize that the rate matters for adaptation (see Analogy 1: Speed Kills). What I was trying to say, and failed to, is the following.

    Whereas everyone has correctly pointed out that the rate challenges us for adaptation, in terms of the final temperature we reach it is not the rate but total CO2 that matters. Whereas rock weathering removes CO2 naturally, this process is far to slow to be effective to combat anthropogenic emissions. So for the current state of affairs, rock weathering is negligible for combating our emissions. I was trying to make the point that if we were to cut our emissions by a factor of 10, but still increased the total atmospheric CO2 loading to 560 ppm (or pick whatever number you want), we would still be in big trouble. In big cities reducing emission rates is effective because outside winds can dilute polluted air to reduce absolute levels, but there is no such mechanism in the atmosphere.

    I will try to rework this analogy, probably using the analogy that when filling a bathtub, to keep it from overflowing (i.e., staying below the 2C limit), it is not the rate at which you fill the tub that matters, but the total amount of water one puts in. We can get embroiled in a discussion of sinks into the ocean, biosphere, etc., but the main point I am trying to make is that whereas auto emission standard matter for local pollution effects, for CO2, all that really matters on any time scale we care about is the total emissions, and not the emission rate. I think the concept of emissions budgets is new to a lot of people, but is certainly not new to the people commenting here).

    I am open to suggestions for how to best phrase this.

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  6. Evan @6, the comments on rate that you have inserted in the article in italics pretty much clarifies it quite well for me.

    If you wanted to rework the article further, you might say something like " the rapid rates of increase in emissions we are seeing will create huge difficulties in adaptation, but simply slowing rates of growth will not be enough. What counts is total emissions load in the atmosphere that we eventually get to, as this will drive up temperatures for millenia, because the earths system will take considerable time to re-absorb CO2. Then add all the detail etc.

    I'm no expert on the science anyway, but I'm interested in how issues are communicated, and how sceptics respond, and the whole psychology thing. You do pretty well and better than I would, but the point is some sceptics will take anything out of context, and twist it, and its best to minimise chances of this. I could see roughly what you were getting at, and knew you were not dismissing rates, but others would twist it out of context by saying "look he doesn't care about rates".

    It's probably best to explain things pedantically eg, "the rate is important, but theres another aspect as well..... Of course it's sad that we have to do this, but that's the world we are in, full of people on the attack, taking things out of context, putting words in peoples mouths,etc.

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  7. nigelj @6. Thanks for your comments.

    I consider it impossible to make any analogy or article we are likely to write in SkS denier proof. My focus is to write for people who are really trying to understand. If we nail down every eventuality that a denier might use to attack an article, it is likely to become imcomprehensible to those who genuinely are trying to understand.

    I could be wrong on this, but this is how I see it. But I like your suggestions, and will try to work it in to improve the analogy further. Thanks for your suggetsions.

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  8. Evan @7, yeah it's impossible to make them totally denier proof. There would be so many qualifications and explanations it would be ridiculous, and loose conciseness and clarity, and all our time would be spent antipating responses rather than thinking about the actual issues. About all we can do is to try to avoid saying things that are obvious huge and easy targets for manipulation.

    So you are not wrong. 

    I would go further. If the science explanations are good, complete and cover all sides of issues as they should anyway (and it doesn't always need lengthy comments  to do this) then its hard for sceptics to manipulate things.

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  9. nigelj@8, what I did for now was to add your comment as a footnote. Your comment is well worded, and it repeats some of the points in a different tone, so is good reinforcement. By putting it as a footnote it does not interrupt the flow of the analogy or make it longer, but it is there for clarification. Perhaps I will have the time later to weave it in to the main body, but I don't want to do a quick edit and make the analogy longer at this point.

    Thanks for you input.

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  10. I sometimes wonder if the same people who copypaste the usual denier talking points including "there was xyz CO2 % during the Ordivocean" are not the same people who argue elsewhere that the Earth is 6000 years old, and evolution/plate tectonics are leftist god-bashing, or whatever.  

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  11. I think your wording Evan is good and thank for this article.

    In context of mitigation, it is very clear that we're talking about rate of CO2 increases due to anthropo emissions and changes of said rate would reflect which escenario be realised in the future. Anyone, who wants to understand this aspect of reality, does not need to consider the rates of natural changes in the past, like Milankovic cycles, because they are at least 100s times slower. There is no point worrying about "impending ice age" that would come (if people don't mess up with carbon cycle so much as to prevent it) in some 20-50ky, when civilisation may be wiped out within couple hundred years if no mitigation is undertaken. I don't need to care about the fact that I'm most likely be dead in say 60 years and become depressed & stop eating any food, when my current and most logical worry is not to die from hunger within few days.

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  12. Driving By @10, I wouldn't be surprised. Never understimate the ability of people to hold foolish and contradictory views in their heads at the same time.

    Labelling something leftist or god bashing is a form of "poisoning the well" fallacy. Calling somebody or some group an emotive or insulting name is an attempt to mentally discredit the source of the statements, and anything further they might say. Poisoning the well is a description of this, and a sort of "analogy" for this form of rhetoric.

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  13. 1. More blankets == more warmth? The source of heat is yourself, more blankets is a better isolation with less losses, not more warmth. (unless you put the blankets on fire).

    2. More blankets means warmer inside, cooler outside? It doesnt cool down outside because you emit less heat into. It's cool down because the cold layer outside is also loosing heat to outside your bedroom. It doesn't heat up as fast as before. Neither will it get any warmer inside than your body temperature.

    And in point 3. you go 'off the rails' just because you took the analogies from the wrong point of reference (inside instead of outside). Rate is very important in establishing an equilibrium. Especially when the heating/cooling is a cyclic process. No matter how high the amount of CO2 is in the atmosphere, if no equilibrium can be reached the system goes banana's. See other planets with an atmosphere e.g. a Venus.   

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  14. Ger@13,

    More blankets means warmer inside, cooler outside? It doesnt cool down outside because you emit less heat into. It's cool down because the cold layer outside is also loosing heat to outside your bedroom. It doesn't heat up as fast as before. Neither will it get any warmer inside than your body temperature.

    (my emphasis)

    Emphasised is the utterly bogus sentence in the context we are considering here. Maybe you think so, because human body inner thermostat (at 36.6degC) seems to you so strong that it can override the thermodynamic laws?

    Or maybe you don't understand this model. The model is: a planet gets energy froma  sun (via visible spectrum where GHG are transparent) just like your body gets energy from food as a rough equivalent. Then the planet glows IR just like your body releases metabolic energy. If you insulated your body completely, you would surely die from overheating. Your internal methabolism can regulate your body temperature only by releasing more heat to the skin, hoping the heat dissipates into the surrounding. It cannot do the opposite. When surrounding is perfectly insulated the body starts overheating because the internal thermal energy cannot simply "disapear". In your own words "the system goes banana's", as on Venus where CO2 insulation is almost perfect. If you do not deny such outcome, why are you at the same time pronouncing bogus statements, such as the emphasised one?

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  15. It's useful to have good analogies and important to work out their kinks.

    To respond to Ger@13's point 1, one could begin with a statement something like "The heat our bodies normally generate is like the solar energy reaching the earth while greenhouse gases are like the blankets you pull over you on a cold winter's night. Like the relative constancy of solar energy flux, our bodies usually can regulate temperature within a narrow range. However, our body parts feel warmer or colder depending on the balance of rates at which they receive and give off energy. Like the poles, our toes are supplied less energy and get cold with too few blankets. As you add blankets, your toes warm up the fastest, just as CO2 warms the poles the fastest." 

    The "inside" vs. "outside" language doesn't quite work for me. How about "skin" vs. "blanket top" temperatures?

    Changing the temperature in the room really messes with the analogy. How about adding a light electric blanket instead of increasing room temperature to represent changes in solar energy inputs?

    Ger@13 is correct: Your skin won't get any warmer than your core body temperature in this scenario, but chriskoz@14 has a point that the body can only reduce metabolism so far before overheating. 

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  16. To be morbid, there is another way that the body can reduce the metabolic production of heat, but I"m sure that nobody here thinks that dying is a solution to overheating. Over at And Then Theres Physics there is a post and discussion on increasing global temperatures, heat stress, and death rates, which includes discussions of how very high temperatures and humidity make it impossible for mammals to remain cool - essentially creating conditions where survival depends on artificial means such as air conditioning (available to humans - not so much to other non-domesticated mammals).

    In the blanket analogy, a set number of blankets will maintain a set body temperature at a set metabolic rate. If the body gets too cold, the body will increase metabolism to produce more heat (e.g. shivering). Or you can get up and move around, or add blankets. Likewise, if it is getting too hot, exercise is not recommended because then the body has to get rid of more metabolic heat. You can get out of the sun, remove blankets, then clothing, but by the time you are naked in the shade then there isn't a lot the body can do but sweat and hope it's not too humid - if the sweat won't evaporate, you're in trouble.

    Body heat doesn't disappear or maintain a constant body temperature through majick - it takes physics.

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  17. Posting problems - took multiple tries, and the pasting in the final try lost the link to the post over at And Then There's Physics:

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  18. Ger @13

    Point 1. "More blankets equals more heat? "I took that to mean more heat 'retained'. Maybe you are being pedantic on this one.

    Point 2. "More blankets means warmer inside, cooler outside?" I think you are right, this stretches the analogy a lot to the point of inaccuracy.

    However looking at points one and two another way, all analogies do simplify by their very nature, and its very hard if not impossible to word them in ways beyond all criticism, without making them so complex, they are pointless and no longer analogies. 

    Point 2 on body heat didnt directly relate to a point in the article and doesn't seem a useful analogy for the real greenhouse effect. 

    Point 3. Fair comment, but I took the article to mean that rate didn't matter as much as total quantities in this sense: Simply slowing down rate of emissions so we reach 600ppm (arbitrary example) CO2  in for example two or three centuries rather than one century doesnt really help, because we still reach a certain total level that will have implications for millenia, and this seems a reasonable concern. I think Evan was trying to point out that fiddling with the problem with small changes will not be enough.

    However the article didnt seem too clear on the rate issue, and rate is clearly important in other respects. 

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  19. If your body temperature goes over 42 C, you die. If it goes under 32 C you die as well. The Earth as a system doesn't die, all life , as we know it will as life isn't capable of adapting that fast to changes. 

    Source of the heat is outside this earth, the sun. The blanket analogy goes wrong by taking the source of the heat on earth. (you under the blanket). Sun does inject a dense ( much kW/m2) form of energy whilst on Earth there are not such hot sources. 

    As said, the CO2 blanket is transparant for short wave radiation, but much less for the longer wave radiation. Adding CO2 will make it rapidly less transparant, even in little bits as the swings in environmental conditions will be bigger than before and go over/under the limits of what life forms can stand. (+50 degrees C and -45 degrees C)

    P.S. if you want to keep ice frozen, you can wrap it in blankets as well. Most of the heat condition is, with the blankets, through heat conduction, not radiation.

    Try the glass greenhouse: transparant for (most) short wave radiation, Double layer glass with vacuum in between the panes passes far less energy out than it lets in short wave radiation.

    Change the CO2 concentration (short wave does get converted into long wave radiation by CO2) and the temperature inside goes up rapidly.  

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  20. Everyone is intimately familiar with warming up their own body with blankets, so this analogy is worth keeping in the tool box. It's actually quite accurate for the Earth at night time and explaining why nighttime lows have been increasing rapidly.

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