Ocean heat content and sea surface temperatures

I had a number of interesting Twitter conversations today and thought I would write about one of them. It started with me retweeting something from Andy Revkin which showed the NOAA ocean heat content, down to a depth of 2000m, from 1960 to now. I include the figure below. It shows that the amount of energy in the oceans (to a depth of 2000m) has increased by about 3 x 1023J since about 1970.

Ocean heat content down to 2000m from 1960 to now (credit : NOAA)

Ocean heat content down to 2000m from 1960 to now (credit : NOAA)


Someone then responded to suggest that it should be temperature not energy so that a direct comparison can be made with atmospheric temperatures. I think this isn’t really correct as they are two different systems with different masses and different specific heat capacities. Anyway, if you do convert to temperature, you discover that the ocean temperature has increased by about 0.11oC since 1970. The rather predictable response to this calculation was, why do we care about such a small temperature increase?

Well, there are a number of reasons why we care. That the ocean heat content has continued to rise tells us that global warming (or global heating) continues, despite the slowdown in the rise in surface temperatures. Oceans are also part of our climate system. Adding energy to the oceans can change ocean circulation and can influence hurricanes and cyclones. Also, ENSO cycles can transport energy throughout the ocean, heating the ocean surface and releasing it into the atmosphere where it can increase atmospheric and land temperatures.

There is also another reason why we should care. Currently the oceans are absorbing a large fraction of the excess energy entering the climate system. If this fraction were to reduce, we will see the rise in surface temperatures accelerate. The response to this point was the claim that this would violate the 2nd law of thermodynamics since energy can’t go from a cooler body (oceans) to a warmer body (atmosphere). The claim being, I believe, that if the oceans are currently absorbing a majority of the excess energy, then this can’t change and hence we have nothing to be concerned about. Now, I think that applying the 2nd law of thermodynamics isn’t really correct here. We’re talking about radiation, not conduction.

I thought I would describe how I, as a physicists, think this works. Firstly, I’m not a climate scientist, so maybe I’ve got it wrong. Secondly, this is going to be quite simple and I will be ignoring a lot of the details. As usual, happy to be corrected if I’m wrong. If the planet was in equilibrium we’d be receiving as much energy from the Sun as we lose back into space. Currently, we appear to be undergoing a phase of global warming in which we receive more energy from the Sun than we’re losing back into space. About 70% of the planet’s surface is ocean which means that about 70% of the incoming energy hits the ocean, and 30% hits the land (ignoring the atmosphere for the moment). One might expect this to imply that 70% of the excess should go into the ocean, and 30% into the land.

However, the amount absorbed by the system will be determined by the difference between the incoming energy and the outgoing energy. The amount going out (or radiated) is essentially determined by the surface temperature. If the oceans and land had the same surface temperature, then we would expect the oceans to absorb about 70% of the excess energy. The sea surface temperature, however, tends to be lower (I believe – although I’ve become slightly concerned that this may be wrong, so may be a flaw in my argument) than the land temperature and hence, on average, the difference between the incoming and outgoing energy is likely to be greater for the oceans than for the land. Hence, the oceans absorb more than 70% of the excess. Currently, consequently, the oceans are absorbing more than 90% of the excess energy.

So, why am I saying this. Well as the oceans absorb more and more energy, the sea surface temperature will have to rise. The difference between the incoming and outgoing energy will have to drop, and the oceans will absorb a smaller fraction of the excess energy. This will then mean that a larger fraction will be available to heat the land and atmosphere and we will start to see the rise in surface temperatures accelerate. Unless global warming were to somehow stop (and it hasn’t) the surface temperatures will have to start rising faster again in the not too distant future.

Anyway, when I started to explain this in Twitter (which is tricky given the 140 character limit) I was asked what would happen if the sea surface temperature rose by 0.1oC. So, I thought I would have a go at working it out. The amount of energy radiated from the surface of the ocean per second is
0.7 x 4 π R2E σ T4,
where RE is the radius of the Earth, and T is the surface temperature of the oceans. The average sea surface temperature is about 290 K. If I solve for the energy radiated per second, I get 1.4314 x 1017 J s-1. Now, if I assume the sea surface temperatures increases instantaneously by 0.1oC to 290.1 K and redo the calculation, I get 1.4334 x 1017 J s-1. The difference is 1.98 x 1014 J s-1. If I multiply by the number of seconds in a year I get, 6 x 1021 J. In other words, if the sea surface temperature were to increase by 0.1oC, the oceans would radiate 6 x 1021 J more per year than they did at the lower temperature.

If you look at the figure included above, you’ll see that the ocean heat content is increasing at about 7.5 x 1021 J per year. So, if the sea surface temperature were to suddenly rise by 0.1oC (which it can’t), instead of the oceans absorbing more than 90% of the excess energy, they’d only be absorbing about 20%. Now, I know this isn’t actually possible and I’m not suggesting that anything like this will happen. All I’m trying to point out is that a relatively small change in the sea surface temperature could change the fraction of the excess energy going into the oceans and hence change the fraction that is available to heat the land and atmosphere.

Anyway, I don’t know if I’ve got this argument quite right. It has to be more complicated than I’ve described here. However, I think the basic calculation is about right. As the ocean heat content rises, it must increase the sea surface temperature. This will have to reduce the difference between the incoming and outgoing energy and will hence reduce the fraction of the excess energy being absorbed by the oceans. Consequently we will see an increase in the fraction available to heat the land and atmosphere. As usual, happy to be corrected by those who know more than I do.

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56 Responses to Ocean heat content and sea surface temperatures

  1. Interesting and informative exercise.

    But, to add a few more points to consider…

    ocean surface temperatures conform more closely to atmospheric values. So the average increase in ocean surface temps is around .6 C while the atmospheric temp increase is .8 C.

    Since heat transfer relative to the atmosphere is delayed through the middle and deep ocean, you end up with an average .11 C increase throughout the entire system with a hotter surface layer.

    That said, since the volume of the ocean is so massive, the smaller proportionate temperature increase takes a much greater degree of heat energy.

    What’s also interesting to consider is that the average temperature of all the water in all the oceans, once you consider the deep ocean, is stunningly close to 0 C. So the whole ocean system, being so large and so cold and sucking up so much of our heat forcing, is a huge damper to atmospheric warming.

    You’ve clearly demonstrated this in these excellent calculations.

    One more point of possible merit is the fact that the ocean system periodically switches from net heat uptake (la Nina) and net heat release (el Niño). The oceans also switch between decadal periods when there are more La Niña years and periods when there are more El Niño years. This cycle is called Pacific Decadal Oscillation (PDO). We are now in the negative, La Niña, phase of PDO. When it switches, the oceans will dump some of that massive extra heat content you mention back into the atmosphere.

    Models show that this could result in decadal temperature increases of around .4 C, which is actually a raging pace when one considers it represents about 10% the difference between now and an ice age, but on the side of hot.

    Perhaps, it’s worthwhile to consider another problem involving this particular ocean heat uptake issue. At this point, the oceans now absorb a significant portion of human CO2 emission. But, as you well know, the ability of a liquid to suspend a gas in solution is proportionately based on its temperature. So as the ocean warms, it is proportionately less able to absorb CO2. Even worse, an ocean saturated with CO2 and then forced to warm may begin to out-gas some of those CO2 stocks. Another reason why ocean heat content is a big deal.

    Lastly, another carbon stock, this set stored in frozen methane hydrates on various ocean floor structures, destabilizes as ocean temperatures rise. While it is less likely that such stocks will catastrophically out gas in a doomsday scenario, their comparatively large volumes means that even a small proportionate release represents an amplifying feedback to the human warming of the atmosphere.

    So three reasons why we should care about warming oceans. And yes, you’re absolutely right about that .11C rise being a value worthy of concern.

  2. Thanks, some very interesting and useful comments. Pleased that it seems that my post wasn’t complete nonsense 🙂

  3. Certainly understandable and I do think you have it right. In fact, Trenberth and other chief climatologists would probably agree wholeheartedly.

    Tackling ocean heat content was a huge advance of the science. I am hoping that more research is done on the CO2 saturation issue. That one could be nasty if it sneaks up on us.

    And just one more off topic question…

    You’ve done a lot of work tracking down the misleading done by Watts. In my view, much of climate denial is based in a political meme that, for whatever reason, attempts to indefinitely delay a needed transition away from fossil fuels.

    But it seems to me that there is a flip side to this meme. The moment it appears that climate change develops into an actual crisis, in the public perception, a second group of denialists called doomers seem to move in to assert — nothing can be done, civilization is doomed. And here I find another face of denial because whether you pretend a crisis isn’t there or you pretend there’s no way to deal with the crisis, the end result is the same — a push for zero action.

    I find this meme to be particularly insidious among environmentalists who, sometimes, have a tendency to be naturally anti- technology. The doomers seem to spin this meme to attack the helpful technologies by endlessly denigrating their value and effectiveness.

    Do you find any of this tendency in your digs through the Watts blog? I’d be interested, because in my focus on the emerging threat that is climate change, they seem to hound me relentlessly.

    So I find myself in what seems to be a propaganda vice between the hammer of complete denial of a critical problem and the anvil of a complete denial that anything can be done about the problem.

    In any case, your thoughts and observations are greatly appreciated.

  4. So, in reading WUWT the standard themes seem to be that CO2 is a weak GHGs and that climate sensitivity is on the low side (although Anthony appears to despise what are called slayers – those who don’t believe in the greenhouse effect), that what is happening is a consequence of natural variability (it’s the Sun, ENSO events,…), that the global climate models have failed and therefore we shouldn’t be basing any future policies on flawed science, that CO2 is good for plants and we will benefit from enhanced CO2 levels and higher temperatures, and that climate scientists are undertaking a massive conspiracy or are fundamentally incompetent. There is a little bit about how green policies will be bad for us economically and that anything we do to act against climate change will harm the poor.

    However, there doesn’t seem to much in the way of people who suggest that although it’s happening, there’s nothing we can do and so should just carry on as we are. If anything, anyone who suggests such a thing is normally criticised for not realising that climate change isn’t happening (or is much less significant than climate scientists suggest). So, I guess no, I haven’t much in the way of doom-mungering. It may still happen but doesn’t seem to be particularly prevalent at the moment.

  5. Skeptikal says:

    Currently, we appear to be undergoing a phase of global warming in which we receive more energy from the Sun than we’re losing back into space.

    That’s normal for our planet… I would be more concerned if the planet was losing more energy than it was receiving.

  6. How is it normal? It appears to have been happening for at least 40 years. That’s longer than the solar cycle and covers the period when TSI was dropping.

    Anyway, did you get the basic point of the post though? It was really just trying to illustrate that you can’t assume that the oceans would continue to absorb most of the excess energy. As the sea surface temperatures rise, the fraction available to heat the land and atmosphere must rise too.

  7. Skeptikal says:

    How is it normal? It appears to have been happening for at least 40 years.

    Is that some kind of joke? Can’t you see what you’ve just written… “for at least 40 years”.

    It’s been happening a lot longer than that… that’s why I say it’s normal for our planet. You’re a physicist… you work it out. I’ll even give you a hint; the planet needs an energy imbalance.

    As the sea surface temperatures rise, the fraction available to heat the land and atmosphere must rise too.

    Yes, I can see the logic there… what I can’t see is the atmospheric temperatures rising.

  8. No, I think you’re confusing global warming (increasing energy) with simply getting energy from the Sun that maintains a stable, quasi-steady climate. I’m referring to the evidence that the total energy in our climate has been increasing with time, not that it’s been maintained at some nice steady level. If global warming were to continue as it is for millenia, we’d become Venus (not that I’m suggesting that this is in any way likely).

    What I’m suggesting is that as sea surface temperatures rise, the oceans will retain a smaller fraction of the excess (extra energy). This will happen because it will be radiating more from it’s surface. This will be radiated at long wavelengths and will have to pass through the atmosphere. It is likely (very probably) that some of this will be absorbed by the atmosphere and hence the atmosphere (and land) will be absorbing a bigger fraction of the excess than it is today and temperatures will have to rise.

  9. Skeptikal says:

    I’m referring to the evidence that the total energy in our climate has been increasing with time, not that it’s been maintained at some nice steady level.

    I never said that anything about maintaining energy at a nice steady level. You’re confusing energy with heat… which is probably why you didn’t understand what I meant by the planet needs an energy imbalance.

    If global warming were to continue as it is for millenia, we’d become Venus (not that I’m suggesting that this is in any way likely).

    If global warming were to continue as it has been for the last decade, we’d hardly notice the difference in a millenia.

    This whole thermageddon thing is wearing a bit thin… which is why people have stopped caring about global warming.

  10. No, you’re completely wrong. I’m not confusing energy with heat. If we receive more energy than we lose, we heat up (or temperature rises, or whatever terminology you want to use). It’s very simple. If global warming were to continue as it has, we would be adding about 1022 J of energy to the system every year. Imagine it all goes into the ocean. The total mass of the oceans is about 1021 kg. It has a specific heat capacity of 4000 J kg-1 K-1. If it was maintained at this level for 10000 years, the ocean temperature would rise by 2.5oC. It would boil within 100000 years. The planet does not need, nor do we want, a long-term energy imbalance.

  11. Oh, and don’t start mis-interpreting what I’m saying. I’m not suggesting that we’re going to turn into Venus nor am I suggesting that the oceans will boil in the next 100000 years. Just illustrations!

  12. Skeptikal says:

    I’m not confusing energy with heat. If we receive more energy than we lose, we heat up (or temperature rises, or whatever terminology you want to use).

    You’re making an assumption that all the energy goes to heat and what does go to heat stays as heat… wrong assumption. A physicist should know better than that.

    If global warming were to continue as it has, we would be adding about 1022 J of energy to the system every year. Imagine it all goes into the ocean.

    You have a vivid imagination. You’re imaging all this energy as heat… but it’s not heat. That’s why we have the ‘missing’ heat… coz it’s not there! Until you stop confusing energy with heat, you’ll never understand why the planet needs an energy imbalance, and why the missing heat is missing.

  13. Firstly, stop lecturing about what a physicist should or shouldn’t know. I think you’re making some fundamentals error here yourself, but I’m trying not to be condescending.

    Secondly, what other form is this energy going into? Sound? Light? Tell me what it is?

    Thirdly, this post is about the ocean heat content. According to the data it has increased by 3 x 1023J since 1970. One can convert this into a temperature (as I did) and it will indicate that the average temperature of the ocean has increased by 0.11oC. That’s based on the specific heat capacity of water. That includes all other possible forms of energy. Now, if you don’t believe the data, fine. That’s your choice. But don’t suggest that continuing to add this much energy to the oceans for millenia will have no discernible effect. That’s nonsense!

  14. Skeptikal says:

    Secondly, what other form is this energy going into? Sound? Light? Tell me what it is?

    This whole idea of energy in must equal energy out (energy balance) is simplistic, silly and just plain wrong. It can only happen on a dead planet, like Mars. You work out where the energy is going… not that you care because you’ve already decided it’s all going to heat the oceans.

    Thirdly, this post is about the ocean heat content. According to the data it has increased by 3 x 1023J since 1970.

    1970 to 2000 was a warming period… the atmosphere also warmed during this period. Go pull the ocean temps for the last decade… hey, what a coincidence… they flatline same as the atmospheric temps.

    But don’t suggest that continuing to add this much energy to the oceans for millenia will have no discernible effect.

    I’m not suggesting that at all. I’m suggesting that a lot of the ‘excess’ energy isn’t going into the oceans. The ‘imbalance’ isn’t the real imbalance anyway, it’s a modelled imbalance. They take the ocean temps and them somehow simulate an imbalance. It’s not an actual observed imbalance.

  15. Sure, it might be simplistic but it’s not plain wrong. It’s approximately right. It’s basic physics. You can’t simply keep adding energy to something without this energy doing something. Sure, we’re not a dead planet and some of this energy does more than simply sit in the oceans, and heat the land and atmosphere, but that’s always been true (or at least over very long timescales). Photosynthesis apparently uses about 1% of the incoming energy, but some of this must be later released and this has been the case for a very long time. We’re talking here about changes that have happened in the last century or so. We can’t invoke some kind of natural change in how the planet “decided” to use this energy.

    I haven’t decided anything. I was illustrating a point with this post that you’ve largely ignored. You think there are problems with OHC data. Fine, I don’t object to that. It’s your right to decide that. I’m less convinced that that is true, but again, that’s my right. There are, however, a number of published works and publicly available data that suggests that the ocean heat content has not flatlined. Either it has or it hasn’t.

    I don’t know quite what else you want them to do to determine the ocean heat content. They have ARGO floats. They have satellite and other measurements of sea level rises. They even have direct measurements of the earth’s energy budget. Sure, modelling is involved in turning that into an estimate of the ocean heat content. That’s very common in science. It’s not unusual to have to make some kind of modelling assumptions when taking some measurements and turning it into data. Maybe it’s completely wrong. I don’t know, but I have no real evidence to suggest that it is completely wrong. I’ll keep reading and making up my own mind (as you should too).

  16. Skeptikal says:

    We’re talking here about changes that have happened in the last century or so. We can’t invoke some kind of natural change in how the planet “decided” to use this energy.

    You can say that the planet has been warming since the Little Ice Age. We can invoke natural change because that’s all we’ve got to explain our exit from that cold period.

    It’s not unusual to have to make some kind of modelling assumptions when taking some measurements and turning it into data. Maybe it’s completely wrong.

    Back in 2004 Hansen modelled the imbalance…

    According to the model, Earth is now absorbing 0.85
    ± 0.15 W/m2 more solar energy than it radiates to space as
    heat.

    http://meteora.ucsd.edu/cap/pdffiles/Hansen-04-29-05.pdf

    In 2012 Hansen modelled the imbalance again, and it’s been marked down…

    According to calculations conducted by Hansen and his colleagues, the 0.58 watts per square meter imbalance implies that carbon dioxide levels need to be reduced to about 350 parts per million to restore the energy budget to equilibrium.

    I’ll post the link to that one in another comment so that wordpress wont flag me for spamming.

  17. I’m not quite sure what you’re getting at with this comment. I’m sure that the change after the LIA was natural. That’s not really in dispute. There has to be period of natural warming (and cooling).

    I would imagine that the two imbalance figures you quote are consistent (I presume the 0.58 watts per square metre has an error). You do realise that those figures are consistent with an increase of energy in the climate system of around 1022 J per year. If this has been happening since the LIA and if only 1% of this was heating the atmosphere, atmospheric temperatures would have risen by 8oC.

  18. Skeptikal says:

    Link for previous comment…

    http://climate.nasa.gov/news/673

    There is definitely an imbalance. As I’ve said previously, there has to be one… but the actual value of that imbalance is something we just don’t know yet with any certainty.

    Hansen couldn’t sell the imbalance at 0.85 W/m2, so now he’s trying to sell it at 0.58 W/m2… I think it’s still a bit high, so I’ll probably wait until he marks it down a bit more before buying.

  19. I don’t get why there has to be an imbalance? I realise that we sequester some energy, but are you actually suggesting that somehow we can have an imbalance of about 0.5 W m-2 without heating up the planet?

  20. Skeptikal says:

    The point is that the models aren’t all that good. How much of that 0.58W is real imbalance? How much of the real imbalance is being consumed by the planet? Actual observed sea surface temps show little, if any, warming over the last decade. It’s only the modelled ocean heat content which shows anything.

    The warming since the LIA hasn’t been linear… but the trend is positive. Who’s to say whether we have fully emerged from the LIA, or if the recent warming is just another burst of warming which is still dragging us out of that cold period.

  21. We should probably just agree to disagree. My understanding is that the amount of energy used by the biosphere is negligibly small (although I do need to check this). If right, most of the imbalance ends up as heat.

    As you probably know, the ocean is massive heat sink. Even with a large change in ocean heat content, we wouldn’t expect a large change in sea surface temperature over a decade.

    As far as coming out of the LIA is concerned. Fine, but what’s the mechanism? TSI is dropping. The planet itself can’t generate energy (well a small amount of geothermal, but that’s not new), so why and how are we continuing to accumulate energy? Also, why is our understanding of the influence of CO2, which has been tested experimentally, wrong?

    I would probably regard my questions as largely rhetorical. I don’t think we’re going to resolve our difference any time soon.

  22. Skeptikal says:

    No, I think the 0.5 W/m2 value is a bit high… but without any imbalance the planet would have to be cooling. You said yourself that photosynthesis consumes energy… not ‘heat’ but energy. Air circulation is driven… it doesn’t come for free. Extreme air movement (hurricane) only forms in tropical waters where enough energy can be drawn from the ocean to power it. How can you power the planet and maintain an in/out energy balance?

  23. Something to bear in mind is that the heat content of the atmosphere and land is reasonably low (I may write about this at a later time). The equilibrium temperature is set by the energy budget. So, indeed, on average we would expect some of the incoming energy to be used by the biosphere and then sequestered. However, the surface temperature will reflect this (it will be slightly lower than if this were not happening). If something were to change then my quick calculation suggests that the surface temperature should re-equilibrate in a matter of months (or maybe a year or so). A long-term (although variable) rise in surface temperatures is very difficult to explain without something in the atmosphere continuing to maintain an imbalance. In other words why did we not reach an equilibrium temperature quickly?

  24. Skeptikal says:

    Also, why is our understanding of the influence of CO2, which has been tested experimentally, wrong?

    I never said it was wrong. I would think of it more as incomplete. We tortured CO2 in a bell jar and found it got excited when bombarded with radiation. What we haven’t done, and cannot do, is an experiment of how CO2 works in a dynamic atmosphere. I suspect that the atmosphere accomodates the extra CO2 with negative feedbacks… the net effect being CO2 having less impact in ‘the real world’ than the benchtests would suggest… possibly even a close to zero effect.

  25. Skeptikal says:

    In other words why did we not reach an equilibrium temperature quickly?

    We did… and we do. You said yourself…

    Something to bear in mind is that the heat content of the atmosphere and land is reasonably low

    Atmospheric temperatures are mostly a response to the surface heating… with some negative (cooling) response to water vapor content. Have a look at the 1998 ENSO event… look at how quickly the atmosphere lost all that gain. Interestingly, have a look at the end of that event… the fall is almost uniform and then we see a small rebound. This shouldn’t happen. If greenhouse gases keep the planet warm, then the end of that event should have resembled the tail end of a bell curve.

  26. chris says:

    You’e “common sense” idea is fooling you I think Skeptikal. In any system at equilibrium (say a live planet or a dead planet), the energy in is equal to the energy out, else it wouldn’t be at equilbrium.

    The Earth (a living planet) would be at thermal/radiative equilibrium if the solar energy absorbed at the top of the atmosphere was equal to the energy (largely infrared) radiated to space. This equilibrium still applies in a living planet where stuff happens (photosynthesis/ocean and wind currents etc.).

    Your notion of an energy imbalance required to “power” stuff like photosynthesis is spurious since it doesn’t take into account the fact that the fauna is more or less also at equilibrium. So solar energy absorbed and converted to chemical energy in photosynthesis (nCO2 + nH2O -> (CH2O)n + nO2) is released as thermal energy when plants die. There would only be a requirement for a planetary energy imbalance if there was a large and persistent increase in the amount of photosynthesis and plant growth in excess of plant decay…

    The fact is that a massive amount of solar energy is being absorbed by the oceans – we can measure this and this can only happen as a result of a large radiative TOA imbalance. This is exactly what one expects from very basic understanding of the greenhouse effect.

  27. Skeptikal says:

    So solar energy absorbed and converted to chemical energy in photosynthesis (nCO2 + nH2O -> (CH2O)n + nO2) is released as thermal energy when plants die.

    I’ve never seen dead plants spontaneously combust… the world must be warmer than I realised.

  28. I’m not sure where I said we reached equilibrium quickly.

    The 1998 ENSO event is probably a good illustration of the point I was making. Any short term variations should disappear on short timescales. The TSI today is only a few tenths of a watt per square metre more than it was about 200 years ago. Surface temperatures are, however, almost a degree higher than they were then. Why? What mechanism is allowing the surface temperatures to remain this high if TSI is only marginally greater than it was then.

    As I’ve said before, we should probably stop this because it’s simply going nowhere.

  29. chris says:

    “You can say that the planet has been warming since the Little Ice Age. We can invoke natural change because that’s all we’ve got to explain our exit from that cold period.”

    That would be astonishing and scary if true Skeptical! If the Earth was still warming as a result of a sort of “recovery” from the LIA then that would indicate a scarily high climate sensitivity. At least in that sense we can relax a little and recognise that we know your idea isn’t true.

    There’s a decent understanding of the contributions to the LIA cooling which had significant contributions from well-characterised changes in solar output and enhanced volcanic activity. But inspection of the surface temperature record shows us that the Earth surface temperature (at least) recovered by the mid 19th century.

    I think we have a pretty good idea of the process underlying temperature rise from the LIA to present. As solar activity resumed to “normal” levels and volcanic activity decreased the resulting radiative imbalance drove temperatures back up to pre-MWP temperatures – this seems to have broadly stabilised by around the mid-late 19th century as inspection of (say) the Hadcrut4 temperature data indicates. Contributions to surface warming during the last century have been characterised in some detail by many groups (see e.g. Lean, J.L., and D.H. Rind, 2008: How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006. Geophys. Res. Lett., 35, L18701.). It’s obvious that massively increased anthropogenic [CO2] levels (not to mention methane, nitrous oxides and CFC’s) have made major contributions to surface warming. It’s silly to pretend we don’t know what we do know!

  30. Skeptikal says:

    I’m not sure where I said we reached equilibrium quickly.

    No, you said that “the heat content of the atmosphere and land is reasonably low”. The point being that it doesn’t take much to move it to equilibrium.

    As I’ve said before, we should probably stop this because it’s simply going nowhere.

    Okay.

  31. chris says:

    aaaah…well now we can see some of the confusion arsing from your misunderstanding Skeptical. Photosynthetic reactions that involve chemical synthesis are endothermic and require energy inputs to drive them forwards. The reverse reactions involved in oxidative decay of plant matter are largely exothermic and release heat to the surrounds. This is <very basic chemistry. Of course that doesn’t mean that dead plants “spontaneously combust”! On the other hand if you stick your thermometer into your compost heap, you will likely find that it can get quite warm…

  32. chris says:

    Whoops..posted this in the wrong place – your post doesn’t seem to have a “Reply” tab…

    anyway….as I just pointed out above your post helps us understaqnd some of the confusion arisng from your misunderstanding Skeptical. Photosynthetic reactions that involve chemical synthesis are endothermic and require energy inputs to drive them forwards. The reverse reactions involved in oxidative decay of plant matter are largely exothermic and release heat to the surrounds. This is <very basic chemistry. Of course that doesn’t mean that dead plants “spontaneously combust”! On the other hand if you stick your thermometer into your compost heap, you will likely find that it can get quite warm…

  33. Thanks Chris. I knew I was missing something obvious in this discussion. Presumably animals also eat (and hence burn) plant matter. Most of the energy associated with photosynthesis must therefore be released and so the net effect must be small. I guess only that biomass that is buried and stored underground or in sea beds, sequesters energy.

  34. Ahh, I see. The reason I said that was because it then becomes difficult to explain why the surface temperature is so much higher today than it was 100 or so years ago, without invoking a significant influence from increased GHG concentrations in the atmosphere.

  35. Skeptikal says:

    On the other hand if you stick your thermometer into your compost heap, you will likely find that it can get quite warm…

    Take the microbes out of that compost heap and then re-measure the temperature. 😉

  36. Yes, but where’s the energy coming from? Surely the microbes are essentially “burning” the plant matter – or where you just joking 🙂

  37. chris says:

    yup the phenomenon of biomass burial and sequestration is very relevant Wotts. In the Carboniferous when bark-bearing plants seem to have “invented” lignin, these became significantly resistant to (exothermic) oxidative decay and so rather than “burning” back to CO2 and water after death, these became buried, and astonishing amounts of solar energy was sequestered. One effect of this of course was to consume large amounts of CO2 from the atmosphere without replacing this with CO2 from oxidative decay. Since CO2 is a greenhouse gas, the greenhouse effect was very significantly reduced resulting in glaciations.

    Of course some people like to pretend that CO2 isn’t much of a greenhouse gas at all, and therefore choose not to believe in such things as rhe Carboniferous and its glaciations!

  38. Skeptikal says:

    I think we have a pretty good idea of the process underlying temperature rise from the LIA to present.

    Personally, I don’t think we have a clue.

  39. chris says:

    absolutely Skeptical…you’re quite right. If those microbes weren’t able to catalyze the oxidative degradation of plant matter in your compost heal and return the bond energy (as heat) and CO2 to the atmosphere we’d be back in Carboniferous-style situation with the sequestration of CO2. If this happened world-wide (not just in your compost heap) we’d be in heaps of trouble!

    Anyway, I guess you get the idea that a living planet doesn’t need a TOA energy imbalance for life and other stuff to happen…

  40. Chris, showing my ignorance here, but what’s change since then? Have animals evolved in order to deal with the lignin so that we’re sequestering less now than during the Carboniferous period?

  41. Skeptikal says:

    They do burn some of it… but chris seems to think that the dead plant matter combusts all by itself.

  42. I think our comments crossed and you’ve answered my question (I think). Thanks.

  43. chris says:

    You’re right with the “personally” Skeptical. Absolutely. It’s good that you recognise that you don’t know much about this subject. However there are many, many people that do, and it’s better to base arguments (and policy) on knowledge (even if second hand) than on ignorance.

  44. chris says:

    This thread is maybe getting out of hand since we’re all responding quite quickly!

    Anyway microorganisms evolved to degrade lignin, and though plants themselves have subsequently evolved all sorts of defenses against bugs, the basic oxidative degradation of plant matter occurs nowadays pretty much in equilibrium with plant growth (chopping down rainforest notwithstanding).

    In fact plants will decay all by themselves – it just takes an extraordinary long time without the catalytic activities of bugs.

  45. Skeptikal says:

    That’s not what I said… I said that I don’t think WE have a clue.

    WE being collectively.

    And I was talking about what triggered the end of the LIA.. so what policy we can implement to change that?

  46. Skeptikal says:

    Anyway, I guess you get the idea that a living planet doesn’t need a TOA energy imbalance for life and other stuff to happen…

    Plants consume solar energy… animals eat plants… animals move around (kinetic energy).

    Where does that kinetic energy come from?

  47. Ultimately from the Sun, typically then through plants which we then eat. What happens to the kinetic energy then though. How do we stop? Typically (maybe always) it gets turned back into heat. That’s why the brakes on your car get so hot. So, as far as I can tell, apart from the biomass that is sequestered, everything else eventually turns back into heat.

  48. chris says:

    Skeptical you think we don’t have a clue. But I know that we do have a clue….lot’s of clues in fact! There is lots of scientific evidence that informs out understanding on the Earth surface temperature record.

    If you look at the sunspot record (for example) as a measure of solar output since the 17th century (try Wikipedia) and (putting a tiny bit more effort in) explore the scientific literature on the volcanic record of the last 400 years, that should help you understand some of the factors involved in the onset of the LIA and its dissipation.

    I’m speaking generally on “policy implications”. The LIA response to changes in solar, volcanic (and ocean current) phenomena informs our understanding of the Earth response to changes in radiative forcing. However in general, it’s a good idea to base policy (in the broadest sense) on knowledge, rather than on ignorance…no!

  49. chris says:

    Kinetic energy from chemical energy which in living things comes (as Wotts said) from the sun. So when you fingers go all tippy-tappy on your keyboard it’s because molecules of ATP are binding to myosin in your myocytes and its hydrolysis causes the myosin to move along actin filaments (rather more complex of course).

    The solar energy is converted to chemical energy (biosynthesis of ATP by oxidative phosphorylation) which is converted in muscle to kinetic energy.

  50. Skeptikal says:

    Except for the work done. If it all gets converted back to heat, then the work was done for free.

  51. Look, I have to go out, but I think you misunderstand energy conservation. If I push a box along a frictionless floor with a force that is in the same direction as the motion, I do work. If it’s frictionless, however, the box will accelerate. The only way to stop it will be to then apply another force in the opposite direction. When the box is stationary again, all the energy will be back in the form of heat. On the other hand, imagine pushing box along a floor that has friction. I push it very slowly for a certain distance and then stop I will do work. However, the box is now stationary again and what the friction has done is converted all the work I’ve done into heat. Ultimately, all energy (by and large) has to end up as heat unless everything keeps moving faster and faster (or ends up higher and higher).

  52. Tom Curtis says:

    Several points, some of which may have been covered before.

    1) It is true that the Earth has on average radiated more energy than it receives from the Sun. In addition to the 239 W/m^2 it receives from the Sun (after albedo effects), it receives a further 0.09 W/m^2 from the Earth’s interior, being partly energy from radioactive decay, and partially energy from lost gravitational potential energy from the original formation of the Earth. The Earth also receives 0.007 W/m^2 from friction related to the tides, not to mention even more inconsequential amounts from meteor bombardment, ion storms, cosmic rays and starlight. The true total energy balance of the Earth includes all these factors, but all other factors together are less than the error of the solar component and can be ignored. (This, however, is not what skeptikal was referring to.)

    2) In addition to energy directly added as heat, some energy is converted to kinetic energy in the form of winds or ocean currents, and some to chemical energy by photosynthesis. A permanent increase in wind velocity would store a small amount of additional energy other than as heat, and an increase in biomass would store an additional amount as chemical energy. However, in the steady state, all kinetic energy is eventually lost as heat, and nearly all chemical energy is likewise lost as heat and hence this does not contribute to a long term energy imbalance.

    3) A small amount of chemical energy is stored by the formation of peats, coals, oils and gases, ie, by biological sequestration. To give an idea of the scale of this sequestration, consider that there are 826 billion tonnes of coal reserves in the world, and that the combustion of each tonne will produce 22 billion joules of energy. That means there are 18.2 x 10^21 joules of energy sequestered as coal. Assume (incorrectly) that they were all stored in the carboniferous. Then over the 60 million years of the carboniferous, that 18.2 x 10^21 joules represents an energy storage of 2 x 10^-8 W/m^2. Granted that total proven reserves are about 100th of total estimated coal resources, and that there are also oil and gas reserves (which are a small fraction of coal reserves), it remains plain that the biological sequestration of energy is inconsequential.

    4) Skeptikal reveals, yet again, his poor understanding of science. He has no doubt heard it said that you need to “expend energy” to do work, and thinks this somehow over rides the first law of thermodynamics. “Expending energy”, however, is a metaphor for changing energy from a low to a high entropy state. The energy still exists. It is just not available for further work because of its high entropy. (I am sure most readers of this blog already understand this, but I just wanted it to be clear for those who may not.)

  53. Thanks Tom, a really nice summary. To be honest, there were aspect of this that were unclear to me and that I’ve started to understand as the discussion progressed.

    I found Skeptical’s misunderstanding about conservation of energy quite interesting. I started this blog because I regularly saw people making these kind of fundamental mistakes. Although I clearly fall on one side of the debate here, I can at least accept that some might interpret the data differently to how I interpret the data. However, we shouldn’t really be disagreeing about something as fundamental as energy conservation. It will be interesting to see how “skeptical” Skeptical actually is. A large part of the argument that they were making on this post appeared to be based on the assumption that energy used to do work has now gone and hence was no longer part of the planet’s energy budget. Given that this is clearly wrong, I wonder if Skeptical will at least consider the possibility that they’ve been mistaken about the basics of global warming and that maybe those who think differently may have a point.

  54. Tom Curtis says:

    Out of curiosity, I calculated the energy gain from the cosmic microwave background radiation, which turns out to be 3 x 10^-6 W/m^2, ie, about on the same order as the chemical energy stored by biological sequestration. I included starlight in my list above out of whimsy, but it turns out that at about 6 x 10^-6 W/m^2 (based on Eddington’s estimate), it is also of the same order as the biologically sequestered energy Skeptikal wants us to include in the calculations. I think it drives home how low is the rate of biological sequestration that starlight energy equivalent to that being stored.

    If Skeptikal returns to this conversation without a robust, and well sourced calculation of the rate of energy storage by biological sequestration to challenge that which I have provided, it will be very clear he is simply blowing smoke.

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