And then there’s the energy imbalance

There are a few things I have been considering writing about, but since I’ve renamed the blog to be more explicitly physics orientated, I thought the first should at least reflect that change. There’s a recent paper by James Hansen – and 17 co-authors – called Assessing ‘‘Dangerous Climate Change’’: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature. It’s an interesting paper because it discusses both the scientific evidence for global warming/climate change and considers various policy options (violating what many would regard as a fundamental rule – I don’t though). The paper’s been discussed in a number of other places already (here, and here for example), but I was going to discuss one very basic thing that I think it covers very well.

Probably the most fundamental aspect of global warming is the existence of an energy imbalance. If the earth is in energy deficit (i.e., it is gaining more energy than it loses) global warming, by definition, is happening. As the paper says

At a time of climate stability, Earth radiates as much energy to space as it absorbs from sunlight. Today Earth is out of balance because increasing atmospheric gases such as CO2 reduce Earth’s heat radiation to space, thus causing an energy imbalance, as there is less energy going out than coming in. This imbalance causes Earth to warm and move back toward energy balance. The warming and restoration of energy balance take time, however, because of Earth’s thermal inertia, which is due mainly to the global ocean.

The paper then discusses how one might determine the energy imbalance. It’s a reasonably tricky thing to determine, but the most promising is to calculate the rate of changing heat content of the ocean, atmosphere, land, and ice, with the oceans being critical as they store 90% of the excess energy. The paper concludes that

Argo data reveal that in 2005–2010 the ocean’s upper 2000 m gained heat at a rate equal to 0.41 W/m2 averaged over Earth’s surface. Smaller contributions to planetary energy imbalance are from heat gain by the deeper ocean (+0.10 W/m2), energy used in net melting of ice (+0.05 W/m2), and energy taken up by warming continents (+0.02 W/m2). Data sources for these estimates and uncertainties are provided elsewhere. The resulting net planetary energy imbalance for the six years 2005– 2010 is +0.58 +- 0.15 W/m2.

So there we have it. Estimates based largely on observations and measurements suggest that the Earth’s climate system accrued energy at a rate of 0.58 +- 0.15 W/m2 over the period 2005 – 2010. Fairly conclusive I would suggest. This of course doesn’t necessarily tell us what’s causing this energy imbalance. The paper, however, does say

If the sun were the dominant forcing, the planet would have a negative energy balance in 2005– 2010, when solar irradiance was at its lowest level in the period of accurate data, i.e., since the 1970s. …. The full amplitude of solar cycle forcing is about 0.25 W/m2, but the reduction of solar forcing due to the present weak solar cycle is about half that magnitude as we illustrate below, so the energy imbalance measured during solar minimum (0.58 W/m2) suggests an average imbalance over the solar cycle of about 0.7 W/m2.

So, more evidence that it’s really not the Sun and, if anything, the influence of the Sun means that the energy imbalance for the period 2005-2010 is slightly below the average for the solar cycle.

The paper also mentions anthropogenic aerosols and says

Earth’s measured energy imbalance has been used to infer the climate forcing by aerosols, with two independent analyses yielding a forcing in the past decade of about -1.5 W/m2, including the direct aerosol forcing and indirect effects via induced cloud changes. …… Increase of Earth’s energy imbalance from reduction of particulate air pollution, which is needed for the sake of human health, can be minimized via an emphasis on reducing absorbing black soot, but the potential to constrain the net increase of climate forcing by focusing on black soot is limited.

So, the conclusion is that anthropogenic aerosols are actually acting to reduce the energy imbalance. As we reduce anthropogenic aerosol emissions, the energy imbalance will increase, increasing the rate of global warming. Maybe we can reduce this slightly by also reducing the amount of black soot (that absorbs energy), but this is likely to not completely counteract the influence of the reduction in anthropogenic aerosols.

So, why have I written this? Well, because the existence of an energy imbalance is fundamental to anthropogenic global warming (AGW). If you think AGW is not real, then there are a number of things you need to be able to show. Firstly, that here’s something wrong with the observations that are used to determine the energy imbalance. Anything’s possible, but just stating that it’s difficult isn’t really sufficient to conclude that the observations are wrong. Secondly, you need to show what’s wrong with fundamental radiative physics. A fairly simple calculation could show that the energy imbalance that we have today is consistent with what we’d expect from basic radiative physics (maybe not trivial, but not that hard). So, if AGW isn’t real you need to both show that there’s something wrong with the observations, and that there’s something fundamentally wrong with basic physics. Anything’s possible I guess but that doesn’t make it likely.

One could argue – I guess – that maybe the observations are right (i.e., there is an energy imbalance), but that it’s natural, not anthropogenic. I’ve already discussed (above) why it can’t be the Sun. It also can’t be some kind of natural cycle (such as Wyatt & Curry’s Stadium Wave). Why? Well, we have plenty of evidence (paleo-climatology) to suggest that the global surface temperature is higher, today, than it’s been for centuries, or even longer. If it’s some kind of natural cycle, then the energy imbalance should vary from being negative (i.e., the Earth should be losing energy when surface temperatures are near the maximum) to positive (i.e., the Earth should be gaining energy when surface temperatures are near the minimum). It really can’t be some kind of natural cycle if the energy imbalance is still positive when the surface temperatures are as high as they are today. That, of course, also ignores that we have no physical mechanism for producing a natural cycle that can produce what we’ve observed with respect to global warming.

Anyway, this has become a rather long post to try and explain why I think understanding basic physics is a crucial part of understanding anthropogenic global warming. If you dispute AGW, either you’re about to become one of the world’s most famous scientists (by, likely, rewriting basic physics) or you don’t understand physics sufficiently well to really have any strong opinions with respect to AGW. As usual, if others disagree or think I’ve got something wrong (as I may well have) feel free to point that out through the comments.

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29 Responses to And then there’s the energy imbalance

  1. I meant to add that this paper by Trenberth & Fasullo is also worth reading.

  2. Bobby says:

    AT, as the first new physics post of this blog, it’s a great way to start. Whenever I talk to a fake skeptic, this is usually my starting point…more energy coming in than going out.

    I usually go to the physics of why. It’s basic physics to look at short wave energy coming in and long wave blackbody energy going out. CO2 doesn’t block much of the short wave coming in, but blocks the long wave going out. More CO2 means more long wave being blocked. Add in feedback forcing because there’s more water in the atmosphere, among other things, and we’re there.

    What I love about this post is you did better. By quoting this paper, you talk about purely observational data to demonstrate the increase in energy. Thanks and long live the new blog!

    BTW, AT doesn’t have to catch on, it just seemed natural to me 🙂

  3. Bobby, thanks. AT doesn’t have to catch on, but the other frontrunner at the moment appears to be UF which is (I hope) intended as an ironic response to someone calling me an “unscientific f**kwit”. Personally, I think I prefer AT 🙂

    More CO2 means more long wave being blocked. Add in feedback forcing because there’s more water in the atmosphere, among other things, and we’re there.

    Yes, that’s what I was referring to when I mentioned that one could roughly estimate the expected energy imbalance relatively easily using basic physics. I guess, in truth, it would take a full radiative transfer calculation to do properly, but physicists like basic estimates 🙂

  4. BBD says:

    OT: AT is preferable to TP which is too close to TB (ThingsBreak) which is already taken 😉

    ATTP is moot for reasons previously aired 😉

    @theresphysics is now in use, I see.

  5. izen says:

    Very nice lucid exposition of the thermdynamic reality underlying the basic physics of AGW.

    The energy balance, or imbalance is also the source of the answer to the rejectionists demand for a definition of what the ‘Natural’ temperature of the globe should be and an explanation of why the present observed warming is NOT a ‘natural variation’ as suggested by Bob Tisdale with his ratcheting ENSO cycle.

    The natural or ‘correct’ temperature of the globe is that when it is in energy balance. When energy in equals energy out. What that may mean in terms of surface temperatures is obviously dependent on the input from the sun and the amount reflected by the surface albedo, but it also depends on the insulating or ‘greenhouse’ properties of the atmosphere which determines the thermal gradient between the surface and the tropopause where the energy balance is established.
    For human convenience it would be best if this natural temperature was compatible with the systems of intensive agriculture that underpin our civilisation.

    Natural variations like ENSO will cause an energy imbalance that will negate the variation. The extra warming during an El Nino phase results in a negative energy imbalance at the TOA with more energy radiated than absorbed. During the La Nina phase this is reversed, a temporary surface cooling reduces radiated energy so that the energy imbalance is positive and the globe gains energy.

    Therefore by definition a surface warming that is accompanied by a positive energy balance cannot be a natural variation. It must be driven by a change in the input or output. We know from measurements that the solar input is changing to little and in the wrong direction to be the source of the imbalance, but the calculated effect of the increased CO2 is comparable to the observed imbalance.
    The observed sea level rise and surface warming of the globe over the last century has a clear and unambiguous cause in the energy accumulated by the imbalance created by the addition of fossil CO2 to the atmosphere. The point at issue is whether the resulting changes in the global climate pose a serious existential threat to the continued functioning of human agricultural and industrial societies, or whether the effects are well within the adaptive capabilities of an evolving technological civilisation.

    On present evidence I would guess our political global governance falls woefully short of being able to cope with even the most meagre of the potential threats.

  6. Rachel says:

    Ant. I think you should be Ant.

  7. Izen,

    Therefore by definition a surface warming that is accompanied by a positive energy balance cannot be a natural variation.

    I’ve thought that this was a fairly obvious conclusion. It’s good to see others agree.

    Rachel,

    Maybe AnT would work. Maybe I should just tell everyone who I am and get over with it 🙂

  8. Rachel says:

    Well until you do, I’m going with Ant. Or AnT if you prefer.

  9. Does that make you Dec, then Rachel? 😉

  10. Rachel says:

    Ha ha, I think I prefer Rachel…..or Tinkerbell 🙂

  11. izen says:

    The assertion that AGW will have a significant impact on the climate is opposed by some outside the crank fringe, who even still publish papers (!) that suggest climate sensitivity may be lower than hypothesised. often this is based on attributing a significant proportion of the observed warming to some element of ‘Natural Variation’. Quite possibly involving clever curve fitting and mathematical hand-waving.

    Further into the fringe I have encountered accusations that AGW theory has never falsified the null hypothesis:- That observed changes are natural.

    It would be tempting to reject any significant role for this speculative natural variation if the simple test of which direction, or sign, the energy imbalance showed was definitive. If by definition a surface warming that is accompanied by a positive energy imbalance cannot be a natural variation. It must be driven by a change in the input or output.

    If the positive, surface warming phase of the PDO was inevitably accompanied by a negative energy imbalance because it was increasing the rate of energy loss, and cooling phases of the NAO showed positive energy imbalances if there was no forcing bias on the system then a credible measure of the energy imbalance, even its sign would go a long way to falsify the null hypothesis and refute those arguing for low climate sensitivity values because of natural cycles, oscillations and periods.

    But clouds….
    If you have a (hypothetical) Natural Cycle, or as we are dealing with a chaotic system, a quasi-periodic variation with a characteristic magnitude and time-scale, that alters the extent and location of clouds then it would alter the energy balance as if there was a change in forcing.
    Lindzen and Svensmark (?spelling?) would be published researcher who have pushed this option for downplaying the magnitude of AGW. If it is possible for a natural variation to change the cloud albedo independently of other climate effects, then it is still hypothetically possible to invoke natural cycles for some fraction of the observed warming, strengthening the argument for a low ECS.
    And leave open the possibility that when whatever cloud altering cycle acts against instead of with any AGW effect the apparent threat will be well within even the adaptability of poorer societies.

    I should make clear that personally I see no reason to view such sciencey mining for loopholes in the AGW physics as other than ill motivated. Good physics that can inform stronger estimates of climate sensitivity and the magnitude of variations would be welcome.
    Although obviously I would be delighted if the speculations of the low climate sensitivity/natural cycle fringe were vindicated and AGW turned out to be a much less serious threat of change than projected by the mainstream research! {grin}

  12. BBD says:

    Presumably a climate system that is sensitive to slight changes in TSI modulated by cloud albedo is going to be sensitive to radiative perturbations in general, including a rapid and significant increase in CO2/GHG forcing? So the cloud people are arguing for a fairly sensitive climate system.

    The natural thermostat argument where cloud albedo is a strongly negative feedback won’t fly because it would render the climate system as a whole insensitive – something paleoclimate variability demonstrates that it is not.

    Like you, I’d be more than happy to be proved wrong, but it just doesn’t look very likely.

  13. Izen, I’m a little confused by what you’re suggesting with respect to clouds. My understanding of why people want to infer the influence of clouds is that it could suggest some kind of negative forcing that might reduce the ECS. This would be a good thing but, as BBD suggests, would seem to be inconsistent with paleoclimatological evidence (and also with what’s presented in the recent IPCC reports). Clouds – I think – still couldn’t explain how we can have had the rise in surface temperature that we’ve had while still having a positive energy imbalance. So, I can’t see how even clouds could provide some kind of natural cycle that’s consistent with what out current observations – or have I misunderstood what role you were suggesting clouds could play?

  14. RB says:

    ‘ATP’ might work for its connections with energy, since you start out there in your first post on this blog. Energy balance considerations still result in leaving TCR estimates reliant on aerosol assumptions if one were to assume no significant modeling issues. For instance, from Kosaka/Xie, Nielsen-Gammon calculates a TCR ~1.05C compared to the GFDL TCR of 1.5C (and his method may or may not turn out to be correct) which is also well below the Gregory et al range. Per Isaac Held (in comments on his hiatus post), Kosaka/Xie uses CMIP5 forcings, So, if one believed that models are getting sensitivity right, one would have to argue on the basis of observation derived sensitivity that CMIP5 significantly underestimates aerosol forcings. On the other hand, if one thought that model sensitivity may be uncertain, you still rely on models to obtain aerosol indirect forcing estimates. It seems like there is considerable uncertainty remaining on this issue of sensitivity vs indirect aerosol forcing estimates.

  15. BG says:

    Dear whatever-your-name-is-or-shall-be,

    As a physicist, but not one of the climate variety, I appreciate and applaud your new direction.

    Had I been naming the new blog, with the new direction in mind, I might have called it Phocus on Physics. And called myself Ph2, or PhD as in Ph-Dos. 🙂

  16. Dave123 says:

    I’m going to suggest a somewhat different flavor here. The oceans are an enormous heat sink. Thus unless and until the entire ocean is the same temperature as the atmosphere (roughly speaking) the earth system is not at thermodynamic equilibrium. Note my emphasis on thermodynamic. The Energy Imbalance TOA is just that, and to the best of my knowledge doesn’t include any assumption one way or another about the millennial constancy ocean’s action as a heat sink.

    E in= E out + E retained
    E retained= E atmosphere + E Ice melting + E land + E oceans

    to make it obvious- imagine an immense engineering project rearranges some geography to use the ocean currents own momentum to drive cold deep waters to the surface. Voila….built in GMST air conditioning…. good until you run out of cold water.

    What fascinates me is that deniers run from this, preferring to invoke unspecified “complexity”, because anything that sets forth the ocean’s role that directly means they get stuck with falsifiable hypotheses and actually have to make predictions.

    But again, even when Ein = E out, we could experience either warming or cooling by alterations in the partition of energy into the available compartments. In fact if Ein=Eout we should be cooling the globe because of how much cold water there is in the deep ocean. But now we’ve left the realm of strict thermodynamics and moved to heat and mass transfer.

  17. jyyh says:

    Dear Antti F., you say “but the most promising is to calculate the rate of changing heat content of the ocean, atmosphere, land, and ice, with the oceans being critical as they store 90% of the excess energy.”, and I wonder is the atmospheric part really necessary to include in the equation? As the surface warms up the height where the radiation equation is at equilibrium rises (it must be at equilibrium at some height since the entropy.). This rises the temperature on the surface layer too, via couple of effects. What is the imbalance? Is it measured from how much the ocean and continents should warm to stop this rise? oh well, maybe it depends on how accurate one wants to be.

  18. dana1981 says:

    Coincidentally I’ll have a post on Trenberth & Fasullo’s paper on Tuesday. It focuses mainly on the ‘hiatus’ but also discusses the global energy imbalance, and also touches on some recent much-touted papers claiming climate sensitivity is relatively low. Trenberth points out that those estimates are sensitive to some large uncertainties, and using different data sets and assumptions brings them in line with the standard 3°C ECS. Not a whole lot of new material in the paper, but what is new is interesting.

    And yes, the global energy imbalance is key to AGW. The oceans in particular are accumulating a whole lot of heat (equivalent to 4 Hiroshima atomic bomb detonations per second, or 2 Hurricane Sandys per second, if you prefer), and that imbalance is caused by external forcings. No natural external forcing(s) can account for it – it’s clearly due to the increased greenhouse effect. And that global energy imbalance is what’s causing global warming.

  19. Dave123, I think what you’ve said is correct. I would add, however, that

    But again, even when Ein = E out, we could experience either warming or cooling by alterations in the partition of energy into the available compartments.

    This is true, but once you’ve undergone any warming or cooling, Ein will no longer equal Eout and there will be an imbalance. However, as I say in the post and as Izen points out, any natural cycle would produce a negative imbalance if the surface were to warm and a positive one were it to cool. Since we have a positive energy imbalance after having undergone warming rules out any natural mechanism.

    jyyh, I think you include everything because you’re computing the energy imbalance which is the rate at which the total energy in the system is changing. If there were no energy imbalance, the energy would be constant.

    Dana, thanks. I look forward to your article on Tuesday.

  20. John Mashey says:

    Well, off to AGU for the week, Trenberth’s speaking on Thursady I recall.
    Although not exactly the same aerosol, to get a more visceral idea of the atmosphere, see The Toxic Smog Cloud Hanging Over Shanghai Looks Just As Bad As It Sounds.

  21. Dave123 says:

    Of course, in fact I make the same argument of energy balance as for CO2 balance. Unless the surface warming is greater than can be accounted for by the TOA imbalance then ‘natural’ forcings provide no explanations. there’s no room for them. You can try to write this larger as “the global energy accumulation” is greater than what can be estimated from the TOA imbalance….but that would seem to violate thermodynamics absent some miraculous new source of energy.

    These kinds of thermodynamic boundaries are very useful in reducing the apparent complexity of some aspects of problems. On the other hand, as I keep mulling Pierrehumberts “Planetary Climatology” and see how much work is needed to adequately describe that radiation imbalance, I’m somewhat amazed that anyone figured it out at all.

  22. dana1981 says:

    Yes, Trenberth is speaking at AGU on Thursday on the energy imbalance. Probably mostly about his new paper, which happens to be published in the first edition of AGU’s new journal, and which I wrote about today (with input from Trenberth).
    http://www.theguardian.com/environment/climate-consensus-97-per-cent/2013/dec/10/global-warming-unpaused-fast-forward

  23. Dana, thanks. I’ve just read your article. I hadn’t appreciated that Trenberth & Fasullo had redone the observationally constrained estimates for the ECS. Very interesting.

  24. RB says:

    I noticed that part of Trenberth & Fasullo as well where they use ORAS-4 estimates of OHC to show how Otto et al ECS could be an underestimate. Given the scepticism towards reanalysis products, we probably are going to need a few more years of OHC observations. But, as Held explains here , you are not going to see the warming from ECS – it just means that you are going to level off at that temperature for a long time to counteract the CO2 that decays out of the atmosphere. There was another paper out from Princeton I think this year showing that there are some non-linearities which will give rise to another 25% warming over 500+ years than indicated by the studies in Held’s post, but even if true, 500 years is not really relevant policy-wise. The new lower sensitivity number studies are important because TCR is more relevant for the next 100 years. And for TCR, I believe it is the aerosol uncertainty that matters more than ocean heat uptake. On the basis of TCR, either models are overestimating sensitivity or aerosol numbers are incorrect. James Annan stated that 2C ECS would also be consistent with the paleo evidence. The good news may be that the policy-relevant TCR number may be better constrained using observations in a meaningful timeframe.

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  26. Steve Bloom says:

    RB, for some reason you seem unwilling to register on the slow feedback issue.

  27. Steve Bloom says:

    And RB, at your link Held notes:

    “One could make a long list of things that could upset this picture, dramatic changes in land surface carbon uptake/release being an excellent example. In any case, it will be interesting to see what emerges from new generations of Earth System Models when applied to this idealized scenario.”

    So while focusing on the long-term course of notional quantities like ECS and TCR is interesting and of course essential for model development, don’t mistake them for the real world and most especially not for anything policy-relevant.

    E.g. James Annan can be quite correct when he says that 2C ECS (at ~560 ppm CO2) is consistent with the paleo evidence, but we know that mid-Piacenzian temps were in the +2-3C range with only ~400 ppm CO2. The latter is the real world. Going farther back, 560 ppm gets a lot worse.

    To be clear, when I say “worse” I’m not referring so much to the direct effect on T as to the ecological effects of a fast transient to such a high-CO2 state.

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