Climate inertia


Imagine you’re on a supertanker that needs to change its direction in order to avoid a collision. What would you do? Would you continue going full steam ahead until you can see the collision object right in front of you? Or would you try to change course early, knowing that changing a supertanker’s course takes a considerable amount of time?

The supertanker’s inertia means that you have to act in time if you wish to avoid a collision.

The climate system also has a tremendous amount of inertia built in. And like with the supertanker, this means that early action is required if we want to change the climate’s course. This inertia is a crucial aspect of the climate system, both scientifically but also societally – but in the latter realm it’s a very underappreciated aspect. Just do a mental check: when did you last hear or read about the climate’s inertia in mainstream media or from politicians?


The inertia of the climate system could be compared to that of a supertanker: if we want to change its course, it’s important to start steering the wheel in the desired direction in time.

Why is it so important? Because intuitively many people might think that as soon as we have substantially decreased our CO2 emissions (which we haven’t), the problem will be solved. It won’t, not by a very long shot. Even if we reduce CO2 emissions to zero over a realistic timeframe, the CO2 concentration in the atmosphere – and thus also the global average temperature- will remain elevated for millennia, as can be seen in the figure below. The total amount of carbon we put in the atmosphere over the course of a few hundred years will affect life on this planet for hundreds of thousands of years. And if we want to reduce the amount of warming that we commit the future to, we need to reduce our carbon emissions sooner rather than later. The longer we postpone emission reductions, the stronger those emissions reductions would need to be in order to have the same mitigating effect on long-term warming.

That’s why climate inertia is so important.

Zickfeld 2013

Modeled response of the atmospheric CO2 concentration (panel b) and surface air temperature compared to the year 2000 (panel c) to prescribed CO2 emissions (panel a). The CO2 concentration remains elevated long after CO2 emissions have been reduced, because the long-term sinks for CO2 operate very slowly (see e.g. IPCC FAQ 6.2 for an explanation of these carbon sinks). Since CO2 impedes infrared heat loss, for millennia the globe will remain warmer than it was before CO2 concentrations rose. The temperature lags behind the CO2 concentration because of the time it takes for the oceans to warm up. Figure from Zickfeld et al (2013).

As I wrote before: Postponing meaningful mitigation action until the shit hits the fan comes with considerable risk, because many changes in climate are not reversible on human timescales. Once you notice the trouble, it’s only the beginning, because of the inertia in the various systems (energy system, carbon cycle and climate system). The conundrum is thus that those who caused the problem are in the best position to solve it, but since the full consequences will not materialize until much later, they have the least incentive to do so.

Over at Bits of Science two Dutch science journalists, Rolf Schuttenhelm and Stephan Okhuijsen, published an interesting piece that focuses on the same issue: we only see a portion of the warming that we have committed ourselves to, due to the thermal inertia provided by the oceans. Just as a pot of water doesn’t immediately boil when we turn on the stove, the oceans take time to warm up as well. And since there’s a lot of water in the oceans, it takes a lot of time.

They included the following nifty graph, with the observed surface temperature but also the eventually expected temperature at the corresponding CO2 concentration (which they dub the ’real global temperature’), based on different approaches to account for warming in the pipeline:

real-global-temperature-graph - Bits of Science

Observed and eventually expected (“real”) temperature at concurrent CO2 concentration, via Bits of Science

This is a nice way to visualize the warming that’s still in the pipeline due to ocean thermal inertia. From a scientific point of view the exact execution and framing could be criticized on certain aspects (e.g. ECS is linearly extrapolated instead of logarithmically; the interpretation that recent record warmth are not peaks but rather a ‘correction to the trend line’ depends strongly on the exact way the endpoints of the observed temperature are smoothed; the effect of non-CO2 greenhouse gases is excluded from the analysis and discussion), but the underlying point, that more warming is in store than we’re currently seeing, is both valid and very important.

Timescales, timescales, timescales. Why art thou missing from the public discussion about global warming?

Update: ClimateInteractive has a good simulation of how this inertia works out in practice. By moving the slider at the bottom the figure you can choose between different emission scenarios. In the graphs above you then see the effect this has on the CO2 concentration, the global average temperature, and the sea level, and how this response is damped. The further down the cause-effect chain, the more damped – or better: the more slowed down- the response is. The sea level will continue to rise the longest (even long after the temperature has stabilized or even starts decreasing), but will take a while to get going. This simulation only runs to the year 2100 though.

A Dutch version of this post can be found on my sister blog KlimaatVerandering.


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20 Responses to “Climate inertia”

  1. vuurklip Says:

    So, “observed” is not “real”? Oh, the hubris …

  2. thomaswfuller2 Says:

    Well, we’ve already implemented enough mitigation activities to render RCP 8.5 obsolete, so we are making progress.

    Since RCP 8.5 was invented in 2007 (I’ve detailed my issues with RCPs in the past)…

    Renewables have grown from 1,140 GWe to 1,849. Windpower has grown from 141 GWe to 433, solar from 16 to 227.

    You can say it isn’t enough. You might even get me to agree. But to imply the world isn’t responding to the threat of global warming on a rapid timescale would seem insulting to me if I had spent my hard-earned money on an electric car or a solar installation.

    Is it now two years in a row that CO2 emissions have remained flat?

  3. William Connolley Says:

    I do wonder how good a metaphor “inertia” is. Because the climate system doesn’t really have literal inertia. If you push it, it doesn’t keep going until something frictional brings it to rest.

  4. Richard Erskine ( @EssaysConcern ) Says:

    may replace “inertia” with “disequilibrium” ?

  5. Windchaser Says:

    But to imply the world isn’t responding to the threat of global warming on a rapid timescale would seem insulting to me if I had spent my hard-earned money on an electric car or a solar installation.

    It shouldn’t, unless you’re confusing your own, personal actions with the actions of the world as a whole, and taking it as some kind of insult, like you hadn’t done “enough”.

    The point is, no, the world isn’t responding very quickly to global warming, no matter what you are personally doing. The US has taken rather little action, and we’re historically the largest emitter. Current action is extremely unlikely to be enough to avoid 2C.

    Is it now two years in a row that CO2 emissions have remained flat?

    Enh. I don’t think two years is significant. The global economy has been weak; let’s see what happens over timespans of 5+ years. There are plenty of countries still planning on ramping up coal power.

  6. Richard Erskine ( @EssaysConcern ) Says:

    Well, it can be insignificant (so far), yet significant (in medium term). Solar energy capacity is doubling say every 5 years. If it is currently, say, only 3% of global capacity, then 32x (or 2^5) is required to get nearly 100%. i.e. 5 doublings = 5 x 5yr = 25 years. It really could happen quite fast, as transformations often can do. In the US, states, cities and communities are moving even while Washington is in perpetual deadlock. Even red-neck farmers in dried out areas of Texas are building wind farms dammit!

    Of course, in 25 years, today’s 100% will not be enough! There will be the electrification of transport, heating, etc., which even allowing for greater efficiencies, will imply greater total energy demand as our 7bn grows in number and standards of living rise.

    Getting to “100%” could easily take a bit longer. 35 years anyone? Both pessimism and optimism are valid at the start of any transition. We are at the start, and it will be a bumpy ride for sure, even in an EV. I remain optimistic about the energy transition. It is inevitable.

    Whereas, on the largely irreversible impacts on the planet we will have baked in before we switch off the gas, how optimistic on that?

    Some seem cautiously optimistic: see for example the paper Sanderson et al. (2016), as discussed by ATTP …
    The paper increasingly relies (somewhat hopefully!) on negative emissions (e.g. BECCS), the longer we delay getting off the RCP8.5 pathway. It’s not clear to me if Sanderson et al. (2016) incorporates ESS (as opposed to ECS), as in the above blog post. Hopefully somebody can eniglighten me.

    In short, the energy transition is underway and inevitable. Even Shell acknowledged this in 2005 with Frank Niele’s epic monograph ‘Energy: Engine of Evolution’. Its only a question of timing. Shell want to leave it as long as possible. Physics and the planet disagree.

    As to the impacts. I think it is clear that the fast we decarbonize – which is proven and feasible – the better the odds of limiting the damage. Betting of negative emissions seems to me a very poor fall-back solution of dubious feasibility.

  7. thomaswfuller2 Says:

    I’ve been saying for eight years that solar’s conquest of the energy field will take 50 years. So I guess it’s now just 42… Where have I seen that number before…?

  8. Leo van Lierop Says:

    The term inertia sounds fine to me, it’s something the public understands as they have fallen victim to the same disease.

  9. Paul Price (@swimsure) Says:


    Isn’t there an important point that is shown in the CO2/warming charts to make a distinction between the natural and human sides of the climate system in terms of where the inertia lies? Perhaps this could be more explicit the text of this post.

    As the charts show, if all human-caused CO2 emissions were to (magically) stop then there is actually no inertia in the natural part of the climate system and little or no ‘warming in the pipeline’ from it. In the models ocean feedbacks of warmth to the atmosphere and CO2 uptake cancel out.

    (This is probably what William Connolley was referring to in his comment above: “the climate system doesn’t really have literal inertia”.)

    Therefore the inertia is almost entirely in the human society side of the climate system. Even if global CO2 emissions peak and decline to net zero then the cumulative emissions until net zero annual emissions is achieved will all add to the committed level of warming above present, a level of warming that will then continue for over a thousand years (ignoring the magic of negative emissions).

    If and when net zero emissions are achieved then the temperature curve will level out (at some dangerous or very dangerous level), but that level depends on the total cumulative emissions under the pathway curve of future global emissions. It’s up to humanity to change the ‘supertanker’ inertia and direction of the fossil-fuelled global economic system.

    Most if not all of the inertia and ‘warming in the pipeline’ depends on humanity’s collective decisions made from now that determine total future emissions to limit the amount of fossil carbon burned and ensure as much as possible of it stays in the ground forever.

    Even if negative emissions are possible at scale, getting on a pathway to limiting warming to the lowest level now possible needs to start now by peaking emissions and heading for zero fast.

  10. Bob Brand Says:

    Hello Paul Price,

    This is probably incorrect:

    … if all human-caused CO2 emissions were to (magically) stop then there is actually no inertia in the natural part of the climate system and little or no ‘warming in the pipeline’ from it.

    At the current CO2-concentration, other GHG’s and the current aerosol-load there is an Effective Radiative Forcing (ERF) of about +2.3 W/m^2.

    See IPCC AR5 Chapter 8 and:

    At the same time the increasing Ocean Heat Content makes it possible to estimate the energy imbalance — how much of this 2.3 W/m^2 has NOT yet been compensated for by the increase in surface temperatures. Recent studies put the energy imbalance at about +0.77 W/m^2 (e.g. Cheng 2016).

    Ergo: 2/3rd of ERF has been compensated for by an increase of surface temperature of about 1.0 °C since pre-industrial.

    1/3rd of ERF (the 0.77 W/m^2) is still in the pipeline. Since 2/3rd of ERF corresponds to 1.0 °C it means that +0.5 °C is still in the pipeline.

    Mind you, this is IF current forcings (concentrations of CO2 etc. as well as aerosols) would remain unchanged. Stopping emissions now would obviously also cancel the (negative) forcing by aerosols. It is true that an hypothetical stop of all emissions would mean that the CO2-concentration would (slowly) start to fall as well.

    However, if you want to estimate the “warming in the pipeline” at the *current* net forcing… this would be in the vicinity of +0.5 °C.

  11. Bob Brand Says:

    There are some obvious caveats with the estimate above:

    1) the energy imbalance of +0.77 W/m^2 has some considerable uncertainties. Across the whole of the literature this is estimated at between +0.5 and +1.0 W/m^2.

    2) I am using the +1.0 °C since pre-industrial as if this is *all* the temperature increase we can expect for 2/3rd of the ERF. This is probably an underestimate, since not all of the feedbacks have had time to come into full effect since the ERF started to rise rapidly.

    3) Again, this is assuming the aerosol load would remain unchanged. If you try to estimate what is currently in the pipeline *and* will be realised in some future situation without this aerosol load, there is more than 1/3rd of current ERF still in the pipeline.

    4) Some current research suggest that the 2.3 W/m^2 is an overestimate (Surface albedo change due to land use may be more like -0.5 W/m^2). This would mean a larger part of ERF is still in the pipeline.

    On that last point, see e.g.:

  12. Paul Price (@swimsure) Says:

    Hi Bob Brand,

    Aerosols and non-CO2 apart, the modelling based estimate that the net system inertia is zero is in the paper ‘Irreversible Does Not Mean Unavoidable’ by Matthews and Solomon (sorry, before posting I managed to edit out the reference in my comment).

    Link to paper is here:

    Click to access Irreversible%20does%20not%20mean%20unavoidable.pdf

    SkS have a good Andy Skuce post on it here:

    In that post at Comment 1 it says Matthews had a paper on aerosols and non-CO2 effects on warming but I don’t know if that has been published.

  13. Bob Brand Says:

    Hello Paul Price,

    In the paper you refer to by Matthews and Solomom, they only say:

    The notion that there will be additional future warming or “warming in the pipeline” if the atmospheric concentrations of carbon dioxide were to remain fixed at current levels (1) has been misinterpreted to mean that the rate of increase in Earth’s global temperature is inevitable, regardless of how much or how quickly emissions decrease (2–4).

    In their paper they say:

    There would indeed be unrealized warming associated with current CO2 concentrations, but only if they were held fixed at current levels (1).

    This does not mean that there is “zero system inertia” or that there would not be “warming in the pipeline”.

    Andy Skuce pointed out in a tweet that he agrees with the blogpost by Bart:

    Excellent piece by @BVerheggen— Andy Skuce (@andyskuce) August 9, 2016


  14. Bob Brand Says:

    Sorry, here is the tweet by Andy Skuce:

  15. Paul Price (@swimsure) Says:


    And I agree this is a good piece too (as always from BV). My comment and this bit of discussion is to try to tease out the human side of the inertia from the natural to add to the discussion.

    If you look again at the article neither of the M&S quotes you give contradict what I have pointed to. Their first figure, ‘How the climate system responds’, very clearly shows their result that “Net system inertia ~ zero” because “Physical climate inertia (warming)” is balanced by “Carbon cycle inertia (cooling)”.

    Under the figure, top of p.439, they say:

    “The climate response to CO2 emissions is influenced by both physical climate and carbon cycle inertia, with the result that the net system inertia is close to zero. Therefore, future climate warming depends only on current and future CO2 emissions, and the rate of warming will respond immediately to CO2 emissions cuts.”

    On p.439, Matthews & Solomon also say:

    “The climate system physics implies that further increases in warming could in principle be stopped immediately, but human systems have longer time scales.”

    Their point (unless you think I am somehow misreading it) is that the natural system has zero net inertia and the human system – including its political economy, infrastructure lock-in and overall rebound-effect behaviour – is where the inertial lies.

  16. Bob Brand Says:

    Hi Paul,

    The Matthews & Solomon paper uses a rather unusual definition of ‘committed warming’ which differs from IPCC AR4 and AR5, where it is considered to be: “The multi-model average warming for all radiative forcing agents held constant at year 2000 …”:

    This is also what I said: “Mind you, this is IF current forcings (concentrations of CO2 etc. as well as aerosols) would remain unchanged.

    Matthews & Solomon however consider a *very* hypothetical case with:

    — an immediate, abrupt and total cessation of all CO2 emissions;
    — while at the same time aerosol pollution would stay as before?

    The lack of realism is not so much in the 100% reduction but that it would be instant, and at the same time the aerosol pollution would remain.

    Note however that there would still exist physical inertia but in THIS particular, special case they claim that the “equal and opposing effects of physical climate inertia and carbon cycle inertia” would cancel out.

    It seems arbitrary to me to base the contention: “the natural system has zero net inertia“, on that ONE very special case where supposedly these two forms of inertia would precisely cancel.

    All the more so, because in reality we have to deal with a very different situation where CO2-emissions will not cease instantly and totally — and then there unavoidably a net physical climate inertia which is not cancelled out…

  17. Bob Brand Says:

    Corrected version of my last paragraph:

    All the more so, because in reality we have to deal with a very different situation where CO2-emissions will not cease instantly and totally — and then there exists unavoidably a net physical climate inertia which is not cancelled out…


  18. Paul Price (@swimsure) Says:


    Good to see we are getting closer to some agreement if not completely!

    Of course, the case of an immediate and total cessation of CO2 emissions is hypothetical but that is the point of M&S article, to separate the natural from the human system. Investigating such thought experiments is an essential part of science.

    You say the M&S paper “uses a rather unusual definition of ‘committed warming’ which differs from IPCC AR4 and AR5′. But the reference you give from AR4 and AR5 both provide a set of alternative definitions of climate change commitment, one of which is the ‘zero emission commitment’ considered by M&S.

    IPCC AR5 WG1 Ch.12 p.1106, FAQ 12.3, says:

    “Stopping emissions today is a scenario that is not plausible, but it is one of several idealized cases that provide insight into the response of the climate system and carbon cycle.”

    And the points M&S make are also made on the next page of the FAQ:

    “Eliminating CO2 emissions only would lead to near constant temperature for many centuries. Eliminating short-lived negative forcings from sulphate aerosols at the same time (e.g., by air pollution reduction measures) would cause a temporary warming of a few tenths of a degree, as shown in blue in FAQ 12.3, Figure 1. Setting all emissions to zero would therefore, after a short warming, lead to a near stabilization of the climate for multiple centuries. This is called the commitment from past emissions (or zero future emission commitment). The concentration of GHG would decrease and hence the radiative forcing as well, but the inertia of the climate system would delay the temperature response.”

    Therefore, it is not ‘arbitrary’ or unrealistic to claim that the natural system has ~ zero net physical inertia, it is the consensus scientific understanding.

    As you say, the reality of our situation is that living within and changing that natural system is human society, which continues to change the surface energy balance by the accumulation on CO2 in the atmosphere due to burning fossil fuels.

    Of course it is correct that future human emissions will add to the present level of warming. Even peaking emissions now and getting to zero emissions at some point could easily add as much CO2 to the atmosphere as released in all of past human history, thereby adding to warming. But this is human-caused inertia due to past, present and future choices.

    To be sure humanity is part of the physical system but we are the agency that has caused and is causing the current rapid global warming, so separating the inertia in the human system from that in the remainder of the physical system seems entirely justifiable and helpful to the analysis.

    (Apart from CO2, cutting aerosol emissions would give more warming, but that could be cancelled out by cutting methane emissions causing cooling.)

    As IPCC and M&S point out, the zero emissions scenario provides important guidance for policy: there is no CO2 warming in the pipeline from the physical system; sustaining annual cuts in human-caused global emissions will reduce future warming starting immediately; and, limiting climate change is possible if emissions go to net zero, resulting essentially immediately in no future CO2 warming from that point.

    Our collective choices determine whether we accept a path to climate stabilisation at the lower end of the range now possible due to our future emissions – a higher average temperature level that will still be very changed from the Holocene climate. Otherwise, in the absence of substantial near-term cuts in emissions, we will continue on the current path to far more dangerous levels of warming.

    The future *is* in humanity’s hands.

  19. Singingway Says:

    “Those who caused the problem are in the best position to solve it, but since the full consequences will not materialize until much later, they have the least incentive to do so.” To me, this is the answer as to why oil company CEOs can sleep at night. Can look at their grandchildren and smile with smug complacency. This is the problem — human lifespans are so short compared to the earth systems we are impacting. The only people trained to think in terms of milleniums are climate scientists, paleontologists, archaeologists, and astronomers.

  20. save_ecosystems Says:

    When more people take part in the degrowth movement, the whole production will be drastically reduced so that the jumbled ecosystems can recover.

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