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Modelling the Apocalypse

Posted on 2 June 2012 by climatesight

This is a re-post from ClimateSight.

Let’s all put on our science-fiction hats and imagine that humans get wiped off the face of the Earth tomorrow. Perhaps a mysterious superbug kills us all overnight, or maybe we organize a mass migration to live on the moon. In a matter of a day, we’re gone without a trace.

If your first response to this scenario is “What would happen to the climate now that fossil fuel burning has stopped?” then you may be afflicted with Climate Science. (I find myself reacting like this all the time now. I can’t watch The Lord of the Rings without imagining how one would model the climate of Middle Earth.)

A handful of researchers, particularly in Canada, recently became so interested in this question that they started modelling it. Their motive was more than just morbid fascination – in fact, the global temperature change that occurs in such a scenario is a very useful metric. It represents the amount of warming that we’ve already guaranteed, and a lower bound for the amount of warming we can expect.

Initial results were hopeful. Damon Matthews and Andrew Weaver ran the experiment on the UVic ESCM and published the results. In their simulations, global average temperature stabilized almost immediately after CO2 emissions dropped to zero, and stayed approximately constant for centuries. The climate didn’t recover from the changes we inflicted, but at least it didn’t get any worse. The “zero-emissions commitment” was more or less nothing. See the dark blue line in the graph below:

However, this experiment didn’t take anthropogenic impacts other than CO2 into account. In particular, the impacts of sulfate aerosols and additional (non-CO2) greenhouse gases currently cancel out, so it was assumed that they would keep cancelling and could therefore be ignored.

But is this a safe assumption? Sulfate aerosols have a very short atmospheric lifetime – as soon as it rains, they wash right out. Non-CO2 greenhouse gases last much longer (although, in most cases, not as long as CO2). Consequently, you would expect a transition period in which the cooling influence of aerosols had disappeared but the warming influence of additional greenhouse gases was still present. The two forcings would no longer cancel, and the net effect would be one of warming.

Damon Matthews recently repeated his experiment, this time with Kirsten Zickfeld, and took aerosols and additional greenhouse gases into account. The long-term picture was still the same – global temperature remaining at present-day levels for centuries – but the short-term response was different. For about the first decade after human influences disappeared, the temperature rose very quickly (as aerosols were eliminated from the atmosphere) but then dropped back down (as additional greenhouse gases were eliminated). This transition period wouldn’t be fun, but at least it would be short. See the light blue line in the graph below:

We’re still making an implicit assumption, though. By looking at the graphs of constant global average temperature and saying “Look, the problem doesn’t get any worse!”, we’re assuming that regional temperatures are also constant for every area on the planet. In fact, half of the world could be warming rapidly and the other half could be cooling rapidly, a bad scenario indeed. From a single global metric, you can’t just tell.

A team of researchers led by Nathan Gillett recently modelled regional changes to a sudden cessation of CO2 emissions (other gases were ignored). They used a more complex climate model from Environment Canada, which is better for regional projections than the UVic ESCM.

The results were disturbing: even though the average global temperature stayed basically constant after CO2 emissions (following the A2 scenario) disappeared in 2100, regional temperatures continued to change. Most of the world cooled slightly, but Antarctica and the surrounding ocean warmed significantly. By the year 3000, the coasts of Antarctica were 9°C above preindustrial temperatures. This might easily be enough for the West Antarctic Ice Sheet to collapse.

Why didn’t this continued warming happen in the Arctic? Remember that the Arctic is an ocean surrounded by land, and temperatures over land change relatively quickly in response to a radiative forcing. Furthermore, the Arctic Ocean is small enough that it’s heavily influenced by temperatures on the land around it. In this simulation, the Arctic sea ice actually recovered.

On the other hand, Antarctica is land surrounded by a large ocean that mixes heat particularly well. As a result, it has an extraordinarily high heat capacity, and takes a very long time to fully respond to changes in temperature. So, even by the year 3000, it was still reacting to the radiative forcing of the 21st century. The warming ocean surrounded the land and caused it to warm as well.

As a result of the cooling Arctic and warming Antarctic, the Intertropical Convergence Zone (an important wind current) shifted southward in the simulation. As a result, precipitation over North Africa continued to decrease – a situation that was already bad by 2100. Counterintuitively, even though global warming had ceased, some of the impacts of warming continued to worsen.

These experiments, assuming an overnight apocalypse, are purely hypothetical. By definition, we’ll never be able to test their accuracy in the real world. However, as a lower bound for the expected impacts of our actions, the results are sobering.

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Comments

Comments 1 to 21:

  1. "For about the first decade after human influences disappeared, the temperature rose very quickly"

    This reminds me of the study of atmospheric response to the grounding of USA passenger jet flights after 9/11. They were grounded for only 3 days and there were measurable differences.

    A study was published in 2004;
    http://facstaff.uww.edu/travisd/pdf/climatepapermar04.pdf

    And like most scientific studies, this one opened up a list of new questions.
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  2. On the face of it this means that, irrespective of what we do from here on, someone is probably going to have to do some serious geoengineering sometime in the next couple of centuries. Let's hope they crack controlled fusion before then.
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  3. It is quite worrying that reducing aerosol emissions seems to be happening before reducing GHG emissions. Therefore it looks like we’ll get both increasing GHG warming and reduced cooling due to cleaner emissions.
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  4. Sceptical Wombat @2,

    My hopes are different. Fusion does not help at all other than satiate the narcisitc quench for energy. IMO such possibility's less realistic than the improvement and expansion of PV panels (or other technology capturing insolation enegry) so that they provide the baseload power. But that's besides.

    My hopes are: they don't keep increasing the energy imbalance (harnessing fusion would just add energy and possibly bigger disaster if it went uncontrolled) but start reversing it. CO2 already in gthe air creates the imbalance of, as Hansen says, 2 Hiroshima explosions/sec. And this is the imbalance that will continue to warm Antarctica. For example, I would dream (this article is about SF dreams isn't it?) they invent an industrial scale artificial photosynthesis, which would cool things by both drawing down CO2 and using sun's irradiance.
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  5. If models predict 8 degrees antarctic heating for our 550 gt carbon load what projections for Antarctic heating can we expect for the additional 450 gt we will likely emit within the next 3 decades?
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  6. I have a variation of these models in mind.

    Let's imagine that the leading industrial nations, China, the U.S., Germany (God bless you for your self-imposed limits to growth (gaseous fuels at least) so far.), etc., decide this year to take aggressive action to shift off of fossil fuels. How long would that take without wrecking their economies, which we can assume they are unwilling to do?

    I'll ballpark 2-3 decades to shift the energy infrastructure to a new paradigm. Let's assume that these leading industrials influence others to follow suit, and so we can map global emissions along the same path. As a rough estimate, we can say that for this approximately 25 years, emissions will be half of what they are now. (Just figure a steady decline from where we are now to zero.) Currently, we are increasing CO2 ppm at a rate very close to 2ppm / year, and in context. So, assuming action this year, halved CO2 output, over 25 years, leads to a ballpark of 425 CO2 ppmv by the time we could level it off, even given a strong desire to do so.

    Climate sensitivity estimates are narrowing in more and more toward about 3 degrees C per doubling of CO2, based on both models and paleoclimate studies. Another source for this estimate is here, complete with about 30 peer-reviewed references.

    That amount of CO2 puts us close enough to 2 degrees C of warming to make me nervous, and does not factor in any feedbacks, like melting permafrost or destabilized clathrates.

    Judging by the lack of any real progress at any of the recent climate change talks, it will be some more years before we get serious about reducing CO2 emissions. So, we are likely going to hit 2 C warming, plus whatever feedbacks ensue. I'm not trying to give credence to those that say there is no point in attempting mitigation, because it is not the case that 2 C of warming will be as bad as 3 C, or 4 C, and so on.
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  7. On the odd chance that it is of any interest, here is a cross-ref to my blog in the local paper. It is a repeat of this comment, plus contains a link to a paper on the polarization of beliefs at the start, which I thought interesting, as well as guesstimates of local climate change impacts, at the end.
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  8. chriskos@4
    Fusion energy go uncontrolled? It cannot happen! Fusion is entirely different from fission (which for current designs in production can and have gone uncontrolled). Fusion requires energy to maintain reactions. But there are fission reactor designs that are inherently safe, such as the Liquid Thorium designs, but they were not supported by the US military in the 60's because thorium reactors are very poor at producing the raw materials for nuclear devices.

    Yes we do have an insatiable appetite for energy; that is a natural consequence of humans wanting to better their living conditions, and the inevitable growth in populations (inevitable because that is the nature of life, even human life). Short of a non-greenhouse gas emitting source of energy, no matter how much we reduce consumption, without a dramatic, no, apocalyptic collape of human society, we won't significantly affect the generation of greenhouse gas.

    So better hope that fusion, and/or a major investment in throium based reactors happens soon.
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  9. Someone please correct me if I have this wrong, but as best I can tell from when I last dug into the aerosol whiplash issue, the EU and the US have made some very good progress in reducing sulfate aerosol emissions, and China is (much more recently) getting serious about controlling them. (I don't know off-hand what the story is with India on this point.)

    This is very bad news, despite the obvious and positive effects from lowering air pollution and acid rain, and it's one of the purest examples I know of the phenomenon I describe by saying "timing is everything, and it's not on our side". Probably the least convenient fact of all is the long atmospheric lifetime of CO2, making those emissions a one-way ratchet in terms of normal human planning horizons.
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  10. To Chris G @7 (5.24 am 3 June 2012)

    Thanks for the reference to the excellent paper on belief polarization, which I’d also recommend for helping us to understand better how others (and ourselves) might think about (-snip-) AGW. (-Snip-)

    (-Snip-).

    To PhilMorris @8 (05.59 am 3 june 2012)

    I agree very much that R & D on thorium should be pursued vigorously.
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    Moderator Response:

    [DB] Offensive terminology snipped.

    Off-topic snipped.

  11. Would local heating at the south pole and local cooling at the north pole not introduce more transport of heat from south to north? It will take quite some time, sure.
    Assuming the whole 'rich' world did economical collapse and there is hardly economical activity which is burning fossils. Tanker ships will still be around going from unfriendly (for humans) areas in the south to almost even unfriendly areas in the North.
    One way of enhancing the transport from north to south would be creating liquid NG from coal deposits and store it up north in empty gas fields.Power to create (hydrolysis of coal with hydrogen) the LNG derived from sun and wind in the south (guess weather does get more violent, so more wind to harvest). Driver to make sense is the temperature difference, a 4 to 5 degrees on the whole range of a 210 degrees difference (from liquid CH4 to room temperature) just a 4% to compensate for transport.
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  12. Aerosols from China, India and similar countries are certainly a cooling factor at the moment but we don't have good enough data on their distribution and what the mix of aerosol types is to quantify the effect that well. Infortunately we haven't been able to successfully launch a satellite to start measuring.

    Current moves to gas instead of coal in many parts of the world may have some interesting implications if the scale keeps ramping up, especially if gas is actually replacing existing coal plant.

    Gas produces less CO2 than Coal for the same amount of net energy produced. So a modest positive in reducing emissions. But Gas burns pretty clean, without generating the same levels of aerosols. So it would contribute to drawing down aerosol levels in the atmosphere and thus removing some of their masking cooling effect and revealing more warming.

    Personally, I think that is a positive occurance. Not that there is more warming, because that warming is already locked in, it will be revealed eventually when we stop burning fossil fuels.

    Rather the more the eventual warming occurs sooner rather than later, the more that can help influence public opinion towards action. Ultimately it is the eventual warming that is the issue. But action seems to need warming now as the basis for action.

    Kate's post also highlights one of the problems with GeoEngineered mitigation of AGW. Even if GeoEngineering results in mitigation of global average temperatures, there will still be substantial regional climate changes.

    This is potentially a legal (and even military) mess. Country A unilaterally starts some GeoEngineering activity, injection of aerosols into the atmosphere being an obvious example. However, even though A's efforts do bring about a net positive benefit globally, County B happens to be a big loser in this, with negative climate changes being dumped on their region.

    What does Country B do? Just live with it? International legal action against A? Military strikes against A's aerosol dispersal infra-structure? How does B weigh up its responsibilities to it's own citizens vs it's responsibilities to the world as a whole

    Messy!
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  13. PhilMorris @ 8

    I couldn't agree more, Thorium nuclear reactors are an excellent way to reduce carbon emissions while maintaining our current standard of living, which is something that many will not sacrifice if they can put off the nasty effects of Climate Change untill later, much later. Let's face it, there are a lot of questions raised about just how good renewables really are.

    This link (if it works - never put one in before!) takes you to a TED talk on the matter.
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  14. "Constant atmospheric carbon dioxide concentrations lead to continued warming for many centuries, whereas the elimination of carbon dioxide emissions leads to approximately stable or decreasing global temperature."

    This is the caption from the blue line graph in the Nat.Geo publication, and this seems rather to totally unrealistic to me purely on the GHG front.

    Why?

    Well from the latest carbon models if CO2 emissions stopped today the fall atmospheric CO2 concentrations aren't falling by much for 1000's of years and as they do fall CO2 stored in the sinks is re-released delaying the fall even further, so stopping emissions today won't see any drastic fall in GHG in the atmosphere in the short term. The rate of drawn down from the recent models is ~0.2ppm per year so a fall of 20ppm in 100years, hardly removing the heater, and that doesn't take many things into account either...e.g. permafrost melt.

    Also what about the CO2 that is always released when the earth warms up, ~14ppm a 1C, what has happened to that?

    And does the albedo feedback just stop? Snow lines are moving north, the arctic is melting (~same size of the N.America Ice sheets when they were present), permaforst is melthing another source of CO2, the CO2 fertilization effect will equalise (see face trials it don't last long anyway) and decrease as soon as CO2 falls at all. Then there is the stopping of the fertilizer affects from man's agricultural practices which as been boosting the land CO2 sink considerably (this would all be lost actualy releasing CO2 as things equilibriated)and overall causing a slight cooling due to this and NO, methane and ozone interactions, and then of course there is the sudden lack of dimming as said which will be significant especially considering SO2 atmospheric concentration haven't actualy fallen world wide since 1980 and have started to rise again in th elast few years as India and China industrialise and finally ther eis the release of methane from melts permafrost and increasing wetlands.

    And what about the warming already stored in the oceans, which most people put at another 0.5-7C to come? According to Hansen the earth heats up 6-80% of its full potential in 100years then the additional 20% takes 1000years or so, so how can warming stop immediately, especially as the heater isn't turned off by stopping emissions it is stopped but reducing atmospheric CO2 concentrations!

    And lets no forget the CFC's. HFC's. NF3 additional GHJG which last for eons and eons.

    Sorry but I find it totally incredulous that zero CO2 emissions from tomorrow would just stop warming in its tracks, and would suspect the model being used is grossly overestimating CO2 drawn down and not taking the stored oceansic heat content into context.

    Bottom line is to prevent 2C we don't just need to stop emissions we need to actively build-up land and oceanic sinks to draw CO2 out of the atmosphere.

    Remember which ever you look at it, when the sun was dimmer than today, the world's geography basicaly the same, a CO2 of 350ppm cuased the world to be 3-5C hotter, so how is stopping at 400ppm going to stop us warming to this full potential???

    SO basically overall saying stopping emission will halt warming is not realistic and actually gives false hope.

    We need to actively get to 350ppm by 2100, and the only way to do that is to stop all emissions for sure and by 2017!!!!!!, and then actively remove CO2 to get to 350ppm by 2100, which if the early Pliocene data is correct still means 1.8-2.4C by 2100.....in Hansens lastests papers this is more like 1.4-1.6C, but he has th eearly Pliocene only 2oC warmer as he uses deep ocean temepratures with a conversion factor whereas all other studies have 3-5C and CO2 concentrations of ~350ppm, upper limit 400ppm but with more specific CO2 proxies only 325ppm....

    Sobbering, but entirely possible, just take everyone to realise it and also realise that 2C isn't dangerous because of potential tipping points but because the climatic shifts and severe weather events, drought s and floods have no mercy on crops or water availability! and a direct threat to us all not just those in other parts of the world.
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  15. ranyl @14, your view is far too pessimistic. Modelling studies have consistently shown that a cessation of CO2 emissions results in the rapid draw down of CO2 concentrations as CO2 partial pressure equilibriates between surface and deep layers of the ocean. According to the most recent such study by David Archer (PDF):

    "The models agree that 20–35% of the CO2 remains in the atmosphere after equilibration with the ocean (2–20 centuries). Neutralization byCaCO3 draws the airborne fraction down further on timescales of 3 to 7 kyr."


    Below are the model results for a 1000 Petagram pulse (1 trillion tonne) Carbon pulse of CO2, an amount widely recognized as a upper limit on cumulative emissions to avoid greater than 2 degrees C temperature increase above pre-industrial levels:



    As can be seen below (fig 1a, blue line), Matthew's model is, if anything, pessimistic on these grounds. That is partly because of the decay of other,short lived green house gases to CO2, and further outgassing from the surface ocean as ocean temperatures rise. However, it probably also reflects a slower draw down of CO2 than is typical of other models:

    (Source)

    The consequences I would expect from a complete cessation of CO2 emissions would be an approach to the equilibrium temperature change of the remnant of CO2 in the atmosphere within a century or so, followed by a slow rise to the Earth System Response as the effect of changing albedo due to melting ice sheets becomes noticable. Ball parked as a funtion of the Transient Climate Response to the peak CO2 concentration, that would represent 1.5 (ratio of Equilbrium response to TCR) * 0.33 (increased CO2 concentration above preindustrial levels after equilibriation with the ocean) * 1.5 (ratio of Earth System Response to Equilibrium Climate Response). Very roughly, that represents 0.75 of the peak temperature reached, but could be only half of that, or equal depending on the precise value of fairly uncertain figures. Matthew's results are certainly plausible, although on the pessimistic side of that range.
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  16. Peter42, I thought the polarization paper was interesting because it steps away from the trap of thinking that people that don't come to the same conclusions as you must not be as smart. Smart people often come to different conclusions, and sometimes this in despite a preponderance of evidence on one side. The mind is not deterministic like a computer, and Spock-like rationality is not a trait many people have.

    Looking at the "Working out climate sensitivity" post (linked above), I tend to agree with mostly with Ranyl's conclusions, even if I don't agree with all points. Ice albedo feedback is already figured in to paleo studies of CO2 sensitivity; any additional CO2 feedbacks change the CO2 level, on which the temperature sensitivity is based. The climate sensitivity estimates for temp record and last millennium in Figure 1 indicate to me that the earth is a bit behind equilibrium with current levels of CO2. Those two are lower than all the others.

    Geoengineering: I believe it will be attempted, and I believe it will be messy, as Glenn says.

    Thorium: Yes, for the points mentioned. Sooner or later though, regardless of energy source and climate, population will have to level off simply because of finite resources. My two cents: Climate change will transform a leveling off into a bottleneck.

    Tom C, I don't think your quote from David Archer that gives a 2-20 century ocean equilibrium timeframe supports any model that shows a temperature leveling within 100 years. It is a bit tricky because a temperature equilibrium could occur prior to an ocean CO2 sat equilibrium as the ocean draws down atmospheric CO2, which is why I'm saying 100 years rather than extending out to the 200-2000 window.
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  17. Chris G @16, I disagree. The time taken for the system to reach the Equilibrium Climate Response (ECR) is likely to be greater than 80 years, and may be over 200. Further, in most models of the carbon cycle, the initial reduction in CO2 is rapid, declining to about 60% (range of about 45 to 80%) within 100 years. That means the initial temperature peak is likely to be equivalent to 45 to 80% of the ECR for the peak CO2 levels, after the negative effects of aerosol forcings are removed. Curiously, the ratio of Transient Climate Response to ECR across AR4 climate models is 0.4-0.8, with a median value 0.55 (Mean = 0.544) (see histogram on third slide)which indicates the ECR to the declining CO2 levels is roughly equivalent to the TCR of the peak level.

    Clearly, the exact behaviour will depend on the exact values of the TCR, ECR, relaxation time to oceanic equilibrium for CO2, and relaxation time to ECR, all of which are uncertain. Nor can we expect an exactly linear response over the first century after ceasing GHG emissions. But nor should we expect the variation from the temperature leveling significantly beyond that which would occur from leveling plus natural variability.

    I consider these facts good news. They mean we have longer to cut GHG emissions to effectively zero before passing the 2 degree C "guard rail" than is often supposed. Unfortunately that extra time only means that we might still make that target if we start cutting emissions radically now, rather than already being beyond that point.
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  18. Tom,
    I think I should have digested your last paragraph a bit more before commenting. Surely not an entirely accurate depiction of what you wrote, but maybe not too far off: As the upwelling of the ocean is helping keep the surface cool, the downwelling is helping to extract/sequester CO2 from the atmosphere. The maximum temp reached is quite a bit lower than what would be expected only from the maximum CO2 level.

    Here's to hoping you are right.
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  19. 16. Schneider B. “Global warmth with little extra CO2”, Nature Geoscience, VOL 3, pg. 6-7, 2010
    17. Csank, A.Z., et al., “Estimates of Arctic land surface temperatures during the early Pliocene from two novel proxies”, Earth Planet. Sci. Lett. (2011)
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    19. Lowe A. et al “How difficult is it to recover from dangerous levels of global warming?” Environ. Res. Lett. 4, (2009)
    20. Solomon S. et al, Persistence of climate changes due to a range of greenhouse gases PNAS. October 26, 2010
    21. Wang Y-P, et al, “Nitrogen constraints on terrestrial carbon uptake: Implications for the global carbon-climate feedbacks”, GEOPHYSICAL RESEARCH LETTERS, VOL. 36, 2009
    22. Boer G.J et al, “Temperature and concentration feedbacks in the carbon cycle” GEOPHYSICAL RESEARCH LETTERS, VOL. 36, 2009
    23. de Boera H. J. et al “Climate forcing due to optimization of maximal leaf conductance in subtropical vegetation under rising CO2” PNAS, Jan 2011
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    In the seriesof papers above it becomes quite clear the CO2 is not going fall rapdily after even a total stopping of Co2 emissions and th epaper by Archer is useful but hten not really, for it assumes continued CO2 fertilization to large degrees and as it puts th etotal pulse of CO2 upfront it creates large atmospheric CO2 to Oceanic CO2 gradients pushing CO2 into the ocean at far greater rates than be expected now.

    Also I woudl suggest that you consdier further the scale of nitrogen fertilization response w ehave had since the 50's, increaseing the land sink and the oceans sink as the nitrogen a spercolated throughout the whole environment, and then of coruse looking at the Archer data even more closely ~50-60% of the CO2 remian in the atmoshpere for ~200years, and the CO2 models used doesn't really account for nutrient deprivation that well, no accoun tof permafrost releases, no accoun tof the increasing SH westerlies upwelling, no accounting for the increasing wetlands were getting, no accounting for the severity of droughts we are having, no accounting for the facts that from the face trials the CO2 fertilizatione ffect is short lived, no accounting for the removal of nitrogen fertilization as an urgent neccessity, no accounti9ng for the reducing sinks in the S. Ocean, North Atlantic, Off Japan for some reason, the loss of Phytoplankton, the increasing forest fires, the fact the Canada has become a carbon source, as have the tropics,no accounting for the facts that as the CO2 falls the sinks will re-relase the carbon they have stored,no accounting for the rise in CO2 as the world warms from oceanic sources and no accounting for the large scale biodiversity losses that are being witnessed that simplify eco-system and reduce carbon storage.

    All the aside an dwhy I mentioned the albedo effect, it is now clear that when ther eis ice on this planet th eeffective CO2 forcing is doubled, and keep in mind the arctic summer ice was 7million km2 recently, tha tis larger than the laurentide ice sheet and the water is darm blue compare dthe lighter land beneath the ice, meanign the albedo effect of a melting sea at the pole is considerable and quick...

    Then back to PETM when CS is higher than 3oC with the latest CO2 proxies by some way, nearer 7C, and then consider that again that the Pliocene was 3-5C warmer at 350ppm.

    And I'm sorry but to suggest that a trillion tonnes of carbon is in anyway safe, especially considering the major weather events and ice melt we all already having seems intellectual denial to me of the real situation..we don't have any room to put more CO2 into the atmosphere indeed if we don't start taking it out, and somehow increase carbon uptake from into the sinks to get the 350ppm then times will be interesting, although the scale of the problem to get to 350ppm is daunting indeed, for using even a simple CO2 with sinks that say high, to get to 350ppm means a 400ppm peak by 2017 and carbon sequestration from that point.
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  20. ranyl @19:

    1) The list of scientific papers you appear to have copy and pasted from some bibliography includes many papers only tangentially related to this topic. The first two, for example, represent estimates of climate sensitivity rather than discussion of the carbon cycle. (I also note in passing that the list violates the intent of the comments policy stipulation that naked links not be provided. If you are going to cite papers, you should at least summarize them unless they are directly related to your comments, and it is clear from context how they are so related.)

    2) Although you make a long list of factors not taken into account by the various models, in fact most of them do take most of those factors into account. Those which are not included (eg, nitrogen fertilization) are recently raised considerations, and it is not at all clear that they are well founded.

    3) Suggesting that loss of the Arctic sea ice will have a similar albedo impact to the loss of the Laurentide Ice Sheet is just rubbish. Regardless of area and underlying surface, there is a vast difference in latitude and hence of effective insolation. Albedo effects from the loss of Arctic sea ice will be significant, but is not the game changer you imagine. Estimates of Equilibrium Climate Sensitivity based on the LGM, such as those by Hansen and Sato, already include the albedo effect of a larger loss of sea ice (a fast feedback) from lower latitudes. Therefore if that feedback is stronger than is thought, it must be because some other feedback is weaker than currently thought, for empirical estimates of climate sensitivity include all fast feedbacks by their nature.

    4) The rate at which CO2 is carried to the deep ocean does not depend on CO2 "gradients". The pCO2 of atmosphere and surface ocean equilibriate in approx a year, with the ongoing removal of CO2 to the deep ocean being effected by the thermohaline circulation rather than by diffusion. As such, the rate of that removal is a function of pCO2 in the surface ocean and the pace of the thermo-haline circulation. Ergo, a pulse gives a reasonable estimate of the time to oceanic equilibrium.

    5) I note, also, that even Lowe et al 2009 (your fourth reference)shows near flat temperatures in the first century after the complete cessation of emissions in all three scenarios she examines, even though she argues and models a very slow decline in CO2 levels:



    She even shows a limited probability of exceeding 2 degrees C provided emissions are kept below the trillion tonne limit (equivalent to the cessation of all emissions in 2050):



    It appears that my conclusion is fairly robust.

    Finally, if your respond again with a gish gallop as in your last post, I will not bother responding again.
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  21. Please excuse my rushed post Tom, and I did not ascert that loss of the Arctic sea ice would entirely mimic the Laurentide Ice sheet loss in anyway, just pointing out it is a large area of sea that is changing colour in the summer when it does get a reasonable amount of insolation on average in the present day of ~180w/m2/pa compared to ~300w/m2/pa for the Laurentide Ice sheet and Laurentide Ice sheet was larger than the summer average summer extent of the sea ice at ~12million km2 compared to 7million km2 (before 2000), therefore clearly less than ice sheet. However the ice sheet would have taken eons to melt whereas the arctic sea ice seems to be melting very quickly especially in the important summer months and in the summer months the insolation in the arctic latitudes is higher than the lower latitudes of the Laurentide ice sheet, at ~500 w/m2/pmonth, compared to 480w/m2/pmonth...http://aom.giss.nasa.gov/cgi-bin/srmonlat.cgi, therefore my pint was not that the alebdo effect was the same as the Laurentide ice sheet more that it is quick and I suspect it is significant due to its size.

    In the Lowe paper the headline detail was that the rate of fall of PCO2 was 0.2ppm per yer, so a whole magnitude less than your ascertation of 2ppm, and this was mainly due to carbon modelling they used including a climate-CO2 positive feedback factor. The majority of this feedback is derived from tropical feedbacks as demonstrated by Roeckner et al(1), and is due to temperature change and water stresses in tropics, however these are very mild for low emissions scenarios and represent a fall in the size of the annual sink not a trnasformation of the sink to a source as has occured in the tropics already. These models by Roeckner also shows however that boreal continue to an ever increasing sink yet it is already been shown the Canadian boreal forest is source, due to forest fires and infestations both factors which are not included in these carbon models and not in Archers paper either. And neither models included permafrost release of CO2 as this has only occurred realistically since 2010. Also Note Lowe didn't include any other GHG for the graph above and they started the simulation from temperature and GHG records in 2000, and thus no heat stored in the ocean for the 2012 no emissions scenario yet both the 2050(so 50years of additional heating) and the 2100 run do and both scenarios continue to warm after the emissions stop.

    Now is it me or is the heating in the pipeline due to lagged the expression of the eenrgy imbalance to surface temeprature expression a myth, as far as I have read the earth is meant to warm to about 1.4C above pre-industrial according Hansen etc whatever we do, due the warming in the system yet these models are showing no additional heating at all.

    (1)Historical and future anthropogenic emission pathways
    derived from coupled climate–carbon cycle simulations
    Erich Roeckner · M. A. Giorgetta · T. Crueger ·
    M. Esch · Julia Pongratz, Climatic Change (2011) 105:91–108
    http://www.springerlink.com/content/q50mp5004654654k/

    I would also suggest you reas the European Nitrogen Assessment on the Nitrogen fertilization effects and ozone interactions with methane, it all seems reasonable, well considered and well investigated.

    You say that the factors I mentioned as not being included in the carbon models are, yet this is not the case, for although they may include the effect of a warming ocean on its ability to absorb CO2 they don't account for the scale of changes being observed and nor do make the Southern ocean a source due ot increasing westerlis as has also been observed, and the changes in North Atlantic and never mimicked by the models, further more the FACE traisl show nutrient deprviation effects and water stress factors that are greater than predicted and they show a cessation of the CO2 fertilization effects after 5-10years whereas the modles keep on increaseing this unless water stress intervenes, and although the models do indeed mimc some eco-systems shifts due to changing climate none of them include eco-systems and biodiversity losses due to oceanic dead zones, pollution, waste, over exploitation, eco-system destabilisation, invasive alien species, and eco-system effects on CO2 sequestration may well be more profound than cliamtic effects,"At the study site, local disturbances appeared to exert an impact on the observed carbon sequestration, whereas climatic factors made moderate contributions." (2).

    2. Detection and attribution of global change and disturbance impacts on a tower observed ecosystem carbon budget: a critical appraisal
    Akihiko Ito, Environ. Res. Lett. 7 (2012) 014013 (6pp)
    http://iopscience.iop.org/1748-9326/7/1/014013

    Then you say that many of the papers I quoted previously were about climate sensitivity, and you say this is off topic, well I disagee aswe seem to be talking about whether we agree that a temprature flatline is realistic with a total cessation of CO2 emissions. I say this is not realistic and the main reason for the lack of warming is due to an overactive draw of CO2 casuing an exagerated cooling influence...and of course there will be further warming due to the other GHG's and sudden loss of aersols that would occur, the heating already in the pipeline and the continued albedo effects, so the assumption for me is incorrect and leads to a false hope.

    Also the CS is critical, and Hasen and Sato CS is for CO2 alone, they are very clear that the albedo effects during the alst several glacials is as strong and they only make the last glacial 4.5C coler and the early Pliocene 2C warmer, whereas many others make the last glacial 6C cooler and the Pliocene 3-5oC warmer, and remember again CO2 was 350ppm then...although Hansen does agree that the arctic sea ice melt shoudln't make a huge difference as it is small, despite its size and influence on th ewhole cliamtic system, which so seems to pumping heat into the arctic at faster rates than anticipated.

    Considering the ppm have risen from 280ppm to 393ppm for ~1/2 Trillion tonnes I presume that another 1/2 trillion tonnes (1 trillion in all) will get us to ~500ppm and you are sayign you feel safe with as all emissions will stop at that point and the overshoot scenario fuesl by carbon drawdown will keep us below 20C, yet all th recent models in the papers previously quoted make 2C inevitable and by 2050 for this size of scale of CO2 in the atmosphere.

    Now I could go on and mention the greater of effects of droughts on the carbon cycle than anticipated, the increases in soil respiration in Autumn, and the recent paper by Shakun (3), where the primary driver for temperature rise is CO2, and alebdo has a surprisingly mainly regional effect, and despite CO2 plateauing at 12000BP the temperature rises a further 1C, as a by the by they have a CO2 rise of 0.44 (180-260ppm) of a doubling and a temperature rise of 3.5C, or a CS for CO2 if the ice albedo is considered a feedback (and small as they suggest) of 7.9C, or a CS of ~4C if split 50/50 into CO2 and ice as Hansen and Sato do.

    Anyway bottom line for me is that 350ppm if the Pliocnee data is right means a shift in climate that is at best risky and means 1.8-3C warming by 2100 unless you use Hansens Pliocene values when we get 1.6C (but this level of warming in temr sof climatic shfits etc is the same as the 1.8-3C above in real terms), is only just safeish considering the events that are already occuring (Missippi Floods, French Floods, Pakistan, Amazon Drought, Queensland floods, Texas Drought, and so on and so on)..

    So for me we are already well over our carbon budget and our eco-systems are feelinjg the strain, so I call not only for 350ppm as a definitive target but also a realisation of what that actually means, I using the MagicC model to get to 350ppm will take a mircale of zero emissions by 2017 and large carbon sequestration after that to increase the 0.2ppm/pa to 0.5ppm/pa, counter the CO2 influxes from permafrost melt, wetland increase, etc.

    And finally in the study by Archer, they pulsed the CO2 into the atmosphere so 50% shoudl have been withdrawn almost immeadiately to keep with the reality we know and therefore to ascertain how slow CO2 will be drawndown once it is at a certain ppm, you have to go to the 50% point(1year) and then see the rate of decline and doing that it takes about 400year to fall to 50% so much slower than the graphic suggests.

    Therefore it is up to you if you feel reassured with putting another 1/2 Trillion tonnes of CO2 into the atmosphere at this point to have a 50/50 chance of missing 2C, like 1.9C is safe!, However I don't and there are many calling for 350ppm amd I agree with them.


    (3)http://sciences.blogs.liberation.fr/files/shakun-et-al.pdf
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    Moderator Response: [DB] Converted Google link string into actual URL.

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