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CO2 lags temperature - what does it mean?

What the science says...

Select a level... Basic Intermediate

CO2 didn't initiate warming from past ice ages but it did amplify the warming.  In fact, about 90% of the global warming followed the CO2 increase.

Climate Myth...

CO2 lags temperature
"An article in Science magazine illustrated that a rise in carbon dioxide did not precede a rise in temperatures, but actually lagged behind temperature rises by 200 to 1000 years.  A rise in carbon dioxide levels could not have caused a rise in temperature if it followed the temperature." (Joe Barton)

Earth’s climate has varied widely over its history, from ice ages characterised by large ice sheets covering many land areas, to warm periods with no ice at the poles. Several factors have affected past climate change, including solar variability, volcanic activity and changes in the composition of the atmosphere. Data from Antarctic ice cores reveals an interesting story for the past 400,000 years. During this period, CO2 and temperatures are closely correlated, which means they rise and fall together. However, based on Antarctic ice core data, changes in CO2 follow changes in temperatures by about 600 to 1000 years, as illustrated in Figure 1 below. This has led some to conclude that CO2 simply cannot be responsible for current global warming.

Figure 1: Vostok ice core records for carbon dioxide concentration and temperature change.

This statement does not tell the whole story. The initial changes in temperature during this period are explained by changes in the Earth’s orbit around the sun, which affects the amount of seasonal sunlight reaching the Earth’s surface. In the case of warming, the lag between temperature and CO2 is explained as follows: as ocean temperatures rise, oceans release CO2 into the atmosphere. In turn, this release amplifies the warming trend, leading to yet more CO2 being released. In other words, increasing CO2 levels become both the cause and effect of further warming. This positive feedback is necessary to trigger the shifts between glacials and interglacials as the effect of orbital changes is too weak to cause such variation. Additional positive feedbacks which play an important role in this process include other greenhouse gases, and changes in ice sheet cover and vegetation patterns.

A 2012 study by Shakun et al. looked at temperature changes 20,000 years ago (the last glacial-interglacial transition) from around the world and added more detail to our understanding of the CO2-temperature change relationship.  They found that:

  • The Earth's orbital cycles triggered warming in the Arctic approximately 19,000 years ago, causing large amounts of ice to melt, flooding the oceans with fresh water. 
  • This influx of fresh water then disrupted ocean current circulation, in turn causing a seesawing of heat between the hemispheres.
  • The Southern Hemisphere and its oceans warmed first, starting about 18,000 years ago.  As the Southern Ocean warms, the solubility of CO2 in water falls.  This causes the oceans to give up more CO2, releasing it into the atmosphere.

While the orbital cycles triggered the initial warming, overall, more than 90% of the glacial-interglacial warming occured after that atmospheric CO2 increase (Figure 2).

Shakun Fig 2a 

Figure 2: Average global temperature (blue), Antarctic temperature (red), and atmospheric CO2 concentration (yellow dots).  Source.

Last updated on 18 June 2014 by dana1981. View Archives

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Further reading

That CO2 lags and amplifies temperature was actually predicted in 1990 in a paper The ice-core record: climate sensitivity and future greenhouse warming by Claude Lorius (co-authored by James Hansen):

"Changes in the CO2 and CH4 content have played a significant part in the glacial-interglacial climate changes by amplifying, together with the growth and decay of the Northern Hemisphere ice sheets, the relatively weak orbital forcing"

The paper also notes that orbital changes are one initial cause for ice ages. This was published over a decade before ice core records were accurate enough to confirm a CO2 lag (thanks to John Mashey for the tip).

Climate 411 have a succinct explanation of the Greenhouse Effect.

Also, gotta love this quote from Deltoid in answer to the CO2 lag argument: See also my forthcoming paper: "Chickens do not lay eggs, because they have been observed to hatch from them".

Further viewing

Comments

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Comments 51 to 100 out of 350:

  1. Re: "On the other hand it's not obvious why you consider a truism to be an assumption! It's been known since the middle of the 19th century that the earth's temperature is defined by the insolation from the sun (which gives the Earth a black body temperature near -15 oC) and the greenhouse effect arising largely from water vapour and CO2 that supplements the black body temperature by around 30 oC."
    Because it has been determined slightly more recently that your truism isn't. It is incomplete. Because it is incomplete the concepts that assumed it to be correct are also incorrect albeit not entirely. Just enough to skew the results and point in the wrong direction.
  2. Really Quietman?

    What specific ("more recent..") evidence informs your opinion that the greenhouse effect doesn't supplement the Earth's global temperature such that we are around 30 oC warmer than we would otherwise be without the greenhouse effect (taking into account the variations I pointed out in 14 and positions of the continents and that sort of thing)? Which specific concepts that were "assumed it to be correct" are now "also incorrect"?

    In what manner specifically does the determinations "more recently" "point in the wrong direction"?

    Please be specific.
  3. At post 43 above “for the last glaciation” appears to have been mistakenly interpreted as the transition from interglacial to glacial. The words were intended to be understood as ‘during the glacial period’ which excludes the interglacials and transitions to avoid these murkier periods and also to avoid significant influence of Milankovitch cycles. It may have been less ambiguous to have said “during the last glacial period” because what is meant is the period from about 115,000 ybp to about 20,000 ybp (and previous glacial periods). Similarly in post 45, ‘glaciations’ is intended to mean ‘during the glacial period’.

    Of course the planet is warmer because of ‘greenhouse gases’ than it would be without the effect. Most people that are knowledgeable on climate understand that positive feedbacks occur with carbon dioxide and water vapor and should understand that the climate responds to NET feedback which is the combined effect of all feedbacks, both positive and negative whether known or not. Much less well understood is that there has to be substantial negative feedback because the trends in the temperature record prove that the NET feedback can not be significantly positive. Without significant net positive feedback, the GCMs do not predict significant global warming.

    The lag of atmospheric carbon dioxide level to changes in global average temperature in paleo data is readily explained by the change with temperature in solubility of carbon dioxide in water.
  4. Has anyone discussed the possibility of bias between the two different ways of measuring CO2 and temperature as the source of the big jump near the end of the hockey stick graph? Thanks.
  5. During the last and previous glacial periods there were temperature and carbon dioxide up-trends and downtrends. Credible data from Vostok and EPICA showing these trends are readily available (e.g. the first graph above). Close examination of these data shows unequivocally that on many occasions temperature trended down for centuries while carbon dioxide level was higher than it had been during a prior temperature uptrend. This shows that, at least at that time, temperature was not driven by carbon dioxide level.

    It is well known that added increments of carbon dioxide have less influence than previous increments. This has been elucidated using the added-blankets metaphor. Since there is more carbon dioxide in the atmosphere today than during the glacial periods, added increments of carbon dioxide today have even less influence than they did during the glacial periods when they did not drive temperature. Thus added atmospheric carbon dioxide today does not drive temperature and AGW that is based on increased atmospheric carbon dioxide is a mistake.
  6. Sadly you're wallowing in logical fallacy Dan.

    Two things we know:

    (i) the ice age cycles were drived by the slow cyclical variations in the orbital properties of the earth, and the associated variation in the pattern of insolation (solar irradiation at the surface) drove temperature variations.

    (ii) atmospheric CO2 is a greehouse gas. The Earth has a temperature response to raised CO2 somewhere near 3 oC of warming per doubling of atmospheric CO2.

    It's fallacious to attempt to insinuate that those two rather well-characterized phenomena are sumehow mutually exclusive!

    I don't think too many people here are buying logical fallacies Dan!
  7. CO2 lags warming by 800 -1000 years, therefore warming is initiated by increased TSI ( whether M cycles or sun activity is moot). That would increase WV which re-inforces the initial warming and temps begin to rise, releasing CO2 from open water and from increased plant growth. No?
  8. Re #57

    Pretty much. The lag may not be as much as that and there are clear hemispheric diferences in the onset of warming during glacial cycles. But yes, the Milankovitch warming is amplified by a rapid (essentially instantaneous) water vapour feedback.

    The CO2 comes from the deep oceans largely I believe. Note that increased plant growth reduces atmospheric CO2, so this should act against warming-induced recruitment of CO2 from terrestrial sinks. I think that the rising sea-levels innundate very larger areas of shallow continental margin and so that reduces plant biomass somewhat returning some CO2 to the atmosphere. But ocean sinks are the main source of enhanced CO2 during the warming phases of the glacial cycles I think...
  9. Chris claims to grasp that solar variation was the main cause of temperature variation during the last glacial period. That is, from about 110,000 ybp until about 20,000 ybp. That does not include periods of transition from glacial to interglacial or interglacial to glacial.

    He/she claims that CO2 is a greenhouse gas. Good. That has been well known for years.

    But then Chris loses it. The 3 C warming that he/she has stated repeatedly is a prediction of faulty computer use and Chris fallaciously states it as if it were fact.

    Apparently Chris is unable to come up with any rational explanation for how a temperature down trend could take place while the atmospheric carbon dioxide level was higher than it had been during a temperature uptrend as it did repeatedly during the last and previous glacial periods. Therefore he/she simply dismisses as a ‘logical fallacy’ that this proves that temperature was not driven by atmospheric carbon dioxide level at that time. That doesn’t cut it. Let’s hear the rational explanation.

    Elsewhere Chris has claimed to grasp that added increments of carbon dioxide have less influence on temperature when the atmospheric carbon dioxide level is higher than the same size increments do when the level is lower. Good. That also has been well known for years.

    But then Chris apparently fails to grasp that increased increments of atmospheric carbon dioxide level now have even less influence on climate than the same size increments did during the last glacial period when they did not drive temperature.
  10. Goodness Dan, you are a master at contrived misunderstanding! This was all explained to you in posts #78 and #80 here:

    http://www.skepticalscience.com/climate-models.htm

    I have a horrible feeling that you're just ignoring the explanations and cited papers which essentially resolve your confusions. Let’s try again:

    ONE: The Milankovitch cycles do not only account for the major glacial <-> interglacial transitions. Remember that the earth’s orbital properties are characterized by three major cycles. Remember also that the three cycles [~100,000 year (eccentricity), 41,000 year (obliquity) and the 23,000 year (precession)], are out of phase. It’s not so difficult to understand that the interplay of these cycles gives multiple cyclical insolation changes that impact not only the major transitions, but the patterns of temperature variation within glacial and interglacial periods.

    That’s easy to see if one takes the parameters of delta-temperature or delta 18O from cores and Fourier transforms these with respect to time. Out pops as clear as day, strong peaks at frequencies at 111 kyr, 41 kyr and 23 kyr. Have a look at the paper I’ve recommended to you a couple of times now (Figure 2 shows the power spectra of delta 18O and delta T):

    Kawamura et al (2007) "Northern hemisphere forcing of climate cycles in Antarctica over the past 360,000 years" Nature 448, 912-919.

    You would also benefit from reading some of the papers John Cook discusses in his article on top of this thread:

    (Petit et al, 1999 and Shackleton, 2000 are useful)


    TWO: It’s been explained to you rather often now that our understanding of climate sensitivity (the earth’s temperature response to doubled atmospheric CO2) comes from a number of analysis of real world measurements. It doesn’t come from “computer use” whatever that might mean. Obviously GCM models are parameterized according to our knowledge of real world phenomena, so it wouldn’t be surprising if computer models were compatible with the climate sensitivity independently determined from analysis of the real world.

    You can read about the wealth of real world measurements that bear on this data here, for example:

    http://www.skepticalscience.com/climate-sensitivity.htm



    THREE: Poor Dan…reduced to telling porkies in para 4…how sad! Of course your logical fallacy that I highlighted in post #56 was the deceit that because ice age cycles weren’t driven by CO2 (CO2 amplified the response), that “added atmospheric CO2 today does not drive temperature”; that’s a grating example of the fallacy of the single cause. BTW, it’s good to see that you’ve dropped the fallacious “argument” that temperature downtrends with still highish CO2 levels doesn’t “prove that net positive feedback does not exist”. So you’ve learned one thing, which is admirable, and that’s really the value of boards like this.

    and you've had your “rational explanation” many times now (e.g. “ONE” just above in this post).


    FOUR: Your last paragraph is a delicious restatement of your fallacy of the single cause.


    it really isn’t difficult to understand Dan (I suspect you're just not trying!):

    (A) CO2 is a greenhouse gas. Raised atmospheric levels cause the earth to warm all else being equal. A large number of empirical (and theoretical) analyses indicate that the earth responds to raised CO2 with a warming near 3 oC per doubling of atmospheric CO2.

    (B) During ice age cycles the primary driver of temperature variations are Milankovitch cycles (see “ONE” just above). The warming is amplified by raised water vapour and raised atmospheric CO2 (see Mizimi’s post #57). The raised CO2 levels were small and extraordinarily slow – more than 100 times slower than the rate at which CO2 levels are rising now. The raised CO2 amplifies the Milankovitch warming and incidentally produces its own water vapour and albedo positive feedback.

    (C) Now the primary driver of temperature change is direct pumping of massive amounts of fossil fuel-derived CO2 into the atmosphere at a phenomenal rate.

    (D) Do you understand Dan? CO2 is a greenhouse gas. However it gets into the atmosphere it results in warming (all else being equal) equivalent to something around 3 oC per doubling of atmospheric CO2.
  11. Sorry for the (very late) drop by! I was informed about this page by a reference from a recent discussion...

    No problem with the first statement: During ice ages/interglacials there is a lag of CO2 after temperature changes of 800 +/- 600 years in upgoing parts and several thousands of years during falling years with a sensitivity of about 800 ppmv/°C. This reduces to about 50 years lag for the MWP-LIA transition (again about 8 ppmv/°C) and 1 to a few months around the upgoing trend today (with about 3 ppmv/°C).

    But a big problem with the second statement:
    "The CO2 record confirms both the amplifying effect of atmospheric CO2 and how sensitive climate is to change."

    The amplifying effect of CO2 is difficult to estimate, as most of the time there is an overlap between the upgoing and downgoing trend of temperature and CO2. But there is an interesting exception: the end of the previous warm(er) period: the Eemian. The CO2 levels remained high while the temperature (and methane levels) dropped to a minimum value and ice sheets did grow again to a maximum. The subsequent decrease of 40 ppmv CO2 doesn't show any measurable drop in temperature outside the error margins. The theoretical change with 3°C/2xCO2 should give a drop of 0.4°C, and that is not visible in the ice core record. That means that the 3°C/2xCO2 is probably overblown. See:
    http://www.ferdinand-engelbeen.be/klimaat/eemian.html

    A second graph which shows that there is not that much feedback from increased CO2 on temperature, is from the very detailed Epica C ice core. The influence of temperature on CO2 (with lag) is clearly visible, but the influence of CO2 on temperature is clearly... absent. That is remarkable for what is assumed to be responsable for about 40% of the increase in temperature... See:
    http://www.ferdinand-engelbeen.be/klimaat/klim_img/epica5.gif
    With thanks to Andre van den Berg who made the graph.

    Thus the science about the feedback and sensitivity of the climate for CO2 changes is far from settled...
  12. Re: "The economic argument that carbon taxes will damage the US economy is bogus."
    This is an unknown. It could go either way depending on exactly who is taxed and how much as well as who is hired and how many.


    No, it's not unknown, it's definitely negative. See "broken windows fallacy."

    http://en.wikipedia.org/wiki/Broken_windows_fallacy

    At best, reducing CO2 is an external good that could have benefits 100 years from now (but won't because nothing short of nuclear will stop the growth of emissions in China, INdia, and Africa). At worst it's like paying one guy to dig a hole and another to fill it in.
  13. Temps drive CO2. That position stands.

    Amplifying effect - could be a thousand things! Studies on the ability of CO2 to "reflect" infrared show that the ability to reflect(absorb) does NOT impove with denser concentrations once past a certain level. This means that Co2 is done with it's "Amplifying effect" once a cetain CO2 level is acheived under normal conditions - I would assume that has to do with the wavelength itself and not CO2. (call in the phycisists)

    http://nov55.com/ntyg.html
  14. An argument I was hoping to find the refutation for here is: "CO2 has been much higher than now in teh past, and species flourished; why wouldn't they do the same now?"

    My understanding has been that because of greatre climate sensitivity to ocean current changes, a little CO2 now has a much bigger change on the climate than back in the days (for example), of Pangaea, when having only one continent created very different ocean currents.

    But I was unable to confirm the correctness of my understanding from this skeptical science site.
  15. MattJ: It has been demonstrated empirically that plants do indeed flourish if CO2 levels are higher than the present 380ppm or so, all other things being equal. Many horticultural industries use CO2 augmentation to grow bigger plants, faster. (Levels of around 1000ppm which is still low enough not to have a deleterous effect on animal health). Coupled with the knowledge that in the deep past the plants we now burn as coal grew in a climate with far higher CO2 levels ( and were adapted to such) and by locking up that CO2 reduced levels to around 200ppm...at which point they had 'starved' themselves..some species to extinction.
    About 8Mya, the grasses appeared - well adapted to thriving with low CO2 levels ( and are arguably the most successful plants we know). So there is no valid counter-argument.
    Climate is a highly complex interactive system and responds to changes in the physics and chemistry of the sun and this planet ( including those produced by life itself) and so it is necessary to look at ALL factors and how they interact, not focuss on a single mechanism.
    In that regard this site actually does quite a good job.
  16. MattJ:
    It is my understanding that in the distant past when CO2 was much more concentrated than today, the sun was also significantly dimmer. It is getting hotter and bigger all the time and in a billion years or so it will swallow the Earth.

    The thing with climate change now is that it is so rapid and because we've fragmented all the Earth's ecosystems they can't "move" to adapt.
  17. If the data were truly being analyzed at face value, as the author of this site suggests, then the only conclusion that can be drawn from the data is the following:

    Some mixture of greenhouse gases (H2O, CO2, Methane, etc), where the ratio of H2O vapor to the others is unknown, but important, MAY contribute to a fixed magnitude amplification of Milankovitch heating, which does NOT produce a positive feedback cycle. Our lack of understanding of the mechanism that drives such temperature amplification without leading to a positive feedback is testament to the complexity of the interactions taking place, and the need for more study.

    The fact is that the data do not support positive feedback, as there is no acceleration in the temperature trends, and as other posters have pointed out, the climate has indeed reversed substantial warming trends while greenhouse gas content continued to rise.

    What I sense is that as a group, CO2 warming supporters are having a hard time admitting to themselves, and to others, that we just don't have a sufficient understanding of all the relevant mechanisms at play to substantially prove our hypotheses.

    I think it's arrogance, personally.
  18. Correct me if I'm wrong, but CO2 is a pretty useless greenhouse gas. Feedback mechanisms and climate disaster modelling is predicated on a small bit of CO2 induced heating leads to increased atmos water vapour+ methane (a bad greenhouse gases) which leads to a large heating. i.e. CO2 starts it off, but watervapour/methane are the true baddies and contributors to the warming.

    If there is a 800 year lag between temp rising and CO2, then it suggests that a water vapour/methane feedback loop has already occurred anyway and, when CO2 turns up, it may add to the problem but it is effectively a side issue, driven by temperature and not the other way round.

    It seems to me that this is the mother of all correlation versus causation mistakes.

    Would like to hear a layman alternative?
    Response: Allow me to correct you. We have directly observed the enhanced greenhouse effect from rising CO2, both by satellites measuring infrared radiation escaping out to space and by surface observations of the infrared radiation returning back to Earth. They find that more heat is being trapped at the wavelengths that CO2 absorbs energy. This is empirical confirmation of the human signature in the greenhouse effect.
  19. toadhall,
    would you say that a lighter is useless to make a gas tank explode?
    More seriously, at equilibrium CO2 alone accounts for about a third of the whole effect, the other 2/3 are feedback. The feedbacks are intrinsic in the climate system, not just related to CO2. And indeed the orbital forcing due to the Milankovitch cycles alone cannot explain the ice ages cycles.

    You are also confusing CO2 as a feedback and as a forcing. What we are seeing now is the increase of CO2 concentration due to an external factor, human emissions. So, CO2 was a feedback in the past but now is acting as a forcing.
  20. I would like to ask a question that I would regard as common sense (the true deficiency of our planet IMHO).

    If temperature increases, whether from co2 or other sources, and that in turn causes the release of more co2 wouldn't that cause what is known in my industry a "feedback loop" which is a perpetual increase where it reaches a limit according to a viability of materials to handle such a load. So basically, it would either keep increasing until something "breaks" or would reach an equilibrium of perpetual continuance. That "balance" would look like; temperature increases with co2 until enough water vapor (the biggest greenhouse gas) would block enough incoming radiation to halt the increase of temperature resulting in a new perpetual balance between co2's greenhouse effect and water vapor's?

    I'm looking for an answer to what ended other warm periods in our history like the Paleocene period. Because if co2 levels lag temperature by roughly 800 years so would it's greenhouse effect, continuing it's "greenhouse" warming creating a cooling buffer but it doesn't, it just drops off like a fat lady falling off her chair at an all you can eat buffet.
    Response: Good question - I considered addressing this in the original article above but opted to keep things simple and address it in a future post. In the case of Milankovitch cycles, just as orbit changes initiate the warming, they also end the warming. Towards the end of the deglaciation, orbit changes cause the amount of June sunlight falling on the northern land masses to change by several tens of percent (not an insignificant change). Gradually over time, northern ice sheets start to grow again.

    For greater time scales (eg - over millions of years), rock weathering is another factor that keeps the climate regulated. Rock weathering is the phenomenon where CO2 is scrubbed out of the atmosphere by chemical reactions with rock surfaces. As temperatures warm, the rate of rock weathering increases - this acts as a natural thermostat to keep CO2 levels from getting too high. However, this process occurs over millions of years so don't expect rock weathering to bail us out of our current situation (although interestingly, there is research into using artificially accelerated weathering as a technique in sequestering CO2).
  21. John,

    This article is a nice explanation of how things have gone in the.

    Regarding the skeptic argument that the modern CO2 rise would be a result of current temperature rise and not the vice versa, there's at least one additional point one could make. Just looking at the numbers in your Fig. 1 would suggest that in order for the CO2 to naturally reach the current level of 385 ppm, would require something like a 7 degrees rise in temperature, instead of the 0,7 degrees observed. Fig. 1 of Falowski 2000 ( http://www.precaution.org/lib/carbon_cycle.000601.pdf ) nicely demonstrates this point.

    Plus, of course, this rise in temp. should have happened a thousand years ago (yeah I know, maybe it did, but people just didn't realise that because they had no thermometers ;) )

    Plus, if the CO2 was still rising naturally to reach a higher equilibrium concentration set by the higher temperature, it wouldn't make much sense that the carbon cycle is currently acting as a sink for the antopogenic emissions...

    These things might also be worthy of pointing out here (or maybe they have already been pointed out in some other article, and I just haven't realised)
  22. Hi John, I really appreciate your effort to explain the science of climate change. Your posts have helped me to solve a lot of doubts I had about the subject.

    I have a question regarding this graph. When the CO2 forcing is added to the Milankovitch cycles forcing after the triggering of deglaciation, shouldn't there be a noticeable increase in the rate of warming? Or is it too small to be noticed?
  23. Why does CO2 drop off when temperature goes back down?
  24. captain_heroic44: The reverse of what is described in this post's paragraph "As the Southern Ocean warms, the solubility of CO2 in water falls (Martin 2005). This causes the oceans to give up more CO2, emitting it into the atmosphere."

    Cooler oceans can hold more CO2, so the oceans suck it out of the atmosphere.
  25. Modelling of past deglaciation by Ganopolski & Roche (2009), summarised in this PIK media release, found both the delayed Arctic warming and the rapid onset of Antarctic warming (i.e. leading CO2 rise) was mainly due to melting northern ice sheets cooling the oceans and disrupting ocean circulation:

    "During the terminations of the glacial cycles due to orbital forcing, the vast ice sheets covering Northern America and Eurasia melted rapidly causing a large fresh water flux into the oceans sufficient to disrupt the Atlantic meridional overturning circulation (AMOC) over many thousand years. The disruption of AMOC, in turn, dramatically reduced the oceanic heat transport from the Southern to the Northern Atlantic and led to a delay in the Northern Hemisphere warming and, at the same time, a more abrupt and strong warming in the Southern Hemisphere. The latter is the primary mechanism explaining Antarctic temperature lead over CO2."
  26. On average, the climate of the last quarter million years have been very much less hospitable to humans and all life in general. It is less than 20% of time that the climate stay hospitable.

    Should humans allow the climate to naturally ebb back into terribly inhospitable cold?

    Do we actually know the mechanisms humans can use to delay the onset of the next apocalyptic ice age?

    Isn't the prevention or delay of ice ages terribly more important than slight rises in temperature?

    Do the druids and "humans should have no climate impact" scientists agree that allowing the globe to slip into the next ice age would be a bad thing? Somehow, I don't think so.

    Beavers had dramatic impact on climate and terrestrial life: If they had become smart enough to become self aware, should they have stopped transforming the planet?
    Response: The possibility of heading back into another ice age has been examined on multiple occasions in the peer-reviewed literature. Ice ages begin when northern ice sheets encroach further southward from year to year, gradually increasing the Earth's albedo. So if a huge ice sheet takes over northern Canada, then yes, be concerned.

    But in the meantime, the two largest ice sheets in the world, Greenland and Antarctica, are losing ice mass at an accelerating rate. You can rest assured that the imminent ice age has been postponed indefinitely. On the contrary, the accelerating mass loss from these ice sheets is predicted to raise sea levels by 1 to 2 metres by the end of this century. For the sake of my 10 year old daughter, I'm more concerned about the 1 to 2 metres sea level rise she'll see in her lifetime than a hypothetical ice age that will arguably occur hundreds of thousands of years into the future.
  27. Use of the phrase "arguably occur hundreds of thousands of years in the future" is only consistent with your quoted scientific projections if and when the CO2 release reaches 5000 gigatonnes. Are you proposing that we should reach that level?

    Your reference to your daughter seems inconsistent with your stated posting policies.
    Response: If we emit 5000 gigatonnes of CO2, the ice age is postponed indefinitely. If 1000 gigatonnes, then still over 100,000 years. We've already gone past the 300 gigatonne mark which will postpone the ice age for at least 50,000 years. If you want to haggle over numbers, let's adopt the most pessimistic worst-case-scenario and say we're staring down the barrel of an ice age in 50,000 years.

    I'm not sure which posting policy I've violated - it seems fairly straightforward that immediate generations are a higher priority than descendents over 5000 generations away.
  28. The study you quote only indicated half a million years for 5000 gigatonnes. (And note these are just projections).

    Please reference the peer reviewed article that claims to know that the next ice age will definitely not occur for the next 50,000 years.

    Using your daughter is clearly an emotional argument- any scientist can recognize that. Is this a forum for emotional arguments?

    Why won't you answer the question about the beavers?
  29. njthinker: An article by Berger and Loutre (2002) explained why this interglacial could last 50,000 years past today.

    The exact number of thousands of years is estimated differently by different researchers; 50,000 is the current best estimate, but nearly all researchers agree that the number is in the tens of thousands of years from now, and all researchers agree that the number is many thousands of years from now.

    You can learn more about the triggers of ice ages by entering "Milankovitch" in the Skeptical Science "Search" field at the top left of every page.
  30. nhthinker writes:

    Please reference the peer reviewed article that claims to know that the next ice age will definitely not occur for the next 50,000 years.

    "Definitely" is not a word that's used much in the geosciences.

    The last couple of interglacials were relatively short, but in recent years people have realized that neither of them is a particularly good analog for the Earth's current orbital geometry, and that comparison to the MIS-11 interglacial is more apt (Berger and Loulette 2002). Even without any anthropogenic CO2, this yields a long interglacial followed by a descent into glacial conditions around 50k years from now:


    Long-term variations of eccentricity (top), June insolation at 65°N (middle), and simulated Northern Hemisphere ice volume (increasing downward) (bottom) for 200,000 years before the present to 130,000 from now. Time is negative in the past and positive in the future. For the future, three CO2 scenarios were used: last glacial-interglacial values (solid line), a human-induced concentration of 750 ppmv (dashed line), and a constant concentration of 210 ppmv (dotted line). Simulation results from (13, 15); eccentricity and insolation from (19). (Berger and Loulette 2002).

    See also the subsequent work by David Archer, described in his book The Long Thaw and in various papers, such as Archer et al. 2005. Archer notes that the projected insolation will come close to the apparent threshold for glaciation in a few thousand years, then move away from that threshold and not cross it until 50k years from now.

    If our understanding of that threshold is correct, it's possible that a mild return to glacial conditions could start in a few thousand years from now. But the most likely scenario is that it won't happen for another 50k years. That's without additional CO2. Here's what Archer et al. 2005 say about adding CO2:

    "Release of 1000 Gton C (blue lines, Figure 3c) is enough to decisively prevent glaciation in the next few thousand years, and given the long atmospheric lifetime of CO2, to prevent glaciation until 130 kyr from now. If the anthropogenic carbon release is 5000 Gton or more (red lines), the critical trigger insolation value exceeds 2 s of the long-term mean for the next 100 kyr. This is a time of low insolation variability because of the Earth’s nearly circular orbit. The anthrogenic CO2 forcing begins to decay toward natural conditions just as eccentricity (and hence insolation variability) reaches its next minimum
    400 kyr from now. The model predicts the end of the glacial cycles, with stability of the interglacial
    for at least the next half million years (Figure 3c)."

    nhthinker writes: Why won't you answer the question about the beavers?

    I'm not sure I understand your point. If your comment above is imagining a hypothetical situation where beavers become intelligent, industrialize, and start to double to CO2 concentration in the atmosphere, then yes, once their scientists understood the probable climate impacts of their activities they would probably be well advised to modify their ways and develop better technologies.
  31. Whoops, Tom has the name right and I have it wrong. It's Berger and Loutre, not Loulette.

    And when I write "If our understanding of that threshold is correct, it's possible ..." that should be incorrect not correct.

    Sorry for the confusion.
  32. nhthinker writes: Using your daughter is clearly an emotional argument- any scientist can recognize that. Is this a forum for emotional arguments?

    I don't see any problem with John mentioning his daughter. Many of us who are scientists do in fact have young daughters, and being normal human beings we may be a bit more motivated in our work by the desire to make the world a better place for them to grow up in.

    In any case, it seems less problematic than your own use of "apocalyptic ice age" and "druids" above. Maybe when you're just starting out participating here you might want to be a little less confrontational? Just a suggestion.
  33. What problem do you have with use of the term "apocalyptic" to describe the hostility to life of the next ice age? Do you know of an adjective that would be more accurate to describe a planet that has lost 80% of its biomass to premature death and starvation?

    You carefully avoided the answer as to whether humans should do what is scientifically necessary to prevent the next ice age. (A response like "we're doing it anyway" is not an answer).

    I assert that humans should intentionally do what ever necessary to prevent the next ice age. It should be done with a significant safety margin of error to account for unusual but expected events like massive volcanoes and asteroid hits. Do you disagree? If so, why?

    If there is full agreement from scientists that humans should, for the good of future generations assure that an "unnatural" amount of CO2 should be kept in the atmosphere to prevent an ice age, then who decides what the right added level should be? Those that are only concerned and emotionally connected with their immediate offspring? Or those that have a more balanced concern with the long term?

    Were the dramatic changes to climate/environment caused beavers considered "natural" because the they were not self-aware of their impacts? Are the changes to the environment changed by self-aware beings any less natural? To see a difference between the beavers and the humans is to agree with the druids.
  34. Nhthinker, you've been provided with excellent information indicating that perhaps 40,000 years from now we should consider another ice age to be reasonably imminent. Right now we have a more urgent problem erupting under our feet, multiple lines of evidence indicating we're in some degree of difficulty due to C02 pollution. Why not check back here in, say, 35,000 years? Meanwhile the rest of us will get on with solving the present issue.
  35. nhthinker, what you're now focusing on is a policy question that is off topic for this thread on CO2 lagging temperature:
    I assert that humans should intentionally do what ever necessary to prevent the next ice age. It should be done with a significant safety margin of error to account for unusual but expected events like massive volcanoes and asteroid hits. Do you disagree? If so, why?
    I'm not sure whether there is an appropriate thread on this Skeptical Science site, since this site focuses on science rather than policy. But you might try The Upcoming Ice Age Has Been Postponed Indefinitely, or maybe Are We Heading Into A New Ice Age? Please don't be upset if off-topic posts get deleted from any of the threads, though.
  36. The entire purpose of this forum is to link to scientific literature that human introduced CO2 is causing global warming and the clear implication here is that extra CO2 is a bad thing.

    The inability of scientists here to discuss what the "right amount" of extra CO2 is the appropriate amount to balance the short term needs versus the long term needs of humanity seems like a very unscientific approach to me.

    You are welcome to call it "policy" question. To me, it clearly has its roots in scientific exploration of causes and effects and near term disasters versus long term disasters.

    But it's your site and you are welcome to limit it to discuss the limited inquiry you want.

    Cheers.
  37. nhthinker writes: What problem do you have with use of the term "apocalyptic" to describe the hostility to life of the next ice age?

    Well, it's awfully slow for an "apocalypse" since it develops slowly over a period of tens of thousands of years. Also, of course, humans have already lived through multiple glacial/interglacial cycles and in fact dramatically expanded our geographic range, our population, and our behavioral development (language, tool usage, etc.) right smack in the middle of the last glacial cycle.

    Do you know of an adjective that would be more accurate to describe a planet that has lost 80% of its biomass to premature death and starvation?

    Source, please. Where does that 80% come from? "Premature death and starvation" seems a bit overdramatic for something that only transpires slowly over a period of millennia.

    You carefully avoided the answer as to whether humans should do what is scientifically necessary to prevent the next ice age. (A response like "we're doing it anyway" is not an answer).

    Again, I'd recommend a little more politeness and a little less confrontational style. I haven't avoided any question in this thread.

    We are, of course, actually in an ice age. As I understand it we're near the start of an interglacial that would probably last for another 50,000 years even if we didn't burn another kg of coal or oil. To answer your question directly, I don't think we should lift a finger to "prevent" the next glacial advance. I think our descendants 2000 generations in the future should be able to decide how they want to handle it.

    In fact, if burning fossil fuels and raising the CO2 concentration of the atmosphere were the best way to prevent a future glacial advance, that would be all the more reason to reduce our consumption of fossil fuels now and save some for the future generations who will really need them, right? Following your logic, we're currently wasting precious resources that will be desperately needed by our 2000x-great-grandchildren in AD 50,000.

    More to the point, worrying about the next glacial advance (which almost certainly won't happen for 50,000 years, and if we burn enough carbon may not occur for 500,000 years or more) is rather foolish when the next century or two will experience serious environmental problems caused by too much warming and the resulting alterations of the hydrologic cycle. What you're suggesting is analogous to worrying about flooding in the middle of a drought. We should focus on more immediate concerns.
  38. nhthinker writes: The inability of scientists here to discuss what the "right amount" of extra CO2 is the appropriate amount to balance the short term needs versus the long term needs of humanity seems like a very unscientific approach to me.

    The fact that people don't choose to discuss things in the way you want doesn't imply any "inability" or "unscientific approach" on their part.
  39. Actually, the purpose of this site seems to be to cite scientific literature that CO2 from humans causes warming and warming in the short term is necessarily bad. That there seems to be an aversion to discuss why some level of human caused CO2 may be necessarily good and an aversion to interest in understanding what that level would be seems like it has some non-scientific motivations to me.

    If you are interested in CO2 but not interested it what the optimum level that the humans should keep in the atmosphere to balance all the potential disasters, seems kind of limited scope of inquiry to me.

    If you want to take the position that the "right" level of CO2 would be the level that would occur without humans, then say so. Such a position does not have a scientific basis unless you consider humans unnatural.
  40. Science doesn't tell us what is "good" or "bad." Those are value judgments. Science tells us "If you increase the radiative forcing from greenhouse gases, the planet will warm." Whether that's good or bad, or more likely some mixture of both, depends on your viewpoint.

    Your repeated insistence that you want people to focus more on value judgments while simultaneously insisting that you want the discussion to be more scientific seems irreconcilable to me.
  41. Most scientists care about what the impact of their scientific inquiry is. So we get pleadings about saving the planet for a scientist's 10-year old daughter and let the future generations fend for themselves. But I guess you don't consider that a value judgment as long as its coming from a scientist "on your side".

    If you want to leave the impression that you think there is no amount of human caused CO2 that would be good, then you have successfully left that impression without actually saying it. But it certainly does not seem that it is coming from scientific curiosity when you make a choice not to consider the question of whether there is any amount of human induced CO2 that could be considered valuable to the environment as a scientifically valid question. One would expect that you as a scientist studying CO2 should be at least be glancingly interested in the answer to such a question.
  42. nhthinker,
    actually you should be satisfied by the interest of climatologists on "the impact of their scientific inquiry", at least for what concern next century. Some of them also addressed the not-so-pressing problem of next ice age tens of thousands years ahead. And, finally, the impact of ongoing climate change has been addressed regionally, some winners and some loosers in the short term, only loosers in the BAU scenario in the long term.
    All of these things has been put on the table for the wider audience to be able to decide what to do. I really don't get about what you're complaining.
  43. nhthinker - the issues associated with human-induced climate are about RATE of change. Who knows what an "optimal level" of CO2 is? What we do know is that changing the climate too fast is highly undesirable. Suppose you decided that 3 degrees would be better earth, would avoid an ice age etc. What you then have to decide is how fast is it safe to make that change over. The environment is stressed by change from ice age to interglacial but not too bad. If you accept rate as safe, then we need to by changing the temperature at around 1/10 of rate we are doing so at the moment.

    Also, I think such engineering is premature. Your efforts would reduced by natural sequestration by the time you needed it. A safer strategy would be as Ned said. Hold your carbon reserves for a few thousand years (or whatever the optimal point is) and then burn
    them - SLOWLY.
  44. scaddenp- Thanks very much for your thoughtful assessment.

    As to abrupt changes changes- sometimes they occur naturally- Volcanoes and asteroids come to mind. Thus having the CO2 in the atmosphere prior to the occurrence of the abrupt cooling event may be necessary to speed the rewarming. How fast can humans safely add CO2 to the atmosphere? I'm not sure there is good analysis on this.

    The current modern temperatures are still significantly less than the highs of the previous interglacial periods.
  45. The fossil record would indicate that abrupt change is very bad, not that it doesnt happen. Asteroids especially come to mind. Single volcanoes certainly make short term changes to temperature but the aerosols are short lived. There is evidence that climate change due to mass volcanism is also highly undesirable. (from the point of view of species that went extinct). The natural ice age cycle has rates that are
    a/ very slow compared to current change
    b/ entirely predictable.

    While I don't know what you regard as "good analysis" of CO2 addition rate, you should be making some risk assessments. The various economic analyses of cost have considered sea level rise of 1m by 2100. The effects of water-cycle disruption are harder to assess but that is what IPCC WG2 is all about. Have you read it? Does that sound "safe" to you?

    Whether the temp. now are less than previous interglacial periods is irrelevant- in the past those temperatures were reached with warming rates much lower than now. Rate is far more important than absolute level because adaptation takes time.
  46. Just to further clarify that. I would accept as reasonably safe, CO2 increases such that rate of temperature change was no faster than that due to Milankovich solar forcings. ie a lot lower than what we doing now.
  47. nhthinker, you did write something that does have appropriate threads on this site: "But it certainly does not seem that it is coming from scientific curiosity when you make a choice not to consider the question of whether there is any amount of human induced CO2 that could be considered valuable to the environment as a scientifically valid question."

    Your comments in that regard would be on topic in either of these threads:
    Global warming is good, which lists side by side the claims of positives and negatives of global warming

    or

    CO2 is not a pollutant

    But further comments on this thread you are reading now, probably will be deleted if they are off topic.
  48. nhthinker, before you post a comment, you should evaluate whether it is on topic for that thread. You should look through the list of Skeptic Arguments to find the most appropriate one. On the left side of every page there is a big thermometer. At the bottom of the thermometer there is a link "View All Arguments...." Click it to see the full list of links.
  49. The quote of Barton is taken out of context: the full paragraph was:
    "Current CO2 levels are around 380 parts per million (ppm); in the past, CO2 levels have exceeded 1,000 ppm [iv]. An article in Science magazine illustrated that a rise in carbon dioxide did not precede a rise in temperatures, but actually lagged behind temperature rises by 200 to 1000 years [v]. A rise in carbon dioxide levels could not have caused a rise in temperature if it followed the temperature. The president of the National Academy of Sciences also testified under oath before the Energy and Commerce Committee on this very issue. "

    reference [iv]:

    "Science 22 July 2005:
    Vol. 309. no. 5734, p. 532
    DOI: 10.1126/science.309.5734.532n

    This Week in Science
    The Eocene was an extended interval of warm climate that lasted from 55 million years ago (Ma) until 34 Ma, when permanent ice sheets developed in Antarctica. Pagani et al. (p. 600, published online 16 June 2005) present a proxy record of atmospheric CO2 concentration for the middle Eocene to the late Oligocene (~45 to 25 Ma), based on the stable carbon isotopic composition of alkenones, a type of molecule produced by certain marine algae. The levels of CO2 during the Eocene ranged from 1000 to 1500 parts per million (ppm), and then rapidly decreased to modern levels of 200 to 300 ppm by the end of the Oligocene. These data have implications for understanding issues such as the expansion of ice sheets and the development of terrestrial C4 photosynthesis."

    reference [v]:

    "Science 12 March 1999:
    Vol. 283. no. 5408, pp. 1712 - 1714
    DOI: 10.1126/science.283.5408.1712

    Ice Core Records of Atmospheric CO2 Around the Last Three Glacial Terminations

    Hubertus Fischer, Martin Wahlen, Jesse Smith, Derek Mastroianni, Bruce Deck

    Air trapped in bubbles in polar ice cores constitutes an archive for the reconstruction of the global carbon cycle and the relation between greenhouse gases and climate in the past. High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 ± 400 years after the warming of the last three deglaciations. Despite strongly decreasing temperatures, high carbon dioxide concentrations can be sustained for thousands of years during glaciations; the size of this phase lag is probably connected to the duration of the preceding warm period, which controls the change in land ice coverage and the buildup of the terrestrial biosphere."

    ----

    Barton was correct in the context of his statement. The author of this article produces a strawman based on intentional or accidental overly terse quoting of Barton.

    It's usually easy to beat up a strawaman.

    If you have a appropriate quote that indicates a skeptic that claims if a condition was not a cause in some cases that it can't be the cause in any cases, then I would appreciate it if you would provide it.
  50. I'm not sure why you think this is a straw-man argument, or what difference you think the context makes.

    The first sentence and reference (iv) are about something else entirely (CO2 levels during the Eocene/Oligocene). That's more or less the argument dealt with on the page Does high levels of CO2 in the past contradict the warming effect of CO2? although it's talking about different times. In any case, that has nothing to do with the Pleistocene glacial/interglacial cycles Barton refers to in the second and third sentences.

    John quoted those two sentences in their entirety. the only thing missing is the footnote and the reference to testimony by someone from NAS. So what's your complaint? The footnote is just providing evidence that a lag occurred. But everyone agrees that the lag occurred, in fact since the warming/cooling was started by orbital forcing it would be very strange if there wasn't a lag. The problem with Barton's statement is that during the glacial/interglacial cycling CO2 acted as a feedback whereas now we're adding it directly to the atmosphere so it acts as a forcing.

    What exactly is your complaint? In what way is Barton being misrepresented? Can you be more specific about what you think is the problem?

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