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CO2 lags temperature - what does it mean?

What the science says...

Select a level... Basic Intermediate Advanced

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, US House of Representatives (Texas) 1985-2019) - Full Statement

At a glance

Antarctic ice-core data today provide a continuous record on temperature and atmospheric composition that goes back for some 800,000 years. The data track the last few glacial periods and their abrupt endings, with rapid transitions into mild interglacials. But in some of the ice-cores, temperature rises first and is followed, a few hundred years later, by rising carbon dioxide (CO2) levels.

Certain purveyors of climate-myths seized on this observation, claiming it to be “proof” that carbon dioxide doesn't cause climate change. Wrong, wrong, wrong. But how? The answer lies in a beer-can.

In fact, you can do this one yourself. You need two cans of any fizzy beer. On a nice summer's day, take one out of the fridge and place it outside in direct sunshine for a few hours. Leave the other where it is. Then open the two at the same time. The warm one will froth like mad, half-emptying the can and making a mess. What is left in the can will be horrible and flat. Conversely, the one straight from the fridge will just give a “pfft” noise and will be pleasant to drink, being cool and fizzy.

What's that got to do with this myth? Well, you have just demonstrated an important point about the solubility of CO2 in water. CO2 gives fizzy drinks their fizz and it is far more soluble in colder water. As the water warms, it cannot hold onto as much CO2 and it starts to degas. Hence that flat lager.

Exactly the same principle applies to the oceans. When global warming is initiated, both land and the oceans start to warm up. On land, permafrost starts to thaw out, over vast areas. Carbon dioxide (and methane) are released, having been trapped in that permafrost deep-freeze for thousands of years. At sea, that “warm beer effect” kicks in. Thanks to both processes, atmospheric CO2 levels rise in earnest, amplifying and maintaining the warmth. That rise in CO2 thereby caused more of the gas to be released, warming things up yet more in a vicious cycle, known as a positive feedback. Other feedbacks kick in too: for example as the ice-sheets shrink, their ability to reflect Solar energy back out to space likewise decreases, so that heat is instead absorbed by Earth’s surface.

The trigger for the initial warming at the end of an ice-age is a favourable combination of cyclic patterns in Earth's orbit around the Sun, leading to a significant increase in the solar energy received by Earth's Northern Hemisphere. That's no secret. Glacial-interglacial transitions are caused by several factors working in combination – triggers and feedbacks. We've understood that for a long time.

And when you think about it, saying CO2 lagged temperature during glacial-interglacial transitions so cannot possibly be causing modern warming is a bit like saying, “chickens do not lay eggs, because they have been observed to hatch from them".

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

That CO2 can lag behind but amplify temperature during a glacial-interglacial transition was in fact predicted as long ago as 1990. In the paper The Ice-Core Record: Climate Sensitivity and Future Greenhouse Warming by Claude Lorius and colleagues published in the journal Nature in 1990, a key passage reads:

"The discovery of significant changes in climate forcing linked with the composition of the atmosphere has led to the idea that 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 and by constituting a link between the Northern and Southern Hemisphere climates."

This was published over a decade before ice core records were accurate enough to confirm a CO2 lag. We now know that CO2 did not initiate the warming from past ice ages but it did amplify the warming. In fact, about 90% of the global warming followed the CO2 increase.

Antarctic ice cores reveal an interesting story, now going back for around 800,000 years. During this period, changes in CO2 levels tend to follow changes in temperatures by about 600 to 1000 years, as illustrated in Figure 1 below. This has led some to disingenuously claim that CO2 simply cannot be responsible for the current global warming. Unsurprisingly, such a claim does not tell the whole story.

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

The initial change in temperature as an ice-age comes to an end is triggered by cyclic changes in Earth’s orbit around the sun, affecting the amount of seasonal sunlight reaching Earth’s surface in the Northern Hemisphere. The cycles are lengthy: all of them take tens of thousands of years to complete.As both land and oceans start to warm up, they both release large amounts of CO2 into the atmosphere, from melting permafrost and from warming ocean water, since CO2 solubility in water is greater in cold conditions. That release enhances the greenhouse effect, amplifying the warming trend and leading to yet more CO2 being degassed. In other words, increasing CO2 levels become both the cause and effect of further warming. Once started, it’s a vicious, self-reinforcing cycle - an excellent example of what science refers to as a positive climate feedback.

Indeed, such positive feedbacks are necessary to complete the shifts from glacial to interglacial conditions, since the effect of orbital changes alone are too weak to fully drive such variations. Additional positive feedbacks which play an important role in this process include other greenhouse gases like methane - you may have seen videos of that gas bubbling up through icy lakes in permafrost country and being ignited. Changes in ice sheet cover and vegetation patterns determine the amount of Solar energy getting absorbed by Earth’s surface or being reflected back out to space: decrease an ice-sheet’s area and warming will thereby increase.

The detailed mechanisms for the above general pattern have of course been investigated. In a 2012 study, published in the journal Nature (Shakun et al. 2012), Jeremy Shakun and colleagues looked at global temperature changes at the commencement of the last glacial-interglacial transition. This work added a lot of vital detail to our understanding of the CO2-temperature change relationship. They found that:

1) 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.

2) This influx of fresh water then disrupted ocean current circulation, in turn causing a seesawing of heat between the hemispheres.

3) 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.

4) Finally, CO2 levels may lag temperature in some ice-core records from Antarctica, but in some other parts of the world the reverse was the case: temperature and CO2 either rose in pace or temperature lagged CO2. Figure 2 demonstrates this graphically and shows how things are never as simplistic as purveyors of misinformation would wish.

Shakun Fig 2a 

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

Last updated on 14 February 2023 by John Mason. 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).

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

Denial101x video

Myth Deconstruction

Related resource: Myth Deconstruction as animated GIF

MD Lag

Please check the related blog post for background information about this graphics resource.


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Comments 51 to 75 out of 451:

  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: 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: 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: 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: 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." 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)
  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 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 ( ) 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."

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