Arguments
CO2 lags temperature - what does it mean?
The skeptic argument...
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)
What the science says...
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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. |
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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 trigger the initial warming (starting approximately 19,000 years ago), which is first reflected in the the Arctic.
- This Arctic warming caused large amounts of ice to melt, causing large amounts of fresh water to flood into the oceans.
- This influx of fresh water then disrupted the Atlantic Ocean 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.
- The warming Southern Ocean then released CO2 into the atmosphere starting around 17,500 years ago, which in turn caused the entire planet to warm via the increased greenhouse effect.
Overall, about 90% of the global warming occurred after the CO2 increase (Figure 2).
Figure 2: Average global temperature (blue), Antarctic temperature (red), and atmospheric CO2 concentration (yellow dots). Source.
Last updated on 9 April 2012 by dana1981. View Archives
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.
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.
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.
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.
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!
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...
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.
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.
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...
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.
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
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.
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.
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.
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.
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?
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.
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.
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).
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)
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?
Cooler oceans can hold more CO2, so the oceans suck it out of the atmosphere.
"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."
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?
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.
Your reference to your daughter seems inconsistent with your stated posting policies.
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.
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?
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
"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."
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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.
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?