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skeptic1223 at 20:41 PM on 11 May 2015Climate's changed before
@466, thanks, this is a nice article, and a great support for my thesis. So, according to the article the ice ages started at levels of CO2 close to today's due mainly to atmospheric and oceanic conditions. Let me quote
"These preconditions—moisture plus an Arctic nucleus for cooling—would have made the climate system highly susceptible to ice sheet growth. Even modest changes in the global environment would have been sufficient to tip the scales and lead to the onset of major Northern Hemisphere glaciation.
Just such a change occurred between 3.1 and 2.5 million years ago, as Earth’s axis fluctuated so that the planet’s tilt toward the sun was less than today’s angle of 23.45 degrees."
So, what's stopping the same thing happening today, I mean not due to an axis tilt but for example due to a major volcanic eruption or decline in solar activity, the other conditions seem to be the same.
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MA Rodger at 19:46 PM on 11 May 2015Climate's changed before
skeptic1223@458.
Within your mercurial argumentation & hypotheising you write:-
@456, 454 - so, why did the ice ages epoch start in the first place then, CO2 concentrations before it started were above current levels. It is of course possible that the CO2 got sucked somewhere first, but do we know of such an event.
A bit of light reading for you. While the conclusions from such studies as presented within the linked document remain incomplete, knowledge of what is under examination may stop painfully simplistic assertons about CO2 levels and the causes of glaciation.
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bozzza at 19:39 PM on 11 May 2015Climate's changed before
@462, do you mean 1-200 ppm from now or from then? Why shouldn't we go up 300 ppm from now to be really safe? (Are you sure you are prepared to be questioned about this ad hoc policy?)
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skeptic1223 at 17:30 PM on 11 May 2015Climate's changed before
@461, I agree :)
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skeptic1223 at 17:28 PM on 11 May 2015Climate's changed before
@460, 457, for GISP2 I meant the green line, but I agree I was wrong, it's not smoothing, it's worse, it's polynomial fit
the Vostock data was an example that quick CO2 decline is possible, I wasn't trying to relate it to the temperature
I don't have the actual data about past temperatures, so I can't quote numbers, that's why in 440 I said that I have to rely on people who do have it and I will quote them again
"Over the last 400,000 years the Earth's climate has been unstable, with very significant temperature changes, going from a warm climate to an ice age in as rapidly as a few decades."
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skeptic1223 at 17:19 PM on 11 May 2015Climate's changed before
@459, not geoengineering, just an increase of CO2 by another 1-200ppm to be on the safe side. The effects of geoengineering as a broad term are not well known while I hope you would agree the effects of CO2 increase are pretty well known
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bozzza at 12:13 PM on 11 May 2015Monthly global carbon dioxide tops 400ppm for first time
@3, these are the problems that arise when governments pick winners aka intervening in the market place: the so called invisible hand of free-market theory can't operate efficiently... so when the phenomena of diminishing returns raises its ugly head how does a pastiche of next-to-random activity logically respond?
Economies are meant to be robust so let us all heil more government intervention to save our skin from the madness of Jevons Paradox!!
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jenna at 11:12 AM on 11 May 2015Monthly global carbon dioxide tops 400ppm for first time
Part of the problem with just hoping fossil fuels will gow away is this; Every new coal fired plant or gas fired plant being built today is going to be around for decades. Govermnents and power utilities don't spend that kind of cash to shut them down after 5 years or so.
We need viable renewables sources now, and the sooner the better. I;'m not just talking about endless solar farms, etc. It's not working in Germany or China (never mind India). Those 3 countries (and others) continue to build coal and gas infrastructure.
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bozzza at 10:01 AM on 11 May 2015Climate's changed before
@ 447, the counter to this is that California isn't a global indicator no matter what those guys handing out cds on the boulevarde say !
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Tom Curtis at 10:00 AM on 11 May 2015Climate's changed before
skeptic123 @457, if you only presented GISP2 as an example of an unsmoothed record, you deliberately presented an irrelevant example in that Marcot et al is not a smooth of the GISP2 record.
Presenting the Vostock graph as an example of rapid declines in CO2 level is even worse for your case given that declines in CO2 level are less rapid than are declines in temperature in the Vostock record. (Ie, my points are even stronger as applied to CO2.)
A 2-3 C drop on global temperature over a century or two would indeed be no fun at all. However, the likelihood of such an event with 280 ppmv of atmospheric CO2 is very low. We know this because only three events in the holocene come close to such a situation. The largest of these, the 8.2 kiloyear event was the result of a sudden spike in sea level resulting from the release of damned melt water durring the melting of the laurentide ice sheet. That cause is not applicable for stable preindustrial conditions or indeed at anytime except following the end of a glacial. The 5.9 kiloyear event and the 4.2 kiloyear event where much smaller and preceded the rise of CO2 concentrations to 280 ppmv. The most recent similar event was the Little Ice Age, with global temperatures declining by just 0.2 to 0.4 C.
With respect to the LIA, if that is the sort of unexpected climate variability we have to worry about, you need to make the difficulty argument that a low risk of a 0.3 C decline in global temperature is more threatening than a very high probability of a 3-5 C rise in global temperature. You also need the face the fact that these events seem to have a period of about 1500 +/- 500 years, and with the most recent event starting less than 500 years ago, the next event cannot be expected for at least another 500 years.
In short, it is absolute folly to not intervene to prevent an almost certain, large and very rapid event starting now because of the low risk of a small, relatively slow event that may occur 500-2000 years from now. Yet that folly is the basis of your argument.
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bozzza at 09:57 AM on 11 May 2015Climate's changed before
@445, So you are promoting geo-engineering of the planet?
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skeptic1223 at 08:56 AM on 11 May 2015Climate's changed before
@456, 452 - I claim that we can not predict volcanic eruptions, not the effects of them
@456, 453 - ok, so where do the statements from IPCC and GRIDA about rapid glaciations in a matter of few decades come from?
@456, 454 - so, why did the ice ages epoch start in the first place then, CO2 concentrations before it started were above current levels. It is of course possible that the CO2 got sucked somewhere first, but do we know of such an event
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skeptic1223 at 08:49 AM on 11 May 2015Climate's changed before
@455, my mistake about GISP2, it was more an example of smoothing
as for the Vostock data, it was given as example of CO2 levels, since CO2 is fairly evenly distributed, it should still be valid even if it is regional
about the rapid changes, a 2-3 degrees drop for a century even if it reverses itself would still have some quite bad effects
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Tom Curtis at 08:13 AM on 11 May 2015Climate's changed before
skeptic123 @452 - In fact climate models predict more abrupt temperature changes as a result of volcanic activity than actually occur. Your claim, therefore, is the exact reverse of the truth.
@453 As I have just shown, changes from interglacial to glacial are relatively gradual, with the most rapid representing a mean rate of temperature change at Vostock of less than 0.01 C per decade, ie, a tenth of the rate of the current trend (which the AGW deniers insist on calling a pause). Transitions from glacial to interglacial are typically much more rapid, and projected temperature increases over the coming century being much more rapid again, with the equivalent temperature increase to that between interglacial and glacial within 200 years on the outside (with BAU).
@454 Actually, the transition from glacial to interglacial typically occurs with CO2 concentrations 20-40 ppmv below preindustrial levels. No such transition has ever occurred with CO2 concentrations at modern values.
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Tom Curtis at 08:04 AM on 11 May 2015Climate's changed before
skeptic123 @428, last and most offensive first! The GISP2 ice core data represents a regional record only, not a global record. Are you seriously trying to suggest that global temperatures vary as rapidly as do regional temperatures (and regional temperatures with one of the most rapid rates of change of temperature found on the planet)? Further, are you seriously trying to suggest that the magnitude of temperature change from a regional record is also to be found in the global record? If so, you have largely disqualified yourself from the conversation on the basis of complete ignorance of basic relevant facts. If not, you have certainly disqualified yourself from the conversation on the basis of deliberately presenting evidence in a form you know to be misleading.
Taking the former, more generous interpretation, consider this graph of eight full holocene regional temperature proxies:
Individual proxies show rapid variation in temperature of considerable amplitude. Of those, GISP2 (light blue) shows the greatest variation, having the highest peak holocene temperature anomaly, and the lowest most recent temperature anomaly. Because peaks in various records rarely coincide, and some records are always out of phase with others (ie, have troughs where the others have peaks), the arithmetic mean of all 8 proxies shows both much less absolute temperature variation, and much lower rates of temperature change than do individual proxies. Consequently, presenting a single proxy (let alone the most variable proxy) as representative of either absolute magnitude of global temperature change or of rates of temperature change over the holocene is fundamentally misleading (whether from ignorance of the effects of regression to the mean, or intent to decieve).
(As an aside, the overall decrease in the mean temperature over the holocene is largely an artifact of a NH bias in the individual proxies (ie, there are more NH than SH proxies presented), a problem also with Marcott et al. An unbiased sample is likely to show much less, or possibly no decline over that period.)
The same basic problems afflict the Vostock proxy record (blue in the above graph). The absolute temperature magnitude shown in the Vostock record is approximately twice the absolute variation in the global record. Further, periods of rapid decline rarely coincide with other regional proxies so that periods of rapid decline in the Vostock record will coincide with much slower decline (or sometimes even increases) in a global record. Further, your quote from the caption of the Vostock graph that you show is misleading out of context, and not supported by the evidence in any event.
In particular, while rapid temperature changes can occur over only a few decades, the trend over successive decades will often greatly slow or reverse direction. The consequence is that multi-century temperaturetrends are typically very slow. This can be seen in a scatter plot of time intervals vs temperature change in the Vostock record:
While there are some very rapid short duration changes, they are seen to quickly reverse themselves. The result is that changes over a century or more are at rates of -1C per century or less. Typically much less. As the transition from inter-glacial to glacial in the Vostock record requires a temperature change of approximately -6C, that means transitions from interglacial to glacial cannot occure in less than 500 years or more. Indeed, based on a pixel count of the graph of the vostock record, the most rapid interglacial to glacial transition (taken as the interval between 0C and the bottom of the first trough below -4C, or to -6 C, which ever is shorter) takes 6250 years (approx 240 thousand years ago). The next most rapid, and most recent took thirteen thousand years.
Finally, the TAR quote references Alley 93, which analysed early icecore data from Greenland. The rapid transition it found was the Younger Dryas, which was primarilly a North Atlantic phenomenon, and which involved much slower transitions in temperature when averaged across a number of diverse locations. (In 1993, only Greenland proxies were available back so far in time.) It is, therefore, obsolete, having been disproved by more recent data.
(I've run out of time, and will return to the CO2 issue later.)
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skeptic1223 at 08:04 AM on 11 May 2015Climate's changed before
@442, well, ice ages started when CO2 levels were about today's, so it is entirely possible
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skeptic1223 at 07:39 AM on 11 May 2015Climate's changed before
@448, well, changes from glacials to interglacial are normally quite rapid (much more rapid than 20th century warming), so rapid warming is not something completely new for the climate system
Before the ice ages started (when CO2 dropped below today's levels) the climate was a lot more stable. I am not talking about extreme CO2 levels, just a 100, at most 200ppm more.
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skeptic1223 at 07:30 AM on 11 May 2015Climate's changed before
@449, I understand that climate models can not predict abrupt changes, that's why I am worried about abrupt climate changes that we can not predict, that's my whole point from the very start
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skeptic1223 at 07:23 AM on 11 May 2015Climate's changed before
@446, that's why I quoted IPCC and GRIDA that abrupt glaciations are possible, volcanic eruptions and solar activity were given just as examples of possible causes that we can not model reliably
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skeptic1223 at 07:10 AM on 11 May 2015Climate's changed before
@444, so, did you all have to pass that course first :)
There is a lot of controversy regarding water vapor, there is the strong green-house effect, but there are also the clouds which reflect sunlight. Also, water vapor is mainly present in the low troposphere where the greenhouse effect is already saturated, above 10km there is virtually no water vapor, that's why there are no clouds above when flying with a passenger jet. And according to skepticalscience "It is the change in what happens at the top of the atmosphere that matters, not what happens down here near the surface." -
DSL at 06:45 AM on 11 May 2015Climate's changed before
Skeptic1223, click on the links I provided. Try not to assume that increased global water vapor means more rain for everyone. I said "precipitation intensity" not "more widespread precipitation." You might check out the observed and modeled expansion of the Hadley circulation as well.
Why wasn't the "pause" in surface temp "predicted" by climate models? Because climate models aren't designed to project sub-decadal trends. The temporal resolution is getting better, and the "pause" has inspired focused science that's been quite fruitful, but the bald fact of the matter--and something that fake skeptics aren't willing to get--is that climate modeling isn't designed for accuracy over the short-term. Do you understand why that might be? -
DSL at 06:40 AM on 11 May 2015Climate's changed before
skeptic1223, just because glacial periods suck bad, that doesn't mean that periods of rapid warming are good. Keep in mind that atmospheric CO2 hasn't risen this quickly in at least 300 million years, and arguably ever. That could easily mean that the climate system is now warming at an unprecedented rate. Remember that life has reached equilibrium with Holocene conditions, and more generally with Pleistocene conditions. A rapid change to Carboniferous conditions (600+ppm) will put the current biosphere up against the wall. Because the climate system is comprehensively integrated, it's not as easy as just popping up the carb-o-stat to 600ppm and popping the cap off a beer: "No problem, mate! No more glacial periods! Let's kick it!" The problems that result from extremely rapid warming may make questions of glacial periods irrelevant.
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skeptic1223 at 06:39 AM on 11 May 2015Climate's changed before
@443, I haven't seen any conclusive evidence about the state of the surface temperatures for the last 15 years (that's why I put it only as a feeling and not a statement), if the mechanism is so obvious why it wasn't included in the climate models and they failed to predict it?
About the precipitable water vapor I could of course counterargue with the drought in California and my child memories of heavily snowy winters during the 1970s dip, but again there isn't conclusive evidence in either direction, so I've put it just as a feeling and not a statement.Moderator Response:[JH] Your "feelings" carry no weight on this website. Please cease and desist from posting them.
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Tom Dayton at 06:27 AM on 11 May 2015Climate's changed before
skeptic1223, your wild guessing about the possible catastrophic cooling effect of volcanic eruptions is, like your wild guessing about solar-caused cooling, wildly out of scale. One way to start replacing your uninformed intuition with data is by reading John Mason's series.
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skeptic1223 at 06:24 AM on 11 May 2015Climate's changed before
@439, "Rising Carbon Dioxide Concentration Stops the Glacial/Interglacial Cycle." - that's exactly what I mean too, it seems we only disagree in the safe level of CO2. As I said in 441, just to be on the safe side it might be a good idea to increase CO2 by another 1-200 ppm to get to pre-ice ages epoch levels.
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Tom Dayton at 06:21 AM on 11 May 2015Climate's changed before
skeptic1223, amazingly, you wrote regarding ice and snow albedo: "unless there is some other major warming positive feed-back effect today." Let's see... how about water vapor?! You really should learn the basics. I suggest you enroll (sorry, Aussies--"enrol") in the Making Sense of the Climate Science Denial course.
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DSL at 06:14 AM on 11 May 2015Climate's changed before
skeptic1223, when you say things like "Finally, the current slow down (if not reversal) of the warming and the last few winters of heavy snow are not very reassuring," strongly suggest a lack of understanding in the basics.
There has been no slowdown in the rate of energy accumulating in the climate system. There has been a slowdown in the rate of surface warming over the last 8-10 years. If you're having a hard time understanding this, there are plenty of threads to help.
Why is heavy snow in some parts of the world at certain times of the year an indication that the climate system is cooling? It is, rather, an indicator of warming, as warming puts more precipitable water vapor (pp. 201) into the atmosphere. -
Tom Dayton at 06:05 AM on 11 May 2015Climate's changed before
skeptic1223, you are correct that at any moment a Vogon constructor fleet might accidentally or haphazardly or maliciously destroy the Sun, thereby inducing a glaciation. But otherwise, solar changes within the empirically and modelled very well supported range of probabilities will barely and temporarily make a dent in the warming that our increased CO2 level is causing and will continue to cause.
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skeptic1223 at 06:04 AM on 11 May 2015Climate's changed before
@438, about the control knob, the past violent climate changes are due to positive feed-back effects, forcings only trigger the feed-back process. The major positive feed-back effect is the albedo acting through the area of ice sheets and snow cover. In an interglacial period the albedo is mostly a cooling positive feed-back due to the small starting size of the ice/snow cover, while in a glacial period it is mostly a warming positive feed-back due to the large area of ice/snow cover. So, unless there is some other major warming positive feed-back effect today, the current climate is more prone to a swing to cold than a swing to hot. It is of course entirely possible and even probable to continue gradually warming with the increase of CO2 if there is no cooling event to trigger the albedo feed-back. However, my worry is if there is a cooling event that we can not model reliably and the albedo feed-back gets triggered. So, just to be on the safe side it might be a good idea to increase CO2 by another 1-200 ppm to get to pre-ice ages epoch levels.
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skeptic1223 at 05:49 AM on 11 May 2015Climate's changed before
@435, I am not saying that abrupt glaciation is the norm, what I am saying is that abrupt glaciation is possible. The bibliography you mentioned discusses the normal process and relies heavily on models. Some events such as solar activity or volcanic eruptions can not be modelled reliably. As for the cherry picking, well, I don't have the actual numbers of the temperature measurements, and unfortunately the publically available graphs don't have sufficient time resolution to draw a positive conclusion, so I have to rely on other people who do have the actual numbers, and I thought that such respected institutions as the IPCC and GRIDA would be trusted with what they say.
@437, yes, I googled it and found it also here
www.odlt.org/dcd/docs/archer.2005.trigger.pdf
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Tom Dayton at 05:37 AM on 11 May 2015Climate's changed before
Ari also has a short but older-than-his-excellent-bibliography article "Rising Carbon Dioxide Concentration Stops the Glacial/Interglacial Cycle."
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Tom Dayton at 04:28 AM on 11 May 2015Climate's changed before
skeptic1223, your worry about climate instability is backward. The past 10,000 years have been unusually stable compared to at least the previous 40,000 years, allowing the rise of agriculture (see also here and later here) and civilization. Humans now have violently spun a major control knob of the climate all the way to 11.
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Tom Dayton at 03:51 AM on 11 May 2015Climate's changed before
By the way, the link to the Archer 2005 paper (Archer & Ganopolski, 2005, "A Moveable Trigger...") is stale in the "Are We Heading Into a New Ice Age" post. The full text of the paper is available elsewhere now.
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Tom Dayton at 03:31 AM on 11 May 2015We're heading into an ice age
Will somebody please add to the Further Reading section of this post, a link to Ari's bibliography of readings on future glaciation?
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bozzza at 03:28 AM on 11 May 2015Climate's changed before
@434, You make some intelligent points yet I can't help but feel you conveniently neglect rates of change aka the time factor.
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Tom Dayton at 03:26 AM on 11 May 2015Climate's changed before
skeptic1223, you are cherry picking quotes to support your intuition, and explicitly rejecting the data-and-model-based conclusions of scientists who have carefully studied glaciations and backed up their conclusions with evidence. Ari has compiled a bibliography of just some of the many other papers explaining that and why we have delayed the next glaciation for many tens of thousands of years.
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skeptic1223 at 02:22 AM on 11 May 2015Climate's changed before
@431,"The huge changes in past climate demonstrate the sensitivity nature of our climate. Small changes in solar output and minor variations in the distribution of solar energy across seasons (from minor changes in the earth’s orbit) have created climate changes that would be catastrophic today. Climate models can explain these past changes. And if we compare the radiative forcing from anthropogenic CO2 with those minor variations we see what incredible danger we have created for our planet."
I agree about all of the above except the last sentence. The thing is that in an interglacial period such as today, one of the major warming feed-backs is not present, ice sheets are small enough so that an increase in temperature would not decrease the albedo noticeably. The opposite, however, is much stronger, a relatively small drop in temperature may increase the ice sheets and snow cover sufficiently to trigger run-away albedo increase.
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skeptic1223 at 02:12 AM on 11 May 2015Climate's changed before
@430, I am not saying that an ice age is imminent, what I am saying is that with an unstable climate we can not really tell when an ice age would come. Surely ice ages have in general been triggered by drops in solar activity and orbital changes, but there are other events too, e.g. major volcanic eruptions, which are even more unpredictable than solar activity. In the past there have been events when glaciation occured unexpectedly and within decades, not centuries, see my post 428. Also, we do not really know the exact CO2 level vs solar irradiation drop that would prevent an ice age from happening. The author in Archer 2005 himself admits that the models are very sensitive to how the parameters are set and this is to be expected since strong positive feedbacks are involved. Finally, the current slow down (if not reversal) of the warming and the last few winters of heavy snow are not very reassuring.
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skeptic1223 at 01:40 AM on 11 May 2015Climate's changed before
@429, Surely there is some averaging in the ice cores resulting from compaction, and I am not an ice core expert, so I don't really know how much it is, but a quick search on the web shows it might not be that much
This 19 cm long of GISP2 ice core from 1855 m depth shows annual layers in the ice. This section contains 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers. From the US National Oceanic and Atmospheric Administration
www.antarcticglaciers.org/glaciers-and-climate/ice-cores/ice-core-basics/
Besides, the fact that the ice ages started only about 3 million years ago still remains.
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Tom Dayton at 01:04 AM on 11 May 2015Climate's changed before
On the general topic of climate variability, Science of Doom has a series of interesting posts called Ghosts of Climates Past.
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Tom Dayton at 00:53 AM on 11 May 2015Climate's changed before
skeptic123, further to Tom Curtis's points, see the post "Are We Heading Into a New Ice Age," the Intermediate version. Read the Archer 2005 paper referenced there.
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Tom Dayton at 00:40 AM on 11 May 2015Climate's changed before
skeptic123: Sorry, my mentioning of the spacing of data points obscured rather than clarified my point about temporal resolution of temperature records. The measurement techniques average across years, decades, centuries, millennia,.... For example, sediments and snow/ice compress over time so the years are not as physically separated, so a sample will be an average across a larger span of time, which will smooth across variations in temperature. That lack of resolution is reflected in the sparcity of data points the farther back in time you look in graphs, because the placement of a datapoint in time is done at the midpoint of the estimated range of times for that temperature.
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skeptic1223 at 23:53 PM on 10 May 2015Climate's changed before
@427
About 3) "The return to the cold conditions of the Younger Dryas from the incipient inter-glacial warming 13,000 years ago took place within a few decades or less (Alley et al., 1993)."www.ipcc.ch/ipccreports/tar/wg1/074.htm
"Over the last 400,000 years the Earth's climate has been unstable, with very significant temperature changes, going from a warm climate to an ice age in as rapidly as a few decades."
www.grida.no/publications/vg/climate/page/3057.aspx
While the overall slide into a full-blown ice age indeed could take a millenium, it does not happen smoothly but in a step-wise manner of a few decades with some steps spanning a few degrees of temperature drop. I am also highly suspicious that an increase of 20-40ppm CO2 could prevent the onset of an ice age, your graph from 1) is quite clear that a 20ppm increase had little effect.
About 2) The estimates in that paper might be a bit too pessimistic, who would have guessed that plants would start eating more CO2 as concentration increased
www.natureworldnews.com/articles/9576/20141014/global-warming-plants-absorbing-more-co2-than-we-thought.htm
Also, past CO2 concentrations seem to show that levels could fall as quickly as in a few centuries
About 1) The last 8000 years have indeed been quite uneventful, luckily for us, however it depends how much smoothing one applies to the data, for example
An it should actually be worrying that the overall trend was still downwards despite the 20ppm CO2 increase.
Finally, I would have been really worried if we were currently at preindustrial levels of CO2, but even at 400ppm we are still below the level when the ice ages started and with the current trend in solar activity and orbital cycles pointing downwards it might take just one major volcanic eruption to trigger the positive feedbacks.
Moderator Response:[RH] The David Lappi graph should be disregarded altogether for the mere fact that he states that GISP2 runs up to the year 2000. This is factually incorrect. The "years before present" represented in the GISP2 data uses 1950 to represent "present." Thus the data only runs up to 1855 (95 years before present).
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Oriolus Traillii at 23:28 PM on 10 May 2015Monthly global carbon dioxide tops 400ppm for first time
Re: TomR: It seems likely, though, that fossil fuel comanies will finance their own research to stay competitive and stay alive for a while yet. Should oil production not be stopped by market forces in time, the softest route left open would be for governments to make giving up the oil business as financially attractive as possible (rewards would be easier than punishments), while dismantling the oil-specific infrastructure wherever an oil firm calls it quits and banning new wells. This might be unpopular and dangerous, because it would involve transferring money to the rich, but it's preferable to no progress at all and to sabotage by frustrated citizens.
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Tom Curtis at 19:53 PM on 10 May 2015Climate's changed before
skeptic123 @425:
1) The long term global temperature trend over the last 8000 years has been flat, or slightly downward:
From this we would expect the CO2 concentration to have declined by about 10 ppmv from the early holocene levels of 260 ppmv of CO2. Instead, it rose to 280pmmv - most probably due to preindustrial activities of humans:
Arguably, even that rise was sufficient to prevent the Earth declining into a new glacial. Ergo your hypothesis is getting well ahead of the evidence even there.
2) More importantly, while restoration of zero net emissions will eventually result in CO2 concentrations declining to pre-industrial levels, it is likely to take much more than 10,000 years to do so:
Indeed, even if we were to return to zero net emissions prior to 2020, temperatures would still be elevated above preindustrial levels by a degree Centigrade 10,000 years from now, assuming no major alteration in natural forcings. Consequently concerns about targetting zero emissions are entirely misplaced. (They may be valid concerns for aggressive CO2 sequestration programs that aim at negative net emissions.)
3) The ice core record is very clear that the slide into a glacial occurs, not over decades but over millenium. Even were CO2 levels low enough for that to be a genuine risk, there would still be ample time to react to such an event by reinitiating the consumption of fossil fuels to raise CO2 levels by the 20-40 ppmv necessary to prevent the onset of the glacial. So, even if you were not ignoring relevant facts (1 and 2 above), preventing anthropogenic global warming would still remain the priority issue, with concerns about the ideal post mitigation CO2 concentration being a third or fourth order issue that can be left to be dealt with several decades or even centuries from now, when our understanding of the science will also be that much better.
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skeptic1223 at 18:20 PM on 10 May 2015Climate's changed before
@423, The data points in this graph seem to be quite equally spaced and the trend of climate instability increase is still quite obvious I think
from wikipedia
en.wikipedia.org/wiki/Geologic_temperature_record
Moderator Response:[RH] Shortened link
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skeptic1223 at 18:16 PM on 10 May 2015Climate's changed before
@422 If we reduce the emissions to preindustrial levels eventually the concentration would follow too. Also, we don't know exactly what is the threshold of CO2 concentration that leads to unstable climate. Before the current ice age epoch started CO2 levels were above today's.
The climate instability is not irrelevant, I think it is actually the most relevant thing. Unstable climates are unpredictable and swings from interglacials to glacials can happen quite rapidly in a matter of a few decades, for example
en.wikipedia.org/wiki/Younger_Dryas#
So, to summarize, in an unstable climate we wouldn't be able to tell if a new ice age is waiting for us just a few decades down the road, we wouldn't be able to prepare for it, and an ice age would have absolutely catastrophic consequences for us. The catastrophic consequences of rapid climate changes has actually been discussed by skepticalscience
www.skepticalscience.com/Rapid-climate-change-deadlier-than-asteroid-impacts.html
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skeptic1223 at 18:04 PM on 10 May 2015Climate's changed before
@421, Surely the time resolution for more recent periods is better than for older ones, however statistics and probability theory tell us that even sparser sampling would still show large variations (the probability of the sparser samples all hitting similar values is miniscule). I hope you would agree that the trend in increasing climate instability in the last 3-5 million years is quite obvious
LINK
the graph is from wikipedia
en.wikipedia.org/wiki/Geologic_temperature_record#
Also, the current ice age epoch started only about 3 million years ago and the difference in temperatures between glacial and interglacial periods has been quite significant, for 260 million years before that there were no ice ages and CO2 levels were relatively high compared to today's
LINKagain from wikipedia
en.wikipedia.org/wiki/Carbon_dioxide_in_Earth's_atmosphere#Moderator Response:[RH] Shortened links that were breaking page format.
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Leto at 13:53 PM on 10 May 20152015 SkS Weekly News Roundup #19B
Chiskoz @1
"unstitution"
That really should be a word.
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bozzza at 11:36 AM on 10 May 20152015 SkS Weekly News Roundup #19B
The reputation of UWA is very proud and if Lomborg got the gig at the insistence of a climate change denying Prime-Minister the laughter throughout the country would bring shame for a century. It was never going to happen.. Perth knew it would never happen as the students that go there only have it's flawless reputation separating them from the riff-raff of other very well educated university graduates around Perth and as we all know---> Perth has an overqualification problem.
The mums and dads of said students are well connected: Perth is a bit of a round-about and the chancellor would have been reminded that this state floats the country and will not be sold a pup by a Liberal Party propping up old technology and foreign vested interests. The people of UWA realised we need our 'clever country' back and now that Tony Abbott has nowhere to hide his infamous flim-flam man I expect the election campaign will be strategically kicking into gear exactly now!
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