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Climate Hustle

CO2 lags temperature - what does it mean?

What the science says...

Select a level... Basic Intermediate

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

Climate Myth...

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

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

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

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

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

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

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

Shakun Fig 2a 

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

Basic rebuttal written by dana1981


Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

 

Last updated on 8 January 2016 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Related Arguments

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

Comments

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Comments 501 to 550 out of 569:

  1. >>Rodger
    >>I am assuming that you have not yourself "counted
    >>the years." For my own part, I have in the past been
    >>content to take the word of others for the recent ice
    >>age cycles being 100,000 years long, this being a
    >>well-known and unchallenged finding.

    If you look at post 479, you will see that the gap between recent interglacials is 109 k years, not 100 k years. And this is supported by this alternate graphic of the Vostok data. And here you will see two 109 k year cycles,* preceded by two 88 k year cycles:**

    https://i1.wp.com/www.brighton73.freeserve.co.uk/gw/paleo/400000yearslarge.gif

    Quite clearly, the Interglacials are following the Milankovitch warming in the NH, with intervals of 4 cycles and 5 cycles (for the last two cycles).

    * A 113 k cycle, and a 109 k cycle.

    ** The difference from my previous post is caused by some confusion over the length of the precessional cycle. It is given as 25,800 years in many texts, but if you look at these graphs they clearly show a 22,000 year cycle. I am not sure why the difference. I simply counted the precessional cycles, rather than counting the years. But if the precessional cycle really is 22,000 years, which is not how I understood it, then the Ice Age cycle lengths are shorter, but still not equal. But there are still two different cycle lengths to Ice ages, and averaging them is not a valid methodology.

     

    >>I am at a loss with what you mean by the
    >>phrases "key factor" and "key feeback"

    The primary feedback. It is highly unlikely that all feedbacks are equal in effect. My point was the albedo feedbacks are probably more important than CO2 feedbacks, because Interglacials react to high latitude NH forcing. That strongly suggests that forcing and feedbacks are a result of changes in albedo, rather than a function of CO2.

     

    >>The full mix of forcings that result in ice age cycles is not
    >>yet fully determined which makes any informed response
    >>to you a tad harder still.

    I thought the 'science was settled'?

    Response:

    [DB] Inflammatory tone snipped.

  2. That's a lot of different cycles mentioned here. What are the statistical criteria to establish the existence of a cycle? What method did you use to identify the cycles? Does this fine cycle discrimination have any reference in the scientific litterature? 

  3. tatelyle @500.

    Concerning your little cycling excursion, it is foolish to ignore apsidal precession which is the "difference" you say you are still "not sure about" and whose inclusion yields the net 21.6ky cycle in precession. I can't say I've ever seen a figure for the size of variation in this cycle length. (I imagine it to be small. Axial precession is 25.7+/0.4ky.) This regional/seasonal cycle is of course modulated by eccentricity that leads rise to talk of the 19ky & 23ky signals which when combined achieve the modulated ampitudes. That said, the graphic you reference @500 allows measurement of the length of the three last ice ages yielding (backward from the present) lengths of 119ky, 107ky & 88ky. I'm not sure how this squares with your measurements or with your attempts to fit climate data with the lengths of multiples of precession cycles. Your efforts in this specific matter appear to be mainly driven by what is a well-known incongruity. That is that the high levels of variation in NH insolation due to orbital precession have small climatic reactions while the low levels of variation due to global orbital eccentricity have very large climatic reactions. This finding is decades old so try not to get too bogged down in it - it is well trampled ground.

    Concerning your resurrection of the incoherence you presented @498, the sentence at which I gave up all hope of identifying your meaning was "The exclusivity of NH insolation triggers strongly suggests that albedo is the key factor and the key feedback regulating Interglacials." I'm afraid that substituting the word "primary" for the word "key" doesn't make your meaning any clearer.

  4. PhillipeChantreau @502, using the following image I calculated by pixel count that Antarctic temperature rose to 0 C, at succussive intervals of, 86 thousand, 91 thousand, 112 thousand and 120 thousand years ago (most ancient to most recent).

     

    That takes us back to 400 Kya.  Prior to that, interglacials are cooler, and more frequent.  Using the initial -4 C line to characterize the frequency, we have intervals of 48, 24, 85, 45, 25, 34, 23, 73, 90, 92, 29, 85, 120 thousand years respectively (counting from 800 Kya).  The underlined pair pair obviously show as a single cycle if we use 0 C to characterize successive cycles.

    This simple count between years of particular phases is a crude method to characterize cycles as you know.  If that was what we had to relly on, we would not be able to characterize the frequency of glaciations in any meaningful way.  More advanced techniques show a clear dominance of the 41 Ky obliquity cycle over the last two million years (panels D and F), with the 100 Ky cycle becoming significantly more important in recent times:

    Over the last 400 Ky, the 100 Ky cycle has become dominant, with the 41 Ky obliquity cycle still having a greater influence than precession cycles:

  5. Thank you Tom, that is much more informative than Tatelyle assertions. The B,D and F graphs in the second figure of yout post are representations of what would be considered reliable ways to determine the presence of a cycle. I had no doubt that this work had been done and that a wide litterature existed on the subject. I am still wondering what is Tatelyle's basis to claim against that existing litterature, perhaps he will tell us more.

  6. It has now been four days since my challenge to tatelylle @496 that he either justify his apparently absurd claim that ice melt is not a feedback on changes in Global Mean Surface Temperature (GMST), or confirm that his argumentation has been based on equivocating between the cause of changes in GMST (in his earliest post, and by context of the main article) and the cause of initial melt of NH ice sheets.  tatelyle has done neither.  Apparently he can neither provide evidence for his claim, nor honestly admit to the equivocation that lies at the heart of his rhetoric.  He has therefore demonstrated that he is either not interested in, or as MA Rodger suggests @499, not capable of coherent and honest discussion of the issues involved.  Consequently I have no further interest in discussing the matter with him.

    For readers following the discussion, however, I need to clarrify some issues.  Specifically, tatelyle continues to make grossly inflated estimates of the Milankovitch forcing involved both changes in GMST and in the initiation of NH ice sheet melt.

    For GMST, global temperatures fluctuate approximately linearly with net global Top Of Atmosphere (TOA) energy flux, subject to a lag based on thermal inertia which is large relative to a single year.  It follows the relevant variation in TOA insolation is the globally, and annually averaged value.  As a less accurate proxy of GMST, we could estimate regionally averaged temperatures as a function of regionally averaged net TOA flux; and from that estimate a global average temperature.  This is less accurate because it ignores the large lateral heat transfers at the Earth's surface due to winds and ocean currents.  However, even doing this we must again take a global, annual average.  That is, if we assume NH summer temperatures vary with TOA solar flux, then the impact of that variation of GMST must still be averaged over the global surface area to reflect the impact on GMST.  Ergo, tatelyle's core argument for higher relevant fluxes is based on the assumption that we are not discussing the effect of Milankovich cycles on GMST (contrary to the clear context in the main post and his initial statement of the issue).

    Turning to the relevant forcing for the initiation of glacial melt, tatelyle is quite correct that it should not be globally, or hemispherically averaged.  Rather, the value should be considered only over the area of ice melt.  Never-the-less, tatelyle's back of the envelope calculations of the value are grossly exagerated.  Specifically:

     1)   tatelyle uses an exagerated estimate of necessary increase in July 65o N insolation. 

    tatelyle uses as the baseline of his estimates a 90 W/m^2 change in mean daily insolation in July at 65o North.  He draws that figure from the graph below, but only one of the upswings in summer insolation shown in that graph equals or excedes 90 W/m^2 (and that one did not result in a deglaciation).  The mean increase in insolation on that chart, averaged across all upswings, is 60 W/m^2 (or 61 W/m^2 if only the two upswings leading to glaciations are counted).  The median is 58 W/m^2 and the 5th percentile is 20 W/m^2.  Clearly based on these figures, tatelyle's figure is at least a 50% and potentially a 350% exageration of the July 60o N insolation necessary for a deglaciation.  As the largest insolation upswing did not result in a full deglaciation, it is clear that no value shown on the chart is sufficient for a deglaciation by itself, but that other factors must also be involved.

    For what follows, rather than trying to estimate the exact insolation change needed, I have used the deglaciation with the smallest change in insolation, ie, the Holocene deglaciation, as a benchmark.  I have calculated the values for the difference in insolation between the inosolation minimum (20 Kya) and respectively, the present, the peak Holocene insolation (9 Kya) and the onset of rapid deglaciation (15 Kya).  For insolation figures I have used the data from Berger (1978) as it is considered most accurate for the present (1950) and equivalent to the more recent 1991 calculations out to 800 Kybp.  As the data comes by 10 degree latitude band, I have calculated the 65o N values by taking an area weighted average of the 70o (75-65o) and the 60o (65-55o) bands.  This may result in a small error as an estimate of insolation at 60o N precisely, but a better estimate of the mean insolation over the band of most significant ice sheet melt.  The calculated insolation difference for July at 65oN from the insolation minimum are for 0 Kybp, 9 Kybp and 15 Kybp are respectively, 7.4 W/m^2, 51.5 W/m^2 and 29.2 W/m^2.

    2)  tatelyle assumes peak montly mean daily insolation over the entire melt season.

    As noted, tatelyle's estimate of a 90 W/m2 insolation increase was based on July at 65o N.  The insolation increase in June and August, let alone April and October, is less.  As a result the mean daily summer insolation change for 65o N for LGM to Holocene maximum (20-9 Kybp) is 44.1 W/m^2, 10% less than the July value.

    Of course, tatelyle challenges the use of only summer insolation.  He considers it obvious that the melt season lasts 40% of the year.  That is far from obvious to me.  I suspect the melt season depends on latitude, altitude and local conditions.  That quibble aside, in Greenland melt occurs between April and October, with the vast majority of the melt occuring in the summer months of June-August.  To estimate a melt season, I note that Peter Huybers (2006) notes prior reports that melt is ice ablation correlates with positive degree days, ie, days when the 2 M air temperature rises above 0 degrees.  He shows that positive degree days are highly correlated with days when TOA insolation exceeds 275 W/m^2.  Using that relationship, I use a melt season consisting of any month in which mean daily insolation averages 275 W/m^2 or more - which turns out to be April-August.  So defined, the TOA insolation difference averaged over the melt season at 65o N turns out to be 2.4 W/m^2 between LGM and present (20-0 Kybp), 32.4 W/m^2 for LGM to Holocene peak (20-9 Kybp), and 25.7 W/m^2 for LGM to onset of rapid deglaciation (20-15 Kybp).

    3)  tatelyle ignores the effect of albedo.

    Being as fair as possible to tatelyle, the 32.4 W/m^2 difference between insolation minimum and maximum is the value he wanted to compute, and is just over his revised estimate of 32 W/m^2.  It might appear that his inaccurate calculation has cancelled out the effect of his theoretical errors.  This would be the case were it not for his most fundamental error - ignoring albedo.

    Solar forcing equals TOA insolation - reflected shortwave radiation at TOA.  Therefore, to calculate the equivalent of the CO2 forcing, tatelyle needs to adjust the TOA insolation for albedo.  Because in this instance we are examining only the impact over the ice sheets durring the glaciation, and as we are examining the no feedback case (both from tatelyle's hypothesis and because we are examining the regional forcing), the appropriate albedo is ice sheet albedo at the start of the melt season.  For Greenland that is 0.835.  Adjusting for Albedo then gives us a melt season 65o N mean daily insolation of 0.4 W/m^2 for the LGM to present (20-0 Kybp), 5.3 W/m^2 for LGM to peak insolation (20-9 Kybp), and 4.2 W/m^2 for LGM to onset of rapid deglaciation (20-15 Kybp).  These are overestimates of the relevant values because the calculation does not include the impact of cloud cover, which further reduces the effective mean daily insolation at the top of the ice sheet.

    These values (although upper limits) are the best comparitors to tatelyles calculated value of 32 W/m^2.  In particular, the difference between the LGM and the onset of rapid deglaciation probably represents the best estimate of the upper limit on the necessary regional insolation forcing change to initiate deglaciation.  Based on that, tatelyle overestimates it by 660%.

    Note, this is for the change in regional forcing directly impacting on the icesheet.  For TOA insolation, his estimate is reasonable, and for global forcing (ie, the most relevant value), the true figure is approximately 1.3 W/m^2 over the melt season and 0.5 W/m^2 averaged over the full years forcing.

  7. I've been reading the above article and subsequent posts (only a fraction of them I confess, I don't have that much free time). One question that I am struggling to find an answer to is why does global warming naturally stop? The mechanisms for the causes of it are covered ad nauseam, but I have yet to find a discussion on why it isn't a run away process resulting in a Venus like Earth, which it clearly hasn't. The forcing by oceanic CO2 release would sugest to me that it should be. So what stops the process?

  8. Twobad @507, this question is discussed in detail here (remember to read the intermediate and advanced versions of the article as well).  

  9. Toobad,

    The biggest negative feedback is that the amount of radiation emitted from the atmosphere goes up as the atmosphere warms.  This increase is to the fourth power of the temperature.  Eventually this increase in emitted energy overcomes any positive feedbacks because the increase in emitted energy is so great.

    Everything considered is much more complicated, but the increase in emitted energy wins out in the end.

  10. If we have verified that CO2 follows the increase of the global temperature in the ice cores with a determined time delay, it is evident that it is not the CO2 that causes the temperature increase, but the opposite. It is a proof that the temperature causes the increase of CO2. So far we are all agreed. But how do you know that CO2 is responsible for current climate changes? Because it is a greenhouse gas? Of course, all greenhouse gases produce a warming (if the theory of greenhouse effect is true) in the global temperature. But, how do you know that the current increase in temperature (+ -0.5 ° C since the end of the Little Ice Age) is due to the action of the tiny fraction of the atmosphere composed of greenhouse gases and among them the tiny part composed of CO2 and within the CO2 of the tiny percentage produced by human industrial societies and not due to the action of other more widespread greenhouse gases or to the huge natural emissions of CO2 or the undisputed influence of the sun on global temperature wich in turn raises the atmospheric CO2 level?

  11. "If we have verified that CO2 follows the increase of the global temperature in the ice cores with a determined time delay"

    And yet the BEST team found that, WRT 'Is CO2 leading or lagging temperature rise':

    "we know that the CO2 is not coming from the oceans but from human burning of fossil fuels"

    And

    "it is clear that it is the CO2 that comes first, not the warming"


  12. "how do you know that the current increase in temperature (+ -0.5 ° C since the end of the Little Ice Age) is due to the action of the tiny fraction of the atmosphere composed of greenhouse gases and among them the tiny part composed of CO2"


    Off-topic, but I'll answer anyway and risk the ire of the moderators.

    Scientists have a pretty good understanding of what the Earth's climate has been throughout it's history, why it has changed over time and what the specific factors are that have made the climate change.

    And the only factor that fully explains all the changes we can see and measure in temperatures, ocean salinity, atmospheric composition, loss of Arctic sea ice volume, changing species habitats & ranges is due to the warming from human-derived fossil-fuel CO2 we have put back into the carbon cycle.

    We have accurate, reliable data for the growth of atmospheric CO2 and for anthropogenic emissions (for details, see Cawley, 2011). The fact that the net natural flux is negative clearly shows that natural uptake has exceeded natural emissions every year for the last fifty years at least, and hence has been opposing, rather than causing the observed rise in atmospheric CO2.

    It is true that the fluxes between the oceans and atmosphere depend on temperature, so all things being equal, one would expect atmospheric CO2 to rise in a warming world.

    However, the thing the fake-skeptics and compulsive liars normally ignore is that CO2 solubility increases with increasing difference in the partial pressures of CO2 between atmosphere and surface waters.

    In the real world, all things are not equal, our emissions have caused a difference in partial pressures, which is increasing the oceanic uptake, which more than compensates for the temperature driven change in fluxes.

    The human-caused origin (anthropogenic) of the measured increase in atmospheric concentrations of CO2 is a cornerstone of predictions of future temperature rises.

    As such, it has come under frequent attack by people who challenge the science of global warming. One thing noteworthy about those attacks is that the full range of evidence supporting the anthropogenic nature of the CO2 increase seems to slip from sight. So what is the full range of supporting evidence?

    There are ten main lines of evidence to be considered:

    1. The start of the growth in CO2 concentration coincides with the start of the industrial revolution, hence anthropogenic;

    2. Increase in CO2 concentration over the long term almost exactly correlates with cumulative anthropogenic emissions, hence anthropogenic;

    3. Annual CO2 concentration growth is less than Annual CO2 emissions, hence anthropogenic; (Link, Link)

    4. Declining C14 ratio indicates the source is very old, hence fossil fuel or volcanic (ie, not oceanic outgassing or a recent biological source);

    5. Declining C13 ratio indicates a biological source, hence not volcanic;

    6. Declining O2 concentration indicate combustion, hence not volcanic;

    7. Partial pressure of CO2 in the ocean is increasing, hence not oceanic outgassing;

    8. Measured CO2 emissions from all (surface and beneath the sea) volcanoes are one-hundredth of anthropogenic CO2 emissions; hence not volcanic;

    9. Known changes in biomass too small by a factor of 10, hence not deforestation; (Link, Link)

    10. Known changes of CO2 concentration with temperature are too small by a factor of 10, hence not ocean outgassing.

    The current, and ongoing, increase in atmospheric carbon dioxide concentration is due to human industrial activities. In scientific circles this is the climatological equivalent of the Earth being round - a fact so plainly obvious and supported by such a vast body of scientific evidence that to question its reality is absurd.

    It quickly becomes clear that it is the humans who have caused the rise in CO2 levels, by burning fossil fuels in the twentieth century. Every other hypothesis makes a host of predictions that do not pass the test of the evidence.

    H/T to Tom Curtis, from which much of the above is sourced.

    Please stay on-topic from now on.  Thousands of threads exist here on virtually every topic related to climate change imaginable.  Use the Search function to find the most appropriate thread and place your questions there.

  13. Adri Norse Fire @510:

    1)

    "If we have verified that CO2 follows the increase of the global temperature in the ice cores with a determined time delay, it is evident that it is not the CO2 that causes the temperature increase, but the opposite."

    As it happens, however, what has been determined over the most recent deglaciation is that 90% of the temperature increase lags the CO2 increase (see final figure in OP, and Shakun et al (2012)).  That is entirely consistent with the standard theory which is that while the deglaciation was triggered by changes in NH insolation due to the Milankovitch cycles, it was then driven by a feedback cycle of greenhouse gases (CO2 and methane) and albedo changes.

    I would be a bizarre form of science that threw out a theory because the data conformed with the expectations from the theory.

    2)

    "But how do you know that CO2 is responsible for current climate changes?"

    A regression of Global Mean Surface Temperature (GMST) against CO2 forcing shows a correlation of 0.9, an R^2 of 0.811, and a temperature change of 0.58 C/(W/m^2), ie, a Transient Climate Responsce (TCR) of 2.14 C per doubling of CO2.  In contrast a similar regression of GMST against Total Solar Irradiance (TSI) shows a correlation of 0.416, an R^2 of 0.173, and a temperature change of 1.77 C/(W/m^2).  Adjusting to the solar forcing, that represents a temperature response of 10.1 C/(W/m^2), or a TCR or 37.3 C per doubling of CO2.

    The high correlation between CO2 forcing and temperature is not due to the CO2 increase being a consequence of temperature increase, both because multiple lines of evidence show the CO2 increase to be due to anthropogenic emissions (as per Daniel Bailey's post @512) and because the correlation between GMST and CO2 forcing (0.9) is higher than the 0.679 correlation between GMST and CO2 concentration.  To reject the dominant role of CO2 forcing in the increase in GMST in this circumstance is to reject that which has strong supporting evidence (CO2 forcing as the cause) in favour of that with only very weak evidence (TSI forcing as the cause); but also to indulge in magical thinking that supposes that like effects (ie, similar values in forcing) are up to 17 times stronger when the cause is solar forcing than when it is CO2 forcing.

    There is much more evidence of the dominant role of CO2 forcing in recent temperature increases than this, and stronger individual items of evidence - but this evidence is very straight forward and easy to understand.  In the end you either accept evidence or you do not.  If you do, you do not have any serious doubt as to the role of the anthropogenic increase in greenhouse gases in the current rapid increase in GMST.

  14. Adri Norse Fire @510: 

    Here's another science-based response to the issue you have raised:


    “Over eight glacial cycles in 650,000 years, global temperature and the amount of CO2 in the atmosphere have gone hand in hand. When temperatures are high, so are CO2 amounts and vice versa. This obvious connection is part of a coupled system in which changes in climate affect CO2 levels, and CO2 levels also change climate. The pacing of these cycles is set by variations in the Earth’s orbit, but their magnitude is strongly affected by greenhouse gas changes and the waxing and waning of the ice sheets.”


    Source: Climate Change: Picturing the Science, Gavin Schmidt and Joshua Wolfe, W.W. Norton Company Ltd, 2009

  15. Based off the carbon dioxide v temp change over 400,000 years graph, it shows for a 80ppm rise in carbon dioxide that the temp increase is 6 degrees C. If you then take Tom Curtis's graph showing todays carbon dioxide level spike which is an increase of 125ppm you can roughly interpolate a future temp rise of around 9 degrees C assuming its linear. This is without even starting to reduce overall global emsiions. This is all assuming co2 causes temp increases(and if it does, humanity has already gone past the point of no return and all this arguing is a waste of time). But it doesnt and I can prove why. If you look at the backsides of the spikes of co2 v temp, you will notice as the suns effect reduces and temp falls, co2 still stays high. If co2 was the driving factor, temp wouldnt suddenly decline, it would plateau(as its a greenhouse remember) and both co2 and temp would come to an equalibrium and fall together. This is not showen to be true based off the historical data.

  16. poncholarpez @515:

    1)  Greenhouse gases account for 46%, and CO2 changes for around 30%, of the temperature change between glacial and interglacial, as shown in the following graph: 

    Based on that, the presumption would be that a 125 ppmv increase in CO2 would drive not a 9 C increase, but a 3 C increase, assuming linearity.  Of course, there is not point in assuming linearity because it is known that temperature responds to the log of CO2 concentration, not linearly.  Factoring that in, the expected equilibrium response (ECS) of the current increase over the preindustrial is about 1.5 C.  To reach the equilibrium response, however, takes decades.  The expected current response is better mapped by the Transient Climate Response (TCR) of about two thirds of the ECS, or about 1 C for the current CO2 concentration.  Of course, the temperature response over the glacial cycle has time for a full equilibrium response rather than just the transient response.

    The upshot is that your entire premise is wrong.

    2)  Moving on from that, because the CO2 response represents only about a third of the total response, it is quite possible that a decline in one of the other factors could lead to a gradual decline in temperature, which leads to a decline in CO2 concentration.  In particular, albedo is likely to increase gradually as NH summer insolation declines as a result of Milankovitch cycles.  

    The upshot is that you have simply demonstrated once again that, as is so often the case, arguments premised on scientists being too stupid to see the obvious merely show the person making the argument to be too ill informed to see what is obvious to those scientists all along.

  17. Eclectic asks elsewhere, with regard to the relative attribution to albedo and ghg contributions to the glacial to interglacial cooling as shown in Hansen and Sato:

    "May I ask you whether the warming-phase figures are similar — or whether the CO2/albedo relationship is asymmetric regarding the actual causation of progressive warming as the planet exits a glacial age (i.e. whether CO2 plays a larger role in the ultimate root cause of the rapid 3-degree warming which terminates the typical glacial age) ?"

    The graph I showed represents the change in radiative forcing and temperatures between the Last Glacial Maximum and the Holocene, ie, over a warming phase.  However, it takes the difference in the values between the two times, and the relative contribution may (indeed, probably) differs at different stages in the process, or by small amounts for different glacial to interglacial (warming) or interglacial to glacial (cooling) transitions.  

    Based on Shakun et al (2012), durring the earliest phase of the most recent glacial to interglacial transition, albedo effects were probably more important than GHG effects, but that means at some stage the GHG effects would have been more important than the albedo effects than is shown in the Hansen and Sato graph.  Otherwise the cumulative effect would not be that shown in their graph.

    Likewise, from the long lag in the previous glacial to interglacial shown in the first graph in the OP, albedo effects were probably more important in the early stages of that transition, with GHG effects becoming more important later on with cumulative contribution from Eemian to LGM likely to approximate to those shown in Hansen and Sato.  That said, lags vary substantially between different transitions, and sometimes though not often CO2 changes precede temperature responses (eg, 325000 years ago in the Vostock graph) - so the exact relative contribution and timing of the contribution must also vary.  In general, however:

    1) Milankovitch effects trigger the temperature response;

    2) Albedo effects seem to follow closely on the Milankovitch effects; and

    3)  GHG effects seem to lag on both, and to lag more in cooling transistions than in warming transitions.

    As to GHG being unimportant, consider this smoothed version of the Vostock graph:

    The smoothing makes clear that the current interglacial is unusual in to respects.  First, in prior interglacials temperatues have declined quite rapidly after the maximum has reached (in geological terms), before dropping through the floor once some threshold is reached.  In contrast, in the Holocene, they have remained near constant.  Second, in prior interglacials, have also declined (though not as rapidly as temperature initially in the Eemian at least).  In contrast, in the Holocene the CO2 concentrations started to decline, and then rose by about 20 ppmv, against the temperature trend.  There is substantial reason to believe that the CO2 increase was due to agricultural practises of preindustrial humans; and that the flat temperatures of the Holocene are due to the temperature increase from the rising CO2 countering the temperature decrease from the known increase in albedo over the same period (due to Milankovitch factors).  (Known increase in albedo because the Arctic was ice free 8000 years ago, and reached a Holocene maximum in sea ice extent in the 19th century.)  The Holocene climate and CO2 record would not have been possible if CO2 had no effect.  Of course, there is far better evidence of the effect of CO2 than this, and I do not expect anybody unwilling to be convinced by that other evidence to be convinced by this.  But it does illustrate that their go to evidence also refutes their case.

  18. Tom Curtis @517

    Thanks for your courteous and prompt reply, especially in view of your workload.   I had been innocently picturing that each of the recent set of glaciations followed a very standardized path, without much variation.  There was an earlier SkS article that linked to a paper showing the Milankovitch orbital fluctuations of the past half-million years, and indicating that in the coming few dozen millennia we would experience a relatively low-eccentricity of orbit, which might have a damping effect on the approach of the next glaciation.   But as you say, Holocene humanity (and its increasing population) would be a more likely explanation for the Holocene's "abnormality".

    Thanks once again, Tom.   And if it's not being too saccharine of me, I'd like to thank you on behalf of all visitors and participants at SkS.   You are a scientific powerhouse in the SkS comments columns.

  19. Tom Curtis. The graph I was quoting in the OP isays it is a direct correlation to historical observed co2 v temp. They rise at the same rate, not at a log offset with an assumed modified result for proportion of co2 making up greenhouse gasses in the atmosphere. If you could accurately subtract other greenhouse gass portion of the temprature into that graph, then you would clearly see that warming trends have no correlation to co2. Very impessive graph though that combined with the feedback given, now further proves my point but in the upside spikes of the graph too. Thanks for that ;)

    The bar graph you used implies that co2 is a warming driver under the greenhouse gasses group, when, this is what is being debated in this thtead, yet it is being taken as gospel that it is?? Furthermore, the bar graph you provided takes no account of water vapour as a greenhouse gass and takes no account of potential cloud cover conditions. Ill informed, nice try.

    Response:

    [JH] Please keep it civil. 

  20. poncholarp @519:

    1)  "The graph I was quoting ....  ...  not at a log offset..."

    The graph plots CO2 and temperature against time.  It does not plot correlation, and if you were to attempt to plot correlation, you would use a scatter plot.  As it happens, the correlation between CO2 concentration and temperature is 0.888 +/- 0.037 using means of 1000 year bins of the data, with bins where one or both data sets had no representatives being excluded.  (The results might differ with other means of dealing with the fact that the actual data do not have CO2 values and deuterium values on the same dates.)  In contrast the correlation of CO2 forcing and temperature is 0.879 +/-0.038.  Both are high, and while (as expected) the CO2 concentration has the higher correlation, both are within error of each other.

    Note that we expect the correlation to be higher for concentration because temperature drives the changes in CO2 concentration, while CO2 forcing only partially drives the temperature over that period.  In contrast, in the modern period, when it is known that temperature is not driving CO2 concentration, we expect CO2 forcing to correlate better with temperature than does CO2 concentration.  And indeed, that is the case.

    In any event the difference between CO2 concentration and CO2 forcing plotted against (in this case the Epica Dome C 800,000 year record) is scarcely noticable to the naked eye:

     

    (Note, the data terminated 24,000 years BP for deuterium, but there was no data for CO2 in the 24,000 - 25,000 years BP bin, hence the first data point is for 25,000 years BP.)

    2)  "If you could accurately subtract..."  What utter tripe, and you know it to be utter tripe because your conditional "If you could" shows that your conclusion that "...you would clearly see that warming trends have no correlation to co2" is simply made up.  As it happens, they also have ice core records of methane and nitrous oxide, and you are simply wrong.  Your made up "fact" is a fiction.

    3)  "Very impessive graph though that ... now further proves my point"  I am very certain it does not, but cannot mount any argument because you have completely failed to provid evidence for this claim.  Given that, it amounts to sloganeering.

    4)  "The bar graph you used implies that co2 is a warming driver... when, this is what is being debated in this thread ..."

    Now, either you are attempting to criticize the standard theory of greenhouse gases and the LGM - which is that temperature responds to the log of CO2, and that CO2 was one of several relevant greenhouse gases, and that changes in albedo had slightly more effect than the combined effect of greenhouse gases.  In that case I do not need to support the graph because it simply presents that theory you are trying to criticize - and shows that you have not accurately presented it.

    Alternatively you are trying to refute a theory of your own concoction that no informed person believes, in which case who cares.  I think, however, that you are trying to pass of the theory of your own concoction as that which climate scientists use, and pretend the refutation of your nonsense thereby refutes thousands of person/years of research. 

    Response:

    [PS] Both of you need to keep it civil. Take a deep breath, ignore provocation and stick to discussing the science.

  21. Your article justifying the IPCC initial panic on Ice Core data which gave rise to concern along the lines of "which came first, the chicken or the egg," or being less frivolous and keeping within the goal posts of "which came first, CO2 or Warming," is nicely handled in describing it much as the God Particle, it being all over the place at one and the same time: "In other words, increasing CO2 levels become both the cause and effect of further warming."

    You then further state, "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." I read this as justification of CO2 being the major influencer as the cause of warming rather than not being a cause - one assumes this is what you are leading us to believe?

    Please correct me and educate me where I am undoubtedly wrong but I thought the Gospel according to the IPCC was that, "In the climate system, CO2 concentration is a forcing, whereas for example, water vapour concentration is a feedback?

    So what exactly is this "positive feedback" or did you mean “positive feedback forcing,” or should I just shut up and admit that I’m not a scientist?

    Yours cordially,
    A Bear with demonstrably little grey matter.

  22. PWL,

    The video attached to the OP directly addresses your questions.  It will be the best way for you to become more scientific.

    The short answer to your question is that at the end of the last Ice Age changes in the Earth's orbit started warming.  the warming released CO2 into the air.  That CO2 caused more warming in a feedback loop.  THus CO2 was both a feedback and a cause of the warming as the ice age ended.

    The situation is different today.  Humans are releasing huge amounts of CO2 into the amosphere.  The CO2 we are releasing is the forcing causing the temperature to rise.  Humans affect the climate in other ways, for example, farming changes how much light is reflected back to space from land, but CO2 is the most important driver of climate.

    At the end of the ice age CO2 was both a forcing and a feedback.  Today CO2 is the primary forcing of climate change.

    The more you read the more you will know.  Keep asking questions about the things you do not understand.

  23. MICHAEL SWEET,

    My thanks for your rapid and courteous reply Sir.

    So basically before the ice core data was interpreted by some as noting that the former IPCC solidly supported claim of "CO2 CAUSES causes global warming" was put in jeopardy, it was felt unnecessary to say "cause and effect."

    And then after some bright wag noted that the ice core data suggested other than what the IPCC had claimed up to a certain date, it was felt necessary to explain it as "cause and effect." And adding into the mix that at the end of the ice age CO2 used to be a forcer and an effector but now it's semi retired back to being a forcer.

    Well that seems perfectly and confusingly acceptable to me. There again when I do jigsaw puzzles I usually use a pair of scissors and a hammer too.

    By the way, I thought we were still in an Ice Age - albeit an inter-glacial one?

    I take it that the CO2 retires from being a feedback during an inter-glacial, shall I?

    Response:

    [RH] Use of all caps is not allowed on SkS (starts to read like yelling).

  24. pwl @523, the very first IPCC report says of the relationship between CO2 and temperature changes between glacial and interglacial, "Variations in carbon dioxide and methane in Ice Age cycles are also very important factors, they served to modify and perhaps to amplify the other forcing factors."   So, from the very first IPCC report, the idea that CO2 was a feedback in the glacial cycles already exists.

    In fact, I can trace the idea further back than that, to at least 1980 when Saltzman and Moritz describe the action of CO2 in a climate model, saying, "Another positive feedback included is due to longwave emissivity changes associated with CO, changes that, in turn, are postulated to arise in response to the variations of mean Ocean temperature Θ."

    The point is that popular presentations, particularly "skepical" presentations often exclude nuance that is found in the scientific literature and IPCC reports.  This may give the appearance that the IPCC is responding to "some bright wag" when popularizers of climate science are merely drawing attention to something that has been in the IPCC account all along.  What has changed is the popular presentation, and that in the face of a misunderstanding that would already have been cleared up from reading the scientific literature or IPCC.  Indeed, it is not unusual to be presented with stunning "new" arguments that merely rehash in an imprecise way a part of a debate that occurred in the scientific literature decades (and in some instances over a century) ago.

  25. Tom Curtis@524

    Thank you for your reply.

    Do you know, I think the best way to solve this whole pro IPCC / anti IPCC Carbon emissions debate and headache would be to just remove all the CO2 from the Earth's atmosphere.

    Once we've done that, there'd be no need for anyone to get all worked up and it wouldn't do that much harm would it. Clearly CO2 is really at the root cause of this whole problem and the sooner we uproot it and get rid of it all, the better.  (snip)

    Response:

    [RH] Before you continue to post, I would highly suggest reading the SkS commenting policies. Please keep your posts to the point and written so that they contribute to a positive, learning conversation.

    Edit: Followup post deleted for moderation complaint. Also, this snipped post has a sarcastic tone not present in Chris Colose's piece. ...Please move on.

  26. I do not understand why no message arrived in my mail, I'm sorry for not responding before.

    Daniel Bailey.

    -It is a joy to see that the conclusions of your "BEST" team coincide with virtually all studies on Antarctic ice cores: "Data from ice core records strongly suggest that the prehistoric carbon dioxide changes were largely a response, ''not a cause'', of temperature changes ''. But, they say: '' However, [...] Seawater has high radiocarbon; Fossil fuels have none. "Forgive my ignorance but how do they know that the radiocarbon is not lost in the process? How do they know that CO2 does not come from other sources that also have low levels of radicarbon? Let me disagree with your best team, but I find their conclusions a bit forced. And they end: "it is clear that it is the CO2 that comes first, not the warming". Well, it is not what your own data show, but I could make some concession for the last century.

    And I think I can rebut some of your 10 main statements:

    1. The beginning of global warming coincides with the end of the small Ice Age, therefore natural;

    2. The stages of higher industrial growth of mankind do not coincide with the increase in temperature.

    3. That does not prove that CO2 produces global warming.

    4. The same.

    5. Again, that only says that the source of co2 has no volcanic origins, but it is not a proof that CO2 produces warming.

    6. Same.

    7. Same.

    8. Same.

    9. Same.

    10. And Same.

    Come on man, my original question was not difficult; Or is it that the basis of global anthropogenic warming is a coincidence?

    Tom Curtis.

    '' [...] Then it was driven by a feedback cycle of greenhouse gases (CO2 and methane) ''. Only? Where are the biggest greenhouse gases in the atmosphere? Like water vapor, for example. Secondly, these are correlations always based on recent times. But the only certainty is that ice cores are not subject to interpretations or complicated mathematical operations that can be manipulated. Anyway, allow me the freedom to doubt the credibility of those correlations you have shown.

    John Hartz.

    Again, how do you know that CO2 is responsible for the observed warming since the end of the small Ice Age? The only way CO2 can influence climate is through the greenhouse effect, but CO2 is only a minor gas between greenhouse gases and the amount of CO2 produced by man is an even smaller percentage. How do you know that the rest of the greenhouse gases have nothing to do with it?

  27. Adri Norse Fire @526 :

    I am sorry to hear that no message arrived at your mail.  Is it possible that you have got your pen-names mixed up for this occasion?

    On your point No. 1 (addressed to Daniel Bailey) :- Why do you think the present rapid global warming must be natural, simply because its beginning coincides (roughly) with the ending of the Little Ice Age ?

    Your argument seems to be a logical non-sequitur.

    Can you explain your thinking? 

  28. Eclectic I still do not know what the problem is, don't worry about that. (I think the web does not allow that option, but I'm not sure anyway)

    Of course, given that the present interglacial period has had shorter phases of warm and cold periods occurring on a regular basis, it is very plausible that the centuries after the end of the small Ice Age the temperature would stabilize again. Does it seem very logical?

  29. Adri... First of all, it seems as though you're working very hard to reject the established scientific understanding on these points, rather than working to try to actually understand them. Skepticism is a good thing when it's properly applied. That requires that you first learn the fundamental science.

    Several folks have patiently explained the science and the article you posting on also explains it. But you've failed to acknowledge that you grasp what's being said and are, instead, compounding your misunderstanding with additional incorrect comments. 

    We see exactly this pattern over and over here at SkS. I'm very interested to get down to why this occurs. 

    Why do you think you're so dismissive of the science? 

  30. Adri Norse Fire @526, with respect to your response to Daniel Bailey, when introducing the list of 10 points to which you respond, he wrote


    "The human-caused origin (anthropogenic) of the measured increase in atmospheric concentrations of CO2 is a cornerstone of predictions of future temperature rises.

    As such, it has come under frequent attack by people who challenge the science of global warming. One thing noteworthy about those attacks is that the full range of evidence supporting the anthropogenic nature of the CO2 increase seems to slip from sight. So what is the full range of supporting evidence?

    There are ten main lines of evidence to be considered:"

    (My emphasis)


    It is quite clear, then, that he was discussing evidence that the CO2 increase over the 19th-21st century was anthropogenic in origin, not the distinct claim that the temperature rise was also anthropogenic in origin.  As such, your repeated iterations of "That does not prove that CO2 produces global warming" or variants is simply non-responsive.  You have conveniently shown his evidence to be "irrelevant" by treating it as addressing of something it was not adduced in support of.

    What is worse, you ask, "How do they know that CO2 does not come from other sources that also have low levels of radicarbon?"  But or course, Daniel Bailey has already answered that question with 10 lines of evidence.  So, your misapplication of the 10 lines of evidence serves you two purposes - both to make them easy to refute as irrelevant to the question they did not address; but also to treat them as not having addressed that question so that you can still consider it open.

    With regard to your response to me:


    "'' [...] Then it was driven by a feedback cycle of greenhouse gases (CO2 and methane) ''. Only?"


    Of course not "only", but only those directly relevant to the discussion.  You are directly denying that a CO2 and CH3 greenhouse effect can be a feedback on the glacial cycle.  Evidence that the theory you are opposing without understanding incorporates such a feedback is, therefore, relevant, as is the evidence that such a feedback exists.

    Actually, the correlations are not always based on recent times.  If you want the correlations over 800,000 years of glacial cycle, see point 1 @520 above.  You can ignore the correlations if you wish, but they are evidence, no matter how much you wish to not see it.

    Finally, I will note that "recovery from the Little Ice Age" is a description of what the temperature does over a period ending about 1850.  It is not an explanation of that warming.  You do not explain things simply by redescribing them in different language.  Now, if you ever come across a theory of what caused the general warming in the century prior to industiralization took of, you are welcome to try and show that it explains the warming in the 20th century as well.  But absent that theory, your playing rhetorical games when you invoke a "recovery from the LIA".  You are not practising, or expounding science.

  31. @ Adri Norse Fire #526:

    I accept the overwhelming and ever-growing body of scientific evidence about manmade climate change. Why do you deny it?

  32. Well, I did not mean to sound pedantic. First of all I want to say that I am not a native speaker of English, I am using the translator to talk to you ... and that may cause some misunderstanding. Anyway, I apologize.

    Rob Honeycutt

    I am not working hard to deny anyone, what I say is what I have seen in documentaries and in magazines, that's all. I'm not an old scientist. But unlike you, Rob, I do not see that the establishment in which you believe has an indestructible foundation, this is not like the theory of gravity, there is a plenty of people who are also scientists who disagree with you In this subject or with the supposed orthodoxy to which you refer.

    '' Why do you think you're dismissive of the science? ''

    I do not despise science, I think that until now my arguments have not been ideological but scientific data that obviously are within the reach of all.

    Tom Curtis

    I want to remember that my first comment was a few months ago, having that in perspective; You're right when you say that my last answer does not exactly respond to his response, but I was thinking in the background of the whole conversation that was whether CO2 and therefore human industrial activity are causing the global rise in temperature.

    ''What is worse, you ask, "How do they know that CO2 does not come from other sources that also have low levels of radicarbon But or course, Daniel Bailey has already answered that question with 10 lines of evidence.'' He didn't and this answer was not addressed to him; That's why I said "sorry for my ignorance," because if you can not know how much low-radiocarbon CO2 comes from other natural sources due to lack of studies on the subject or for any reason, how can you faithfully calculate the amount Of CO2 emitted by human industrial activity? I mean, we can distinguish that something has different properties, but we do not seem to know how these properties work or whether they hold them through their natural cycles which is an imperative for the final calculation.

    I did not say that CO2 or CH3 does not produce a greenhouse effect, but the feedback effect of CO2 and other minor gases is irrelevant to climate compared to other greenhouse gases.

    If you like correlations so much why do not you look for some of the temperature and CO2 for the last 10,000 years? Does this correlation count as evidence?

    http://www.lunarplanner.com/SolarCycles-images/Climate-Timeline-10000yrs.png

    http://www.ferdinand-engelbeen.be/klimaat/klim_img/antarctic_cores_800kyr.jpg

    And what about this chart?

    http://kabarkampus.com/wp-content/uploads/2014/04/Dede-Prabowo-Wiguna_ilustrasi-1.jpg

    http://s3.amazonaws.com/wboc-digital/production/sites/wboc-weather/wp-content/uploads/2016/04/28214154/Capture21.png

    The question is whether we have the highest concentration of atmospheric CO2 in 800,000 years, without going further, why the current temperature is 1.5 ° lower than the medieval warm period?

    ''Finally, I will note that "recovery from the Little Ice Age" is a description of what the temperature does over a period ending about 1850. It is not an explanation of that warming.'' Indeed it is an assumption that the rise in temperature was related to the Little Ice Age. This also explains the warming of the 20th century. Someday I'll explain my crazy theory, but not right now. I apologize again.

    John Hartz

    Only me?

  33. Adri Norse Fire @532.

    You say you use "scientific data." The four graphs you present do not provide scientific data of temperature. Instead the one temperature graph you do present is schematic, and also flat wrong. It says it plots Northern Hemisphere temperatures yet shows less than 0.1ºC increase in NH temperature since 1850. HadCRUT4 (which is known to underestimate the warming due to poor Arctic coverage) puts the NH temperature increase since 1850 at 1.05ºC while GISTEMP (which provides a more realistic assessment of Arctic temperatures) puts the rise since 1880 as 1.25ºC. Note also that this graph you present does not support your assertion that "the current temperature is 1.5 ° lower than the medieval warm period."(And that stands whatever the º you intend.)

  34. Adri...  Well, unfortunately, man-made climate change is very much is like the theory of gravity in terms of how solid the science is. 

    The point I'm trying to make is this. You currently have a very poor understanding of the science. By your own admission, what you do believe is not based in actual scientific research, but is derived from documentaries and magazines.

    What I'm trying to understand is, why? 

    Why would you believe non-scientific sources over actual published science?

  35. Ardi, I would second RH comment. When you see conflicting information from various sources, what are your processes in determining what information you trust? What raises a red-flag when something comes from a science source?

  36. Adri Norse Fire @532, first, let me say you are coping quite well with the language difference given that you are using a machine translator.


    "''What is worse, you ask, "How do they know that CO2 does not come from other sources that also have low levels of radicarbon But or course, Daniel Bailey has already answered that question with 10 lines of evidence.'' He didn't and this answer was not addressed to him"


    On the contrary, five of the ten lines of evidence falsify the theory that the increase in CO2 in modern times is a consequence of increased vulcansim; and a sixth renders it unlikely:

     As fossil fuel and volcanic CO2 are the only C14 - free sources of carbon on the Earth, that precludes the origin being a C14 free source other than fossil fuels.

    I am not sure what you meant by "this answer was not addressed to him" given that the sentence I quoted clearly came from the section of your comment headed "Daniel Bailey".  I assume it is an inaccurate translation.


    "I did not say that CO2 or CH3 does not produce a greenhouse effect, but the feedback effect of CO2 and other minor gases is irrelevant to climate compared to other greenhouse gases."


    It is true that water vapour is a significant feedback on any warming.  However, it contributes approximately 1C of warming for each 1 C contributed from another source.  That means that for the glacial/interglacial cycle, including water vapour, albedo effects will have most likely contributed <30% directly, CO2 and CH4 <25%, with H2O most likely contributing <45%.  Less than, because there are other short term feedbacks that are most likely to contribute about 0.5 C for each 1 C of direct warming, but may contribute 4 times that amount, but may have been a negative feedback.

    Firstly, I will note that 6 - 25% contribution from CO2 and CH4 (once we account for the effect of water vapour) is not a negligible contribution.

    Secondly, I will further note that H2O has a very short time to return to equilibrium in the atmosphere (weeks), so that its total atmospheric contribution is almost entirely governed by temperature.  That means when we wish to determine the effect of an increase in CO2 concentration on the Earth's temperature, we can treat H2O as a feedback - and need not track it independently.  That is particularly important for graphs such as this one:

    It is well known that the direct temperature effect of a change in forcing is about 1 C to 1.2 C per 3.7 W/m^2 change, and hence about 0.8 to 0.9 C for the change in forcing from last glacial maximum to the holocene.  The calculation of the implied sensitivity, therefore, is not an attempt to determine that direct effect, but to determine the result of the direct temperature effect plus all short term feedbacks, including H2O.  That turns out to be about 2.8 C per 3.7 W/m^2.

    Because I (and others) understand the purpose examining the causes of the difference in temperature between the last glacial maximum and the holocene, we do not bother mentioning the details about components of the short term feedbacks.  I will grant that when talking with a popular audience, who are not aware of the reasons for focussing on CO2 and change in glacial ice extent, that is a mistake.  We should clarrify the role of short term feedbacks, and why we are focussing on CO2 (as I have now done).


    "If you like correlations so much why do not you look for some of the temperature and CO2 for the last 10,000 years? Does this correlation count as evidence?"


    First, if you want to be taken seriously in a scientific discussion, don't source evidence from astrology sites, as you have done with that first chart.  Granted the author of that site attributes the chart to a climate scientist (Schoenwiese) without specification as to year, or publication.  Fortunately the chart has been examined as an example of the misuse of scientific charts by climate "skeptics" (Schneider et al 2014).  The chart is from Schoenwiese 1995, and based on Daansgard (1984) (published online in 2013).  Schneider et al (2014) comment:


    "many authors of skeptical media (for example Avery, 2009, and Vahrenholt und Lüning, 2012) fail to mention that this temperature estimate is based on an ice-core record from Greenland and may thus not be representative of global temperatures."


    Of course, in your version it is labelled Northern Hemisphere temperatures, not global temperatures.  The point still stands, however.  A Greenland ice core no more shows Northern Hemisphere temperatures by itself than does a thermometer in Moscow show temperatures in Tucson, Arizona.  It can be used (as Daansgard used it) as an indication of North Atlantic temperatures, but beyond the North Atlantic, its accuracy as a temperature index will rapidly fall.

    Schneider et al go on:


    "Most importantly, in Schönwiese's 1995 version the current and near future temperature changes are included. The recent warming goes far beyond the historic warm periods of the last 12000 years and should therefore have been included in the graph."

    (My emphasis)


    You should recognize that yourself.  Taken at face value, the chart indicates that the Little Ice Age terminated 400 years ago.  If we allow a more recent (circa 1850) termination then we must, according to that chart, acknowledge that for most of the LIA it was as warm as the peak of the Medieval Warm Period; and of course, that temperatures have since risen significantly above that peak.

    Finally, here is a chart which has a fair claim to represent global holocene temperatures (but note caveats):

     Note that 2004 is significantly warmer than any period prior to 1900, and that it has warmed appreciably since then.

    All of this may be a side issue, but I am unsure as to what point you are trying to make with two charts of CO2 concentration over the last 800,000 years, or the chart of CO2 concentration over the Holocene.


    "why the current temperature is 1.5 ° lower than the medieval warm period?"


    It isn't.  See chart above.

    Response:

    [PS] added obvious but important missing word.

  37. Tom Curtis @536,

    For completeness, the origin of the temperature graph linked by  Adri Norse Fire@532 is (as you say) discussed by Schneider et al (2014)  who trace the actual graphic back to Goreham, Steve. (2012) 'The Mad, Mad, Mad World of Climatism.' New Lenox Books. Note that an earlier origin of the actual graphic is the denialist web-paper Archibald, David. (2007) 'The Past and Future of Climate.'
    And the Schoenwiese (1995) graphic on which it is based can be seen here.

  38. MA Rodger @537, interesting.  From the last link, the translated text after the figure says:

    "Climate development of the last 10,000 years (From: http://lbs.hh.schule.de/index.phtml?site=themen.klima)
    It should be noted that "the current atmospheric temperature at 15.5 ° C is the" today "(right edge of the figure at" 0 "), according to climate scenarios (which are not a forecast!) Over the next 100 years ° C. "Today" is still under the so-called climate optimum of the Middle Ages and the Roman era. Note also that these periods, which were quite warmer than today, were regarded as optimal, whereas today's temperature rise is often classified as dangerous - which, however, it will probably be in the projection to 2100."

    (Courtesy of Google translate)

    That is quited different from the text within the figure, and likely comes from a different source.  The full spike up to 19 C is undoubtedly a projection, so that much is correct.  It is unclear, however, what the temperatures represent.  Nor is it clear that the full spike is projections.  Taking the plateau before the spike as being the 1750-1900 average, then observed global temperatures were 0.6 C warmer than that at time of publication, and have since increased another 0.4 C.  How much of that would show at the resolution of the chart I do not know.  Ignoring resolution issues, it is warmer than the temperatures shown for the MWP and Roman Optimum.  Further, the proxy used turns out to be the Camp Century ice core (from North West Greenland), and Greenland is almost unique across the globe in meing warmer than the 1961-1990 average:

    Projecting a Greenland Ice Core temperature as a global, or even Northern Hemisphere average is completely unjustified.

    It remains, however, that part at least of Schneider et al's critique that I quoted above is dubious at best.  Trimming projections is certainly justifiable, and it is ambiguous how much of the spike is projection, and how much direct observation.

  39. Tom Curtis @538,

    The other point of note is how the graphic has slowly lost almost all the warming of recent decades as each denialist has manipulated the image.

    In the 2006 Wehry version (this a different PDF version of the same thing) you display @538 (& we can but presume this is a faithful reproduction of the Schoenwiese (1995) graphic), the trace is four or five pixels broad which is about 100 years of horizontal axis and 0.025ºC vertically. But it does show an edge disappearing into the vertical post-2000 temperature rise which scales to 15.9ºC. By the time it appears in the 2007 Archibald paper, the edge has dropped to 15.75ºC. Then it features in the 2009 Denis Avery version by which tme it has dropped more to 15.6ºC and in the most recent version introduced @532, the 2014 NA Florenza version it has dropped again to 15.55ºC.

    Strangely, that feature so loved by the Little Ice Age Revivaists maintains its top edge at 15.5ºC throughout this process of hidden decline.

  40. MA Rodger
    What I meant was that I am using scientific data in the sense that my arguments are exclusively in scientific terms, regardless of whether my claims are true or not.

    Rob Honeycutt/scaddenp

    Why do you say that I am not using scientific data? Do not scientific documentaries and scientific journals make scientific knowledge public? Is that knowledge invalid? So everything the public knows is a lie ... including global warming, right?

    When I said that the current temperature was below about 1.5 ° I relied on a documentary where a gentleman, I think he was Norwegian who was in the Antarctic and claimed that the ice cores of his own research proved that the temperature was 1.5 ° higher to the present during the Medieval Warm Period. But also, it is known that historically the peoples of contemporaries of that time recorded that in Greenland agriculture was possible, among other things, etc. I think it is out of place to think that everything is part of a subtle conspiracy, of wich I am part, of course.

    Tom Curtis

    Thank you.

    Okay, this is the kind of thing I said that misinterpretations were likely to occur. I have not said that the current increase in CO2 comes from volcanoes. And you're right, I thought it was a question I asked John Hartz, it's my fault. Sorry. Again you are right, I have no problem accepting that the recent increase in CO2 is due to human industrial activity, although there are other scientists who deny that conclusion with their own data, since from the beginning I said CO2 does not cause the current global warming by greenhouse effect or by feedback. I just do not see it likely. Sources I read some time ago claimed that water vapor is the main greenhouse gas and that it is responsible for two-thirds of the natural greenhouse effect. As you say very well it is a stable process, but the Earth makes all kinds of movements and we do not really know how much impact the orbital changes have on the greenhouse effect and Milankovich attributed the intervals of glacial periods and warm periods to the orbital changes. Which is no small thing in terms of climate.

    Sorry for putting that graphic, I knew it was just a very nice graphic. I have taken note.

    Well, as I said above the Antarctic data show also, that the temperature was higher than the current approximately 1.5 degrees during the Medieval Warm Period.

    "All of this may be a side issue, but I am unsure as to what point you are trying to make with two charts of CO2 concentration over the last 800,000 years, or the chart of CO2 concentration over the Holocene." Why the current Temperature is 1.5 ° lower than the medieval warm period? " It is not. See chart above.'' Yes it was, why do you think it was called the Medieval Warm Period? Let's look at some recent research:

    Working with a 2.5-foot-long core of peat in Penido Vello (Galicia, Spain) Martinez-Cortizas et al. (1999), a Mercury deposit record was extracted that extended until 4000 years ago. The work revealed that warm periods were characterized by a low accumulation of mercury. They also standardized the variables extracted and related them to the temperatures of the last 30 years. The work revealed that the medieval warm period in the northwest of Spain was 1.5 ° C warmer than the current one and that the average temperature of the warm Roman period was in no less than 2 ° C. Even a period of 80 years in the Middle Ages with average temperatures 3 ° higher than the current ones.

    Desprat et al. (2003) studied the climatic variability of the last three millennia through the sediments of the Vigo estuary, clearly recognizing three warm periods and three cold periods, without seeming to be a relation between the variability and the increase of carbon dioxide. The authors concluded that the solar radiative balance and the ocean circulation seem to be the main mechanisms that force these cyclical variations in the Peninsula.

    Pla and Catalan (2005) analyzing sediments of chrysophytes in more than 100 lakes of the Pyrenees reproduced a record of winter and spring temperatures during the Holocene. Warm and cold oscillations were recognized for these oscillations over the past few millennia. From the Medieval period it is deduced that the temperatures were then 0.25 ° higher than the current ones.

    Here a chart: http://www.biocab.org/Holocene-Delta_T_and_Delta_CO2.jpg And as I liked the dissection you did to the other here is more: http://www.biocab.org/Boreholes_Reconstruction.jpg http://3.bp.blogspot.com/_H07QGNhZQzA/S_gGpyDlDQI/AAAAAAAAAHw/ADQvLwN-9U0/s1600/temperaturas+%C3%BAltimos+2000+a%C3%B1os.jpg http://www.biocab.org/Holocene_Delta_T_and_Delta_CO2_Full.jpg

    ''Of course, in your version it is labelled Northern Hemisphere temperatures, not global temperatures. The point still stands, however. A Greenland ice core no more shows Northern Hemisphere temperatures by itself than does a thermometer in Moscow show temperatures in Tucson, Arizona.'' The question then remains valid, but to avoid falling into the little trick of geography I will rephrase: Why the current temperature of Spain is lower (0,25º - 1,5º) than the Spain's Medieval Warm Period, if the current concentrations of atmospheric CO2 in Spain is higher without any doubt?

    (Can we extend the geographical scope to the Mediterranean and even Europe? I do not know; http://science.sciencemag.org/content/291/5508/1497 , http://science.sciencemag.org/content/342/6158/617)

    --And someone asked me why I'm so skeptical or something--

    Well, it is not very difficult to be a skeptic of anything since we have been able to see everything from the millionaire Red Cross scam in Haiti after the earthquake to hear the Greenpeace co-founder say that this organization has become a corrupt gang and then you see scandals with emails and what some IPCC scientists say, and so on. When I saw the Al Gore's documentary I believed it and when I saw the documentary of The Great Scam of Climate Change, I also believed it. So we must be very careful not to be deceived by the official tone, as some have pointed out: http://joannenova.com.au/2010/10/is-the-western-climate-establishment-corrupt-part-4-past-temperatures/

    MA Rodger

    It's funny that you mention sidelong to the ''Little Ice Age revivalists'' because according to NASA members, this very century we can face a solar minimum such as the Maunder Minimum or the Dalton Minimum and presumably a new Little Ice Age. Here's a link: http://www.forbes.com/sites/peterferrara/2013/05/26/to-the-horror-of-global-warming-alarmists-global-cooling-is-here/#5c8c582669bb

    Response:

    [JH] Sloganeering snipped.

  41. Tom Curtis 

    I'm a bit confused with the image you've shown me, the image is composed of a large map and a small one so what are the real data?

    As far as I have been able to investigate the large image plots ice core data, covering the past 11,700 years, where does the small figure come from?

    Because the main one points to periods of the Holocene with higher temperature than now. So?

  42. Adri...  From the warning snip portion of your comment at 540 I think we can gather that "dismissiveness" (as I framed it) is based in distrust of government. You can correct me if I'm wrong. 

    I can promise you, you're interpretting the science very wrong. Everyone here at Skeptical Science has been through this a 100 times before. What we find is, as we explain the science, people like you are generally driven further into denial. And as you get more and more frustrated with not getting the answers you prefer, you end up getting angry and frustrated, and we ultimately have to delete your access to comment.

    We can start going through the science if you like, but if you want to avoid this predictable outcome, you would have to bring an open mind to the conversation. 

    I know it's probably very hard for you to see the difference, but many of the sources you're using are not about the science. Biocab.com, Jonova.com... These are websites that do not present the actual scientific research. They're designed to confuse. And they do a very good job of that.

  43. Adri Norse Fire @541,

    The graphics you present do not support your assertions of a toastie warm MWP. In truth, they are a bit of a joke.

    The first graphic Change of T & Change of CO2 Holocene Epoch is not supported by the document it says it sources for temperature data - Broecker (2001). While this paper itself is old and in many respects speculative, it does set its position out that "Holocene temperature fluctuations ... were probably less than 1°C." So for this graphic you present to show fluctuations of 8°C puts it quickly in the bin.

    The second graphic plots a tiny part of one of two a Greenland borehole temperature reconstruction from Dahl-Jensen (1998) but the graphic for some reason cites a secondary source (Bond et al 2001). The other trace on this graphic is called Yang-Delta T but what this is plotting is not entirely clear. I would assume it is the 'weighted' China trace from figure 3 in Yang et al (2002) but there appears to have been some fiddling with this data in the most recent period plotted.

    The third graphic is simply figure 2 from Loehle & McCulloch (2008) which presents a global temperature reconstruction to 1935. Note the peak of the MWP sits just 0.5°C above the 1935 level. Thinks - I wonder what has happened to global temperatures since 1935?

    The final graphic is another stab at Holocene temperature & CO2 levels with various temperature reconstructions presented (including the borehole data used in the first graphic above) citing Bond et al (2001) again. It certainly is plotting out the bottom two traces from fig 5A in the paper but using the wrong x-axis. Of the other two traces presented, one does seem to be using the x-axis properly but where it is sourced is not at all evident. And as a parting shot at this rubbish, note that the CO2 trace in this graphic is saying CO2 topped 300ppm in about 1780AD, assuming the grapher managed to plot it against the x-axis correctly. If the x-axis is wrong, the y-axis is also up the spout as well.

  44. Adri Norse Fire @541, the graph (not map) that I showed as the third image @536 is the simple mean of:

    The following data sources were used in constructing the main plot:

    1. (dark blue) Sediment core ODP 658, interpreted sea surface temperature, Eastern Tropical Atlantic: M. Zhao, N. A. S. Beveridge, N. J. Shackleton, M. Sarnthein, and G. Eglinton. "Molecular stratigraphy of cores off northwest Africa: Sea surface temperature history over the last 80 ka". Paleoceanography 10 (3): 661-675. doi:10.1029/94PA03354
    2. (blue) Vostok ice core, interpreted paleotemperature, Central Antarctica: Petit J. R., Jouzel J., Raynaud D., Barkov N. I., Barnola J. M., Basile I., Bender M., Chappellaz J., Davis J., Delaygue G., Delmotte M., Kotlyakov V. M., Legrand M., Lipenkov V., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M.. "Climate and Atmospheric History of the Past 420,000 years from the Vostok Ice Core, Antarctica". Nature 399: 429-436. doi:10.1038/20859
    3. (light blue) GISP2 ice core, interpreted paleotemperature, Greenland: Alley, R. B.. Quaternary Science Reviews. doi:10.1016/S0277-3791(99)00062-1
    4. (green) Kilimanjaro ice core, δ18O, Eastern Central Africa: Thompson, L. G., E. Mosley-Thompson, M. E. Davis, K. A. Henderson, H. H. Brecher, V. S. Zagorodnov, T. A. Mashiotta, P.-N. Lin, V. N. Mikhalenko, D. R. Hardy, and J. Beer. "Kilimanjaro Ice Core Records: Evidence of Holocene Climate Change in Tropical Africa". Science 298 (5593): 589-593. doi:10.1126/science.1073198
    5. (yellow) Sediment core PL07-39PC, interpreted sea surface temperature, North Atlantic: Lea, D. W., D. K. Pak, L. C. Peterson, and K. A. Hughen (2003). "Synchroneity of tropical and high-latitude Atlantic temperatures over the last glacial termination". Science 301 (5638): 1361-1364. doi:10.1126/science.1088470
    6. (orange) Pollen distributions, interpreted temperature, Europe: B. A. S. Davis, S. Brewer, A. C. Stevenson, J. Guiot (2003). Quaternary Science Reviews 22: 1701-1716. doi:10.1016/S0277-3791(03)00173-2
    7. (red) EPICA ice core, δDeuterium, Central Antarctica: EPICA community members (2004). "Eight glacial cycles from an Antarctic ice core". Nature 429 (6992): 623-628. doi:10.1038/nature02599
    8. (dark red) Composite sediment cores, interpreted sea surface temperature, Western Tropical Pacific: L. D. Stott, K. G. Cannariato, R. Thunell, G. H. Haug, A. Koutavas, and S. Lund (2004). "Decline of surface temperature and salinity in the western tropical Pacific Ocean in the Holocene epoch". Nature 431: 56-59. doi:10.1038/nature02903

    It shows the individual proxies in the background.

    The inset shows the following temperature reconstructions over the last 2000 years:

    1. (orange 200-1995): P. D. Jones and M. E. Mann (2004). "Climate Over Past Millennia". Reviews of Geophysics 42. doi:10.1029/2003RG000143
    2. (red-orange 1500-1980): S. Huang (2004). "Merging Information from Different Resources for New Insights into Climate Change in the Past and Future". Geophys. Res Lett. 31: L13205. doi:10.1029/2004GL019781
    3. (red 1-1979): A. Moberg, D. M. Sonechkin, K. Holmgren, N. M. Datsenko and W. Karlén (2005). "Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data". Nature 443: 613-617. doi:10.1038/nature03265
    4. (thin black line 1856-2004): Instrumental global annual data set TaveGL2v [2]: P. D. Jones and A. Moberg (2003). "Hemispheric and large-scale surface air temperature variations: An extensive revision and an update to 2001". Journal of Climate 16: 206-223.

    Over the last 2000 years, the reconstructions are to be preferred, as each uses more than 8 proxies, but there is little difference between the mean of those reconstructions and the mean of the 8 proxies over that period.

    Further details about the graph are here.

    Almost any modern multi-proxy temperature reconstruction is preferable to taking the value of a single site, or just a few.  The one exception is Loehle and McCulloch (which you use).  That is because they use a heavilly biased sample of proxies but then take a simple mean of those proxies.  As I explain elsewhere, this is equivalent to assuming that "...that 66.7% of the Earths Surface is in the NH extratropics, 22.2% in the tropics, and just 11.1% in the SH extratropics".  Probably the best, and certainly the one using the most proxies, is that from the PAGES2000 consortium, shown here compared to four recent reconstructions (top of panel):

     

  45. I find it worrying that you would uncritically accept a comment from a TV documentary and assume that it invalidates the science. Misinformation organisations make documentaries to confuse eg "Great global warming swindle", and "climate hustle" which misrepresent science for the gulliable. As has been shown above by Tom and MA Rogers, the sources you have been trusting are not reliable and in fact are doctoring the truth. And you and many others have fallen for it. It is extremely hard to have a discussion when misinformation is uncritically accepted and hard-core, peer-reviewed, widely accepted science papers are treated as unreliable. As Rob says, it implies a strong bias against science. You must have searched some very dubious sources to find these and yet trust them rather than the IPCC expert review of published science.

    When shown that your evidence is invalid, do you change your mind or go frantically searching for confirmation of your bias from yet more dubious sources?

    Is there actually any point in us discussing data with you? In your own mind, what data would cause you to change your position?

    Also, just make sure that you do understand the extent of agriculture in Greenland.

  46. Adri Norse Fire @540

    You mention a New little ice age, coming in the next few years and decades.   That is the assertion by Mr Peter Ferrara in Forbes Magazine in 2013 (the link supplied by you).

    Since 2013, the world has had its three hottest years in recorded history ( 2014 / 2015 / 2016 ).    And there is absolutely no sign that Mr Ferrara's assertion could become true.   His assertion is total Unsinn (as the Germans say).   Total nonsense.

    Adri, you should not be surprised to find Unsinn coming from Mr Ferrara.   He is a lawyer and a professional propagandist and an Amerikaner . . . a truly toxic combination!!   Mr Ferrara is paid to give you Dreck instead of Wahrheit / Sanningen / Truth.  And it is the same with JoanneNova.

    Adri, please attempt to be scientific with your thinking.   When you wish to assess the health of a forest, then you should look at the health of all the trees - not simply look at the healthiest 4 trees which you can find to please you.

  47. Rob Honeycutt

    You're right. I simply answered a question that alluded to my convictions or motivations, but I understand the censorship, I do not set the rules, much less want to change them. And I can assure you that I am not confused, annoyed or angry with any of you who are answering me and I think the conversation so far has been very correct. We are going through the path of science, you believe that what I say is not science because they are sources with which you are not familiar, I will not deny that some of the data I have mentioned come from sources that are openly against anthropogenic climate change and may be biased, but you can not deny that you are using an ad hominem fallacy as the truth of their arguments does not imply a direct relationship with their personal convictions.

    It's like saying, the sky is not blue because Stalin said it was blue. In the end we refer to scientific research, as I put above.

    MA Rodger

    I do not know if it's a good way to discredit me by supposing that those graphics are maliciously manipulated, that they are biased or that they are directly garbage.

    <I wonder what has happened to global temperatures since 1935?> Me too.

    Tom Curtis

    <Probably the best, and certainly the one using the most proxies, is that from the PAGES2000 consortium,>

    As you say about the reconstruction of Loehle and McCulloch, the reconstruction of PAGES2000 consortium is also a biased reconstruction since it has many more proxies in some areas than others as we can see. It is true that for the average global temperatures it is necessary to perform tests on different continents, but it is not necessary when we are talking about a particular region. So I wonder where the investigations of the four reproductions above were made, (whether global or regional) because they are closer to me than to you. And according to the graph of PAGES2000 consortium, you must recognize that in the last 2,000 years there have been periods, at least as warm as the current one.

    scaddenp

    <I find it worrying that you would uncritically accept a comment from a TV documentary and assume that it invalidates the science.>

    Is it not science? When Jane Goodall is talking in a documentary about the behavior of chimpanzees is not science?

    The IPCC review? Is it not true that there are a large number of non-scientific personnel among the IPCC? And then, why only the IPCC?

    <Is there actually any point in us discussing data with you? In your own mind, what data would you change?> Of course, you can convince me if what you say can be scientifically tested directly and not based on an assumption. Because if we agree that the truth of this subject depends on assumptions because it can not be scientifically demonstrated directly, then as long as we both have different assumptions we have become believers of our own conclusions. So when you can raise the temperature of a huge biosphere box by adding CO2, I'll believe you.

    <Also, just make sure that you do understand the extent of agriculture in Greenland.> I find the link very interesting, but I think you have not noticed some comments below.

    Eclectic

    <Since 2013, the world has had its three hottest years in recorded history ( 2014 / 2015 / 2016 ).>

    Really? Can you tell me the degree of difference between those years? Can you give me more information about these investigations? I would appreciate it. I have never been a detractor of global warming, but I did not know that it was so marked, especially by the cold waves that have lashed Europe lately.

    But going back to the subject, I do not really know what an 'Amerikaner means', but these statements do not come from Mr. Ferrara, (by the way you were making the ad hominem fallacy an art) come from NASA scientists and others. And especially of Russian scientists of whom I can not remember the name now. The theory is essentially that solar observations are increasingly recording fewer sunspots and it is thought that solar cycle 25 or 26 will practically have no stains, a event that has precedents +200 years ago where especially the Maunder Minimum coincided with the colder phase of the Little Ice Age. They believe that something like a new short cold period can happen between 2030 and 2050 and it seems to me, that nobody should be underestimated, even though they have worked as lawyers and 'propagandists'.

    1.- Link, NASA: http://www.thedailysheeple.com/nasa-admits-solar-cycle-is-the-weakest-in-200-years-the-link-between-sunspots-global-cooling-and-agenda-21_112013

    2.- Link, (independent?): https://www.vencoreweather.com/blog/2016/6/23/1015-am-the-sun-goes-blank-again-during-the-weakest-solar-cycle-in-more-than-a-century

  48. And Tom Curtis, thanks for the info. I almost forget it.

  49. Adri Norse Fire @548, when you have different numbers of proxies in different areas, you can either  take a simple mean (as did Loehle and McCulloch), or you can divide the globe into different areas, determine the temperature for each individual area from the proxies within it, and then determine the global temperature by taking an area weighted mean of the reconstructed temperatues for each area.  There are a variety of other techniques which approximate to the effects of one or the other.  If you do the first of these, you get a biased temperature record.  If you do the second, you get an unbiased temperature record, but with some regional temperatures being more reliable than the other.  What was done by the PAGES 2000 project approximated to the second method.

  50. Adri Norse Fire @549, your discussion is becoming increasingly wide ranging, and off topic.  I am sure the moderators would appreciate your taking the various points to their most appropriate threads.  In particular, where you say,

    "The theory is essentially that solar observations are increasingly recording fewer sunspots and it is thought that solar cycle 25 or 26 will practically have no stains, a event that has precedents +200 years ago where especially the Maunder Minimum coincided with the colder phase of the Little Ice Age."

    You should read, and take further discussion to this article.

    Discussion of the MWP should be taken to one of numerous threads devoted to it, or that on Pages 2k.  That includes discussion of farming in Greenland, although this thread would be more apt.  Discussion of Holocene temperatures should probably be taken to a thread on Marcott et al.  

     

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