The World Meteorological Organization (I always think of Team America: World Police whenever “World” and “Organization” appear in the same title) recently announced that atmospheric greenhouse gases had once again set a new record.
Greenhouse gases reach another new record high!
Records are made to be broken
I wonder if the folks at the WMO are aware of the following three facts:
1) The first “record high” CO2 level was set in 1809, at a time when cumulative anthropogenic carbon emissions had yet to exceed the equivalent of 0.2 ppmv CO2?
- Figure 1. The Original CO2 “Hockey Stick.” CO2 emissions data from Oak Ridge National Laboratory’s Carbon Dioxide Information Analysis Center (CDIAC). The emissions (GtC) were divided by 2.13 to obtain ppmv CO2.
2) From 1750 to 1875, atmospheric CO2 rose at ten times the rate of the cumulative anthropogenic emissions…
- Figure 2. Where, oh where, did that CO2 come from?
3) Cumulative anthropogenic emissions didn’t “catch up” to the rise in atmospheric CO2 until 1960…
- Figure 3. It took humans over 100 years to “catch up” to nature.
The emissions were only able to “catch up” because atmospheric CO2 levels stalled at ~312 ppmv from 1940-1955.
The mid-20th century decline in atmospheric CO2
The highest resolution Antarctic ice cores I am aware of come from Law Dome (Etheridge et al., 1998), particularly the DE08 core. Over the past decade, the Law Dome ice core resolution has been improved through denser sampling and the application of frequency enhancing signal processing techniques (Trudinger et el., 2002 and MacFarling Meure et al., 2006). Not surprisingly, the higher resolution data are indicating more variability in preindustrial CO2 levels.
Plant stomata reconstructions (Kouwenberg et al., 2005, Finsinger and Wagner-Cremer, 2009) and contemporary chemical analyses (Beck, 2007) indicate that CO2 levels in the 1930′s to early 1940′s were in the 340 to 400 ppmv range and then declined sharply in the 1950’s. These findings have been rejected by the so-called scientific consensus because this fluctuation is not resolved in Antarctic ice cores. However, MacFarling Meure et al., 2006 found possible evidence of a mid-20th Century CO2 decline in the DE08 ice core…
The stabilization of atmospheric CO2 concentration during the 1940s and 1950s is a notable feature in the ice core record. The new high density measurements confirm this result and show that CO2 concentrations stabilized at 310–312 ppm from ~1940–1955. The CH4 and N2O growth rates also decreased during this period, although the N2O variation is comparable to the measurement uncertainty. Smoothing due to enclosure of air in the ice (about 10 years at DE08) removes high frequency variations from the record, so the true atmospheric variation may have been larger than represented in the ice core air record. Even a decrease in the atmospheric CO2 concentration during the mid-1940s is consistent with the Law Dome record and the air enclosure smoothing, suggesting a large additional sink of ~3.0 PgC yr-1 [Trudinger et al., 2002a]. The d13CO2 record during this time suggests that this additional sink was mostly oceanic and not caused by lower fossil emissions or the terrestrial biosphere [Etheridge et al., 1996; Trudinger et al., 2002a]. The processes that could cause this response are still unknown.
 The CO2 stabilization occurred during a shift from persistent El Niño to La Niña conditions [Allan and D’Arrigo, 1999]. This coincided with a warm-cool phase change of the Pacific Decadal Oscillation [Mantua et al., 1997], cooling temperatures [Moberg et al., 2005] and progressively weakening North Atlantic thermohaline circulation [Latif et al., 2004]. The combined effect of these factors on the trace gas budgets is not presently well understood. They may be significant for the atmospheric CO2 concentration if fluxes in areas of carbon uptake, such as the North Pacific Ocean, are enhanced, or if efflux from the tropics is suppressed.
From about 1940 through 1955, approximately 24 billion tons of carbon went straight from the exhaust pipes into the oceans and/or biosphere.
Figure 4. Oh where, oh where did all that carbon go?
If oceanic uptake of CO2 caused ocean acidification, shouldn’t we see some evidence of it? Shouldn’t “a large additional sink of ~3.0 PgC yr-1″ (or more) from ~1940–1955 have left a mark somewhere in the oceans? Maybe dissolved some snails or a reef?
Had atmospheric CO2 simply followed the preindustrial trajectory, it very likely would have reached 315-345 ppmv by 2010…
Figure 5. Natural sources probably account for 40-60% of the rise in atmospheric CO2 since 1750.
Oddly enough, plant stomata-derived CO2 reconstructions indicate that CO2 levels of 315-345 ppmv have not been uncommon throughout the Holocene…
Figure 6. CO2 from plant stomata: Northern Sweden (Finsinger et al., 2009), Northern Spain (Garcia-Amorena, 2008), Southern Sweden (Jessen, 2005), Washington State USA (Kouwenberg, 2004), Netherlands (Wagner et al., 1999), Denmark (Wagner et al., 2002).
So, what on Earth could have driven all of that CO2 variability before humans started burning fossil fuels? Could it possibly have been temperature changes?
CO2 as feedback
When I plot a NH temperature reconstruction (Moberg et al., 2005) along with the Law Dome CO2 record, it sure looks to me as if the CO2 started rising about 100 years after the temperature started rising…
Figure 7. Temperature reconstruction (Moberg et al., 2005) and Law Dome CO2 (MacFarling Meure et al., 2006)
The rise in CO2 from 1842-1945 looks a heck of a lot like the rise in temperature from 1750-1852…
Figure 8. Possible relationship between temperature increase and subsequent CO2 rise.
The correlation is very strong. A calculated CO2 chronology yields a good match to the DE08 ice core and stomata-derived CO2 since 1850. However, it indicates that atmospheric CO2 would have reached ~430 ppmv in the mid-12th century AD.
Figure 9. CO2 calculated from Moberg temperatures (dark blue curve), Law Dome ice cores (magenta curve) and plant stomata (green, light blue and purple squares).
The mid-12th century peak in CO2 is not supported by either the ice cores or the plant stomata. The correlation breaks down before the 1830’s. However, the same break down also happens when CO2 is treated as forcing rather than feedback.
CO2 as forcing
If I directly cross plot CO2 vs. temperature with no lag time, I get a fair correlation with the post DE08 core (>1833) data and no correlation at all with pre-DE08 core (<1833) data…
Figure 10. Temperature and [CO2] have a moderate correlation since ~1833; but no correlation at all before 1833.
If I extrapolate out to about 840 ppmv CO2, I get about 3 °C of warming relative to 275 ppmv. So, I get the same amount of warming for a tripling of preindustrial CO2 that the IPCC says we’ll get with a doubling.
Figure 11. CO2 from the Law Dome DE08 core plotted against Moberg’s NH temperature reconstruction.
Based on this correlation, the equilibrium climate sensitivity to a doubling of preindustrial CO2 is ~1.5 to 2.0 °C. But, the total lack of a correlation in the ice cores older than DE08 is very puzzling.
Ice core resolution and the lack a CO2-temperature coupling before 1833
Could the lack of variability in the older (and deeper) cores have something to do with resolution? The DE08 core is of far higher resolution than pretty well all of the other Antarctic ice cores, including the deeper and older DSS core from Law Dome.
Figure 12. The temporal resolution of ice cores is dictated by the snow accumulation rate.
The amplitude of the CO2 “signal” also appears to be well-correlated with the snow accumulation rate (resolution) of the ice cores…
Figure 13. Accumulation rate vs. CO2 for various ice cores from Antarctica and Greenland.
Could it be that snow accumulation rates significantly lower than 1 m/yr simply can’t resolve century-scale and higher frequency CO2 shifts? Could it also be that the frequency degradation is also attenuating the amplitude of the CO2 “signal”?
If the vast majority of the ice cores older and deeper than DE08 can’t resolve century-scale and higher frequency CO2 shifts, doesn’t it make sense that ice core-derived CO2 and temperature would appear to be poorly coupled over most of the Holocene?
Why is it that the evidence always seems to indicate that the IPCC’s best case scenario is the worst that can happen in the real world?
Brad Plummer’s recent piece in the Washington Post featured a graph that caught my eye…
Figure 14. The IPCC’s mythical scenarios. I think the shaded area represents the greentopian range.
It appears that a “business as usual” (A1FI) will turn Earth into Venus by 2100 AD.
But, what happens if I use real data?
Let’s assume that the atmospheric CO2 level will rise along an exponential trend line until 2100.
Figure 15. CO2 projected to 560 ppmv by 2100.
I get a CO2 level of 560 ppmv, comparable to the IPCC SRES B2 emissions scenario…
Figure 16. IPCC emissions scenarios.
So, business as usual will likely lead to the same CO2 level as an IPCC greentopian scenario. Why am I not surprised?
Assuming all of the warming since 1833 was caused by CO2 (it wasn’t), 560 ppmv will lead to about 1°C of additional warming by the year 2100.
Figure 17. Projected temperature rise derived from Moberg NH temperature reconstruction and Law Dome DE08 ice core CO2.
Projected Temp. Anom. = 2.6142 * ln(CO2) – 15.141
How does this compare with the IPCC’s mythical scenarios? About as expected. The worst case scenario based on actual observations is comparable to the IPCC’s best case, greentopian scenario…
Figure 18. Projected temperature rise derived from Moberg NH temperature reconstruction and Law Dome DE08 ice core CO2 indicates that the IPCC’s 2°C “limit” will not be exceeded.
- Atmospheric CO2 concentration records were being broken long before anthropogenic emissions became significant.
- Atmospheric CO2 levels were rising much faster than anthropogenic emissions from 1750-1875.
- Anthropogenic emissions did not “catch up” to atmospheric CO2 until 1960.
- The natural carbon flux is much more variable than the so-called scientific consensus thinks it is.
- The equilibrium climate sensitivity (ECS) cannot be more than 2°C and is probably closer to 1°C.
- The worst-case scenario based on the evidence is comparable to the IPCC’s most greentopian, best-case scenario.
- Ice cores with accumulation rates less than 1m/yr are not useful for ECS estimations.
The ECS derived from the Law Dome DE08 ice core and Moberg’s NH temperature reconstruction assumes that all of the warming since 1833 was due to CO2. We know for a fact that at least half of the warming was due to solar influences and natural climatic oscillations. So the derived 2°C is more likely to be 1°C. Since it is clear that about half of the rise from 275 to 400 ppmv was natural, the anthropogenic component of that 1°C ECS is probably less than 0.7°C.
The lack of a correlation between temperature and CO2 from the start of the Holocene up until 1833 and the fact that the modern CO2 rise outpaced the anthropogenic emissions for about 200 years leads this amateur climate researcher to concluded that CO2 must have been a lot more variable over the last 10,000 years than the Antarctic ice core indicate.
Appendix I: Another Way to Look at the CO2 growth rate
In Figure 15 I used the Excel-calculated exponential trend line to extrapolate the MLO CO2 time series to the end of this century. If I extrapolate the emissions and assume 55% of emissions remain in atmosphere, I get ~702 ppmv by the end of the century, with an additional 0.6°C of warming. A total warming of 2.5°C above “preindustrial.” Even this worse than worst case scenario results in about 1°C less warming than the A1B reference scenario. It falls about mid-way between A1B and the top of the greentopian range.
Appendix II: CO2 Records, the Early Years
Whenever CO2 records are mentioned or breathtaking pronouncements like, “Carbon dioxide at highest level in 800,000 years” are made, I always like to take a look at those “records” in a geological context. The following graphs were generated from Bill Illis’ excellent collection of paleo-climate data.
Greenhouse gases reach another new record high! Or did they? The “Anthropocene” doesn’t look a heck of a lot different than the prior 25 million years… Apart from being a lot colder.
The “Anthropocene’s” CO2 “Hockey Stick” looks more like a needle in a haystack from a geological perspective. And it looks to me as if Earth might be on track to run out of CO2 in about 25 million years.
One of my all-time favorites! Note the total lack of correlation between CO2 and temperature throughout most of the Phanerozoic Eon.
In the following bar chart I grouped CO2 by geologic period. The Cambrian through Cretaceous are drawn from Berner and Kothavala, 2001 (GEOCARB), the Tertiary is from Pagani, et al. 2006 (deep sea sediment cores), the Pleistocene is from Lüthi, et al. 2008 (EPICA C Antarctic ice core), the “Anthropocene” is from NOAA-ESRL (Mauna Loa Observatory) and the CO2 starvation is from Ward et al., 2005.
“Anthropocene” CO2 levels are a lot closer to the C3 plant starvation (Ward et al., 2005) range than they are to most of the prior 540 million years.
[SARC ON] I thought about including Venus on the bar chart; but I would have had to use a logarithmic scale. [SARC OFF]
Appendix III: Plant Stomata-Derived CO2
The catalogue of peer-reviewed papers demonstrating higher and more variable preindustrial CO2 levels is quite impressive and growing. Here are a few highlights:
Wagner et al., 1999. Century-Scale Shifts in Early Holocene Atmospheric CO2 Concentration. Science 18 June 1999: Vol. 284 no. 5422 pp. 1971-1973…
In contrast to conventional ice core estimates of 270 to 280 parts per million by volume (ppmv), the stomatal frequency signal suggests that early Holocene carbon dioxide concentrations were well above 300 ppmv.
Most of the Holocene ice core records from Antarctica do not have adequate temporal resolution.
Our results falsify the concept of relatively stabilized Holocene CO2 concentrations of 270 to 280 ppmv until the industrial revolution. SI-based CO2 reconstructions may even suggest that, during the early Holocene, atmospheric CO2 concentrations that were .300 ppmv could have been the rule rather than the exception.
The ice cores cannot resolve CO2 shifts that occur over periods of time shorter than twice the bubble enclosure period. This is basic signal theory. The assertion of a stable pre-industrial 270-280 ppmv is flat-out wrong.
McElwain et al., 2001. Stomatal evidence for a decline in atmospheric CO2 concentration during the Younger Dryas stadial: a comparison with Antarctic ice core records. J. Quaternary Sci., Vol. 17 pp. 21–29. ISSN 0267-8179…
It is possible that a number of the short-term fluctuations recorded using the stomatal methods cannot be detected in ice cores, such as Dome Concordia, with low ice accumulation rates. According to Neftel et al. (1988), CO2 fluctuation with a duration of less than twice the bubble enclosure time (equivalent to approximately 134 calendar yr in the case of Byrd ice and up to 550 calendar yr in Dome Concordia) cannot be detected in the ice or reconstructed by deconvolution.
Not even the highest resolution ice cores, like Law Dome, have adequate resolution to correctly image the MLO instrumental record.
Kouwenberg et al., 2005. Atmospheric CO2 fluctuations during the last millennium reconstructed by stomatal frequency analysis of Tsuga heterophylla needles. Geology; January 2005; v. 33; no. 1; p. 33–36…
The discrepancies between the ice-core and stomatal reconstructions may partially be explained by varying age distributions of the air in the bubbles because of the enclosure time in the firn-ice transition zone. This effect creates a site-specific smoothing of the signal (decades for Dome Summit South [DSS], Law Dome, even more for ice cores at low accumulation sites), as well as a difference in age between the air and surrounding ice, hampering the construction of well-constrained time scales (Trudinger et al., 2003).
Stomatal reconstructions are reproducible over at least the Northern Hemisphere, throughout the Holocene and consistently demonstrate that the pre-industrial natural carbon flux was far more variable than indicated by the ice cores.
Wagner et al., 2004. Reproducibility of Holocene atmospheric CO2 records based on stomatal frequency. Quaternary Science Reviews. 23 (2004) 1947–1954…
The majority of the stomatal frequency-based estimates of CO 2 for the Holocene do not support the widely accepted concept of comparably stable CO2 concentrations throughout the past 11,500 years. To address the critique that these stomatal frequency variations result from local environmental change or methodological insufficiencies, multiple stomatal frequency records were compared for three climatic key periods during the Holocene, namely the Preboreal oscillation, the 8.2 kyr cooling event and the Little Ice Age. The highly comparable fluctuations in the paleo-atmospheric CO2 records, which were obtained from different continents and plant species (deciduous angiosperms as well as conifers) using varying calibration approaches, provide strong evidence for the integrity of leaf-based CO2 quantification.
The Antarctic ice cores lack adequate resolution because the firn densification process acts like a low-pass filter.
Van Hoof et al., 2005. Atmospheric CO2 during the 13th century AD: reconciliation of data from ice core measurements and stomatal frequency analysis. Tellus 57B (2005), 4…
Atmospheric CO2 reconstructions are currently available from direct measurements of air enclosures in Antarctic ice and, alternatively, from stomatal frequency analysis performed on fossil leaves. A period where both methods consistently provide evidence for natural CO2 changes is during the 13th century AD. The results of the two independent methods differ significantly in the amplitude of the estimated CO2 changes (10 ppmv ice versus 34 ppmv stomatal frequency). Here, we compare the stomatal frequency and ice core results by using a firn diffusion model in order to assess the potential influence of smoothing during enclosure on the temporal resolution as well as the amplitude of the CO2 changes. The seemingly large discrepancies between the amplitudes estimated by the contrasting methods diminish when the raw stomatal data are smoothed in an analogous way to the natural smoothing which occurs in the firn.
The derivation of equilibrium climate sensitivity (ECS) to atmospheric CO2 is largely based on Antarctic ice cores. The problem is that the temperature estimates are based on oxygen isotope ratios in the ice itself; while the CO2 estimates are based on gas bubbles trapped in the ice.
The temperature data are of very high resolution. The oxygen isotope ratios are functions of the temperature at the time of snow deposition. The CO2 data are of very low and variable resolution because it takes decades to centuries for the gas bubbles to form. The CO2 values from the ice cores represent average values over many decades to centuries. The temperature values have annual to decadal resolution.
The highest resolution Antarctic ice core is the DE08 core from Law Dome.
The IPCC and so-called scientific consensus assume that it can resolve annual changes in CO2. But it can’t. Each CO2 value represents a roughly 30-yr average and not an annual value.
If you smooth the Mauna Loa instrumental record (red curve) and plant stomata-derived pre-instrumental CO2 (green curve) with a 30-yr filter, they tie into the Law Dome DE08 ice core (light blue curve) quite nicely…
The deeper DSS core (dark blue curve) has a much lower temporal resolution due to its much lower accumulation rate and compaction effects. It is totally useless in resolving century scale shifts, much less decadal shifts.
The IPCC and so-called scientific consensus correctly assume that resolution is dictated by the bubble enclosure period. However, they are incorrect in limiting the bubble enclosure period to the sealing zone. In the case of the core DE08 they assume that they are looking at a signal with a 1 cycle/1 yr frequency, sampled once every 8-10 years. The actual signal has a 1 cycle/30-40 yr frequency, sampled once every 8-10 years.
30-40 ppmv shifts in CO2 over periods less than ~60 years cannot be accurately resolved in the DE08 core. That’s dictated by basic signal theory. Wagner et al., 1999 drew a very hostile response from the so-called scientific consensus. All Dr. Wagner-Cremer did to them was to falsify one little hypothesis…
In contrast to conventional ice core estimates of 270 to 280 parts per million by volume (ppmv), the stomatal frequency signal suggests that early Holocene carbon dioxide concentrations were well above 300 ppmv.
Our results falsify the concept of relatively stabilized Holocene CO2 concentrations of 270 to 280 ppmv until the industrial revolution. SI-based CO2 reconstructions may even suggest that, during the early Holocene, atmospheric CO2 concentrations that were >300 ppmv could have been the rule rather than the exception (23).
The plant stomata pretty well prove that Holocene CO2 levels have frequently been in the 300-350 ppmv range and occasionally above 400 ppmv over the last 10,000 years.
The incorrect estimation of a 3°C ECS to CO2 is almost entirely driven the assumption that preindustrial CO2 levels were in the 270-280 ppmv range, as indicated by the Antarctic ice cores.
The plant stomata data clearly show that preindustrial atmospheric CO2 levels were much higher and far more variable than indicated by Antarctic ice cores. Which means that the rise in atmospheric CO2 since the 1800’s is not particularly anomalous and at least half of it is due to oceanic and biosphere responses to the warm-up from the Little Ice Age.
Kouwenberg concluded that the CO2 maximum ca. 450 AD was a local anomaly because it could not be correlated to a temperature rise in the Mann & Jones, 2003 reconstruction.
As the Earth’s climate continues to not cooperate with their models, the so-called consensus will eventually recognize and acknowledge their fundamental error. Hopefully we won’t have allowed decarbonization zealotry to bankrupt us beforehand.
Until the paradigm shifts, all estimates of the pre-industrial relationship between atmospheric CO2 and temperature derived from Antarctic ice cores will be wrong, because the ice core temperature and CO2 time series are of vastly different resolutions. And until the “so-called consensus” gets the signal processing right, they will continue to get it wrong.
Anklin, M., J. Schwander, B. Stauffer, J. Tschumi, A. Fuchs, J.M. Barnola, and D. Raynaud. 1997. CO2 record between 40 and 8kyr B.P. from the Greenland Ice Core Project ice core. Journal of Geophysical Research 102:26539-26545.
Barnola et al. 1987. Vostok ice core provides 160,000-year record of atmospheric CO2.
Nature, 329, 408-414.
Berner, R.A. and Z. Kothavala, 2001. GEOCARB III: A Revised Model of Atmospheric CO2 over Phanerozoic Time, American Journal of Science, v.301, pp.182-204, February 2001.
Boden, T.A., G. Marland, and R.J. Andres. 2012. Global, Regional, and National Fossil-Fuel CO2 Emissions. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A. doi 10.3334/CDIAC/00001_V2012
Etheridge, D.M., L.P. Steele, R.L. Langenfelds, R.J. Francey, J.-M. Barnola and V.I. Morgan. 1998. Historical CO2 records from the Law Dome DE08, DE08-2, and DSS ice cores. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.
Finsinger, W. and F. Wagner-Cremer. Stomatal-based inference models for reconstruction of atmospheric CO2 concentration: a method assessment using a calibration and validation approach. The Holocene 19,5 (2009) pp. 757–764
Fischer, H. A Short Primer on Ice Core Science. Climate and Environmental Physics, Physics Institute, University of Bern.
Garcıa-Amorena, I., F. Wagner-Cremer, F. Gomez Manzaneque, T. B. van Hoof, S. Garcıa Alvarez, and H. Visscher. 2008. CO2 radiative forcing during the Holocene Thermal Maximum revealed by stomatal frequency of Iberian oak leaves. Biogeosciences Discussions 5, 3945–3964, 2008.
Illis, B. 2009. Searching the PaleoClimate Record for Estimated Correlations: Temperature, CO2 and Sea Level. Watts Up With That?
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Jessen, C. A., Rundgren, M., Bjorck, S. and Hammarlund, D. 2005. Abrupt climatic changes and an unstable transition into a late Holocene Thermal Decline: a multiproxy lacustrine record from southern Sweden. J. Quaternary Sci., Vol. 20 pp. 349–362. ISSN 0267-8179.
Kouwenberg, LLR. 2004. Application of conifer needles in the reconstruction of Holocene CO2 levels. PhD Thesis. Laboratory of Palaeobotany and Palynology, University of Utrecht.
Kouwenberg, LLR, Wagner F, Kurschner WM, Visscher H (2005) Atmospheric CO2 fluctuations during the last millennium reconstructed by stomatal frequency analysis of Tsuga heterophylla needles. Geology 33:33–36
Ljungqvist, F.C.2009. Temperature proxy records covering the last two millennia: a tabular and visual overview. Geografiska Annaler: Physical Geography, Vol. 91A, pp. 11-29.
Ljungqvist, F.C. 2010. A new reconstruction of temperature variability in the extra-tropical Northern Hemisphere during the last two millennia. Geografiska Annaler: Physical Geography, Vol. 92 A(3), pp. 339-351, September 2010. DOI: 10.1111/j.1468-0459.2010.00399.x
Lüthi, D., M. Le Floch, B. Bereiter, T. Blunier, J.-M. Barnola, U. Siegenthaler, D. Raynaud, J. Jouzel, H. Fischer, K. Kawamura, and T.F. Stocker. 2008. High-resolution carbon dioxide concentration record 650,000-800,000 years before present. Nature, Vol. 453, pp. 379-382, 15 May 2008. doi:10.1038/nature06949
MacFarling Meure, C., D. Etheridge, C. Trudinger, P. Steele, R. Langenfelds, T. van Ommen, A. Smith, and J. Elkins (2006), Law Dome CO2, CH4 and N2O ice core records extended to 2000 years BP, Geophys. Res. Lett., 33, L14810, doi:10.1029/2006GL026152.
McElwain et al., 2001. Stomatal evidence for a decline in atmospheric CO2 concentration during the Younger Dryas stadial: a comparison with Antarctic ice core records. J. Quaternary Sci., Vol. 17 pp. 21–29. ISSN 0267-8179
Moberg, A., 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, Vol. 433, No. 7026, pp. 613-617, 10 February 2005.
Morice, C.P., J.J. Kennedy, N.A. Rayner, P.D. Jones (2011), Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: the HadCRUT4 dataset, Journal of Geophysical Research, accepted.
Pagani, M., J.C. Zachos, K.H. Freeman, B. Tipple, and S. Bohaty. 2005. Marked Decline in Atmospheric Carbon Dioxide Concentrations During the Paleogene. Science, Vol. 309, pp. 600-603, 22 July 2005.
Rundgren et al., 2005. Last interglacial atmospheric CO2 changes from stomatal index data and their relation to climate variations. Global and Planetary Change 49 (2005) 47–62.
Smith, H. J., Fischer, H., Mastroianni, D., Deck, B. and Wahlen, M., 1999, Dual modes of the carbon cycle since the Last Glacial Maximum. Nature 400, 248-250.
Trudinger, C. M., I. G. Enting, P. J. Rayner, and R. J. Francey (2002), Kalman filter analysis of ice core data 2. Double deconvolution of CO2 and δ13C measurements, J. Geophys. Res., 107(D20), 4423, doi:10.1029/2001JD001112.
Van Hoof et al., 2005. Atmospheric CO2 during the 13th century AD: reconciliation of data from ice core measurements and stomatal frequency analysis. Tellus 57B (2005), 4
Wagner F, et al., 1999. Century-scale shifts in Early Holocene CO2 concentration. Science 284:1971–1973.
Wagner F, Aaby B, Visscher H, 2002. Rapid atmospheric CO2 changes associated with the 8200-years-B.P. cooling event. Proc Natl Acad Sci USA 99:12011–12014.
Wagner F, Kouwenberg LLR, van Hoof TB, Visscher H, 2004. Reproducibility of Holocene atmospheric CO2 records based on stomatal frequency. Quat Sci Rev 23:1947–1954
Ward, J.K., Harris, J.M., Cerling, T.E., Wiedenhoeft, A., Lott, M.J., Dearing, M.-D., Coltrain, J.B. and Ehleringer, J.R. 2005. Carbon starvation in glacial trees recovered from the La Brea tar pits, southern California. Proceedings of the National Academy of Sciences, USA 102: 690-694.