Current Period Warmest Yet in 1000 Years

[bdude]

BBC link

In the late 20th Century, the northern hemisphere experienced its most widespread warmth for 1,200 years, according to the journal Science.

The findings support evidence pointing to unprecedented recent warming of the climate linked to greenhouse emissions.

I do not see why this fact is still being disputed. The evidence is undeniable and is right in front of our eyes.

Will anything be done? Probably not.
Should anything be done? At the least, we should contemplate these climate changes on a policy level.

 

[dmcowen674]

Originally posted by: bdude

BBC link

In the late 20th Century, the northern hemisphere experienced its most widespread warmth for 1,200 years, according to the journal Science.

The findings support evidence pointing to unprecedented recent warming of the climate linked to greenhouse emissions.

I do not see why this fact is still being disputed. The evidence is undeniable and is right in front of our eyes.

Will anything be done? Probably not.
Should anything be done? At the least, we should contemplate these climate changes on a policy level.

Nothing will happen except it will get worse. The rich boys will not accept anything less.

 

[Todd33]

Liberal science. Our CEOs and their politcal friends know best, stop trying to hurt the bottom line.

 

[Whoozyerdaddy]

Originally posted by: dmcowen674

Originally posted by: bdude

BBC link

In the late 20th Century, the northern hemisphere experienced its most widespread warmth for 1,200 years, according to the journal Science.

The findings support evidence pointing to unprecedented recent warming of the climate linked to greenhouse emissions.

I do not see why this fact is still being disputed. The evidence is undeniable and is right in front of our eyes.

Will anything be done? Probably not.
Should anything be done? At the least, we should contemplate these climate changes on a policy level.

Nothing will happen except it will get worse. The rich boys will not accept anything less.

No crack at Republicans? :shocked:
Are you feeling ok Dave?

 

[EagleKeeper]

People are not willing to give up their lifestyles for what they do not see as a problem that impacts them.

 

[Stunt]

How often do ice ages occur?
What happens between ice ages?

Do we REALLY know enough about global warming and how much of an impact we are making if any?

 

[Strk]

Originally posted by: Stunt
How often do ice ages occur?
What happens between ice ages?

Do we REALLY know enough about global warming and how much of an impact we are making if any?

Of course not, since the world is only 6,000 years old!

(Yeah, that's meant as sarcasm, if you couldn't figure it out )

 

[bdude]

The article itself if anyone is interested.

http://www.sciencemag.org/cgi/content/full/311/5762/841

Science 10 February 2006:
Vol. 311. no. 5762, pp. 841 - 844
DOI: 10.1126/science.1120514

Prev | Table of Contents | Next
Reports
The Spatial Extent of 20th-Century Warmth in the Context of the Past 1200 Years
Timothy J. Osborn* and Keith R. Briffa

Periods of widespread warmth or cold are identified by positive or negative deviations that are synchronous across a number of temperature-sensitive proxy records drawn from the Northern Hemisphere. The most significant and longest duration feature during the last 1200 years is the geographical extent of warmth in the middle to late 20th century. Positive anomalies during 890 to 1170 and negative anomalies during 1580 to 1850 are consistent with the concepts of a Medieval Warm Period and a Little Ice Age, but comparison with instrumental temperatures shows the spatial extent of recent warmth to be of greater significance than that during the medieval period.

Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK.

* To whom correspondence should be addressed. E-mail: t.osborn@uea.ac.uk

Establishing the history of hemispheric or global temperatures is one fundamental requirement for identifying the contributions of different natural forcings to past climate variability and for quantifying the significance of greenhouse gas?induced warming during the 20th century (1?3). A number of studies (1, 4?14) have selected, combined, and then calibrated multiple climate proxy records to provide assessments of temperature variability on near-hemispheric scales for the past few hundred to two thousand years. Both individually and taken as a whole, these reconstructions have been used to support the conclusion that it is likely that the late 20th century was the warmest period during the past millennium (15, 16) or longer (11, 12, 17) in the Northern Hemisphere (NH).

Assessing whether these recent temperatures are unprecedented depends on comparing the recent instrumental temperature record with the earlier proxy-based temperature reconstructions. Quantitative calibration of the reconstructions is essential, and the comparison with the instrumental record is only valid if it takes account of the uncertainties associated with interpreting a specific reconstruction as an estimate of the "actual" temperature. Of the studies cited above, some do not provide reconstructions that cover the whole of the millennium (1, 8, 13, 14), whereas some others either do not estimate reconstruction uncertainty at all (4, 6, 7, 10) [note that reconstruction uncertainty for (4) was later estimated by (16)] or do not estimate reconstruction uncertainty in a way that is appropriate for assessing the significance of very late 20th-century warmth (9, 12); see (18). There are, therefore, currently only three studies (5, 11, 16) that allow a formal quantitative comparison of late 20th-century instrumental temperatures against reconstructed temperatures for the past 1000 years or more. These three studies all found that recent temperatures are above the 95% uncertainty range estimated to be appropriate for their reconstructions of all earlier temperatures.

The published uncertainties were calculated from the regression residuals during the calibration period (19) and probably underestimate the true uncertainties, because additional unquantified error might arise (i) from nonstationarities in proxy-climate (5), interseason, (20) or land-ocean (21) relationships; (ii) from the use of the same period to select and calibrate temperature-sensitive proxies as well as for estimating uncertainty; or (iii) from biases inherent in the calibration method (22) [but see (23)]. For these reasons, the Intergovernmental Panel on Climate Change (15) correctly judged that the conclusion that recent warmth is unprecedented in the context of the past 1000 years could be made with only 66 to 90% confidence, despite recent temperatures exceeding the published 95% uncertainty ranges of all earlier reconstructed values (5, 11, 16).

A separate analysis on a record-by-record basis of many environmental and climate proxies concluded that the 20th century was probably not the warmest of the last millennium (24). This study has been criticized (25) for its lack of rigour in assessing whether the proxies used are useful indicators of temperature, for not distinguishing between regionally restricted anomalies and hemispheric-scale warmth, and for providing no calibration or uncertainty estimates that would enable comparison with late 20th-century temperatures. Here, we investigated whether a more carefully designed assessment of proxy records on an individual basis supports the conclusion that recent NH temperatures are unusual in the context provided by these records. We only used proxy records that are positively correlated with their local temperature observations, and, critically, periods with synchronous "warm" or "cold" anomalies in many proxies were used to infer hemispheric-scale climate anomalies as distinct from asynchronous warming or cooling in different regions. This restricts the analysis to those proxy records that are accurately dated. Analysis of synchronous anomalies in a number of independent records is indicative of the geographical extent of anomalous temperatures.

The criteria that proxy records must be well dated and sufficiently resolved and up to date to allow a quantitative comparison with instrumental temperatures eliminates many of the records used by (24). Here, we have pooled all of the proxy records used by (9) and (25) with those high-resolution NH series used by (11), then removed duplicates and those that were not positively correlated with their local temperature observations (26). Table S1 provides details of the 14 proxy series used here.

The 14 proxy series were each smoothed to remove variations on time scales shorter than 20 years and then "normalized" (26) to have zero mean and unit standard deviation (SD) over the full period of analysis, 800 to 1995. The analysis was not continued beyond 1995 because fewer than five of the proxy series were available after 1995. Individually, these records present a relatively complex picture of variability over the last 1200 years (Fig. 1). Although there are periods with coherent changes across a number of records, the implications of such periods cannot be quantified or adequately intercompared by a purely visual analysis.


Figure 1 Fig. 1. The 14 temperature-related proxy records used in this study, filtered to remove variations on time scales less than 20 years and then normalized to have zero mean and unit standard deviation during the period from 800 to 1995 [with adjustments made to the shorter records (26)]. [View Larger Version of this Image (47K GIF file)]


The proxy records were analyzed simply by counting the fraction of those series that have data in any given year whose smoothed and normalized values exceed certain thresholds (26). The thresholds used are the series mean and 1 or 2 SD above or below the mean. The differences between pairs of these fractional exceedance time series were also analyzed (i.e., the fraction of records at least 1 SD above the mean minus the fraction that are at least 1 SD below the mean). All proxies are given equal weight in this analysis.

The statistical significance of the difference time series was established by using a Monte Carlo approach (26). The values in each smoothed proxy time series were shifted by a randomly chosen number of years, with values that were shifted beyond the end date of the record cycled back to the start date of the record. The random shifting of the records destroys the calendar alignment between values in different proxy records but maintains the autocorrelation structure of the individual series. The exceedances, differences, and filtering were recalculated from the randomly shifted records, with the entire procedure repeated 10,000 times to build up a distribution of possible values.

Although there are some individual years when the smoothed records are all positive or all negative, these are not sustained sufficiently long for the 20-year smoothed counts of the fractional exceedances to reach one (Fig. 2). Nevertheless, almost all of the series are positive for much of the 20th century, peaking in number between 1935 and 1955. At the end of the analysis period in the early 1990s, 70% of the records have positive values whereas 30% are negative. Of the 70% with positive values, all exceed 1 SD above their respective mean and half exceed 2 SD above their mean, whereas throughout the 20th century the number of records more than 1 SD below their mean is nearly zero. The pre-20th-century periods when no series fall below ?1 SD occur mostly between 890 and 1100, and at these times typically 30 to 40% of series simultaneously exceed +1 SD (light red shading in Fig. 2). The periods when no series exceed 1 SD or at least 30% fall below ?1 SD (light + blue shading) occur mostly between 1230 and 1360 or 1575 and 1840.


Figure 2 Fig. 2. Fraction of the records available in each year that have normalized values > 0 (red line), > 1 (light red shading), > 2 (dark red shading), < 0 (blue line), < ?1 (light blue shading), and < ?2 (dark blue shading), with the latter three series multiplied by ?1 before plotting. The series are shown from 800 to 1995 and have been filtered to remove variations on time scales less than 20 years. [View Larger Version of this Image (19K GIF file)]


The fraction of positive records and the fraction of negative records do, of course, provide the same information, and thus their difference (Fig. 3A) has the same shape, with the highest value being reached in the mid-20th century and the lowest in the first half of the 17th century. These values far exceed even the 1st and 99th percentiles of the Monte Carlo results, providing support for a climate signal that deviates significantly from the overall mean state. The significance levels in all three panels of Fig. 3 vary through time according to the number of series that are available in each year; the greatest number are available between 1352 and 1947, and the detectability of significant anomalies is enhanced during this period (27). The value (Fig. 3A) at the very end of the analysis period would have exceeded the 95th percentile if it had occurred when the full set of proxy records were available, but because of the widening of the percentiles after some series end in the late 20th century, the 1995 value falls on the 90th percentile. Significant positive deviations also occur at intervals between 890 and 1170 and near to 1400, whereas significant negative deviations occur between 1200 and 1350, near 1460, and in the late 1600s and the early 1800s.


Figure 3 Fig. 3. Difference between the fraction of the records available in each year that have normalized values (A) > 0 and < 0, (B) > 1 and < ?1, (C) > 2 and < ?2, and (D) as (A) but using a shorter (1865 to 1995) reference period for normalization. The difference series are shown for 800 to 1995 and have been filtered to remove variations on time scales less than 20 years. Zero indicates that the number of series exceeding the upper threshold equals those with values below the lower threshold. In (A) to (C), the highest values achieved by each difference series are indicated by the horizontal black lines; the red and blue lines show the 99th, 95th, 90th, 10th, 5th, and 1st percentiles of distributions obtained by repeating the analysis 10,000 times with each proxy time series shifted randomly in time; and dark red and blue shading indicates times when the difference series exceeds the 95th or 5th percentiles. In (D), results based on annual-mean instrumental temperatures from grid boxes throughout the NH (red curve) or only in regions close to the proxy records (green curve) are shown for 1856 to 2004 (also normalized over the period from 1856 to 1995). [View Larger Version of this Image (33K GIF file)]


A similar picture emerges when considering the difference between counts of records more than 1 SD above and below their means (Fig. 3B), except that the values at the end of the analysis period (early 1990s) are similar to those in the mid-20th century. The 20th century is the most anomalous period in the record, with values far exceeding both the 99th percentile of the Monte Carlo results and all earlier values, right through to 1995.

The difference between the high and low 2 SD exceedances (Fig. 3C) shows only small deviations from zero throughout the analysis period except during the late 20th century, which exceeds all other periods, including the mid-20th century. This conclusion relies on the very small number of records whose values depart by more than 2 SD from their means at this time and is more sensitive to the selection of the proxy records than the results obtained using the less extreme thresholds (Fig. 3, A and B). There are earlier intervals with predominantly positive or negative deviations, but very few of these periods lie outside the range expected by chance.

Direct comparison of these results with instrumental temperatures is not possible because the latter records cannot be normalized over the 800-to-1995 period. The proxy data analysis was instead repeated with each series normalized over the 1856-to-1995 period of overlap with the instrumental temperatures. The difference between the fraction of proxy records with positive versus negative anomalies, relative to the shorter 1856-to-1995 reference period mean (Fig. 3D), shows a similar time evolution as the longer 800-to-1995 reference period results (Fig. 3A), although shifted vertically, of course.

The same analysis (filtering, normalizing, and counting values that exceed the various thresholds) was also applied to annual mean instrumental temperatures (28) from all grid boxes with data available in the NH or alternatively only to grid boxes close to the locations of the 14 proxy records. The similarity of the two instrumental temperature curves (Fig. 3D) indicates that the 14 proxy sites provide sufficient coverage to estimate the NH temperature behavior and that the limiting factor is likely to be the skill with which each proxy chronicles its local temperature variations. The instrumental temperature results show a close correspondence with the proxy records, particularly for the early 20th century increase and the variations during the 1930 to 1975 period. Each of the proxy records undoubtedly includes some variance that is unrelated to local temperature variations, and the characteristics of this "noise" determine the extent to which the signal shown by the counts of threshold exceedances and their differences will be expressed. The slight underestimation by the proxy results of the early 20th century rise and the absence of a further increase at the end of the records could both be examples of the expected consequences of noise in the proxy records. Virtually every grid-box instrumental temperature series in the NH exceeds its 1856 to 1995 mean level by the end of these records in 2004.

Similar results are obtained for the 1 or 2 SD thresholds, but these results are not shown here because estimating the SD of 20-year smoothed time series using this relatively short reference period (140 years) results in larger uncertainty in the counts of exceedances than for the results shown in Fig. 3D.

The multidecadal intervals (Figs. 2 and 3) with significantly widespread positive anomalies between 890 and 1170 and significantly widespread low proxy values between 1200 and 1850 (interspersed by periods with high or near-zero anomalies) provide support for the concepts of anomalous medieval (29) and Little Ice Age (30) periods (particularly from the late 1500s to the mid-1800s), although they are clearly discontinuous in time (with consequently ill-defined dates of onset and termination) and geographically restricted. The 20th century is the most anomalous interval in the entire analysis period, with highly significant occurrences of positive anomalies and positive extremes in the proxy records. These results are not dependent on the inclusion of specific individual proxies or the choice of reference period (figs. S2 to S6).

The approach used here is complementary to those studies that combined multiple proxy records into a calibrated time series of past large-scale or NH mean temperatures. By analyzing the raw proxy records themselves, some of the issues associated with the combination and calibration of records have been avoided [e.g., choice of optimum regional or seasonal temperature (13, 20); sensitivity to calibration period, time scale, and regression method (13, 31); and potential bias in some regression methods (22, 23)]. In avoiding these issues, however, we have been compelled, thus far, to restrict the interpretation of our results to periods of "unusually high or low" proxy values rather than as indicative of "warm" or "cool" periods.

There is support, however, for interpreting the results of Figs. 2 and 3 as indicators of NH temperature: (i) there is strong evidence for a common environmental signal in the proxy records because the counts of simultaneous threshold exceedances lie well outside the ranges obtained by the Monte Carlo simulations; (ii) this environmental signal is most likely to be a climate signal because the departures from the Monte Carlo ranges do not just occur during the twentieth century, when very wide-spread nonclimatic anthropogenic disturbances could arguably have driven a common response in some proxies; (iii) this climate signal is likely to be, at least partly, a temperature indicator, because the proxy records were screened so that only those that were positively correlated with their local instrumental temperatures were selected (table S1); (iv) the analysis of instrumental temperatures indicates that 14 good temperature proxies are sufficient to represent NH mean temperature on 20-year and longer time scales; and (v) the comparison of results using proxy records and instrumental temperatures confirms that the analysis of these proxy records is a useful indicator of NH temperatures.

On this basis it is reasonable to conclude that this study provides evidence for intervals of significant warmth in the NH within the so-called Medieval Warm Period and for significantly colder intervals during the so-called Little Ice Age period. The most widespread and thus strongest evidence indicative of a significantly warm period occurs during the twentieth century [see also Supporting Online Material (SOM) Text], when greenhouse gas concentrations were at their highest during the analysis period. The proxy records indicate that the most widespread warmth occurred in either the mid- or late-twentieth century, but instrumental temperatures provide unequivocal evidence for continuing geographic expansion of anomalous warmth through to the present time.


References and Notes

* 1. M. E. Mann, R. S. Bradley, M. K. Hughes, Nature 392, 779 (1998). [CrossRef] [ISI]
* 2. T. J. Crowley, Science 289, 270 (2000).[Abstract/Free Full Text]
* 3. G. C. Hegerl, T. J. Crowley, S. K. Baum, K. Y. Kim, W. T. Hyde, Geophys. Res. Lett. 30, 1242 (2003). [CrossRef]
* 4. P. D. Jones, K. R. Briffa, T. P. Barnett, S. F. B. Tett, Holocene 8, 455 (1998). [CrossRef] [ISI]
* 5. M. E. Mann, R. S. Bradley, M. K. Hughes, Geophys. Res. Lett. 26, 759 (1999). [CrossRef] [ISI]
* 6. K. R. Briffa, Quat. Sci. Rev. 19, 87 (2000). [CrossRef] [ISI]
* 7. T. J. Crowley, T. S. Lowery, Ambio 29, 51 (2000). [ISI]
* 8. K. R. Briffa et al., J. Geophys. Res. 106, 2929 (2001). [CrossRef] [ISI]
* 9. J. Esper, E. R. Cook, F. H. Schweingruber, Science 295, 2250 (2002).[Abstract/Free Full Text]
* 10. T. J. Crowley, S. K. Baum, K. Y. Kim, G. C. Hegerl, W. T. Hyde, Geophys. Res. Lett. 30, 1932 (2003). [CrossRef]
* 11. M. E. Mann, P. D. Jones, Geophys. Res. Lett. 30, 1820 (2003). [CrossRef]
* 12. A. Moberg, D. M. Sonechkin, K. Holmgren, N. M. Datsenko, W. Karlen, Nature 433, 613 (2005). [CrossRef] [ISI] [Medline]
* 13. S. Rutherford et al., J. Clim. 18, 2308 (2005). [CrossRef] [ISI]
* 14. H. N. Pollack, J. E. Smerdon, J. Geophys. Res. 109, D11106 (2004). [CrossRef]
* 15. IPCC, Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, J. T. Houghton et al., Eds. (Cambridge Univ. Press, Cambridge, UK, 2001), p. 881.
* 16. P. D. Jones, T. J. Osborn, K. R. Briffa, Science 292, 662 (2001).[Abstract/Free Full Text]
* 17. P. D. Jones, M. E. Mann, Rev. Geophys. 42, RG2002 (2004). [CrossRef]
* 18. Esper et al. (9) estimated only the uncertainty of their tree-growth series rather than its representation of NH temperature variability and (12) only estimated the uncertainty for time scales of 80 years and longer, which is inappropriate for a formal comparison with the mean temperature of a single decade or even a 30-year period.
* 19. With inflation to account for autocorrelation in the residuals, and (16) included additional uncertainty associated with the regression model coefficients.
* 20. P. D. Jones, K. R. Briffa, T. J. Osborn, J. Geophys. Res. 108, 4588 (2003). [CrossRef]
* 21. G. R. Bigg, T. D. Jickells, P. S. Liss, T. J. Osborn, Int. J. Climatol. 23, 1127 (2003). [CrossRef] [ISI]
* 22. H. von Storch et al., Science 306, 679 (2004); published online 30 September 2004 (10.1126/science.1096109).[Abstract/Free Full Text]
* 23. We note first that the bias may be smaller than indicated by (22) [see (32, 33)] and second that this bias affects the coldest periods much more than temperatures that are of comparable warmth to the calibration period.
* 24. W. Soon, S. Baliunas, Clim. Res. 23, 89 (2003). [ISI]
* 25. M. Mann et al., Eos 84, 256 (2003).
* 26. Materials and methods are available as supporting material at Science Online.
* 27. The percentiles of the Monte Carlo distributions are nearer to zero then, and thus smaller anomalies may still be significant.
* 28. P. D. Jones, A. Moberg, J. Clim. 16, 206 (2003). [CrossRef] [ISI]
* 29. H. H. Lamb, Climate History and the Future, Vol. 2, Climate: Present, Past and Future (Methuen, New York, 1977), p. 835.
* 30. A. E. J. Ogilvie, T. Jonsson, Clim. Change 48, 9 (2001). [CrossRef] [ISI]
* 31. J. Esper, D. C. Frank, R. J. S. Wilson, K. R. Briffa, Geophys. Res. Lett. 32, L07711 (2005). [CrossRef]
* 32. T. J. Osborn, S. C. B. Raper, K. R. Briffa, Clim. Dyn., in press.
* 33. M. E. Mann, S. Rutherford, E. Wahl, C. Ammann, J. Clim. 18, 4097 (2005). [CrossRef] [ISI]
* 34. Supported by the European Community under research contract EVK2-CT2002-00160 SOAP. M. Mann, P. Jones, J. Esper, and E. Cook are thanked for making proxy data records available to us.

 

[Stunt]

According to this chart, our highest CO2 levels were 325,000 years ago. Our planet has also experienced much higher temperatures.

There's so much we don't know; and I have a tough time putting limits on our standard of living (GDP growth and productivity) for something which could be so insignificant. If the earth is going through a cycle, and we try to reduce it with our activities, it may be like stopping a train by standing in front of it!

Edit: sp

 

[bdude]

Article taken from http://www.cnrs.fr/cw/en/pres/compress/mist030699.html

Originally posted by: Stunt
According to this chart, our highest CO2 levels were 325,000 years ago. Our planet has also experienced much higher temperatures.

There's so much we don't know; and I have a tough time putting limits on our standard of living (GDP growth and productivity) for something which could be so insignificant. If the earth is going through a cycle, and we try to reduce it with our activities, it may be like stopping a train by standing in front of it!

Edit: sp

420,000 years of atmospheric history revealed by the Vostok ice core, Antarctica.

Paris, June 3, 1999



French, Russian and American researchers have measured the temperature, the aerosol and greenhouse gas concentration and various other climate and environmental parameters over the last four climate cycles. The results confirm the idea that climate variations are caused by the Earth?s orbital changes and to a large extent amplified by greenhouse gases. The high concentrations of greenhouse gases, unprecedented in the past 420,000 years, underscore their role in the possible warming of the planet?s climate. This study was published in Nature by 19 researchers from three participating countries. They include thirteen glaciologists and climatologists from CNRS laboratories in Grenoble and the joint CEA-CNRS unit in Saclay (1).

The 3,623 meters of ice core bored in Vostok, Antarctica, are the result of a 10-year collaboration between Russia, France and the United States (2). The Vostok site is considered one of the least hospitable on Earth, since its altitude is 3,500 meters and its average yearly temperature is minus 55° C.
The analysis of this ice core provides a record of the atmosphere during the last four climatic cycles. For the first time, researchers were able to establish, over such a long period, a simultaneous record of temperature variations, carbon dioxide (CO2), methane (CH4) and oxygen proportions in the atmosphere, of the quantity of dust blown from the desert and aerosols from sea spray.
The climate and environment parameters show the existence of four major cycles, with a periodicity of 100,000, 40,000 and 20,000 years. During the four cycles, the atmospheric characteristics varied within rather stable limits, with a temperature amplitude variation in Antarctica of about 12°C at land level and 8°C in the troposphere. Between cold and hot periods, the greenhouse gas concentrations in the global atmosphere varied between 180 (ppmv (parts per million in volume) and 280 ppmv for carbon dioxide, and between 350 ppbv (parts per billion in volume) and 700 ppbv for CH4.
According to these findings, the greenhouse gas concentrations are correlated to the Antarctic temperature over the entire period under study, which confirms previous observations made for the last 150,000 years. This link also appears during the warmest interglacial periods, when greenhouse gas concentrations were at their highest (300 ppmv of CO2 and 750 ppbv of CH4). These values are nevertheless far below the level of present concentrations ? 360 ppmv of CO2 and 1,700 ppbv of CH4. Such levels are unprecedented during the past 420,000 years.
Each of the four large glaciation periods was followed by a transitional interglacial period, towards the years ? 310,000, -240,00, -135,000 and ?15,000. The end of the glacial period was usually the coldest, and the transition towards a warmer climate took 5 to 10,000 years. In each of the four transitional periods, according to the analysis of the ice samples, the same sequence of events took place: the increase in the concentration of greenhouse gases (CO2 and CH4) was almost immediately (more or less 1,000 years) followed by the warming of the upper southern latitudes. And only several thousand years later, the Northern hemisphere warmed up and the ice caps that had formed massively merged. These findings show how the climate transmission system between the two hemispheres worked, and will serve as a basis for climate modelling systems.
The climate cycles, just as those observed for marine sediments, show the impact of the changes, however slight, in the Earth?s orbit on climate variations. But yet more has been discovered. Our warm period, which began 11,000 years ago, seems to be longest ever in 420,000 years. The sunshine variations are not significant enough to explain the amplitude of the observed climate changes. These findings confirm the idea, suggested a decade ago, that greenhouse gases, by amplifying the variations initiated by the orbital variations of the Earth, were also responsible for the glacial/interglacial changes. The actual mechanisms still remain to be determined.

(1) Climate and Atmospheric History of the past 420,000 years from the Vostok Ice Core, Antarctica, by 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.M., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M., Nature, 3 June 1999.

(2) The project is supported by the Russian Ministry of Sciences, and in the United States, by the Office of Polar Programs of the NSF. In France, the project is coordinated by the Laboratoire de Glaciologie et Géophysique de l?Environnement du CNRS and carried out in the framework of a close collaboration between the CNRS/INSU, the CEA/DSM and the Institut français de recherche et technologie polaire in Brest. It is also supported by the National Programme for the study of climate dynamics of the European Commission, the Fondation de France, the Rhônes-Alpes region and the J. Fourrier University in Grenoble.

Researcher contacts:
Jean Robert Petit and Dominique Raynaud
Laboratoire de Glaciologie et Géophysique de l?Environnement ? CNRS
Tel: 33 4 76 82 42 44/42 45
(Photos available at the laboratory)
Jean Jouzel
Laboratoire des sciences du climat et de l?environnement CEA-CNRS
Tel: 01 69 08 77 13
Press contact:
Séverine Duparcq
Tel: 33 1 44 96 46 06

Please take note, the figure you point out is one published by the author of this paper.

 

[Todd33]

Originally posted by: Stunt
According to this chart, our highest CO2 levels were 325,000 years ago. Our planet has also experienced much higher temperatures.

There's so much we don't know; and I have a tough time putting limits on our standard of living (GDP growth and productivity) for something which could be so insignificant. If the earth is going through a cycle, and we try to reduce it with our activities, it may be like stopping a train by standing in front of it!

Edit: sp

That's a pretty long timeline. I don't think the GW talk is about natural long term cycles, but short term impact of humans on top of the natural long term cycles. If the temp is supposed to go up 2C from 5,000BC to 5,000AD, what if we are adding another 2C on top of that in the last 200 years?

 

[Stunt]

There's just so many respectable scientists on both sides of the argument.

You can throw as many articles as you want at me, and I'd be in no position to comment, argue or criticize any position. I am however a huge supporter of research in this field. One thing I do know is, Kyoto would have little to no effect on global warming.

 

[Aimster]

wow I did find: Bush

0 results found

Impressive

 

[bdude]

Originally posted by: Stunt
There's just so many respectable scientists on both sides of the argument.

You can throw as many articles as you want at me, and I'd be in no position to comment, argue or criticize any position. I am however a huge supporter of research in this field. One thing I do know is, Kyoto would have little to no effect on global warming.

The article I threw at you, flies in the face of what you stated. Our highest levels of CO2 were NOT 325,000 years ago, for your edification.

Other than that, if you are no position to criticize the science (as you say), your basis for criticizing the Kyoto protocols is just as shaky as your statements above.

 

[Stunt]

Originally posted by: bdude

Originally posted by: Stunt
There's just so many respectable scientists on both sides of the argument.

You can throw as many articles as you want at me, and I'd be in no position to comment, argue or criticize any position. I am however a huge supporter of research in this field. One thing I do know is, Kyoto would have little to no effect on global warming.

The article I threw at you, flies in the face of what you stated. Our highest levels of CO2 were NOT 325,000 years ago, for your edification.

Other than that, if you are no position to criticize the science (as you say), your basis for criticizing the Kyoto protocols is just as shaky as your statements above.

My source says different, where does that put us now? Nowhere.

I am indeed in no position to criticize the science, but Kyoto is a whole other beast.

 

[EndGame]

Are you also aware that 80% of the countries that did sign Kyoto (sp?) will NOT be able to meet the provisions set forth in the treaty even with major cut backs and more to come? And the culprit is.........PLANT LIFE!

Like Clinton said, there is/was nothing wrong with the treaty in therory and something MUST be done, but the wording/conditions of it made the treaty un-doable. Why sign something that we already knew we would not be able to acheive?

 

[imported_Condor]

Population! Food must be prepared, shelters must be heated, goods must be delivered! Population! The more people, the fewer trees and the more of the above must be done.

 

[Cerb]

Y'all up fer some mutatin' flu? Wonderful NPG that'd be, huh?

 

[ericlp]

Well, acording to the bush admin and stunt.

The hurracain and tornado out look looks grand. I wonder how much bigger they will get this year.

To deny that we are having an impact on the earth or even having trouble trying to figure it out is pretty sad. Ya know if you can't figure it out pretty quickly it's like a frog being in a pot... If you slowly turn up the heat you are cooked and it's too late to save yourself. It's not rocket science... I'm kinda of looking forward to see what happens this year ...