Causes of Climate Change Over the Past 1000 Years
Abstract
Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000 years allow the warming of the 20th century to be placed within a historical context and various mechanisms of climate change to be tested. Comparisons of observations with simulations from an energy balance climate model indicate that as much as 41 to 64% of preanthropogenic (pre-1850) decadal-scale temperature variations was due to changes in solar irradiance and volcanism. Removal of the forced response from reconstructed temperature time series yields residuals that show similar variability to those of control runs of coupled models, thereby lending support to the models' value as estimates of low-frequency variability in the climate system. Removal of all forcing except greenhouse gases from the ∼1000-year time series results in a residual with a very large late-20th-century warming that closely agrees with the response predicted from greenhouse gas forcing. The combination of a unique level of temperature increase in the late 20th century and improved constraints on the role of natural variability provides further evidence that the greenhouse effect has already established itself above the level of natural variability in the climate system. A 21st-century global warming projection far exceeds the natural variability of the past 1000 years and is greater than the best estimate of global temperature change for the last interglacial.
Get full access to this article
View all available purchase options and get full access to this article.
REFERENCES AND NOTES
1
Santer B. D., et al., Nature 382, 39 (1996);
Hegerl G. C., et al., Clim. Dyn. 13, 613 (1997);
North G. R., Stevens M. J., J. Clim. 11, 563 (1998);
Tett S. F. B., et al., Nature 399, 569 (1999) ;
Barnett T. P., et al., Bull. Am. Meteorol. Soc. 80, 2631 (1999);
; G. C. Hegerl et al., Clim. Dyn., in press.
2
Barnett T. P., Santer B. D., Jones P. D., Bradley R. S., Briffa K. R., Holocene 6, 255 (1996).
3
Robock A., Science 206, 1402 (1979);
Wigley T. M. L., Raper S. C. B., Nature 344, 324 (1990) ;
Kelly P. M., Wigley T. M. L., Nature 360, 328 (1992);
Friis-Christensen E., Lassen K., Science 254, 698 (1991);
Crowley T. J., Kim K.-Y., Quat. Sci. Rev. 12, 375 (1993);
Rind D., Overpeck J., Quat. Sci. Rev. 12, 357 (1993);
Cubasch U., et al., Clim. Dyn. 13, 757 (1997);
Damon P. E., Peristykh A. N., Geophys. Res. Lett. 26, 2469 (1999);
Lean J., Rind D., J. Atmos. Sol. Terr. Phys. 61, 25 (1999).
4
Hoyt D. V., Schatten K. H., J. Geophys. Res. 98, 18895 (1993).
5
Lean J., Beer J., Bradley R., Geophys. Res. Lett. 22, 3195 (1995).
6
Overpeck J., et al., Science 278, 1251 (1997).
7
Briffa K. R., Jones P. D., Schweingruber F. H., Osborn T. J., Nature 393, 450 (1998).
8
Mann M. E., Bradley R. S., Hughes M. R., Nature 392, 779 (1998).
9
Crowley T. J., Kim K.-Y., Geophys. Res. Lett. 26, 1901 (1999).
10
Free M., Robock A., J. Geophys. Res. 104, 19057 (1999).
11
Mann M. E., Bradley R. S., Hughes M. K., Geophys. Res. Lett. 26, 759 (1999).
12
Crowley T. J., Lowery T. S., Ambio 29, 51 (2000).
13
Jones P. D., et al., Holocene 8, 467 (1998).
14
Briffa K. R., Quat. Sci. Rev. 19, 87 (2000).
15
Although it is well known that many proxy climate indices are strongly influenced by seasonal variations, such variations map into and influence mean annual temperatures [
Crowley T. J., Kim K.-Y., Geophys. Res. Lett. 23, 359 (1996);
; G. C. Jacoby and R. D. D'Arrigo, Geophys. Res. Lett.23, 2197 (1996);
Crowley T. J., Kim K.-Y., Geophys. Res. Lett. 23, 2199 (1996)].
16
Jones P. D., New M., Parker D. E., Martin S., Rigor I. G., Rev. Geophys. 37, 173 (1999).
17
Graybill D. A., Idso S. B., Global Biogeochem. Cycles 7, 81 (1993).
18
Although borehole estimates of temperature change over the past few centuries are greater in magnitude than surface proxy data [
Huang S., et al., Nature 403, 756 (2000);
], there are concerns about the potential effects of changes in land use on borehole records [
Skinner W. R., Majorowicz J. A., Clim. Res. 12, 39 (1999);
]. (See the “Discussion” section of this paper for further comments on this issue.)
19
A. Robock and M. P. Free, in Climatic Variations and Forcing Mechanisms of the Last 2000 Years, R. S. Bradley, P. D. Jones, J. Jouzel, Eds. (Springer-Verlag, Berlin, 1996), pp. 533–546.
20
Hammer C. U., Clausen H. B., Dansgaard W., Nature 288, 230 (1980);
Crowley T. J., Christe T. A., Smith N. R., Geophys. Res. Lett. 20, 209 (1993).
21
Zielinski G. A., J. Geophys. Res. 100, 20937 (1995).
22
Langway C. C., Osada K., Clausen H. B., Hammer C. U., Shoji H., J. Geophys. Res. 100, 16241 (1995).
23
T. Simkin and L. Siebert, Volcanoes of the World(Geoscience Press, Tucson, AZ, ed. 2, 1994).
24
An exception is the June 1783–January 1784 Laki (Iceland) eruption, which had an estimated Northern Hemisphere sulphur loading comparable to the combined effect of the three Caribbean eruptions in 1902 (21). Although this eruption primarily increased the tropospheric aerosol loading, the persistence and magnitude of the eruption may have approached anthropogenic troposphere sulfur emission values and had a discernible influence on Northern Hemisphere temperatures [
Hammer C., Nature 270, 482 (1977);
; H. Sigurdsson, Eos 63, 601; (7); G. J. Jacoby, K. W. Workman, R. D. D'Arrigo, Quat. Sci. Rev. 18, 1365 (1999)].
25
Hyde W. T., Crowley T. J., J. Clim. 13, 1445 (2000).
26
An informal survey of published historical records also failed to yield any clear evidence for extremely severe agricultural disruptions at this time (as would be expected if linear scaling of the ice core sulphate concentration applies). The study by Langway et al. (22) clearly indicates that evidence of this eruption occurs in both Greenland and Antarctic ice cores.
27
Pinto J. P., Turco R. P., Toon O. B., J. Geophys. Res. 94, 11165 (1989).
28
Sato M., Hansen J. E., McCormick M. P., Pollack J. B., J. Geophys. Res. 98, 22987 (1993).
29
Because of the noisy nature of the volcanic series, EBM runs were used to correlate the two long volcano time series illustrated in Fig. 2A. The 11-point smoothed correlation for the interval 1405–1960 is 0.78 (P < 0.01).
30
Beryllium-10 measurements are from
Bard E., et al., Earth Planet. Sci. Lett. 150, 453 (1997);
; the irradiance estimates derived from the 10 Be measurements are from
Bard E., et al., Tellus B 52, 985 (2000).
31
Stuiver M., Braziunas T. F., Radiocarbon 35, 137 (1993).
32
Denton G. H., Karlén W., Quat. Res. 3, 155 (1973).
33
Lean J., Skumanich A., White O., Geophys. Res. Lett. 19, 1591 (1992).
34
Lockwood M., Stamper R., Geophys. Res. Lett. 26, 2461 (1999).
35
Etheridge D. M., et al., J. Geophys. Res. 101, 4115 (1996).
36
Myhre G., Highwood E. J., Shine K. P., Stordal F., Geophys. Res. Lett. 25, 2715 (1998).
37
D. Schimel et al., in Climate Change 1995, J. T. Houghton et al., Eds. (Cambridge Univ. Press, Cambridge, 1996), pp. 65–132.
38
Haywood J. M., Ramaswamy V., J. Geophys. Res. 103, 6043 (1998);
Penner J. E., Chuang C. C., Grant K., Clim. Dyn. 14, 839 (1998);
Kiehl J. T., Schneider T. L., Rasch P. J., Barth M. C., Wong J., J. Geophys. Res. 105, 1441 (2000).
39
Kim K.-Y., Crowley T. J., Geophys. Res. Lett. 21, 681 (1994).
40
Wigley T. M. L., Raper S. C. B., Nature 330, 127 (1987).
41
Cubasch U., et al., Clim. Dyn. 8, 55 (1992);
Manabe S., Stouffer R. J., Nature 363, 215 (1993).
42
A. Kattenberg et al., in Climate Change 1995, J. T. Houghton et al., Eds. (Cambridge Univ. Press, Cambridge, 1996), pp. 285–358.
43
Although the effects of volcanism are primarily manifested in the summer hemisphere, these changes map into mean annual temperature variations at a reduced level, and the EBM is tuned to simulate mean annual temperatures. The reliability of this approach is supported by good agreement between the EBM and recent GCM studies (P. Stott et al., Clim. Dyn., in press) of a decadally averaged cooling effect from volcanism during the late 20th century. The EBM predicts a 0.2°C cooling; the GCM predicts a 0.3°C cooling. Given the facts that the ensemble GCM run has noise in it and that the GCM has a sensitivity greater than the EBM, the EBM-GCM results are not considered to be significantly different.
44
An alternate approach using 8-point smoothing followed by 5-point smoothing yields virtually identical correlations (such sequential smoothing can substantially improve the filter characteristics of a running average).
45
T. J. Crowley, data not shown.
46
Manabe S., Stouffer R. J., J. Clim. 9, 376 (1996);
Voss R., Sausen R., Cubasch U., Clim. Dyn. 14, 249 (1998);
; M. Collins, S. F. B. Tett, C. Cooper, Clim. Dyn., in press.
47
There are a number of uncertainties with respect to the estimate of unforced variability from proxy data. Because proxy reconstructions do not correlate perfectly with temperature, proxy variance may differ from the true variance. Also, residuals may include some component of forced variability due to errors in the forcing or temperature reconstructions. If multiregression is used to best fit the model to observations, the residuals will also differ slightly.
48
R. J. Stouffer, S. Manabe, K. Y. Vinnikov, Nature 367, 634;
Stouffer R. J., Hegerl G., Tett S., J. Clim. 13, 513 (2000).
49
Delworth T. L., Knutson T. R., Science 287, 2246 (2000);
; T. L. Delworth and M. E. Mann, Clim. Dyn., in press.
50
Despite clear evidence for seasonal and regional temperature changes greater than the present during the last interglacial (120,000 to 130,000 years ago), there are few quantitative estimates of global temperature change for this time. The most comprehensive assessment is based on an analysis of sea surface temperature (SST) variations [
Ruddiman W. F., Members CLIMAP, Quat. Res. 21, 123 (1984);
], which indicate an average SST for the last interglacial within 0.1°C of the mid-20th-century calibration period. This result agrees closely with that produced from a coupled ocean-atmosphere simulation [
Montoya M., Crowley T. J., von Storch H., Paleoceanography 13, 170 (1998);
]. The same model yields global temperatures only 0.3°C warmer than the control run [
Montoya M., von Storch H., Crowley T. J., J. Clim. 13, 1057 (2000);
]. The reason why regional temperatures greater than at present during the last interglacial do not translate into a large global temperature difference is because winter cooling offsets summer warming in some time series and because there are significant phase offsets between the timing of peak warmth in different regions [
Crowley T. J., J. Clim. 3, 1282 (1990)].
51
Preliminary results suggest that a 2.0°C sensitivity slightly overestimates the response (G. C. Hegerl and T. J. Crowley, in preparation), but it is not yet clear whether this result reflects lower best fit sensitivity or errors in forcing and temperature estimates.
52
Allen M. R., Tett S. F. B., Clim. Dyn. 15, 419 (1999).
53
Bonan G. B., Pollard D., Thompson S. L., Nature 359, 716 (1992);
Pielke R. A., Vidale P. L., J. Geophys. Res. 100, 25755 (1995);
Brovkin V., et al., Global Ecol. Biogeogr. 8, 509 (1999).
54
Oerlemans J., Science 264, 243 (1994).
55
Broecker W. S., Sutherland S., Peng T.-H., Science 286, 1132 (1999).
56
As a further test of this conclusion, correlations of the Mann et al. and CL 1005–1850 records with an index of North Atlantic Current intensity range from 0.26 for the smoothed Mann et al. (11) index to 0.58 for the CL index; the large difference in the correlations reflects the greater trend in the CL index (detrended correlations are 0.09 and 0.23, respectively). The North Atlantic Current index (T. J. Crowley, in preparation) is an estimate of relative warmth in the subpolar North Atlantic sector and is a composite of δ18O variations in the GISP2 and Dye3 Greenland ice cores and in a winter sea ice record from Iceland [
Bergthorsson P., Jokull 19, 94 (1969);
; W. Dansgaard et al., in Greenland Ice Core: Geophysics, Geochemistry, and the Environment, C. C. Langway et al., Eds. (American Geophysical Union, Washington, DC, 1985), pp. 71–76;
Stuiver M., Grootes P., Braziunas T., Quat. Res. 44, 341 (1995)].
57
Berger A. L., Quat. Res. 9, 139 (1978).
58
A seasonal two-dimensional EBM [
Hyde W. T., Crowley T. J., Kim K.-Y., North G. R., J. Clim. 2, 864 (1989);
] actually yields a very slight warming (0.006°C) over the past 1000 years, because perihelion is now about 2 weeks closer to the Northern Hemisphere summer solstice (it coincided with the winter solstice about 900 years ago). The EBM has a sensitivity comparable to many GCMs [
Crowley T. J., Baum S. K., Hyde W. T., J. Geophys. Res. 96, 9217 (1991);
]. A nonlinear version of this model [
Hyde W. T., Kim K.-Y., Crowley T. J., North G. R., J. Geophys. Res. 95, 18653 (1990);
] indicates that snow/ice feedback would increase the sensitivity of the calculated response by about 25%.
59
Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment, J. T. Houghton, B. A. Callendar, S. K. Varney, Eds. (Cambridge Univ. Press, Cambridge, 1992).
60
Supported by NOAA grant NA96GP0415 and by a separate NOAA/DOE grant through Battelle/Pacific Northwest Laboratories. I thank E. Bard, S. Baum, M. Collins, G. Hegerl, W. Hyde, P. Jones, K.-Y. Kim, J. Lean, T. Lowery, M. MacCracken, M. Mann, G. North, H. Oerlemans, W. F. Ruddiman, M. Stuiver, R. Voss, and the reviewers for comments and/or assistance.
(0)eLetters
eLetters is a forum for ongoing peer review. eLetters are not edited, proofread, or indexed, but they are screened. eLetters should provide substantive and scholarly commentary on the article. Embedded figures cannot be submitted, and we discourage the use of figures within eLetters in general. If a figure is essential, please include a link to the figure within the text of the eLetter. Please read our Terms of Service before submitting an eLetter.
Log In to Submit a ResponseNo eLetters have been published for this article yet.
Information & Authors
Information
Published In
Science
Volume 289 | Issue 5477
14 July 2000
14 July 2000
Submission history
Received: 12 May 2000
Accepted: 22 June 2000
Published in print: 14 July 2000
Authors
Metrics & Citations
Metrics
Article Usage
Altmetrics
Citations
Cite as
- Thomas J. Crowley
Export citation
Select the format you want to export the citation of this publication.
Cited by
- Tree-Ring Chronologies and Climate Variability, Science, 296, 5569, (848-849), (2021)./doi/10.1126/science.296.5569.848
- Indirect Aerosol Forcing, Science, 290, 5491, (407-407), (2021)./doi/10.1126/science.290.5491.407a
- The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System, Science, 290, 5490, (291-296), (2021)./doi/10.1126/science.290.5490.291
- Lessons for a New Millennium, Science, 289, 5477, (253-254), (2021)./doi/10.1126/science.289.5477.253
- Recent Warming Reverses Long-Term Arctic Cooling, Science, 325, 5945, (1236-1239), (2021)./doi/10.1126/science.1173983
- Comment on "Reconstructing Past Climate from Noisy Data", Science, 312, 5773, (529-529), (2021)./doi/10.1126/science.1120866
- The Spatial Extent of 20th-Century Warmth in the Context of the Past 1200 Years, Science, 311, 5762, (841-844), (2021)./doi/10.1126/science.1120514
- A Stellar View on Solar Variations and Climate, Science, 306, 5693, (68-69), (2021)./doi/10.1126/science.1101694
- Reconstructing Past Climate from Noisy Data, Science, 306, 5696, (679-682), (2021)./doi/10.1126/science.1096109
- European Seasonal and Annual Temperature Variability, Trends, and Extremes Since 1500, Science, 303, 5663, (1499-1503), (2021)./doi/10.1126/science.1093877
- See more
Loading...
View Options
Check Access
Log in to view the full text
AAAS login provides access to Science for AAAS Members, and access to other journals in the Science family to users who have purchased individual subscriptions.
- Become a AAAS Member
- Activate your AAAS ID
- Purchase Access to Other Journals in the Science Family
- Account Help
Log in via OpenAthens.
Log in via Shibboleth.
More options
Purchase digital access to this article
Download and print this article for your personal scholarly, research, and educational use.
Buy a single issue of Science for just $15 USD.