Arctic environmental change of the last four centuries

Science

Volumn 278, Issue 5341, 1997, Pages 1251-1256

  Overpeck, J ^a,b   Hughen, K ^b   Hardy, D ^c   Bradley, R ^c   Case, R ^d   Douglas, M ^e   Finney, B ^f   Gajewski, K ^g   Jacoby, G ^h   Jennings, A ^b   Lamoureux, S ⁱ   Lasca, A ^j   MacDonald, G ^d   Moore, J ^b   Retelle, M ^j   Smith, S ^c   Wolfe, A ^b   Zielinski, G ^k  

^a NATIONAL GEOPHYSICAL DATA CENTER   (United States)

^b UNIVERSITY OF COLORADO   (United States)

^c UNIVERSITY OF MASSACHUSETTS   (United States)

^d UNIVERSITY OF CALIFORNIA   (United States)

^e UNIVERSITY OF TORONTO   (Canada)

^f UNIVERSITY OF ALASKA FAIRBANKS   (United States)

^g UNIVERSITY OF OTTAWA   (Canada)

^h International Research Institute for Climate and Society   (United States)

ⁱ UNIVERSITY OF ALBERTA   (Canada)

^j BATES COLLEGE   (United States)

^k UNIVERSITY OF NEW HAMPSHIRE   (United States)

more..

Author keywords

[No Author keywords available]

Indexed keywords

ENVIRONMENTAL CHANGE; PALAEOCLIMATE; SOLAR IRRADIANCE; VOLCANIC ACTIVITY; WARMING;

ARCTIC CLIMATE; ATMOSPHERIC PRESSURE; ENVIRONMENTAL MONITORING; GLOBAL CLIMATE; HISTORY; PRIORITY JOURNAL; REVIEW; VOLCANIC ASH; WARMING;

ARCTIC;

EID: 14444287752     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.278.5341.1251     Document Type: Review

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31. The proxy temperature time series in Fig. 2 were chosen because they were available in time series form. Most of the paleoclimate time series have been calibrated against instrumental data, but the scarcity of weather stations in the Arctic makes it necessary to rely on similar records that have been calibrated directly against instrumental data, or to use theory, in order to define the nature of the climate signal represented in a few of the proxy records. For example, ice cores are commonly far from any instrumental station, but theory supports the interpretation of ice core melt layers as a proxy of summer temperature [whereas ice core stable isotopic variations are more complex on decadal time scales (10)]. Likewise, the selection of site characteristics ensures that tree ring chronologies correlate well with summer or annual temperatures where they can be compared with nearby instrumental records, reinforcing the likelihood that tree ring width also correlates well with summer or annual temperature at sites remote from any instrumental station (8, 9, 26). Theory and (in cases where nearby meteorological data are available) direct correlation with instrumental data support the assertion that the lake sediment records included in this study are also useful centuries-long proxies for early summer temperatures (20, 21, 65) [D. R. Hardy et al., J. Paleolimnol. 16, 227 (1996)]. Thus, although most of the time series summarized here have been calibrated quantitatively against summer temperature, it is more appropriate to plot raw proxy data (x) in terms of "sigma units" defined as normalized deviations (z) from the 1901-1960 mean (m): z = (x - m)/s, where s is the standard deviation of the raw series for the period 1901-1960. The reference period was selected to highlight the 20th century in the context of preceding centuries. Five-year averages are plotted to emphasize the lower frequency patterns of variability and to accommodate the ∼1% temporal error that characterizes the sediment and ice core-based records. Tree ring chronologies generally are accurate at annual resolution, but they may be biased in Alaska after 1970 by moisture stress or new anthropogenic causes (58).
32. The 400-year Arctic average summer temperature series (Fig. 3) was generated by first averaging the standardized 5-year-averaged series (Fig. 2) for each of the groups circled in Fig. 1 (to eliminate site density bias) and then averaging the group averages with the other single sites not circled in Fig. 1. Sites 8 and 29 were excluded because of their subdecadal resolution.
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37. Borehole climate reconstructions do not have the high temporal resolution of the records shown in Fig. 2, but they provide a clear confirmation of the recent warming trend seen in the annually dated proxies, as well as useful quantitative estimates of the magnitude of warming [A. H. Lachenbruch et al., J. Geophys. Res. 87, 9301 (1982); A. H. Lachenbruch and B. V. Marshall, Science 234, 689 (1986); S. Kakuta, Palaeogeogr. Palaeoclimatol. Palaeoecol. 98, 225 (1992); H. Beltrami and A. E. Taylor, Global Planet. Change 11, 127 (1995)].
38. Borehole climate reconstructions do not have the high temporal resolution of the records shown in Fig. 2, but they provide a clear confirmation of the recent warming trend seen in the annually dated proxies, as well as useful quantitative estimates of the magnitude of warming [A. H. Lachenbruch et al., J. Geophys. Res. 87, 9301 (1982); A. H. Lachenbruch and B. V. Marshall, Science 234, 689 (1986); S. Kakuta, Palaeogeogr. Palaeoclimatol. Palaeoecol. 98, 225 (1992); H. Beltrami and A. E. Taylor, Global Planet. Change 11, 127 (1995)].
39. Borehole climate reconstructions do not have the high temporal resolution of the records shown in Fig. 2, but they provide a clear confirmation of the recent warming trend seen in the annually dated proxies, as well as useful quantitative estimates of the magnitude of warming [A. H. Lachenbruch et al., J. Geophys. Res. 87, 9301 (1982); A. H. Lachenbruch and B. V. Marshall, Science 234, 689 (1986); S. Kakuta, Palaeogeogr. Palaeoclimatol. Palaeoecol. 98, 225 (1992); H. Beltrami and A. E. Taylor, Global Planet. Change 11, 127 (1995)].
40. Borehole climate reconstructions do not have the high temporal resolution of the records shown in Fig. 2, but they provide a clear confirmation of the recent warming trend seen in the annually dated proxies, as well as useful quantitative estimates of the magnitude of warming [A. H. Lachenbruch et al., J. Geophys. Res. 87, 9301 (1982); A. H. Lachenbruch and B. V. Marshall, Science 234, 689 (1986); S. Kakuta, Palaeogeogr. Palaeoclimatol. Palaeoecol. 98, 225 (1992); H. Beltrami and A. E. Taylor, Global Planet. Change 11, 127 (1995)].
41. Other quantitative records include: P. E. Calkin, Quat. Sci. Rev. 7, 159 (1988); _ and G. C. Wiles, in International Conference on the Role of Polar Regions in Global Change, G. Weller, Ed. (University of Alaska, Fairbanks, AK, 1991), pp. 617-625; C. Caseldine and J. Stötter, The Holocene 3, 357 (1993); J. M. Szeicz and G. M. MacDonald, Quat. Res. 44, 257 (1995); L. H. Evison et al., The Holocene 6, 17 (1996).
42. Other quantitative records include: P. E. Calkin, Quat. Sci. Rev. 7, 159 (1988); _ and G. C. Wiles, in International Conference on the Role of Polar Regions in Global Change, G. Weller, Ed. (University of Alaska, Fairbanks, AK, 1991), pp. 617-625; C. Caseldine and J. Stötter, The Holocene 3, 357 (1993); J. M. Szeicz and G. M. MacDonald, Quat. Res. 44, 257 (1995); L. H. Evison et al., The Holocene 6, 17 (1996).
43. Other quantitative records include: P. E. Calkin, Quat. Sci. Rev. 7, 159 (1988); _ and G. C. Wiles, in International Conference on the Role of Polar Regions in Global Change, G. Weller, Ed. (University of Alaska, Fairbanks, AK, 1991), pp. 617-625; C. Caseldine and J. Stötter, The Holocene 3, 357 (1993); J. M. Szeicz and G. M. MacDonald, Quat. Res. 44, 257 (1995); L. H. Evison et al., The Holocene 6, 17 (1996).
44. Other quantitative records include: P. E. Calkin, Quat. Sci. Rev. 7, 159 (1988); _ and G. C. Wiles, in International Conference on the Role of Polar Regions in Global Change, G. Weller, Ed. (University of Alaska, Fairbanks, AK, 1991), pp. 617-625; C. Caseldine and J. Stötter, The Holocene 3, 357 (1993); J. M. Szeicz and G. M. MacDonald, Quat. Res. 44, 257 (1995); L. H. Evison et al., The Holocene 6, 17 (1996).
45. Other quantitative records include: P. E. Calkin, Quat. Sci. Rev. 7, 159 (1988); _ and G. C. Wiles, in International Conference on the Role of Polar Regions in Global Change, G. Weller, Ed. (University of Alaska, Fairbanks, AK, 1991), pp. 617-625; C. Caseldine and J. Stötter, The Holocene 3, 357 (1993); J. M. Szeicz and G. M. MacDonald, Quat. Res. 44, 257 (1995); L. H. Evison et al., The Holocene 6, 17 (1996).
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112. This work is a Paleoclimates of Arctic Lakes and Estuaries (PALE) contribution to the NSF Arctic System Science (ARCSS) Program. It is also a product of the NSF- and NOAA-sponsored Analysis of Rapid and Recent Climatic Change (ARRCC) and other non-PALE (for example, dendroclimatic) projects, and is also a result of research funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), including the Paleoecological Analysis of Circumarctic Treeline (PACT) program. The Polar Continental Shelf Project provided logistical field support. We thank our colleagues for discussion of our work at ARCSS workshops, as well as J. Cole, J. Lean, A. Ogilvie, and two anonymous reviewers for critical comments on the manuscript.-