HR: 1020h
AN: PP52A-0662    [Abstracts]
TI: Improved agreement between borehole and other proxy reconstructions of paleoclimate via a new common temperature reference scheme
AU: * Smerdon, J E
EM: jsmerdon@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W P.O. Box 1000, Palisades, NY 10964 United States
AU: Pollack, H N
EM: hpollack@umich.edu
AF: University of Michigan, 1100 N. University Ave., Ann Arbor, MI 48109-1005 United States
AB: Comparisons between temperature reconstructions derived from proxy data require common temperature reference. Given any number of proxy time series scaled to temperature, one must decide how to reference each reconstruction on a common temperature scale such that their relative variability has comparable meaning. Two choices are common: 1) an absolute temperature scaling in which time series are referenced to the Kelvin, Celsius or Fahrenheit scales; or 2) an anomaly scaling in which each time series is referenced to its own mean during a specified time interval. This latter choice is typically applied because the relative variability of each proxy time series is often the topic of interest. For example, a widely applied convention references all temperature reconstructions to their mean temperature during the 1961-90 time interval. While this scheme is appropriate for reconstructions with equal temporal resolution, it can lead to inappropriate comparisons between reconstructions with different resolutions. We demonstrate that comparisons between borehole reconstructions, comprising piecewise centennial trends, with other annually-resolved proxy reconstructions have inadvertently exaggerated the amount of disagreement between the two estimates of past climate change. This exaggeration arises because the borehole reconstructions have been referenced to other anomaly series using the mean temperature of the 20th-century borehole trend between 1961 and 1990. A more appropriate referencing scheme for the borehole reconstructions pins the zero crossing of the 20th-century trend in the borehole time series to the equivalent point in the linear trend of the 20th-century instrumental record. Such a referencing approach reduces the disagreement between borehole reconstructions and other estimates of past climate change. For example, the difference in minimum 16th-century temperatures in the Northern Hemisphere between borehole and other proxy-based estimates is reduced by approximately 0.2 K. Attention to this simple referencing scheme is therefore an important consideration for comparisons between borehole-derived estimates of climate change and other proxy reconstructions that have higher temporal resolution.
DE: 1610 Atmosphere (0315, 0325)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1626 Global climate models (3337, 4928)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 4920 Dendrochronology
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005