Relationship of Northern hemisphere mean (NH) temperature with 3 candidate forcings
between 1610 and 1995. (i) reconstructed NH temperature series from 1610-1980 update with
raw data from 1981-1995.
(i) greenhouse gases represented by atmospheric CO2 measurements.
(ii) reconstructed solar irradiance.
(iii) weighted volcanic dust veil index (DVI).
(iv) evolving multivariate correlation of NH series with the 3 forcings (i) (ii) and (iii).
The time axis denotes the center of a 200 year moving window. One-sided (positive) 90%, 95%, 99% significance levels (see text) for correlations with CO2 and solar irradiance are shown by horizontal dashed lines, while the one-sided (negative) 90% significance threshold for correlations w/ the DVI series is shown by the horizontal dotted line. The gray bars indicates two different 200 year window of data, with the long-dashed vertical lines indicating the center of the corresponding windows and intersecting the 3 curves at their corresponding values. The upper gray bar spans the window from 1751-1950 (centered at '1850'), while the lower gray bar indicates the final data window from 1796-1995 (window centered at '1895') correspond to the final estimates from the moving multivariate correlation. While generalizations of our approach which exploit temporal autocovariance and error covariance estimation could provide for an even more efficient calibration of the multiproxy network, we established a satisfactory statistical efficiency of our particular approach through synthetic experiments based on small trainee networks of 'pseudo-proxies' constructed as linear combinations of the actual PCs immersed in additive noise. These synthetic experiments demonstrated that the reconstructed fields asymptotically approach their exact counterparts as the number of trainee records and resolvable eigenvectors is increased. These experiments also demonstrate that any climatic indicator with a linear relationship to any combination of large-scale temperature eigenvectors such as sea level pressure or precipitation indicators, adds incremental value in the calibration process.
of temperature, and precipitation/drought. Other studies have demonstrated that particularly well-chosen regional proxy climate reconstructions can act as surprisingly representative surrogates for larger-scale features such as hemispheric mean temperature, ENSO or North Pacific and North Atlantic sea level pressure and temperature patterns.