Extended Data Fig. 1: Effect of time uncertainty on the spectral estimates of local and hemispheric temperature.
From: Millennial-scale climate variability over land overprinted by ocean temperature fluctuations
The summer-JJA temperature data of the TraCE-21ka simulation over 0–8 ka BP is extracted at the location of the pollen records to create a surrogate database with and without time-uncertainty (See Methods) from which are computed and shown the mean of all local spectra and the spectra of the hemispheric average temperature; logarithmically spaced axes were used. Only one realization of the surrogate database for each level of time-uncertainty τε is shown for simplicity as very similar results are obtained for any given realization. The average spectrum of local temperature variability, which is employed in this study, is robust to irregularity of the pollen records and time-uncertainty. In contrast, the spectra of average (hemispheric) temperature show a strong power-loss due to those effects. This implies that the amplitude of centennial to millennial temperature variations from large spatial scale averages cannot be quantitatively interpreted without the knowledge of the amount and structure of time uncertainty. Shading indicates 90% confidence intervals around the mean.
