Abstract:
The recent availability of global networks of annual or seasonal resolution proxy data, combined with the few long instrumental and historical climate records available during the past few centuries, make it possible now to reconstruct annual and seasonal spatial patterns of temperature variation, as well as hemispheric, global-mean, and regional temperature trends, several centuries back in time. Reconstructions of large-scale global or hemispheric trends during centuries past can place the instrumental assessments of climate during the twentieth century in a longer-term perspective and provide more robust evidence regarding the roles of potential climate forcings over time. The reconstructed spatial patterns lead to important inferences regarding ENSO-scale variability, the spatial influences of climatic forcings, and the regional patterns that underlie large-scale climate variations. Here proxy-based annual global temperature pattern reconstructions described recently by Mann et al. are expanded upon. For the first time seasonally resolved versions of the proxy-reconstructed surface temperature patterns are presented, and the seasonal differences between key climate indices and patterns of variations are diagnosed. The reader is enabled to interactively examine spatial as well as temporal details (and their uncertainties) of yearly temperatures back in time for both annual-mean and seasonal windows. Annual and seasonal time histories of reconstructed Northern Hemisphere, Southern Hemisphere, and global-mean temperature are made available, as are time histories of the Niño-3 index describing El Nin˜o– related variations, time histories for particular regions of interest such as North America and Europe, and time series for temperature variations in different (e.g., tropical and extratropical) latitude bands. Time histories for specific grid points are available along with their estimated uncertainties. Time histories for the different eigenvectors [i.e., the reconstructed principal components (RPCs)] are also available, along with the raw instrumental series, which underlie the temperature pattern reconstructions. For both the annual-mean and seasonally resolved temperature reconstructions, the reader can directly compare reconstructed patterns for different years, as well as the raw and reconstructed patterns during calibration and verification intervals, and view animated year-by-year sequences of reconstructed global temperature patterns. The statistical relationships between climate forcings and temperature variations are also analyzed in more detail, taking into account potential lagged responses to climate forcings in empirical attribution analyses.
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