Abstract
Abstract. This study addresses the possibility of carrying out spatially resolved global reconstructions of annual mean temperature using a worldwide network of proxy records and a method based on the search of analogues. Several variants of the method are evaluated, and their performance is analysed. As a test bed for the reconstruction, the PAGES 2k proxy database (version 1.9.0) is employed as a predictor, the HadCRUT4 dataset is the set of observations used as the predictand and target, and a set of simulations from the PMIP3 simulations are used as a pool to draw analogues and carry out pseudo-proxy experiments (PPEs). The performance of the variants of the analogue method (AM) is evaluated through a series of PPEs in growing complexity, from a perfect-proxy scenario to a realistic one where the pseudo-proxy records are contaminated with noise (white and red) and missing values, mimicking the limitations of actual proxies. Additionally, the method is tested by reconstructing the real observed HadCRUT4 temperature based on the calibration of real proxies. The reconstructed fields reproduce the observed decadal temperature variability. From all the tests, we can conclude that the analogue pool provided by the PMIP3 ensemble is large enough to reconstruct global annual temperatures during the Common Era. Furthermore, the search of analogues based on a metric that minimises the RMSE in real space outperforms other evaluated metrics, including the search of analogues in the range-reduced space expanded by the leading empirical orthogonal functions (EOFs). These results show how the AM is able to spatially extrapolate the information of a network of local proxy records to produce a homogeneous gap-free climate field reconstruction with valuable information in areas barely covered by proxies and make the AM a suitable tool to produce valuable climate field reconstructions for the Common Era.
Highlights
Climate field reconstruction (CFR) methods (Rutherford et al, 2005; Luterbacher et al, 2004; Mann et al, 2008; Smerdon et al, 2010) aim at reconstructing the spatially resolved time evolution of climate fields based on the information contained in a relatively sparse network of proxy archives, which usually encode only local information about past surface climate
The search within the space spanned by the first empirical orthogonal functions (EOFs) leads to a similar pointwise correlation as in the former case, which is somewhat expected since the metric is the same
This study presents a framework to carry out global CFRs using the analogue method (AM) based on a pool of the PMIP3 ensemble simulations (Taylor et al, 2012)
Summary
Climate field reconstruction (CFR) methods (Rutherford et al, 2005; Luterbacher et al, 2004; Mann et al, 2008; Smerdon et al, 2010) aim at reconstructing the spatially resolved time evolution of climate fields based on the information contained in a relatively sparse network of proxy archives, which usually encode only local information about past surface climate. To achieve spatially resolved reconstructions, the different proxy records have to be combined in proxy networks to cover wider regions, and some type of method is required to interpolate, and sometimes to extrapolate, this information and reconstruct complete gridded climate fields. Gómez-Navarro et al.: PPE for the analogue method in the Common Era proxy records to obtain a complete gridded reconstruction of particular climate variables. This is not the only strategy possible. We test the performance of a more recent CFR method, the analogue method (AM), that does not necessarily estimate the spatial climate co-variability from observations but instead combines proxy records and climate simulations to reconstruct the global near surface temperature field
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