Abstract
This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe.
Highlights
The well-documented changes in a number of observational variables demonstrate a significant role of anthropogenic activities in modifying the Earth's climate
It is possible that the BARCAST AR(1) model assumption itself is improper for the North Atlantic CESM target sea surface temperature (SST) data, and that violation of the BARCAST assumptions causes the underestimation of the posterior AR(1) coefficient a
The northern North Atlantic marine proxy network is subject to age-uncertainties and proxy noise, and our analyses demonstrate that the analogue method is superior to BARCAST for SST reconstruction under these premises
Summary
The well-documented changes in a number of observational variables demonstrate a significant role of anthropogenic activities in modifying the Earth's climate. Recent proxy development and improved statistical methods in age-model simulation and CFR contribute to our confidence that the field of northern North Atlantic SST can be skillfully reconstructed (Pyrina et al, 2017; Reynolds et al, 2018), despite the shortcomings of the marine proxy data. Two state-of-the-art CFR methods are described and tested in detail, evaluating their skill in reconstructing northern North Atlantic SST over the past millennium with annual and decadal resolution. An extended version of the methodology is applied, allowing age-uncertain proxy records following Werner and Tingley (2015) This functionality is critical for handling age uncertainties properly when reconstructing northern North Atlantic SST.
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