New Tree-Ring Evidence from the Pyrenees Reveals Western Mediterranean Climate Variability since Medieval Times


Paleoclimatic evidence is necessary to place the current warming and drying of the western Mediterranean basin in a long-term perspective of natural climate variability. Annually resolved and absolutely dated temperature proxies south of the European Alps that extend back into medieval times are, however, mainly limited to measurements of maximum latewood density (MXD) from high-elevation conifers. Here, we present the world’s best replicated MXD site chronology of 414 living and relict Pinus uncinata trees found >2200 m asl in the Spanish central Pyrenees. This composite record correlates significantly (p ≤0.01) with May-June and August-September mean temperatures over most of the Iberian Peninsula and northern Africa (r =0.72 1950-2014). Spanning the period 1186-2014 CE, the new reconstruction reveals overall warmer conditions around 1200 and 1400, and again after ~1850. The coldest reconstructed summer in 1258 (-4.4°C wrt 1961-1990) followed the largest known volcanic eruption of the CE. The 20th century is characterized by pronounced summer cooling in the 1970s, subsequently rising temperatures until 2003, and a slowdown of warming afterwards. Little agreement is found with climate model simulations that consistently overestimate recent summer warming and underestimate pre-industrial temperature changes. Interannual to multi-decadal co-variability with regional hydroclimate includes summer pluvials after large volcanic eruptions. Our study demonstrates the relevance of updating MXD-based temperature reconstructions, not only back in time but also towards the present, and emphasizes the importance of comparing temperature and hydroclimatic proxies, as well as model simulations for understanding regional climate dynamics.
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