Chironomid-based Holocene summer temperature dynamics from southern Spain

Global warming is generating substantial environmental modifications in fragile alpine areas. Past temperature reconstructions are necessary to evaluate how climate change modified alpine environments before instrumental measurements. In this study, we present a reconstruction of Holocene mean July and summer air temperatures, derived from chironomid and pollen assemblages preserved in the sedimentary record from Laguna de la Mosca (LdlMo), an alpine lake located in the Sierra Nevada of southern Spain. The ∼8500-year-long LdlMo record shows highest temperatures reached during the Early and Middle Holocene from ∼8500 until ∼7100 calibrated 14 C years BP (cal yr BP), when a first drop in temperatures occurred. Temperatures stabilized during the Middle Holocene and a second drop happened at ∼4500 and 4200 cal yr BP, possibly associated with the 4.2 kyr climatic event. Temperatures remained generally low during the Late Holocene, interrupted by warming between 2300 and 1600 cal yr BP during the Iberian Roman Humid Period (IRHP), and around 1000 cal yr BP during the Medieval Climate Anomaly (MCA). Minimum temperatures are recorded during the end of the Little Ice Age (LIA) at ∼1800 CE. A sudden and rapidly increasing trend in temperatures of ∼2.5 °C occurred since 1955 CE related to anthropogenic climate warming. This study confirms the rapid recent warming at high elevations, affecting the very sensitive chironomid assemblages and compromising these fragile and unique alpine lake ecosystems. • Warmest temperatures occurred between 8500 and 7100 cal yr BP related to insolation. • Subsequent cooling occurred in two steps, at 7100 and 4200 cal yr BP. • Cold and arid conditions recorded in Sierra Nevada during 4.2 kyr event. • Modern climate warming during summer in Sierra Nevada exceeds 2 °C.