Climate change will increase the exposure of organisms to higher temperatures, but can also drive phenological shifts that alter their susceptibility to conditions at the onset of breeding cycles. Organisms rely on climatic cues to time annual life-cycle events, but the extent to which climate change has altered cue reliability remains unclear. Here, we examine the risk of a ‘climate trap’ – a climatically-driven desynchronisation of the cues that determine life-cycle events and fitness later in the season in a temperate reptile, the European adder (Vipera berus). During the winter, adders hibernate underground, buffered against sub-zero temperatures, and re-emerge in the spring to reproduce. We derived annual spring-emergence trends between 1983 and 2017 from historical observations in Cornwall, United Kingdom, and related these trends to the microclimatic conditions that adders experienced. Using a mechanistic microclimate model, estimates of below- and near-ground temperatures were used to derive accumulated degree-hour and absolute temperature thresholds that predicted annual spring-emergence timing. Trends in annual emergence timing and subsequent exposure to ground frost were then quantified. We found that adders have advanced their phenology towards earlier emergence. Earlier emergence was associated with increased exposure to ground frost and, contradicting the expected effects of macroclimate warming, increased post-emergence exposure to ground frost at some locations. The susceptibility of adders to this ‘climate trap’ was related to the rate at which frost risk diminishes relative to advancement in phenology, which depends on the seasonality of climate. We emphasise the need to consider exposure to changing microclimatic conditions when forecasting biological impacts of climate change.

This spreadsheet contains nine tabs to present the data used in the article 'Microclimate-driven trends in spring-emergence phenology in a temperate reptile (Vipera berus): Evidence for a potential ‘climate trap’?' (Turner & Maclean, 2022; Ecology and Evolution). The first tab, labelled 'Metadata_README', contains metadata for the dataset, including identification and affliliations of the authors, a description of the tabs in the spreadsheet, and descriptions of data labels used in the spreadsheet tabs. The second tab, labelled 'adder_sightings', comprises of records of Vipera berus (adder) sightings in Cornwall, United Kingdom, sourced from the Environmental Records Centre for Cornwall and the Isles of Scilly (www.erccis.org.uk), the Record Pool (www.recordpool.org.uk) and the Cornish Biodiversity Network (www.cornishbiodiversitynetwork.org). Due to data sensitivities and issues associated with the General Data Protection Regulation, information pertaining to the locations and dates of adder sightings in some instances in the dataset have only be provided at reduced spatial and temporal resolutions. A unique identification code for locations has been attributed to records. For full-resolution access, contact the data custodian and corresponding author. The raw datasets of adder sightings were filtered prior to inclusion in the analysis in Turner and Maclean. See the main text for all filtering procedures and microclimate modelling. The remaining tabs contain data relating to each adder sighting location in 'adder_sightings' for each year 1983 - 2017 computed from microclimate models using the microclima R package (Maclean et al., 2019). The third tab, labelled 'total_spring_frost', contains annual rates of spring ground frost. The fourth, fifth and sixt tabs, labelled 'Cue1(i)', "Cue1(ii)', and 'Cue1(iii)', each contain predicted annual adder emergence timing and computed rates of post-emergence spring ground frost using the 5th, 2.5th and 10th percentile thresholds, respectively, of an accumulated (degree-hours) temperature cue for adder emergence. The seventh tab, labelled 'Cue2', contains predicted annual adder emergence timing and computed rates of post-emergence spring ground frost using a sharp rise in accumulated (degree-hours) temperature cue for adder emergence. The eighth tab, labelled 'Cue3', contains predicted annual adder emergence timing and computed rates of post-emergence spring ground frost using a below-ground temperature gradient collapse cue for adder emergence. Lastly, the ninth tab, labelled 'Cue4', contains predicted annual adder emergence timing and computed rates of post-emergence spring ground frost using a critical air temperature (10°C) cue for adder emergence. The main text presents the analysis of adder emergence and spring ground frost data from the 'Cue1(i)'. Analysis of data from 'Cue1(ii)', 'Cue1(iii)', 'Cue2', 'Cue3', and 'Cue4' are presented in the Supplementary Information for Turner and Maclean.