Climate refugia: from the Last Glacial Maximum to the twenty-first century.

ThehistoryofEarth is ahistoryof recurrent climate change.Today’s globalbiodiversitydemonstrates thatmany specieshavebeenable to cope with climate shifts in the past. Yet great concern exists that modern climate change is likely to overstrain the capacity of many species to track suitable climate spaces, potentially leading to widespread extinctions through the coming decades. This view is further promoted by a large number of species distribution modeling (SDM) forecasts. It remains, however, relatively little appreciated that the deeply troubling picture stands in contrast to empirical records of species responses to past climatic changes (Botkin et al., 2007). Fossil data indicate that extensive range dynamics andmassive community reshuffling occurred during past periods of rapid climate transitions. But, at least for plants, there is little evidence that pastmajorwarming eventswere accompaniedby increased global-scale extinction rates (Willis & MacDonald, 2011). One possible explanation for this apparent contradiction is that climate refugia – areas where local populations of a species can persist throughperiods of unfavorable regional climate– could have beenmuchmore commonandwidespread thanpreviously thought. Such areas would have helped sustain regional biodiversity through periodsofadverseclimateormajorclimatic transitions, andservedas sources for the subsequent re-expansion of confined populations. The existence and identification of refugia during the Last Glacial Maximum (c. 19–26 kyr BP; Clark et al., 2009) has been a topic of active research for decades. Recent evidence indicates that many temperate and boreal species have maintained populations at considerably higher latitudes than previously assumed (Hu et al., 2009;Mosblech et al., 2011). Such locations are commonly referred to as ‘cryptic refugia’, a term that nicely conveys the difficulties in inferring the past existence of these small and scattered refugial populations. The crucial role of climate refugia for the long-term maintenance of regional to global biodiversity, and the growing awareness that refugia may be similarly relevant as ‘safe havens’ under future climate warming, have sparked great interest in their identification and functioning (e.g. M edail & Diadema, 2009; Stewart et al., 2010; Keppel et al., 2012). Joining research perspectives and approaches