current rates of species extinction have been inferred to be orders of magnitude above background levels , based on well known groups with a fossil record , but whether these taxa are representative for biodiversity in general is not known . there is concern that we are currently entering a mass extinction event comparable to the previous five greatest mass extinctions in the history of life . currently , most human - induced extinctions result from habitat destruction and overexploitation of species . climate change caused by greenhouse gas emissions may become a similarly severe threat , and will add to present challenges for global biodiversity . the ability to assess the potential species loss the number of species on earth is not known even to the order of magnitude , and the geographic distributions and ecology is poorly known for most taxa described by science . extinctions of species where climate change is thought to be the ultimate cause may have already occurred , but pinpointing the ultimate cause of an extinction event is difficult . to assess the magnitude of the problem in the future , modelling is required . despite the challenge of incomplete knowledge , rough predictions of the number of species threatened with extinction by climate change have been made [ 8 - 10 ] . the general method in such predictions has been to project the degree of habitat loss expected as a result of geographic range adjustments in response to climate change , and then use species - area equations to assess potential species loss as a result of range contractions . depending on the climate change scenario used and dispersal ability of species , thomas et al .   projected that 18 - 35% of species are at risk of extinction in their sample of regions across the earth . the paper and similar efforts are controversial , however , and both the methods   and the way the results have been presented in the media   have been criticized . nevertheless , realistic predictions of climate - driven extinction risk are needed for climate mitigation and species conservation efforts . the accuracy of extinction risk predictions depends on the ability to project how species will adjust to climate change . to survive climate change that is beyond its tolerance , a species may either adapt to the new climate locally , or shift its geographical distribution to climatically suitable areas . a critical question is whether species will be able to evolve tolerance to new climatic conditions at the pace of climate change . species distribution models utilize species distribution records and correlations with climate to project where species will occur in the future under the assumption of no evolutionary change . these models are not only used to predict extinction risk , but by providing projections of where species may occur in a future climate , they form the basis of adaptation strategies to conserve biodiversity . when the ability of species distribution models to predict future distributions has been checked , however , their performance has been less than satisfying , although the methods are rapidly improving . reasons for poor model performance and inconsistencies among models include variation among climate change scenarios , poor species distribution data , variation in modelling methods , and violation of model assumptions . one way of gaining insight into the constraints and opportunities offered by extinction risk assessments is to examine how species have responded to similar climatic challenges in the past , and to examine how biodiversity is distributed at large spatial scales and the underlying causes of this distribution , sometimes referred to as below i highlight recent advances in the knowledge of how species adjust their ranges in response to climate change now and in the past , which may help assess the risk for climate - induced species extinctions . if species can evolve rapidly enough in response to climate change , projections of extinction risk based on species distribution modelling may be overestimated . recent empirical evidence suggests that evolution is responsive to climate variation and may occur at rates that make evolutionary change a plausible alternative to geographical range shifts . adaptive evolution in local populations may , however , be counteracted by competition from immigrating organisms pre - adapted to the new climate . the dominant response to quaternary climate changes comprised geographical range shifts rather than morphological adaptation in situ . both in situ persistence and range shifts may involve evolutionary processes that enhance adaptations to new climatic conditions - for example , by selection for enhanced tolerance in migrating populations . an increasing body of data documents that species and assemblages respond to warming as predicted by models , adjusting their ranges polewards and towards higher elevations . this lends support to bioclimatic modelling approaches and projections of species extinction . the most common data record latitudinally expanding range limits of temperate taxa colonizing habitats that have become climatically suitable [ 21 - 23 ] . records of latitudinal range contractions are mostly anecdotal , but a few recent studies document elevational range shifts [ 25 - 27 ] . range shifts on tropical mountains in response to warming raise double concerns ; many high - elevational species are at risk of becoming extinct if mountains are  too low to offer them habitat after the climate zones have shifted upwards . in addition , tropical lowlands might be depleted of species as more and more species shift their ranges towards higher latitudes and elevations . data on range shifts from tropical mountains have been mostly missing , but recently chen et al .   documented 102 insect species shifting their distributions an average of 62 m upwards on mount kinabalu , borneo , between 1965 and 2007 . raxworthy et al .   found that 30 species of reptiles and amphibians had shifted their elevational midpoints upslope by 19 - 51 m on madagascar , in agreement with recent regional warming . some climate types are predicted to completely disappear , threatening species assemblages living in these vanishing environments with extirpation . in the majority of cases , however , the environments of species will shift geographically to various degrees , necessitating modelling of range adjustments and extinction risk . beale et al .   found that null models of species - climate associations established using bioclimatic models were no better than chance for 68 of 100 european bird species . many factors other than climate , such as species interactions and human impact , set the limit of species ranges , all contributing to weaken species - climate associations . if species do not occur everywhere their climatic requirements are met ( global dispersal ) due to migration barriers , this will also reduce the ability of projecting future geographic distributions . as a result , modelled climatic tolerances will be more narrow than real ones , overstating extinction risk . on the other hand , such a situation also implies that many species are likely to have problems colonizing new areas that become climatically suitable . svenning and skov   found that european tree species occupy only 38% of their calculated potential climatic ranges . frequent successful naturalizations of tree species outside their native ranges confirm the climatic suitability of modelled potential ranges . if dispersal limitation is common , species or species diversity patterns can not be expected to be in steady - state with contemporary climate . the pattern of diversity for european tree species with restricted ranges was best explained by climatic conditions occurring at the last glacial maximum about 21,000 years ago , whereas the diversity of widely distributed species correlates with present day climate . this suggests that some species were unable to expand their ranges following deglaciation and holocene warming to occupy their potential niches . this interpretation is supported by the demonstration that species richness of tree species in northern europe can be explained by differential rates of dispersal out of glacial refugia . in line with these results , arajo et al .   demonstrated that species richness of narrow - ranging amphibians and reptiles in europe was better explained by climatic stability between the last glacial maximum and the present day than by the present climate . a question related to dispersal limitation in explaining present distributions is whether species will be able to keep up with future climate change . models of species ' future distributions usually assume either full adjustment of species ranges - that is , that species can colonize any suitable habitat - or no range adjustment at all , implying only range contraction in response to climate change . the finding that species richness of butterflies in britain increases with climate change , but that species richness change lags behind climate change   sheds some light on this question . generalist species responded quicker than specialist ones , suggesting that species with high specialization and low vagility will have the greatest difficulties in tracking their habitat . lag times should be longer and dispersal barriers more difficult to overcome in taxa less vagile than butterflies . when using information on how species responded to past climatic shifts , we are faced with a conundrum . climate shifts during the quaternary were thought to be as rapid and large as those expected during the 21st century . despite that filtered by a previous challenge or catastrophe usually experience little extinction when faced by similar subsequent challenges . for example , the first continental glaciation in europe in the plio - pleistocene caused a wave of extinction in , for example , tree species , but the following glacial periods resulted in few extinctions , despite an increase in the amplitude of climate shifts . the first cooling event pruned the european tree species pool of cold - intolerant taxa , whereas the remaining taxa could persist . secondly , present global climate is close to the peak average temperature attained during the quaternary . many species have never experienced such a situation , potentially resulting in extinction of intolerant taxa . thirdly , during previous climatic shifts , species were able to shift their distributions without interference from humans . humans now dominate most ecosystems , resulting in barriers to dispersal and combined threats of climate change , habitat destruction and overexploitation of species . the combined effect of human overexploitation and climate change has been implicated in the extinction of the megafauna in eurasia and america at the beginning of the holocene . bioclimatic models show that the ranges of many species , such as the woolly mammoth , drastically declined during deglaciation , but megafaunal species had survived many similar climate shifts in the past , and the coup de grce was probably caused by human hunting . where are species most at risk from climate change ? given that observed and projected climate change is larger towards the poles , most attention has been directed towards high - latitude environments , with polar bears as iconic species in the public mind . depending on the vulnerability of species , geographic patterns of extinction risk may , however , deviate from geographic patterns of warming . deutsch et al .   showed that tropical insects are more sensitive to warming than high - latitude ones , because they already live close to their limit of climatic tolerance , whereas the fitness of many high - latitude species may increase as a result of warming . moreover , tropical assemblages contain more species with poor dispersal ability , high specialization and small geographic ranges , all characteristics that make them vulnerable to climate change . mccain   recently found support for janzen 's hypothesis   that the elevational range sizes of organisms are smaller on tropical than high - latitude mountains , making them more vulnerable to warming and upslope range shifts . narrow range - sizes also mean that for many tropical mountain species there will be no overlap between present and projected future distributions , increasing the risk for dispersal failure and extinction . in an assessment of global extinction risk in birds , jetz et al . projected many extinctions of tropical narrow - ranged species , although land conversion is presently a greater threat than climate change . as a result of narrow climatic tolerances , relatively small temperature changes may have large effects on species distributions in the tropics . in a record of forest turnover during 48,000 years in the amazon basin , forest cover was found to be continuous , but a temperature change of only 1c during the transition from glacial to holocene resulted in a large turnover in species composition . if species can evolve rapidly enough in response to climate change , projections of extinction risk based on species distribution modelling may be overestimated . recent empirical evidence suggests that evolution is responsive to climate variation and may occur at rates that make evolutionary change a plausible alternative to geographical range shifts . adaptive evolution in local populations may , however , be counteracted by competition from immigrating organisms pre - adapted to the new climate . the dominant response to quaternary climate changes comprised geographical range shifts rather than morphological adaptation in situ . both in situ persistence and range shifts may involve evolutionary processes that enhance adaptations to new climatic conditions - for example , by selection for enhanced tolerance in migrating populations . an increasing body of data documents that species and assemblages respond to warming as predicted by models , adjusting their ranges polewards and towards higher elevations . this lends support to bioclimatic modelling approaches and projections of species extinction . the most common data record latitudinally expanding range limits of temperate taxa colonizing habitats that have become climatically suitable [ 21 - 23 ] . records of latitudinal range contractions are mostly anecdotal , but a few recent studies document elevational range shifts [ 25 - 27 ] . range shifts on tropical mountains in response to warming raise double concerns ; many high - elevational species are at risk of becoming extinct if mountains are  too low to offer them habitat after in addition , tropical lowlands might be depleted of species as more and more species shift their ranges towards higher latitudes and elevations . data on range shifts from tropical mountains have been mostly missing , but recently chen et al .   documented 102 insect species shifting their distributions an average of 62 m upwards on mount kinabalu , borneo , between 1965 and 2007 . raxworthy et al .   found that 30 species of reptiles and amphibians had shifted their elevational midpoints upslope by 19 - 51 m on madagascar , in agreement with recent regional warming . some climate types are predicted to completely disappear , threatening species assemblages living in these vanishing environments with extirpation . in the majority of cases , however , the environments of species will shift geographically to various degrees , necessitating modelling of range adjustments and extinction risk . beale et al .   found that null models of species - climate associations established using bioclimatic models were no better than chance for 68 of 100 european bird species . many factors other than climate , such as species interactions and human impact , set the limit of species ranges , all contributing to weaken species - climate associations . if species do not occur everywhere their climatic requirements are met ( global dispersal ) due to migration barriers , this will also reduce the ability of projecting future geographic distributions . as a result , modelled climatic tolerances will be more narrow than real ones , overstating extinction risk . on the other hand , such a situation also implies that many species are likely to have problems colonizing new areas that become climatically suitable . svenning and skov   found that european tree species occupy only 38% of their calculated potential climatic ranges . frequent successful naturalizations of tree species outside their native ranges confirm the climatic suitability of modelled potential ranges . if dispersal limitation is common , species or species diversity patterns can not be expected to be in steady - state with contemporary climate . the pattern of diversity for european tree species with restricted ranges was best explained by climatic conditions occurring at the last glacial maximum about 21,000 years ago , whereas the diversity of widely distributed species correlates with present day climate . this suggests that some species were unable to expand their ranges following deglaciation and holocene warming to occupy their potential niches . this interpretation is supported by the demonstration that species richness of tree species in northern europe can be explained by differential rates of dispersal out of glacial refugia . in line with these results , arajo et al .   demonstrated that species richness of narrow - ranging amphibians and reptiles in europe was better explained by climatic stability between the last glacial maximum and the present day than by the present climate . a question related to dispersal limitation in explaining present distributions is whether species will be able to keep up with future climate change . models of species ' future distributions usually assume either full adjustment of species ranges - that is , that species can colonize any suitable habitat - or no range adjustment at all , implying only range contraction in response to climate change . the finding that species richness of butterflies in britain increases with climate change , but that species richness change lags behind climate change   sheds some light on this question . generalist species responded quicker than specialist ones , suggesting that species with high specialization and low vagility will have the greatest difficulties in tracking their habitat . lag times should be longer and dispersal barriers more difficult to overcome in taxa less vagile than butterflies . when using information on how species responded to past climatic shifts , we are faced with a conundrum . climate shifts during the quaternary were thought to be as rapid and large as those expected during the 21st century . despite that first , assemblages that have been  filtered by a previous challenge or catastrophe usually experience little extinction when faced by similar subsequent challenges . for example , the first continental glaciation in europe in the plio - pleistocene caused a wave of extinction in , for example , tree species , but the following glacial periods resulted in few extinctions , despite an increase in the amplitude of climate shifts . the first cooling event pruned the european tree species pool of cold - intolerant taxa , whereas the remaining taxa could persist . secondly , present global climate is close to the peak average temperature attained during the quaternary . many species have never experienced such a situation , potentially resulting in extinction of intolerant taxa . thirdly , during previous climatic shifts , species were able to shift their distributions without interference from humans . humans now dominate most ecosystems , resulting in barriers to dispersal and combined threats of climate change , habitat destruction and overexploitation of species . the combined effect of human overexploitation and climate change has been implicated in the extinction of the megafauna in eurasia and america at the beginning of the holocene . bioclimatic models show that the ranges of many species , such as the woolly mammoth , drastically declined during deglaciation , but megafaunal species had survived many similar climate shifts in the past , and the coup de grce was probably caused by human hunting . where are species most at risk from climate change ? given that observed and projected climate change is larger towards the poles , most attention has been directed towards high - latitude environments , with polar bears as iconic species in the public mind . depending on the vulnerability of species , geographic patterns of extinction risk may , however , deviate from geographic patterns of warming . deutsch et al .   showed that tropical insects are more sensitive to warming than high - latitude ones , because they already live close to their limit of climatic tolerance , whereas the fitness of many high - latitude species may increase as a result of warming . moreover , tropical assemblages contain more species with poor dispersal ability , high specialization and small geographic ranges , all characteristics that make them vulnerable to climate change . mccain   recently found support for janzen 's hypothesis   that the elevational range sizes of organisms are smaller on tropical than high - latitude mountains , making them more vulnerable to warming and upslope range shifts . narrow range - sizes also mean that for many tropical mountain species there will be no overlap between present and projected future distributions , increasing the risk for dispersal failure and extinction . in an assessment of global extinction risk in birds , jetz et al . projected many extinctions of tropical narrow - ranged species , although land conversion is presently a greater threat than climate change . as a result of narrow climatic tolerances , relatively small temperature changes may have large effects on species distributions in the tropics . in a record of forest turnover during 48,000 years in the amazon basin , forest cover was found to be continuous , but a temperature change of only 1c during the transition from glacial to holocene resulted in a large turnover in species composition . even if the assumptions in bioclimatic models are frequently violated , they remain a primary strategy to project the future of biodiversity . the methods are also developing rapidly , with prospects of accounting for variability among models and relaxing some of the critical assumptions . information on how species responded to climate change in the past serves as a  reality check of model projections . further advances could be made by taking advantage of new knowledge about past climate change . for example , studies of species responses to pleistocene climate oscillations have focused on the role of refugia , with recent interest in microrefugia ( survival of taxa in small habitat pockets ) , to explain the speed of post - glacial recolonization . the concept of microrefugia should also be relevant in projecting the effects of climate change . survival in small patches may be incorporated into models , and management and creation of microrefugia could be used as an active adaptation strategy . an area in need of more . some species may be more tolerant than indicated by present species - environment relationships , whereas others live close to their tolerance limits . much of our present knowledge is derived from studies of europe and north america , which may not be relevant for the rest of the world , such as the hotspots of species richness and endemism where most of earth 's biodiversity reside . rapid progress in this field is urgently needed to avoid the prospect of a wave of climate change - induced extinction becoming inevitable .