The levels of CO(2) in the atmosphere have already far exceeded values attained at any other time over at least the past 650,000 years. Temperature increases due to rising greenhouse gases will be amplified in Arctic and subarctic regions, and winter warming will be enhanced relative to summer warming. Climate in large areas of high latitudes may have no analogue in current climates or those of the recent geological past. Experimental field manipulations and laboratory studies indicate that plants will exhibit complex responses in photosynthesis, growth rates, phenology and reproductive functioning due to this combination of increasing temperatures, changing seasonality and increasing levels of CO(2). The resulting changes in the abundance, distribution, growth rates and production of fruit and phenology of plant species will in turn impact animal populations. In predicting what the future biota of the 'New Arctic' will be like and developing appropriate conservation strategies, Grinnellian niche-based approaches are likely to be insufficient, and experimental ecological studies of organism response to specific anticipated changes in climate are crucial.