The variability of the mild Irish climate is described. The effect of a slight rise in temperature is discussed as far as aquatic organisms are concerned. The effect is likely to be most marked on pelagic populations of marine organisms such as squid and also on intertidal animals. A rise in mean sea level is an indirect result of global warming, and this is likely to have an effect on estuarine organisms and mud flat dwellers. It is suggested that those organisms which are close to the southern limits of their distribution in Ireland may disappear from our fauna. Examples are given from earlier periods and from the present-day fauna. There is likely to be an expansion of the distribution of southern forms which at the moment are near the northern limit of their range. As far as terrestrial animals are concerned, the problem of whether the rainfall pattern will also change is discussed. The likely effects of this on parasite and free-living populations (including the fauna of temporary water bodies, common in West Ireland) are discussed. The complications introduced by diapause and related factors are considered. The fauna of peat bogs may be seriously affected and also those organisms dependent on certain food plants. The peculiar problems of Ireland in having so many empty niches is considered in relation to the increased dangers of accidental introductions.