No-analog communities, novel climates, and ecological surprises: Past and future

Jack Williams, University of Wisconsin

As human-produced greenhouse gases accumulate in the atmosphere, it is increasingly likely that a) some future climates will be ‘novel’ or ‘no-analog’, i.e. will differ fundamentally from present-day climates and b) some present-day climates will disappear. Analyses of IPCC AR4 climate simulations for the 21^st -century consistently show that novel climates are mostly likely to develop in the lowland tropics and subtropics, whereas areas with disappearing climates are concentrated in poleward and tropical montane regions. These patterns are primarily due to global increases in temperature and secondarily by shifts in precipitation patterns. Interestingly, because we use a standardized index of climate change, in which 21^st -century changes are standardized against late-20^th -century interannual variability, our analyses highlight the tropics as being at greatest risk to climate change, because temperature variability is so low. Novel and disappearing climates carry distinct ecological risks. Novel climates pose a predictive challenge for ecological models, because these models are at least partially based on modern species-climate relationships and must be extrapolated into these future novel climates. Late-Quaternary paleovegetational records show a strong correspondence between no- analog climates and no-analog plant communities, consisting of species still alive today, but in combinations not found at present. We thus believe it likely that new species associations will arise in areas with novel future climates; the composition of these associations may be difficult to predict in advance. Conversely, disappearing climates may disrupt existing species associations and raise the risk of extinction for species endemic to these climates. Because the identified climatic disappearances are global, species endemic to these regions may have nowhere to go, challenging efforts to preserve biological diversity.