Historically, these refugia, in Dobrowski's words, were "typically thought of as large regions in which organisms took refuge during glacial advances and retreats during the Pleistocene, which then acted as sources for colonization during more favorable climatic periods," but he states that "in addition to these large-scale refugia, there is compelling evidence that climatic refugia occurred at local scales during the Last Glacial Maximum and were also utilized during interglacial warm periods, including the current interglacial (Willis and Van Andel, 2004; Birks and Willis, 2008)."

Further with respect to this refugia size differential, Dobrowski notes that "modeling using global climate models (GCMs) and regional climate models (RCMs) is done at scales of tens to hundreds of kilometers, whereas research suggests that temperature varies at scales of < 1 km in areas of complex terrain (Urban et al., 2000; Fridley, 2009)." In fact, he reports that "Hijmans et al. (2005) showed that there can be temperature variation of up to 33°C within one 18-km raster cell." In addition, he notes that "GCMs and RCMs can simulate free-air conditions but fail to accurately estimate surface climate due to terrain features that decouple upper atmospheric conditions from boundary layer effects (Grotch and Maccracken, 1991; Pepin and Seidel, 2005)."

The University of Montana (USA) scientist also says that many researchers "have recently commented on the potential of topographically driven meso- or micro-climatic variation in mountain environments for providing refugia habitats for populations of species threatened by climate warming," citing the work of Luoto and Heikkinen (2008), Randin et al. (2009) and Seo et al. (2009). And he notes that these researchers "point to lower rates of predicted habitat loss and lower predicted extinction probabilities from species distribution models when using finely resolved climate data as compared with coarse scaled data," stating that "they suggest that this is evidence of 'local scale refugia' (Randin et al., 2009) or 'reserves to shelter species' (Seo et al., 2009)."

In concluding his review of the subject, Dobrowski writes that "microrefugia are likely to be found in terrain positions that promote the consistent decoupling of the boundary layer from the free-atmosphere," and that "these terrain positions are likely to have climate states and trends that are decoupled from regional averages," which is "a requisite for microrefugia to persist through time." Thus, he concludes by stating that "convergent environments (local depressions, valley bottoms, sinks, and basins) are primary candidates for microrefugia based on these criteria," which observations bode well for the once-thought-to-be-impossible survival of many species of plants and animals within the context of a possible further warming of the planet.

Sherwood, Keith and Craig Idso

References
Birks, H.J.B. and Willis, K.J. 2008. Alpine trees and refugia in Europe. Plant Ecology and Diversity 1: 147-160.

Dobrowski, S.Z. 2011. A climatic basis for microrefugia: the influence of terrain on climate. Global Change Biology 17: 1022-1035.

Fridley, J.D. 2009. Downscaling climate over complex terrain: high finescale (< 1000 m) spatial variation of near-ground temperatures in a montane forested landscape (Great Smoky Mountains). Journal of Applied Meteorology and Climatology 48: 1033-1049.

Grotch, S.L. and Maccracken, M.C. 1991. The use of general circulation models to predict climatic change. Journal of Climate 4: 283-303.

Hijmans, R.J., Cameron, S.E., Parra, J.L., Jones, P.G. and Jarvis, A. 2005. Very high resolution interpolated climate surfaces for global land areas. International Journal of Climatology 25: 1965-1978.

Luoto, M. and Heikkinen, R.K. 2008. Disregarding topographical heterogeneity biases species turnover assessments based on bioclimatic models. Global Change Biology 14: 483-494.

Pepin, N.C. and Seidel, D.J. 2005. A global comparison of surface and free-air temperatures at high elevations. Journal of Geophysical Research 110: 10.1029/2004JD005047.

Randin, C.F., Engler, R., Normand, S., Zappa, M., Zimmermann, N.E., Pearman, P.B., Vittoz, P., Thuiller, W. and Gisan, A. 2009. Climate change and plant distribution: local models predict high-elevation persistence. Global Change Biology 15: 1557-1569.

Seo, C., Thorne, J.H., Hannah, L. and Thuiller, W. 2009. Scale effects in species distribution models: implications for conservation planning under climate change. Biology Letters 5: 39-43.

Urban, D.L., Miller, C., Halpin, P.N. and Sephenson, N.L. 2000. Forest gradient response in Sierran landscapes: the physical template. Landscape Ecology 15: 603-620.

Willis, K.J. and Van Andel, T.H. 2004. Trees or no trees? The environments of central and eastern Europe during the last glaciation. Quaternary Science Reviews 23: 2369-2387.