Volume 16, Number 19: 8 May 2013
In a paper recently published in Global Change Biology, Dobrowski et al. (2013) write that "anthropogenic climate change is considered a threat to ecosystem services and to global biodiversity because of its magnitude, the potential for novel climatic conditions (Williams et al., 2007), and the rate at which it is occurring (Parmesan and Yohe, 2003; Montoya and Rafaelli, 2010)," but they state that "species have always been subject to changing climatic regimes and have responded through adaptation (Davis and Shaw, 2001; Hoffman and Sgro, 2011), changes in phenology (Cleland et al., 2007), range shifts (Davis and Shaw, 2001), and the use of climate refugia (Dobrowski, 2011; Hampe and Jump, 2011)." In addition, they remind us that "the fossil record suggests that widespread extinctions of plant species were rare during periods of rapid warming (~2-10°C/century) such as the Pleistocene-Holocene transition (Willis and MacDonald, 2011), noting that instead of species disappearing, "ecological turnover and range shifts were common responses to rapid climate changes of the past (Botkin et al., 2010; Hof et al., 2011; Willis and MacDonald, 2011)."
Delving into the subject in more detail, the seven U.S. scientists assessed "climate velocity (both climate displacement rate and direction) for minimum temperature, actual evapotranspiration, and climatic water deficit over the contiguous U.S. during the 20th century (1916-2005)." And in doing so, they discovered "a complex picture of the climate in the contiguous U.S.," wherein "velocity vectors vary regionally, show variable and opposing directions among the variables considered, and shift direction through time."
As examples of these diverse findings, Dobrowski et al. report that: (1) "Tmin vectors calculated over decadal and century scales demonstrate complex dynamics (e.g. northerly and southerly directions, direction reversal through time) that vary regionally," that (2) "climate displacement vectors for metrics of the water balance were predominantly oriented toward the west and south, showing regional variability," and that (3) "divergent climate vectors between temperature and water balance may help explain why roughly 10-30% of species assessed in previous climate change studies have not shifted their ranges whereas nearly 25% of species have shifted their ranges in a direction counter to expectations (Parmesan and Yohe, 2003; Chen et al., 2011; Crimmins et al., 2011)."
These results, in their estimation, "suggest that the expectation of poleward and upward shifts associated with all taxa, previously referred to as a 'globally coherent fingerprint' (Parmesan and Yohe, 2003), may be derived from an oversimplification of the climate dynamics that have been observed over the 20th century." Indeed, they conclude that their findings suggest that "a more full understanding of changes in multiple climatic factors, in addition to temperature, may help explain unexpected or conflicting observational evidence of climate-driven species range shifts."
In light of these developments, Dobrowski et al. additionally suggest that "moving away from viewing climate as simple monotonic changes in temperature is a necessary step in advancing our understanding of how species have and will respond to climate shifts," and, we would add, how they have been able to largely avoid massive extinctions of the type that climate alarmists typically predict for them if the world continues to warm as their models say it will.
Sherwood, Keith and Craig Idso
References
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