by Dr. Craig Loehle, NCASI Naperville, IL
The climate change “biodiversity crisis” is like a whack-a-mole game (a carnival game where plastic animals pop out of holes and you try to whack them with a mallet), with an almost-daily claim popping up about this species or that at risk from climate change. Not just polar bears and coral reefs, but even avocados are going to disappear! Whacking each silly claim one by one is an impossible task, and the claims get into public consciousness whereas the refutations do not.
I like to unpack the assumptions in any study, and doing so in the case of claims made about biodiversity endangerment have led me to conclude that there are a few simple flaws common to most of these studies that entirely determine their outcomes:
1) They almost always pick the most extreme model and scenario for evaluating impacts of climate change.
2) They oversimplify the environment in their model or analysis.
3) The assumption is made that species’ environmental tolerance is equal to the place where it is currently found, and any change will be fatal.
I have documented assumption 1 (Loehle 2011). If we note that even the cooler model/scenario combinations are running hotter than the data (see many WUWT posts), it is easy to see that an extreme choice can lead to temperatures by 2100 of up to 8°C above current. Such a warm up would indeed cause problems, but is not even remotely probable.
Assumption 2 is used when a study tries to be mechanistic but models the landscape at too coarse a scale or with only a single soil type. This can lead to adverse forecasts for species whereas persistence on the landscape is likely with more refined models that incorporate spatial heterogeneity (see citations in Loehle 2011).
Assumption 3, however, is the most critical and worst assumption. An analysis begins with a map of a species’ current range. For this region, the climate is characterized and it is assumed that this climate is what limits the species. But this assumption is not true. While plants may be limited by cold at the cold end of their ranges, they are very tolerant of warmer temperatures, as I show in my new paper (Loehle 2014, http://www.ncasi.org/Downloads/Download.ashx?id=9268). As an example, Figure 1 below shows that a typical “Canadian” tree can be found growing in botanical gardens in the South. In my paper I also document that virtually every Canadian tree species can be found in botanical gardens in Australia.
Figure 1. Example range of a boreal species (Abies balsamea) compared to locations where it is found in botanical gardens. Abies in Virginia and West Virginia (small gray circles) are located at higher elevations.
Because plants can tolerate warmer temperatures, what limits their southern (warm) range margin? I have argued (Loehle 1998) that it is competition; more southern trees have an inherently faster growth rate but less frost tolerance. If it warms, one should expect a slow invasion process that could take hundreds or thousands of years in the case of trees (Loehle 2003; Loehle and LeBlanc 1996). In the above references I cite dozens of papers supporting this point of view, and other arguments against a coming mass extinction can be found in Botkin et al. (2007).
But how is whack-a-mole played? Not by these rules. As early as 1989, Davis (1989), among many others, posited that plants would not be able to migrate fast enough to keep up with rapid climate change. She showed a map similar to my Figure 2 here. The old range and the new range after climate change only have a small region of overlap, and invasion (red border) is assumed to be too slow to occupy all of the new range. It is implicitly assumed that the species will die out in the old zone. If the surviving zone area plus the invasion zone are small, it is assumed that the risk of extinction goes up. If the old and new ranges don’t overlap, it is assumed that extinction is certain.
Figure 2. Assumption underlying extinction risk claims is that species bioclimate zones will shift in the next few decades. In the cross-hatched zone, the species will perish. If there is no overlap, extinction will occur.
The problem with the hundreds (thousands?) of papers that use the static approach is that the evidence is squarely against their underlying assumptions. While many papers have documented species being found north of where they used to be found (a sign of adaptation), the extinction risk results from dieback (loss) from the species’ old range (hatched area, Fig. 2). Almost no evidence for such dieback or loss can be found. Hundreds of experiments show that rising CO2 and warmer temperatures increase plant growth (see Craig Idso’s excellent site http://www.co2science.org). Most birds and mammals in the eastern US range from Florida to the Great Lakes; i.e., they have a wide temperature tolerance.
The whole enterprise of estimating extinction risk due to climate change is underpinned by a static and fragile view of nature. The assumptions underlying these analyses can be tested (and are false), but the “extinction risk” industry has no interest in examining them. Combining the choice of high-end warming scenarios with fragile models of species responses to warming leads to alarming claims like 50% of all species are endangered by climate change. These claims have no basis in reality. Species are at far more risk from other human activities, such as subsistence hunting.
Reprints of articles available. Email me at craigloehl at aol dotcom.
Botkin, D.B., H. Saxe, M.B. Araújo, R. Betts, R. Bradshaw, T. Cedhagen, P. Chesson, M.B. Davis, T. Dawson, J. Etterson, D.P. Faith, S. Ferrier, A. Guisan, A.S. Hansen, D. Hilbert, P. Kareiva, C. Loehle, C. Margules, M. New, F. Skov, M.J. Sobel, D. Stockwell, and H.-C. Svenning. 2007. Forecasting effects of global warming on biodiversity. Bioscience 57:227-236.
Davis, M.B. 1989. Lags in vegetation response to greenhouse warming. Climatic Change 15:75-82.
Loehle, C. 1998. Height growth rate tradeoffs determine northern and southern range limits for trees. Journal of Biogeography 25:735-742.
Loehle, C. 2003. Competitive Displacement of Trees in Response to Climate Change or Introduction of Exotics. Environmental Management 32:106-115.
Loehle, C. 2011. Criteria for assessing climate change impacts on ecosystems. Ecology and Evolution doi:10.1002/ece3.7.
Loehle, C. 2014. Climate change unlikely to cause a biodiversity crisis: Evidence from northern latitude tree responses to warming. Energy and Environment 25:147-153.
Loehle, C. and D.C. LeBlanc. 1996. Model-based assessments of climate change effects on forests: A critical review. Ecological Modelling 90:1-31.