Will climate change really cause species extinctions? It’s not a simple question to synthesise the connections between the richness of different natural systems of forests and savannas and reefs with the climate models used to make projections of future climates, and then translate this knowledge into useful conservation advice.
The recent state of art complied in the book “Saving a Million Species: Extinction Risk from Climate Change” suggests that many experts continue to support the view expressed by the influential work by Thomas et al 2004 finding species extinction by climate change is a serious and urgent concern. However, conservation biologist Daniel Botkin reviews the book, finding the scientific debate over global warming and its possible environmental effects is narrow and lacking in rigor:
“…it becomes clear that the title gives away the editor’s prejudice. If ‘Saving a Million Species’ assumes, as it seems to, that these [species] are threatened overwhelmingly by global warming and that forecasts supporting this in general correct, then the book fails, in total, to provide that much-needed objective analysis.”
Fails to provide “that much-needed objective analysis”? Ouch! Surely a scientific manuscript must have objectivity as a first priority. Is Botkin suggesting that belief in a massive increase in species extinctions is merely subjective?
The starting point of any objective analysis is to examine one’s assumptions, and the trajectory of global warming is surely the most central. The IPCC’s projections are the typical starting points for any scientific study of climate change’s effects on species. Science provides an example:
“Even the most optimistic estimates of the effects of contemporary fossil fuel use suggest that mean global temperature will rise by a minimum of 2°C before the end of this century and that CO2 emissions will affect climate for tens of thousands of years. ”
Yet climate sensitivity to atmospheric CO2 has been downgraded in the latest IPCC report, and so should the forward projections. The observed rate of warming is less than 0.2C per decade, and so below 2°C, and well below the minimum warming scenario of 1.25C by 2050 or 0.25C per decade used in Thomas et al 2004.
The lesson of the ‘climategate’ emails, the ‘hockeystick wars’, and the recent ‘pause’ is that the IPCC reports have a tendency to be self-serving. Blind faith in the IPCC projections shows subjectivity, if not outright naïveté. To the degree that studies base their estimates on a rate of warming far greater than observed, published extinction estimates from climate change should also be down graded.
Could the analytical methods be subjective as well? Expected species’ extinctions from climate change are derived from Species Area Relationships (or SARs), which is an empirical relationship between an area of habitat, such as forest or grassland, and the number of species it contains. A statistical method called Niche Modelling is used to extrapolate the area of suitable habitat of a species before and after climate change. The species with reduced area are selected (I would say ‘cherry-picked’) and then the average areal loss is plugged into the SAR relationship to give the number of species lost in a given climate change.
The problem of ‘circular reasoning’ with the SAR method was raised here and in Botkin’s“Forecasting the effects of global warming on biodiversity”, and stems from the accentuation of the losers and deprecation of the winners. Due to the cherry-picking of species with areal reductions, any change at all increases extinctions, and so the outcome is predetermined. The circular fallacy can be further illustrated by imaging what would happen in a global cooling scenario. SAR-based methods would cherry-pick the species that lose habitat due to cooling and so again predict an increase in extinctions. The SAR method is biased and decidedly anti-change.
The problem with circular reasoning is that it is simply prejudice. While the method may help identify those species potentially at risk, it cannot tell you objectively if climate change is good, bad or indifferent. I identified a similar flaw due to ‘cherry-picking’ in the development of the ‘hockey stick’ graphs here, and as with species extinctions, the practitioners appear blissfully unaware of their methods’ lack of objectivity.
Another portrait in subjectivity is former Climate Commissioner Tim Flannery in “Jellyfish they’re taking over” in speculating that anthropogenic global warming has caused the world jellyfish population to explode. While reports of 20 year cycles in jellyfish abundance are outpaced by jellyfish horror stories in the popular press, there is no robust evidence for a global increase in jellyfish, other than the natural cycle. Subjective impressions from partial population die-outs are often attributed to climate disruption, but then turn out to be natural, or premature — such as the white lemuroid possum extinction, and the polar bear hoax.
A more objective approach to environmental effects must go beyond the static ‘niche’ concept linking the species and environment, and use more dynamic approaches such as ‘universal neutral theory’ by Hubbard (2011). One simple example of the application of neutral theory is island populations, where the closer islands to the mainland have more species than the further ones, and ‘niche’ differences between the islands have little to no effect.
Neutral theory finds that dispersal is crucial for maintaining and even increasing biodiversity. Conversely, a stable unvarying environment is ultimately detrimental. An analogy is the ‘creative destruction’ of capitalism, where the rapid turnover of new businesses increases productivity and choice, as opposed to moribund economies organized around established businesses that keep out new contenders. Neutral theory is largely supported by the fossil record, which finds relatively few extinctions from quite large and rapid climate changes in the past (see also Botkin et al. 2005), and slow declines in diversity during periods of stable climate.
Perhaps the biggest surprise of neutral theory is that the dominant species can completely turn-over at random intervals without any prompting from changes in the environment. Pollen records from lake beds and other sources going back thousands of years show it is normal for large parts of populations to die out and then suddenly (over paleo-time scales, that is) return to domination.
We do know is that small localized populations known as ‘endemics’ are at risk from broad scale habitat destruction by agriculture and urbanization, and from dispersals of novel diseases and predators. But these processes are not at all like climate change, and extreme events like fire, floods and cyclones seem to maintain and promote natural diversity. There is also evidence of some benefits from the increased productivity that comes with increased atmospheric CO2 concentrations.
How can a scientific assessment be objective when the methods themselves are of dubious validity, and still highly contentious? A balanced appraisal would highlight the ecological theory, paleo-evidence and respected opinion that suggests it is plausible, and even likely, that moderate climate change is not harmful to species diversity and may even be beneficial.
Dr David Stockwell, Adjunct Researcher, Central Queensland University