A Strange Impact of Global Warming: Biodiversity Increases

     In their paper published this September, Mayhew et al. concluded as their title illustrates that 'Biodiversity tracks temperature over time'. Their finding that Earth's biodiversity has a general pattern of increase with increasing temperature seems completely at odds to the type of mass extinction generally associated with global warming. This follows the known understanding that biodiversity constantly decreases with latitiude; reaching its peak species richness in warmer biomes, although the finding contrasts strongly with extinction models of global warming; making the paper of great interest.

    These findings may cause some to debate any models which predict increasing extinctions with future anthropogenic global warming. However, Mayhew openly debates the use of his paper in this way, stating that emergence of new species due to genetic adaptation still leads to extinctions (a few million years later), and that current species do not flourish, but new species take their place. The graph below from Mayhew et al., 2012, demonstrates that extinction rates also increased, and it is only that the emerge of new species was slightly greater than this. Additionally, it is likely that models for present global warming still hold - this is because temperature increases are happening on such a faster scale that speciation cannot keep up with the increased amounts of extinction:
       
"I'm afraid it's not good news in terms of what we might experience from global warming in the next few decades. Because obviously extinction can happen rapidly, but speciation [the generation of new species] can't happen rapidly. So unfortunately we're quite likely, simply because of the rate of climate change today, to see extinctions occurring. And we're unlikely to see the benefits that might go along with that, which is the generation of new species."  Mayhew speaking on his study.

Graph from Mayhew et al., 2012, B and D displaying the positive
correlation of speciation and extinction with temperature.

    Contrastingly to this paper, however, is the fact that their previous similar study (albeit with inferior techniques, as they note) from 2008 contradicts this finding, where biodiversity was found to decrease with increasing temperature - although this does seem unlikely, given the current spacial increase in species richness with temperature (i.e. towards the equator). Additionally, focusing purely on temperature correlations (by proxy measures and carbon dioxide concentrations) seems much less reliable than a cohesive study with several possible impactors of biodiversity; this may have been the reason why not all studied periods in Mayhew et al., 2012, showed an increase in biodiversity with temperature (or this was due to palaeontological sampling bias; a very real issue, as they note).