It has subsequently been pointed out to us that the points on our Figure 1 (Pounds et al. Figure 4c) are not actually amphibian populations but simply a sampling of weather stations in the regions studied by Pounds et al.
It seems that Michaels could not bring himself to mention my name or link to my correction. (Nor do they accept trackbacks.)
Michaels comes with a different way of calculating the percentage of species that could become extinct because of the change in temperatures:
we should have cast the climate-change induced chytrid range expansion simply in terms of an elevation shift. When doing this, we find that the range expansion is about 250 meters (from our Figure 1). Since the amphibians range from near sea-level to greater than 4,000 meters (Pounds et al., Figure 4d), the range expansion for optimal chytrid infestations cover only about 6.25% (250/4,000) of the total range. If the number of species were evenly distributed across the entire range, then this would mean that climate change has potentially introduced an additional 6.25% of the amphibian species to better chytrid-growth conditions. Taking into account that there are about twice as many amphibian species living in the middle of the range than the low and high extremes (Pounds et al., Figure 4d), we’ll up the number from 6.25% to somewhere around 12.5% — virtually the same number that we originally calculated.
This is a better way to do the calculation. However, the slope in figure 1 is 1.0 degrees per 200 m of altitude, so 1.0 degrees increase in the minimum and 0.6 degrees decrease in the maximum corresponds to a 320 m increase in the range of the fungus, so the temperature changes could have wiped out 15% of the species. Pounds also suggests that increased cloud cover could contribute as well as temperature changes. Michaels argues against this with cloud data that I find worthless since it is completely the wrong scale (a map of the entire world used to deduce changes to cloud cover on mountain slopes). If you want my guess (based on knowing almost nothing about the matter) neither “recent introduction of fungus” or “climate change” are sufficient by themselves to explain what was going on. “Climate change” doesn’t explain the number of extinctions, while “recent introduction” doesn’t explain the temperature link to the extinctions. So my guess is that both factors are involved.