Paper Reviewed
Bi, Y., Xu, J., Gebrekirstos, A., Guo, L., Zhao, M., Liang, E. and Yang, X. 2015. Assessing drought variability since 1650 AD from tree-rings on the Jade Dragon Snow Mountain, southwest China. International Journal of Climatology 35: 4057-4065.

Drought is a natural hazard that climate alarmists have predicted will increase in the future in consequence of CO2-induced global warming. One way to gauge the validity of such predictions is by examining long-term historic trends in drought to see if there is anything unusual about their occurrence over the past few decades, during which time climate alarmists claim the Earth has experienced unprecedented global warming due to rising atmospheric CO2 emissions. And that is exactly what the seven member research team of Bi et al. (2015) did in assessing drought variability for southwest China over the past three-and-a-half centuries.

To accomplish their objective, Bi et al. analyzed 39 tree ring cores obtained from 23 Picea likiangensis trees growing on Jade Dragon Snow Mountain (27.14°N, 100.23°E), located at the southern part of the Hengduan Mountains, southwest China, to reconstruct a historical spring season Palmer Drought Severity Index (PSDI) for this region. The resulting series is presented in the figure below.

Figure 1. Reconstructed spring PDSI (from March to May) for Jade Dragon Snow Mountain, southwest China. The thin line represents the annual value, while the thick line is an 11-year smoothing average. Adapted from Bi et al. (2015).

As shown above, there have been multiple wet (positive PSDI values) and dry (negative PSDI values) periods over the 361-year record. And with respect to extremely wet or dry years (more than 2 standard deviations above or below the mean), Bi et al. note such events occurred in 1674, 1712-1714, 1728, 1824-1827, and 1941-1942 for extremely wet years and in 1736-1737, 1758, 1762, 1766, 1768-1769, 1819, 1969 and 2008 for extremely dry years. They also report that although the 2000s was a relatively dry decade, "our study reveals that spring drought events during this period were not as extreme as in some other periods within the time scope of our study." Consequently, given the findings presented above, there appears to be nothing unusual, unnatural or unprecedented about the recent drought history of the Jade Dragon Snow Mountain region, suggesting rising atmospheric CO2 has had no measurable impact on this hazard phenomenon. And since it has had no impact on the past, there is no compelling reason to conclude that it will have any measurable impact in the future.