Paper Reviewed
Cheng, L., Hoerling, M., AghaKouchak, A., Livneh, B., Quan, X.-W. and Eischeid, J. 2016. How has human-induced climate change affected California drought risk?

Asking themselves the question posed in the title of this review (Has Human Induced Climate Change Caused California Drought?), Cheng et al. (2016) employed observations and model experimentation to characterize the recent California drought using "metrics that synthesize drought duration, cumulative precipitation deficit, and soil moisture depletion." And what did they thereby learn?

The six scientists report that "the net effect of climate change has likely made severe to extreme agricultural drought less [our emphasis] likely," indicating that "the current severe impacts of drought on California's agricultural sector, its forests and other plant ecosystems have not been substantially caused by long-term climate change." In other words, as they continue, "droughts are not a more frequent condition in the current climate as a result of long-term change," likely because of the fact that "the deep root zone soil moisture is shown herein to be more sensitive to the increase in precipitation than to the increase in surface temperature, resulting in less severe droughts."

Consequently, Cheng et al. conclude that "the net effect of climate change has made agricultural drought less [our emphasis] likely and that the current severe impacts of drought on California's agriculture have not been substantially caused by long-term [such as historical CO2-induced] climate changes."