Paper Reviewed
Hessl, A.E., Anchukaitis, K.J., Jelsema, C., Cook, B., Byambasuren, O., Leland, C., Nachin, B., Pederson, N., Tian, H. and Hayles, L.A. 2018. Past and future drought in Mongolia. Science Advances 4: e1701832.

According to Hessl et al. (2018), "both scholarly and popular sources have attributed [recent droughts in Mongolia] to anthropogenic climate change," yet this team of ten scientists notes "the instrumental record of moisture [in this region] is sparse and the satellite record short, making it difficult to assess whether 21st century drying is without precedent" and truly of anthropogenic origin. Thus, in an effort to make a proper assessment of this claim, Hessl et al. used dendrochronology to reconstruct a 2060-year record of summer drought for central Mongolia to evaluate whether recent drying there was "unprecedented in its joint duration and severity over the Common era."

The record was derived from Siberian pine tree rings from two locations in north central Mongolia that were calibrated against a modern record of the Palmer Drought Severity Index. Results indicated, in the words of the authors, that "although the most recent drought and pluvial were highly unusual in the last 2000 years ... these events were not unprecedented in the 2060-year reconstruction." And in this regard, they note that longer and more severe droughts occurred during the Medieval Climate Anomaly. Furthermore, in placing the extreme drought of 2001 in perspective (this is the modern drought that sparked claims of an anthropogenic origin), Hessl et al. report its magnitude was eclipsed on sixteen other occasions, clearly demonstrating that although it was unusual, it was not unprecedented. Consequently, there is no compelling reason to link the cause of the early 21st-century super drought to anything other than natural variability.