What was done
The authors studied decadal-scale temperature variations of the past six centuries derived from four high-resolution temperature indicators -- the δ¹⁸O and δ¹³C of bulk carbonate, total carbonate content, and the detrended δ¹⁵N of organic matter -- which they extracted from Lake Qinghai (36°32'-37°15'N, 99°36'-100°47'E) on the northeast Qinghai-Tibet plateau, comparing the resultant variations with proxy temperature indices derived from nearby tree rings and reconstructed solar activity.

What was learned
Xu et al. report that "there are four obvious cold intervals during the past 600 years at Lake Qinghai, namely 1430-1470, 1650-1715, 1770-1820 and 1920-1940," and that these cold intervals are "synchronous with those recorded in tree rings at the northeast Qinghai-Tibet plateau." In addition, they note that the first three cold intervals, which occurred during the Little Ice Age, "are also synchronous with the minimums of the sunspot numbers during the past 600 years, suggesting that solar activities may dominate temperature variations on decadal scales at the northeastern Qinghai-Tibet plateau."

What it means
Although the three Chinese researchers note that "the physics behind the solar-earth climate relationship is not fully understood," their findings add to the growing body of evidence that suggests that such a relationship does in fact exist, which further suggests that much of the Little Ice Age-to-Current Warm Period transition may have simply been caused by the "relaxation" of the solar forcing that was responsible for the most extreme cold of the Little Ice Age, and that it was not a result of anthropogenic CO2 emissions.