Read here. One of the major stuck-on-stupid positions that global warming alarmists claim is that only human CO2 increases cause climate change. This idiotic stance eventually resulted in the bogus hockey-stick study that the world's preeminent statisticians found to be so....well....really bogus. The hockey-stick of course purported to show that no climate changes had occurred over the last 1,000 years until the late 20th century. This idiocy became so apparent that even the IPCC retired the hockey-stick to barely a footnote in its last report.
In spite of the bogus hockey-stick, researchers across the world kept working to better understand past climate change. Another study just released has found that the arid central Asia (ACA) region has had significant climate change over the last 1,000 years during periods of low, unchanging CO2 levels.
"The nine researchers report that the effective moisture (precipitation) in the ACA has a generally inverse relationship with the temperature of the Northern Hemisphere, as portrayed by Moberg et al. (2005), China, as portrayed by Yang et al. (2002), and Central Asia, as portrayed by Esper et al. (2007). That is to say, as they describe it, the "wet (dry) climate in the ACA correlates with low (high) temperature." And stating it in yet another way, they indicate that the ACA "has been characterized by a relatively dry Medieval Warm Period (MWP; the period from ~1000 to 1350 AD), a wet little Ice Age (LIA; from ~1500-1850 AD),"....."which cooling was brought about by the gradual demise of the Medieval Warm Period, which in turn speaks volumes about the great significance of that centuries-long period of much-lower-than-present atmospheric CO2 concentration but of equivalent or even greater warmth than that of the Current Warm Period, which ultimately suggests that the 20th-century increase in the air's CO2 content may have had little, or maybe even nothing, to do with 20th-century global warming"..... and [finally] "a return to arid conditions [from warming] after 1850 AD," which has been slightly muted..."
Additional climate history postings.