Tree rings capture an abrupt irreversible shift in east Asia's climate

November 26, 2020

The abrupt shift to hotter and drier conditions over inner East Asia is unprecedented and may herald an irreversible shift to a new climate regime for the region, according to a new study. The findings reveal a positive feedback loop fueled by declining soil moisture, which may have nudged the area's climate over an important tipping point. Extreme heatwaves and droughts are two of society's most pressing concerns as climate change driven by human activity continues unabated. Global warming has already led to recent and rapid shifts in climate worldwide, including inner East Asia, which has experienced some of the most pronounced heatwave-drought concurrences in recent decades. It's thought that such abrupt and substantial changes represent the crossing of critical thresholds within the climate system and signal irreversible shifts from one climate regime to another. But, identifying tipping points and new climate norms is difficult; not only does it require a thorough understanding of a region's natural climate variability over timescales that often exceed available records, regime shifts are likely triggered by complex interactions between a variety of poorly understood factors in the highly dynamic climate system. To determine whether the heatwave-drought trends observed in inner East Asia indeed exceed the range of natural climate variability, Peng Zhang and colleagues used tree-ring data to reconstruct a record of heatwave frequency and soil moisture for the region spanning the past 260 years. Zhang et al. found that the rise in concurrent heatwave-drought events over the last two decades is unique and beyond the natural variability revealed by their centuries-long record. What's more, the authors demonstrate that the rise in heatwave-drought events may be caused by a positive feedback loop between decreasing soil moisture and increasing surface warming - a pattern that's potentially the start of an irreversible trend that's likely to produce more frequent and severe events. While much remains to be understood about the occurrence and mechanisms of climate regime shifts, developing trustworthy long-term climate records is crucial in detecting changes in the interactions of climate variables, discovering past shifts and predicting tipping points of potential future shifts, write Qi-Bin Zhang and Ouya Fang in a related Perspective.

American Association for the Advancement of Science

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