Attribution and projection of anthropogenic suppression on frost extremes in China

Frost poses a major threat to agriculture, ecosystems, and socioeconomic development; however, to what extent anthropogenic forcing has affected frost extremes and how they evolve across different historical periods remain poorly understood. This study presents a comprehensive attribution analysis of multiple frost indices—first frost date (FFD), last frost date (LFD), frost period (FP), frost days (FD), and the maximum frost intensity (minimum of daily minimum temperatures, TNn)—across key region of China, using a novel “frost year” (previous August– next July) framework. Through model-specific threshold calibration and a risk-ratio-based attribution approach, we quantify human influence on severe events across different historical period and events defined by different return periods. Results show that since the mid-20th century, China has experienced delayed FFD, advanced LFD, warming TNn, and marked shortening of FP and FD. In early historical periods, human influence was negligible in strong frost years, but after 2000 it reduced the probability of severe frost events to 22–62% of natural conditions, with stronger influence on more severe extremes. As frost severity weakened in the warmer post-2010 climate, anthropogenic suppression was reduced. Future projections show continued weakening of frost events, with probability ratios (PRs) for 5-, 10-, and 20-year events declining below 1/1000 by the end of 21st century. FD decreases most rapidly, whereas FFD and FP exhibit slower declines. All these provided clear evidence of human influence on frost risks from historical period into the future, with critical implications for climate adaptation and agricultural planning. • Human influence has reduced frost extremes in China since the 1980s. • Anthropogenic forcing lowered probability of severe frosts to 22–62% of natural likelihoods since the 2000s. • Frost risks will keep diminishing, with extreme frost events becoming increasingly rare by the end of the century.