As the amplifier of global climate change, climate warming exerts an important impact on the freezing/thawing cycles of soil over the Tibetan Plateau, and it shapes the trend of permafrost degradation. Intensified frozen soil collapse causes severe effects on ecosystem water and energy balance as well as on carbon cycle. Previous studies have focused on the direct effects of climate change on permafrost degradation. However, there is also growing evidence showing vegetation growth can affect regional climate system, and consequently we hypothesize that vegetation autumn phenology (i.e., the end of the growing season, EOS) may influence the start date of frozen (SOF) through feedbacks to regional climates. Using satellite greenness data derived EOS and the microwave remote sensing generated SOFESDR (freeze-thaw Earth system data record) over 2001-2018, we showed a dominant-negative (13.1% vs. 0.9%) relationship between SOFESDR and EOS, suggesting an earlier SOFESDR with a delayed EOS. We found that biogeophysical indicators served as potential connections, including surface al-bedo, soil temperature, soil water content, and evapotranspiration, for the observed relationship. We therefore proposed a new site-level SOFf(EOS)xESDR algorithm based on the EOS-SOF relationship. With ground SOFALT observed from the active layer thickness at 63 sites over Tibetan Plateau, the new model provided significantly improved estimates of SOF with Pearson's correlation coefficient (R) of 0.84 and root mean square error (RMSE) of 7.63 days, comapred with current remote sensing-based SOF product (R = 0.26, RMSE = 22.60 days). We further proposed a look-up table approach to map the SOF over TP and found an overall earlier SOF (24.0 +/- 15.8) than current SOFESDR products. Therefore, our results identified a significant correlation between the autumn phenology and the SOF variability, highlighting the importance of feedbacks of autumn phenology on climate change.

The global cryosphere, Earth's frozen water, is in precipitous decline. The ongoing and predicted impacts of cryosphere loss are diverse, ranging from disappearance of entire biomes to crises of water availability. Covering approximately one-fifth of the planet, mass loss from the terrestrial cryosphere is driven primarily by a warming atmosphere but reductions in albedo (the proportion of reflected light) also contribute by increasing absorption of solar radiation. In addition to dust and other abiotic impurities, biological communities substantially reduce albedo worldwide. In this review, we provide a global synthesis of biological albedo reduction (BAR) in terrestrial snow and ice ecosystems. We first focus on known drivers-algal blooms and cryoconite (granular sediment on the ice that includes both mineral and biological material)-as they account for much of the biological albedo variability in snow and ice habitats. We then consider an array of potential drivers of BAR whose impacts may be overlooked, such as arthropod deposition, resident organisms (e.g., dark-bodied glacier ice worms), and larger vertebrates, including humans, that transiently visit the cryosphere. We consider both primary (e.g., BAR due to the presence of pigmented algal cells) and indirect (e.g., nutrient addition from arthropod deposition) effects, as well as interactions among biological groups (e.g., birds feeding on ice worms). Collectively, we highlight that in many cases, overlooked drivers and interactions among factors have considerable potential to alter BAR, perhaps rivaling the direct effects of algal blooms and cryoconite. We conclude by highlighting knowledge gaps for the field with an emphasis on the underrepresentation of genomic tools, understudied areas (particularly high-elevation glaciers at tropical latitudes), and a dearth of temporal sampling in current efforts. We detail a global framework for long-term BAR monitoring that, if implemented, would yield a tremendous amount of insight for BAR and would be particularly valuable in light of the rapid ecological and physical changes occurring in the contemporary cryosphere.