In this study, the instability of extreme temperatures is defined as the degree of perturbation of the spatial and temporal distribution of extreme temperatures, which is to show the uncertainty of the intensity and occurrence of extreme temperatures in China. Based on identifying the extreme temperatures and by analyzing their variability, we refer to the entropy value in the entropy weight method to study the instability of extreme temperatures. The results show that TXx (annual maximum value of daily maximum temperature) and TNn (annual minimum value of daily minimum temperature) in China increased at 0.18 degrees C/10 year and 0.52 degrees C/10 year, respectively, from 1966 to 2015. The interannual data of TXx' occurrence (CTXx) and TNn' occurrence (CTNn), which are used to identify the timing of extreme temperatures, advance at 0.538 d/10 year and 1.02 d/10 year, respectively. In summary, extreme low-temperature changes are more sensitive to global warming. The results of extreme temperature instability show that the relative instability region of TXx is located in the middle and lower reaches of the Yangtze River basin, and the relative instability region of TNn is concentrated in the Yangtze River, Yellow River, Langtang River source area and parts of Tibet. The relative instability region of CTXx instability is distributed between 105 degrees E and 120 degrees E south of the 30 degrees N latitude line, while the distribution of CTNn instability region is more scattered; the TXx's instability intensity is higher than TNn's, and CTXx's instability intensity is higher than CTNn's. We further investigate the factors affecting extreme climate instability. We also find that the increase in mean temperature and the change in the intensity of the El Nino phenomenon has significant effects on extreme temperature instability.

Degrading permafrost in steep rock walls can cause hazardous rock creep and rock slope failure. Spatial and temporal patterns of permafrost degradation that operate at the scale of instability are complex and poorly understood. For the first time, we used P wave seismic refraction tomography (SRT) to monitor the degradation of permafrost in steep rock walls. A 2.5-D survey with five 80m long parallel transects was installed across an unstable steep NE-SW facing crestline in the Matter Valley, Switzerland. P wave velocity was calibrated in the laboratory for water-saturated low-porosity paragneiss samples between 20 degrees C and -5 degrees C and increases significantly along and perpendicular to the cleavage by 0.55-0.66km/s (10-13%) and 2.4-2.7km/s (>100%), respectively, when freezing. Seismic refraction is, thus, technically feasible to detect permafrost in low-porosity rocks that constitute steep rock walls. Ray densities up to 100 and more delimit the boundary between unfrozen and frozen bedrock and facilitate accurate active layer positioning. SRT shows monthly (August and September 2006) and annual active layer dynamics (August 2006 and 2007) and reveals a contiguous permafrost body below the NE face with annual changes of active layer depth from 2 to 10 m. Large ice-filled fractures, lateral onfreezing of glacierets, and a persistent snow cornice cause previously unreported permafrost patterns close to the surface and along the crestline which correspond to active seasonal rock displacements up to several mm/a. SRT provides a geometrically highly resolved subsurface monitoring of active layer dynamics in steep permafrost rocks at the scale of instability.