Comparison of Environmental Conditions on Summits of Mount Everest and K2 in Climbing and Midwinter Seasons

(1) Background: Today’s elite alpinists target K2 and Everest in midwinter. This study aimed to asses and compare weather at the summits of both peaks in the climbing season (Everest, May; K2, July) and the midwinter season (January and February). (2) Methods: We assessed environmental conditions using the ERA5 dataset (1979–2019). Analyses examined barometric pressure (BP), temperature (Temp), wind speed (Wind), perceived altitude (Alt), maximal oxygen uptake (VO 2 max), vertical climbing speed (Speed), wind chill equivalent temperature (WCT), and facial frostbite time (FFT). (3) Results: Most climbing-season parameters were found to be more severe ( p < 0.05) on Everest than on K2: BP (333 ± 1 vs. 347 ± 1 hPa), Alt (8925 ± 20 vs. 8640 ± 20 m), VO 2 max (16.2 ± 0.1 vs. 17.8 ± 0.1 ml·kg −1 ·min −1 ), Speed (190 ± 2 vs. 223 ± 2 m·h −1 ), Temp (−26 ± 1 vs. −21 ± 1°C), WCT (−45 ± 2 vs. −37 ± 2 °C), and FFT (6 ± 1 vs. 11 ± 2 min). Wind was found to be similar (16 ± 3 vs. 15 ± 3 m·s −1 ). Most midwinter parameters were found to be worse ( p < 0.05) on Everest vs. K2: BP (324 ± 2 vs. 326 ± 2 hPa), Alt (9134 ± 40 vs. 9095 ± 48 m), VO 2 max (15.1 ± 0.2 vs. 15.3 ± 0.3 ml·kg −1 ·min −1 ), Speed (165 ± 5 vs. 170 ± 6 m·h −1 ), Wind (41 ± 6 vs. 27 ± 4 m·s −1 ), and FFT (<1 min vs. 1 min). Everest’s Temp of −36 ± 2 °C and WCT −66 ± 3 °C were found to be less extreme than K2’s Temp of −45 ± 1 °C and WCT −76 ± 2 °C. (4) Conclusions: Everest presents more extreme conditions in the climbing and midwinter seasons than K2. K2’s 8° higher latitude makes its midwinter BP similar and Temp lower than Everest’s. K2’s midwinter conditions are more severe than Everest’s in the climbing season.