A questionnaire survey was conducted to understand how a mountain ecosystem in northern Bhutan is perceived by local yak herders to be changing under climate warming. One hundred elderly herders were selected using a 2-stage sampling. The questionnaire sought information on herders' awareness and perceptions of weather patterns, climate changes, and their impact on vegetation, herding practices, and livelihoods. Most study participants were aware of global warming. They perceived that global warming has led to warmer and longer vegetation growing periods, increased rainfall, decreased water availability, more frequent droughts, the ascent of snow lines, and an increase in flash floods and landslides. Many herders also perceived that vegetation is growing faster, new vegetation is gradually becoming established in formerly barren lands, and meadows have been encroached on by rhododendrons, which has reduced grassland size and caused a decline in forage availability and quality. Warming was perceived to have caused difficulties in herding and transhumant migration. It was also perceived to have caused a decrease in milk production and increase in livestock predation, which affected the livelihoods of herders who rely on yak. The study concluded that yak herders' perceptions provide critical signs of warming and their vulnerability to changing climatic conditions in the alpine environment.