The Himalayas are the water source for more than 20% of the global population, living in southern and south-eastern Asia. Changing global environment has influenced regional warming and it has been larger in the Himalayas over the 100 years than the global average. In the future, high mountain areas are expected to warm more rapidly than lower elevation regions. Snow cover and glacier extent already retreat, making the Himalayas one of the global vulnerability hot spots and climate change-related risks. Affected sectors include agriculture, forestry, energy, transportation, flood protection, environmental conservation, water supply and air quality. The Himalayas are characterised by extremely diverse climatic conditions over short distances, mainly due to large topographical diversity associated with high-altitude, rugged terrain, and the impact of atmospheric circulation, namely the Indian summer monsoon. Understanding basic climatic conditions, climate variability and trends on different temporal and spatial scales is therefore crucial. It can be noted that climate change research in Bhutan still is in its infancy. Yet, the country is at the frontline of climate change-related threats. Bhutan depends highly on agriculture and forestry; both sensitive to increasing temperatures and changes in water availability. The melting of Bhutan’s Himalayan glaciers affects hydropower—the main source of governmental revenues—and freshwater generation by seasonal changes of water availability. The safety of settlements, economic facilities (including hydropower), agricultural plains, touristic activities and natural/cultural heritage sites located near rivers remain vulnerable to glacier lake outburst floods (GLOFs)—flood events caused by dam failure of lakes formed and fed by glacier melt water. Glacier thinning and retreat lead to larger melt water fluxes, which increase the risk of GLOFs. Local observations are therefore mainly suitable to describe present weather conditions and peculiarities, but are currently inappropriate for thorough investigations of climate variability and trends. To compensate for such shortcomings, global meteorological reanalysis data can be used. In this study, the focus is on air temperature. While investigations of changes in the Bhutanese precipitation regime are urgently needed, available precipitation data from local and global datasets are currently not robust enough to fulfil the task with the necessary accuracy and precision.