Climate change and global warming have become household names in the society during the last few decades. The words like greenhouse gases have also become popular in public without understanding what the word stood for. Change in climate is emerging as the main environmental challenge to all living beings including domestic large and small ruminants on the Himalayas, threatening their well-being and existence. Global warming caused by the accumulation of greenhouse gases such as carbon dioxide, methane, and nitrous oxide in the atmosphere is now a reality. Many reports have indicated that hill and mountain environment was particularly sensitive to the effect of global warming. The impact of climate change and consequential heat stress conditions have been found to affect the growth and production, feed intake, milk yield, reproduction, and other biological functions of the productive animals. As per the prediction of the intergovernmental panel on climate change, by the year 2100, the global surface temperature may be increased by 3.7–4.8 °C. It has been advised that the impact of climate change on pastoral nomads and their animals is likely to be devastating. The centuries-old practice of nomadic transhumance on the mountains is under serious threat. In case of pastoral nomads, global warming and heat stress would not only affect the productive performance of migratory animals but also badly disturb their transhumant cycle and routine of upward and downward journeys on the hills. Scientists are predicting an increase in unpredictable weather events as a result of global warming. Various reports show that the nomads are already experiencing increased temperature resulting in drying up of water resources, reduced and untimely rainfall and other extreme events, and reduced quality and quantity of pastures replaced by weedy and unwanted plants. During the past few years, we have come a long way to understand the climate and its role in warming the earth. This chapter endeavors to explain the basic concepts of climate, definition of climate and related terms, historical journey on the role of atmospheric gases in global warming, and the process of buildup of greenhouse gases (GHG) in the atmosphere leading to a rise in global temperature. We have elaborately covered the role of livestock in contributing to the GHG emission and global warming and also the source, sector, and country-wise emissions of GHG from the livestock. The special features of Indian livestock’s contribution to the emission of GHG has been discussed separately. The most important variable in the climate affecting the exposed animals is heat stress. This chapter addresses in detail the impact of heat stress on physiological and productive attributes of large and small ruminants. Thermal stress was found to reduce feed intake and cause a significant decline in milk yield and milk quality in both large and small ruminant species. Heat stress caused a reduction in milk protein, milk fat, casein, and fatty acids. Exposure of animals to hot environment was accompanied with increase in incidence of infertility, cases of anestrus and embryonic mortality in females, and impairment of reproduction in males causing reduced quantity and quality of sperm production. Heat stress affected immune system negatively, causing a reduction of cytokines. Global warming is having a devastating effect on health status of livestock. Rising temperature has been found to increase the development of certain pathogens and affecting non-vector borne diseases. Among small ruminants, sheep and goats are well adapted to the hot environment. An important observation reported in sheep was that ewes were most affected by heat stress from 5 days prior to estrus, during estrus, and then for ensuing 5 days suggesting vulnerability of this period to thermal stress. Finally, major strategies related to climate stress comprising of measures to reduce enteric methane emissions by reducing number of ruminant livestock, reducing the enteric methane emission, selecting heat-tolerant and disease-resistant breeds, and alleviation of heat stress physically have been discussed elaborately.