Polar and hot desert ecosystems that function under extreme climatic conditions, where high or low temperature and limited water availability is normal, are particularly sensitive to climatic changes. Hence, even minor climatic changes may have disproportionally large impacts on these ecosystems with unknown feedbacks at local to global scales. For example, rapid warming occurring in the Arctic and Antarctic is affecting hydrology, biodiversity above- and belowground, nutrient cycling, and the connectivity within the landscape. However, the implications for local methane and global carbon flux differ between the two regions. Therefore, it will be valuable to determine similarities and differences in responses to climate changes across extreme ecosystems. This symposium will examine responses of polar and hot desert ecosystems to changes in temperature and moisture availability, and compare patterns across systems and spatial scales through talks by experts ranging from soil chemists to plant community ecologists. As these ecosystem types cover a large proportion of the earth’s land surface area, are very sensitive to climate changes, and show divergent rates of climate change they may be of particular value for such comparisons. Presentations will include experimental and observational data showing the consequences of climate change on ecosystems and their functioning, and will be linked with potential impacts in other ecosystems. An ‘open floor session’ will be used to initiate a discussion that may form the basis for a synthesis of climate change effects in these ecosystems and their potential for predicting climate change responses in other ecosystem types.