Microorganisms have been changing the climate, and have been changed by the climate, throughout Earth’s history. As we experience unprecedented environmental impacts from climate change, microorganisms will respond, adapt and evolve in their surroundings. Because they have generation times as short as a few hours, they will do so at higher rates than most other organisms. This makes microbes ideal sentinels for understanding the effects of climate change on biological systems and the global biogeochemical cycles that microbes mediate. Scientists can study the effects of climate change on microbes to both understand and hopefully predict the future effects of climate change on all forms of life. This colloquium brought together members of the American Society for Microbiology and the American Geophysical Union because understanding climate change impacts requires experts from many scientific disciplines. The collaboration between these 2 societies intermingled scientists knowledgeable about microbial contributions and responses to climate change across global settings (terrestrial polar regions; soil, agriculture and freshwater; oceans) and able to think broadly about the functions of microbiomes. Although scientists have been studying microbial ecosystems for many years, we realize we have much more to learn and understand about complex and interconnected microbial functions. The information in this report reflects the current understanding of microbes and our changing climate, as well as gaps and priorities for future study.