Climate change poses major scientific, economic, and societal challenges. For example, climate scientists are striving to discern the natural climate variability from the one that arises from human activities. Our ability to address this problem hinges on advancing the knowledge of how: (i) the climate system as a whole operates; (ii) the atmosphere, hydrosphere, cryosphere, land surface, and biosphere change and interact with one another; (iii) the various forcing, feedback, and response mechanisms that operate on different timescales and shape the Earth’s climate and promote its variability