evidence: Beyond the next few decades, how much the climate changes will depend primarily on the amount of greenhouse gases emitted into the atmosphere; how much of those greenhouse gases are absorbed by the ocean, the biosphere, and other sinks; and how sensitive Earth’s climate is to those emissions.23 Climate sensitivity is typically defined as the long-term change that would result from a doubling of carbon dioxide in the atmosphere relative to preindustrial levels; its exact value is uncertain due to the interconnected nature of the land–atmosphere–ocean system. Changes in one aspect of the system can lead to self-reinforcing cycles that can either amplify or weaken the climate system’s responses to human and natural influences, creating a positive feedback or self-reinforcing cycle in the first case and a negative feedback in the second.18 These feedbacks operate on a range of timescales from very short (essentially instantaneous) to very long (centuries). While there are uncertainties associated with modeling some of these feedbacks,24,25 the most up-to-date scientific assessment shows that the net effect of these feedbacks over the industrial era has been to amplify human-induced warming, and this amplification will continue over coming decades18 (see Box 2.3).