Climate Sensitivity and Feedbacks

Climate sensitivity describes how increases in CO2 (and other greenhouse gases) affect global near-surface air temperature. Following an initial immediate change in the radiative balance of the atmosphere, this characteristic of the climate system emerges from many feedbacks on a wide range of time scales. Incorporating these feedbacks and contributing to research on identifying and quantifying them is critical to maintaining the accuracy of our climate-model projections. Feedbacks influence the initial warming of the climate system, which is caused, for example, by increasing carbon dioxide levels. On decadal timescales, the following feedbacks are of primary importance: water vapor feedback, lapse-rate feedback, surface albedo feedback, and cloud feedback. They account for roughly two-thirds of the warming expected in the twenty-first century. Water vapor feedback is the strongest positive feedback, with surface albedo and cloud feedbacks being smaller positive feedbacks. The lapse-rate feedback is negative feedback that partially offsets the water vapor feedback. The cloud feedback is the most uncertain, accounting for much of the variation in future climate change predictions among climate models.