Tropical upper‐troposphere clouds are expected to rise under global warming, contributing a positive radiative feedback. Here we show that Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals over 2002–2021 from the Terra and Aqua satellites report a tropical‐mean high‐cloud altitude increase of 6.9 ± 2.7 m yr−1 (±2σ), while atmospheric models report 5.6 ± 3.0 m yr−1 over 1979–2014. During their common overlap period, however, the observed trend is greater than that of the models. The atmospheric models also show a tropically confined cloud‐height response to El Nino, whereas the observed cloud height response peak extends into the subtropics. Poleward of the mid‐latitudes, Aqua and Terra MODIS have cloud‐height drifts relative to each other, highlighting the need for deeper investigation of potential time‐dependent biases in MODIS cloud retrievals. Both sensors report significant tropical cloud height increases since 2002, which are statistically consistent with those simulated by climate models.

Cloud feedback has prevailed as a leading source of uncertainty in climate model projections under increasing atmospheric carbon dioxide. Cloud‐controlling factor (CCF) analysis is an approach used to observationally constrain cloud feedback, and subsequently the climate sensitivity. Although high clouds contribute significantly toward uncertainty, they have received comparatively little attention in CCF and other observational analyses. Here we use CCF analysis for the first time to constrain the high‐cloud radiative feedback, focusing on the cloud amount component owing to its dominant contribution to uncertainty in high‐cloud feedback. Globally, observations indicate larger decreases in high cloudiness than state‐of‐the‐art climate models suggest. In fact, half of the 16 models considered here predict radiative feedbacks inconsistent with observations, likely due to misrepresenting the stability iris mechanism. Despite the suggested strong high‐cloud amount decreases with warming, observations point toward a near‐neutral net high‐cloud amount radiative feedback, owing to almost canceling longwave and shortwave contributions.

Precipitation is expected to increase in a warmer global climate, yet how sensitive precipitation is to warming depends on poorly constrained cloud radiative processes. Clouds respond to surface warming in ways that alter the atmosphere's ability to radiatively cool and hence form precipitation. Here we examine the links between cloud responses to warming, atmospheric radiative fluxes, and hydrological sensitivity in AMIP6 simulations. The clearest impacts come from high clouds, which reduce atmospheric radiative cooling as they rise in altitude in response to surface warming. Using cloud locking, we demonstrate that high cloud radiative changes weaken Earth's hydrological sensitivity to surface warming. The total impact of cloud radiative effects on hydrological sensitivity is halved by interactions between cloud and clear‐sky radiative effects, yet is sufficiently large to be a major source of uncertainty in hydrological sensitivity.

arming. Warming and cooling aerosols can also interact with clouds, changing their ability to form and dissipate, as well as their reflectivity and precipitation rates. Clouds can contribute both to cooling, by reflecting sunlight, and warming, by trapping outgoing heat. Climate Feedbacks Climate feedbacks are natural processes that respond to global warming by offsetting or further increasing change in the climate system. Feedbacks that offset the change in climate are called negative feedbacks. Feedbacks that amplify changes are called positive feedbacks. Water vapor appears to cause the most important positive feedback. As the earth warms, the rate of evaporation and the amount of water vapor in the air both increase. Because water vapor is a greenhouse gas, this leads to further warming. The melting of Arctic sea ice is another example of a positive climate feedback. As temperatures rise, sea ice retreats. The loss of ice exposes the underlying sea surface, which is darker and absorbs more sunlight than ice, increasing the total amount of warming. Less snow cover during warm winters has a similar effect. Clouds can have both warming and cooling effects on climate. They cool the planet by reflecting sunlight during the day, and they warm the planet by slowing the escape of heat to space (this is most apparent at night, as cloudy nights are usually warmer than clear nights). Climate change can lead to changes in the coverage, altitude, and reflectivity of clouds. These changes can then either amplify (positive feedback) or dampen (negative feedback) the original change. The net effect of these changes is likely an amplifying, or positive, feedback due mainly to increasing altitude of high clouds in the tropics, which makes them better able to trap heat, and reductions in coverage of lower-level clouds in the mid-latitudes, which reduces the amount of sunlight they reflect. The magnitude of this feedback is uncertain due to the complex nature of cloud/climate inter