Elevated heating of the atmosphere by large plateaus has been argued to influence regional climate in Asia and other regions, but the mechanisms that cause the troposphere to equilibrate at warmer temperatures over elevated terrain are not well understood. This paper quantitatively describes the physics that controls temperatures over elevated terrain in radiative-convective equilibrium (RCE). First, a cloud-system-resolving model (CSRM) is used to simulate RCE states over surfaces with various elevations. Then, a theory for the influence of surface elevation on temperatures in RCE is presented. Together with offline radiative transfer calculations, this theory is used to quantitatively attribute the magnitude of the elevated heating effect to topof- atmosphere radiative flux changes caused by decreases in longwave absorption, shortwave scattering, and the moist lapse rate that occur as surface pressure drops. Sensitivity functions obtained through these offline calculations suggest that elevated heating is weaker in warmer climates, and additional CSRM simulations support this hypothesis. Under certain circumstances, even the sign of the elevated heating effect can change to produce cooler temperatures at a given pressure level as the surface is lifted in RCE.

All else being equal, a given atmospheric pressure level is thought to be warmer over a plateau than over surrounding nonelevated terrain because of orographic “elevated heating.” However, elevated surfaces are also typically brighter due to reduced vegetation and increased ice cover. Here we assess the degree to which surface albedo compensates for orographic elevated heating. We confirm that land surface albedo generally increases with surface elevation in observations. Using a cloud system-resolving model, we show that increased surface albedo strongly compensates for orographic elevated heating in radiative-convective equilibrium. A nonelevated surface with the albedo of modern India would enter a runaway greenhouse regime without ventilation by monsoonal winds, while a surface with the albedo and elevation of Tibet would achieve a cooler radiative-convective equilibrium. Surface albedo changes may thus be just as important as surface elevation changes for the evolution of low-latitude regional climate throughout Earth's history.

While the Atlantic Meridional Overturning Circulation (AMOC) is projected to slow down under anthropogenic warming, the exact role of the AMOC in future climate change has not been fully quantified. Here, we present a method to stabilize the AMOC intensity in anthropogenic warming experiments by removing fresh water from the subpolar North Atlantic. This method enables us to isolate the AMOC climatic impacts in experiments with a full-physics climate model. Our results show that a weakened AMOC can explain ocean cooling south of Greenland that resembles the North Atlantic warming hole and a reduced Arctic sea ice loss in all seasons with a delay of about 6 years in the emergence of an ice-free Arctic in boreal summer. In the troposphere, a weakened AMOC causes an anomalous cooling band stretching from the lower levels in high latitudes to the upper levels in the tropics and displaces the Northern Hemisphere midlatitude jets poleward.

Most state-of-art models project a reduced equatorial Pacific east-west temperature gradient and a weakened Walker circulation under global warming. However, the causes of this robust projection remain elusive. Here, we devise a series of slab ocean model experiments to diagnostically decompose the global warming response into the contributions from the direct carbon dioxide (CO₂) forcing, sea ice changes, and regional ocean heat uptake. The CO₂ forcing dominates the Walker circulation slowdown through enhancing the tropical tropospheric stability. Antarctic sea ice changes and local ocean heat release are the dominant drivers for reduced zonal temperature gradient over the equatorial Pacific, while the Southern Ocean heat uptake opposes this change. Corroborating our model experiments, multimodel analysis shows that the models with greater Southern Ocean heat uptake exhibit less reduction in the temperature gradient and less weakening of the Walker circulation. Therefore, constraining the tropical Pacific projection requires a better insight into Southern Ocean processes.