Extratropical Cooling, Interhemispheric Thermal Gradients, and Tropical Climate Change

Abstract

Recent studies suggest the existence of a global atmospheric teleconnection of extratropical cooling to the tropical rainfall climate, mediated through the development of a thermal contrast between the hemispheres-an interhemispheric thermal gradient. This teleconnection has been largely motivated by studies that show a global synchronization of rapid climate change during abrupt climate changes of the last glacial period, in addition to attribution studies of twentieth-century Sahel drought and studies that examined the climate impacts of anthropogenic aerosols. This research has led to interesting developments in atmospheric dynamics of the underlying mechanisms and in applications toward understanding past and present tropical climate change. The emerging teleconnection hypothesis promises to offer new insights into understanding future patterns of tropical rainfall changes due to interhemispheric thermal gradients from greenhouse warming, aerosols, and land-use change.

Green Mountains and White Plains: The Effect of Northern Hemisphere Ice Sheets on the Global Energy Budget

“…This tallies with previous studies that have shown that an increase in the albedo causes a change in the atmospheric energy transports, brought about by a change in the position of the zonal mean ITCZ (Chiang and Bitz 2005). Figure 4 shows that the heat transport across the equator is partitioned approximately equally between the atmosphere and the ocean.…”

“…Although many studies report that with an increase in elevation the surface cools, it is unclear whether this cooling is due merely to lapse rate effects, to the fact that a higher surface will be cooler, or to additional feedbacks that alter the climate's energy balance, particularly those that reduce the amount of energy incident at the surface. Slab model experiments in which the topography and albedo are changed individually (Chiang et al 2003) show that there are feedbacks that can alter the response of the atmosphere to an ice sheet: they also emphasize the nonlinearity of these feedbacks highlighting the differences between an albedo-alone response and a topography-alone response.…”

“…While the local effects of the ice sheet on the midlatitude circulation have long been considered (e.g., Cook and Held 1988;Kutzbach and Wright 1985), their global impact has been somewhat ignored and never examined with a fully coupled oceanatmosphere climate model (Manabe and Broccoli 1985). There has been much written recently about the effect that changing the contrast between the temperature and energy balance in the Northern and Southern Hemispheres can have on the position of tropical rain belts and transports of energy across the equator (e.g., Yoshimori and Broccoli 2008;Kang et al 2008;Chiang and Friedman 2012;Donohoe et al 2013). This framework has proven itself quite useful for understanding changes in the large-scale circulation.…”

“…A number of sets of simulations have shown that as an ice sheet's topography changes so does its impact on the climate (Chiang et al 2003;Li and Battisti 2008;Lee et al 2015;Ullman et al 2014). It is likely that such effects on the climate imply some changes in the climate's energy balance.…”

Prospecting Glacial Ages and Paleoclimatic Reconstructions Northeastward of Nevado Coropuna (16° S, 73° W, 6377 m), Arid Tropical Andes

“…Although with some uncertainties, we believe that the proposed ideas construct a coherent regional interpretation, explaining the 3 He and 36 Cl ages reasonably from Coropuna, Hualca Hualca and their surroundings ( [7,37]; this work), as well as the other glacial chronologies available from the Arid Tropical Andes: Sajama [121], Tunupa [8] and Uturuncu [9]. The glacial ages and paleoclimatic proxies seem consistent with evidence showing a link between tropical glaciers and the Northern Hemisphere cooling episodes, through the tropical circulation southward shift [20][21][22][23][24]. [37,38]; This work; Hualca Hualca [7], Sajama [121] Tunupa [8] and Uturuncu [9].…”