Although a minority of researchers has pointed to certain high-altitude Andean valleys, where local records suggest slight cooling, a recent synthesis concludes that over the past several decades mean temperatures have risen more rapidly across the Tibetan Plateau than in surrounding lowland regions. Investigators have long hypothesized that several distinct mechanisms produce larger thermal excursions at high elevations than at lower ones. First, extensive portions of the plateau are mantled in snow and ice, which are strongly reflective; when that cover recedes, the newly exposed ground absorbs solar radiation and amplifies further warming. Second, the atmosphere at such elevations is rarefied, so comparatively little energy is needed to raise its temperature. Third, a smaller fraction of incoming solar energy is dissipated through evaporation at these cold, high altitudes than in the humid tropics.

Consider each of the choices separately and select all that apply.

The passage identifies which of the following as mechanisms that may generate substantial temperature variation at high elevations?

A. the proportion of solar energy dissipated through evaporation at high altitudes
B. the exposure of ground surfaces following the loss of snow cover
C. the rarefied character of the atmosphere at high elevations



In citing the apparent cooling in certain high-altitude Andean valleys, the researchers mentioned in the passage intend to raise which of the following as a question?

A. whether the Andes are less prone to extreme temperature shifts than are other high-elevation regions
B. whether those localized cooling records might point to a meaningful pattern that the broader warming average does not capture
C. whether the temperature trajectory in those Andean valleys might soon reverse
D. whether the mechanisms governing temperature change in those valleys differ from those operating elsewhere at high elevation
E. whether the Andes receive more snow and ice than do other high-elevation regions