Soru

In his 1864 treatise on climate dynamics, astronomer James Croll posited that periodic variations in Earth’s orbital geometry alter the latitudinal distribution of solar radiation, thereby initiating glacial epochs. While Croll's contemporaries overwhelmingly attributed continental glaciations to static oceanic current shifts, he insisted that gravitational perturbations induced by Jupiter and Saturn modify Earth’s eccentricity—the degree of elongation of its orbital ellipse. When this parameter reaches a local maximum during periods of peak axial tilt, winter insolation in the northern hemisphere decreases sharply, accelerating the accumulation of polar ice sheets. Crucially, Croll argued that these structural alterations in Earth's orbit do not directly cool the atmosphere sufficiently to freeze vast terrestrial basins; rather, they act as subtle triggers for self-reinforcing feedback loops. Primary among these amplification mechanisms is the albedo effect of expanding snow cover, which reflects incoming shortwave radiation back into space. Although geologists initially rejected Croll's hypothesis due to flawed chronological alignments with mid-Pleistocene strata, modern paleoclimatologists acknowledge that it correctly identified the astronomical pacing of ice ages.

In the passage, the pronoun "they" in the fourth sentence ("rather, they act as subtle triggers...") refers to which of the following?