Putnam reported in mid-2022 that At the peak of the last ice age, about 20,000 years ago, vast ice sheets covered northern portions of continents in Earth’s Northern Hemisphere, and glaciers extended from mid-latitude mountain chains in both hemispheres. These regions were simultaneously locked into a climate marked by cold temperatures and advancing glaciers, yet Earth’s orbital history suggests that summers should have been warm in the Southern Hemisphere and cool in the Northern Hemisphere. Since this conundrum emerged several decades ago, scientists have grappled with its implications, and its relationship with the origins of glacial cycles, which had varied regularly for hundreds of thousands of years.
What caused synchronized bipolar ice-age cooling? And did glaciers in the tropics vary with the same rhythm as did those at higher latitudes? On page 301, Rodbell and colleagues show that the timing of glacial variations in the tropical Andes is strikingly similar to that at higher latitudes over a period of nearly 700,000 years.
Mountain glaciers are highly sensitive, purely physical monitors of climatic conditions. The worldwide retreat of mountain glaciers that has occurred over the past century or so in response to industrial-age warming is an iconic demonstration of ongoing climate change. Likewise, glaciers have sensitively monitored climate changes in the past. Evidence for ancient glacier fluctuations is imprinted on the landscape and preserved in sediments. One means of reconstructing past glacier variations involves the mapping and dating of glacial landforms, such as moraine ridges, which form from the material dumped at the edge of a stabilized glacier and delineate former ice boundaries. These landforms provide direct, physical evidence of the extent of previous glaciers.
Read on ....
[Looking into recent papers on impact of earth's orbit relative to the sun as additive to climate changes?]
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