Late Cenozoic uplift of mountain ranges and global climate change: chicken or egg? – Peter Molnar & Philip England, 1990 By Kevin Darole ESS 433

Overview  The causes of the high elevations of most mountain ranges around the globe such as the Appalachians or the Southern Alps in New Zealand have been attributed to Late Cenozoic uplift.  One theory states that uplift of these mountain ranges occurred more recently due to geomorphological, sedimentation, and paleo-botanical evidence.  An alternate theory proposes that global climate change during the late Cenozoic is the cause; lower temperatures, alpine glaciation, stormy climates, precipitation, etc.  The biggest question is did climate cause the uplift of these mountains or did uplift cause climate change?

Definition(s) of Uplift  Uplift is the relation between the Earth’s surface to the sea level.  Uplift is a vector opposite to the gravity vector, and a meaningful definition must specify a reference frame and an object that moves, and in this case Earth’s sea level (geoid) corrected for eustatic changes vs the Earth’s surface.

Uplift effects on climate  Increased elevations at high latitudes can extend winter duration, which in turn increases duration of snow cover, increasing albedo.  Increased elevation can largely affect atmosphere circulation.  Chemical weathering of minerals exposed to colder environments that are transported to warmer, lower elevations would be able to absorb more CO2 from the atmosphere, decreasing the “greenhouse effect”.

Cenozoic Climate  Earth has experienced a variable, unsteady cooling period over the past 50 Myr  Sudden drops of global temperature occurred ~36 Myr ago, ~ 15 Myr ago, and ~2.5 Myr ago. The last one being associated with glaciation beginning to occur in the Northern Hemisphere.

Evidences of Recent Uplift due to Climate:  Morphology - incisions by streams and rivers into relatively flat, high areas provided the streams enough potential energy to incise the surface  Sedimentation - Thick deposits dating to late Cenozoic conglomerates surround the bases of most high mountain ranges.  Paleobotany* - Taxonomic relations

Climate Change with uplift as a result:  Aforementioned evidence has exaggerated claims - Isostatic rebound from rapid erosion/incision and sedimentation will elevate remaining terrain but the uplift of peaks to compensate does not actually increase overall elevation - most of the claims supporting paleo-botanical evidence ignore global cooling of the Earth’s surface completely - While uplift can effect global climate, in higher elevations, glaciation/climate is dominant erosional process

Conclusion  We can safely say that they hypothesis stating that uplift of the mountain ranges caused climate change is false.  However, we cannot fully confirm that climate change caused mountain range uplift.  It can possibly be a mix between the two hypotheses in which uplift and climate change occurred simultaneously.

Sources Molnar, Peter, and Philip England. "Late Cenozoic uplift of mountain ranges and global climate change: chicken or egg?." Nature (1990):