Climate change as a reality of nature: By the 18th century, literate people recognized that climate conditions described by Classical and Medieval authors were often different from those that they witnessed. Today we note that the canals of the low countries are no longer the reliable winter highways for skaters depicted by Peter Brueghel or described in Hans Brinker, or the Silver Skates. It is apparent that climate changes over time. As the science of geology arose, the attention of geologists was drawn to ancient climates for which no eye-witness accounts existed.
Louis Agassiz: (1807 - 1873) Swiss geologist, paleontologist, paleoclimatologist. Investigated reports of glacial erratics (glacier-transported boulders) in places where contemporary glaciers couldn't possibly transport them, such as the Jura Mts. of France and Switzerland. In 1840, published Etudes sur les glaciers (Study of Glaciers), proposing that the prehistoric Earth had experienced an ice age in which a continental glacier similar to that of Greenland had covered the Alps and had lapped against the Juras. As more information rolled in, it became clear that the the ice age glaciations had occurred at high elevations throughout the world and throughout high latitudes.

To know what kind of landforms led to this conclusion, one needs to understand the deposition of continental glaciers today:
Land forms resulting from continental glaciers: Continental scale glaciation creates interesting opportunities for ice to interact with large volumes of sediment. Results include:

Periglacial features: Beyond features created by glacial ice, itself, the regions adjacent to continental glaciers display characteristic features owing to:

Resulting land-forms reflect interaction of regolith and ice:

  • Patterned ground - Polygons formed by ice wedges. extending into the soil.
  • Pingoes - Bodies of ice that rise up through the regolith in response to burial pressure.
    Ice ages:

    So what has the global distribution and age of the glacial and periglacial features taught us?

    The Cretaceous and early Paleogene was a greenhouse world. From the Late Plaeogene onward, we have been in an ice house conditions occurred during that interval. During last 2 million years (the Quaternary Period), the situation has become extreme, an ice age with major continental glaciations alternating with interglacials. The interval from 2 mya to 10,000 years ago is called the Pleistocene Epoch. The last interglacial of the Quaternary Period (the one we are in) is the Holocene Epoch.

    Pleistocene temperature and "proxy data": The first reliable thermometers went into use in Italy in the late 17th century. The first continuous records of daily temperature didn't begin until the early 19th century in England, so how do we know about ancient temperatures? We infer them indirectly through proxy data:


    The Oxygen isotope record: During the late 20th century, a new technique allowed us to refine this sequence.

    Condition 18,000 years ago during the last glacial maximum:


  • Today's ice caps grew to 3x their current area and were up to 3 km thick

  • Cold weather zones expanded and warm weather zones contracted into a thinner strip of warm tropical weather.

  • Regions of highest rainfall shifted to higher latitudes, forming large, rain-fed pluvial lakes. (These can be mapped using ancient wave-cut platforms).

  • The land deformed isostatically upon loading by the ice sheets. In some locations, the land is still responding isostatically to the removal of the ice. E.g. Scandinavia (1m / century), Ohio valley.

  • As a consequence of isostatic deformation, the land buckled downward near the edge of the ice. Glacial meltwater pooled up at margins of glaciers forming large meltwater lakes. The Great Lakes are stranded remnants of such.

  • At the climax of the last glaciation, 18,000 years ago, accumulation of all that ice and snow - sea level dropped 120 m. Some of the major geographic differences from the modern Earth (besides the presence of so much continental ice):
  • Last remnant of North American Ice sheets melted roughly 10,000 years ago. At the end of the last ice age lots of North American animals went extinct - especially large plant-eating mammals and the predators that fed on them, including:

    Was this due to:

    An irrationally emotional debate rages. (Psst! Merck bets on the third option in most cases.)


    The Ice-Age is still with us:

    In this and many other lectures, we discuss various natural processes and patterns as if the Earth were at equilibrium. The fact is that it isn't. We can list ways in which equilibration is still occurring:


    Key concepts and vocabulary: