Laboratory Manual for Introductory Geology 4e

15.5 Glaciers and Climate Change
Intense weather events such as tornadoes, hurricanes, and typhoons, a rising sea
level, and persistent drought have brought the issue of global climate change from
the field sites and laboratories of geologists and meteorologists to media headlines
and the world political arena. Glacial landforms and sophisticated studies of polar
ice provide the best record of atmospheric changes over the past several hundred
thousand years, enabling us to base hypotheses about future changes on solid fact
rather than guesswork.
Glacial deposits provide evidence that the ice ages during what geologists call
the Pleistocene Epoch involved four glaciations, in which continental glaciers
advanced across the northern hemisphere, followed by interglacials, in which the
ice retreated or melted completely. Carbon dating of wood from glacial and interglacial
sediments shows that the first glaciation began about 700,000 years ago,
and the last continental glaciers in Europe and North America disappeared about
12,000 years ago.
Although the Pleistocene glaciers have disappeared from North America and
Europe, the continental glaciers that remain in Antarctica and Greenland record
atmospheric temperatures and concentrations of greenhouse gases (CO 2
, methane)
over the hundreds of thousands of years that they have existed. Geologists have
drilled into these glaciers and collected ice cores (FIG. 15.16) for study in refrigerated
laboratories.
FIGURE 15.16 An ice core showing seasonal layering and a dark layer of volcanic ash.
When the ice froze, it incorporated small bubbles of the air that existed at the
time. The ice can be dated and the amounts of greenhouse gases incorporated in
it can be measured, providing a timeline against which modern conditions can be
compared (FIG. 15.17). We will look at climate change in more detail in Chapter 18
as one of the types of global change we can expect in the next 50 years.
404 CHAPTER 15 GLACIAL LANDSCAPES