THE NEXT ICE AGE: HOW THE EARTH WENT FROM GLACIAL TO INTERGLACIAL 

Did you know that scientists have recorded five significant ice ages throughout the Earth’s history, and that an increase in global temperature, as is now being experienced, could be a sign of an impending ice age?

The Ice Ages began 2.4 million years ago and lasted until 11,500 years ago. During this time, the earth’s climate repeatedly changed between very cold periods, during which glaciers covered large parts of the world, and very warm periods during which many of the glaciers melted. The cold periods are called glacials (ice covering) and the warm periods are called interglacials.

Scientists have recorded five significant ice ages throughout the Earth’s history: the Huronian (2.4-2.1 billion years ago), Cryogenian (850-635 million years ago), Andean-Saharan (460-430 mya), Karoo (360-260 mya) and Quaternary (2.6 mya-present). Approximately a dozen major glaciations have occurred over the past 1 million years, the largest of which peaked 650,000 years ago and lasted for 50,000 years. The most recent glaciation period, often known simply as the “Ice Age,” reached peak conditions some 18,000 years ago before giving way to the interglacial Holocene epoch 11,700 years ago.

At the height of the recent glaciation, the ice grew to more than 12,000 feet thick as sheets spread across Canada, Scandinavia, Russia and South America. Corresponding sea levels plunged more than 400 feet, while global temperatures dipped around 10 degrees Fahrenheit on average and up to 40 degrees in some areas. In North America, the region of the Gulf Coast states was dotted with the pine forests and prairie grasses that are today associated with the northern states and Canada.

The origins of ice age theory began hundreds of years ago, when Europeans noted that glaciers in the Alps had shrunk, but its popularization is credited to 19th century Swiss geologist Louis Agassiz. Contradicting the belief that a wide-ranging flood killed off such megafauna as the wooly mammoth, Agassiz pointed to rock striations and sediment piles as evidence of glacier activity from a destructive global winter. Geologists soon found evidence of plant life between glacial sediment, and by the close of the century the theory of multiple global winters had been established.

A second important figure in the development of these studies was Serbian mathematician Milutin Milankovitch. Seeking to chart the Earth’s temperature from the past 600,000 years, Milankovitch carefully calculated how orbital variations such as eccentricity, precession and axial tilt affected solar radiation levels, publishing his work in the 1941 book Canon of Insolation and the Ice Age Problem. Milankovitch’s findings were corroborated when technological improvements in the 1960s allowed for the analyzation of deep sea ice cores and plankton shells, which helped pinpoint periods of glaciation.

Along with solar radiation levels, it is believed that global warming and cooling is connected to plate tectonic activity. The shifting of the Earth’s plates creates large-scale changes to continental masses, which impacts ocean and atmospheric currents, and triggers volcanic activity that releases carbon dioxide into the air.

An ice age causes enormous changes to the Earth’s surface. Glaciers reshape the landscape by picking up rocks and soil and eroding hills during their unstoppable push, their sheer weight depressing the Earth’s crust. As temperatures drop in areas adjacent to these ice cliffs, cold-weather plant life is driven to southern latitudes. 

Meanwhile, the dramatic drop in sea levels enables rivers to carve out deeper valleys and produce enormous inland lakes, with previously submerged land bridges appearing between continents. Upon retreating during warmer periods, the glaciers leave behind scattered ridges of sediment and fill basins with melted water to create new lakes.

There were at least 17 cycles between glacial and interglacial periods. The glacial periods lasted longer than the interglacial periods. The last glacial period began about 100,000 years ago and lasted until 25,000 years ago. Today we are in a warm interglacial period. We know this because when a glacier (or ice sheet) grows and moves across the landscape, it pushes rocks and sediments. When the glacier melts, it leaves piles of these rocks behind. The rock piles are called moraines. These moraines provide evidence that glaciers once covered large parts of the world. Scientists also study the chemicals in ice cores from Greenland (a country in the far north) and rock deposits from the ocean floor. Those chemicals indicate what the climate was like when the ice or rocks were formed.

As only 11,000 years have passed since the last Ice Age, scientists cannot be certain that humans are indeed living in a post-glacial Holocene epoch instead of an interglacial period of the Pleistocene and thus due for another ice age in the geologic future. Some scientists believe that an increase in global temperature, as is now being experienced, could be a sign of an impending ice age and could actually increase the amount of ice on the earth's surface.

The cold, dry air above the Arctic and Antarctica carries little moisture and drops little snow on the regions. An increase in global temperature could increase the amount of moisture in the air and increase the amount of snowfall. After years of more snowfall than melting, the polar regions could accumulate more ice. An accumulation of ice would lead to a lowering of the level of the oceans and there would be further, unanticipated changes in the global climate system as well.

Mankind's short history on earth and even shorter records of the climate keep people from fully understanding the implications of global warming. Without a doubt, an increase in the earth's temperature will have major consequences for all life on this planet.