No one can say when the next ice age will occur, but we can look to previous ice ages and see what caused them. With that knowledge we can understand what events might cause another ice age.

What is an ice age

There are major ice age or glacial periods in Earths history. As the overall temperature of the planet cools the winter snows don’t melt over the summer. The snow continues to build up with each winter and again each summer not all of it melts, leaving it over for another winter. More snow on the ground will reflect the warmth of the sun, causing further cooling, this is called the albedo effect. Each winter the snows build up and each summer more snow fails to melt. The snow then compacts and becomes heavy and moves in the form of glaciers. As more snow and ice cover larger parts of the planet thus causing even further cooling.

Previous ice ages

Scientist now believe there have been four major ice age periods in Earths past. The earliest well-documented ice age occurred about 700 million years ago when the entire earth could have been covered with ice, called snowball earth. And ironically what ended this major ice age was global warming in a sense, the greenhouse effect from volcanoes. Scientist don’t know exactly what caused these ice ages either, there is speculation that maybe the oceans were warmer causing more evaporation, causing more cloud cover and precipitation which built up the snow pack. There was also an ice age 450 million years ago with the last one starting 2.5 million years ago, some scientist say we are still in that ice age because there are still ice sheets covering Antarctica and Greenland.

There are the glacial (glaciers advancing) periods and interglacial (glaciers retreating) periods. The planet has seen this cycle of glacial and interglacial periods on a time scale of 40,000 to 100,000 years. The Earth is currently in an interglacial period and has been in this period for about 11,000 years now.

What causes ice ages to start

There are several theories as to what causes an ice age to start.

• The composition of the atmosphere, concentrations of carbon dioxide, CO₂.
• The Earths orbit around the sun. The Earths orbit changes with what’s known as the Milankovitch cycle.
• The suns orbit in our galaxy and the suns energy output.
• Changes in ocean currents, which affect our weather.
• The moons orbit around the Earth.
• The impact of a large meteor.
• Large volcanic eruptions.

Recent history – the little ice age

In the recent past there have been times when the earth cooled significantly. What is known as the little ice age lasted from 1350 to 1850; peaking in the 17^th century, though the time duration is argued. During this time the average temperature fell by 2-3Ëš F (1-1.5Ëš C). Winters lasted longer, crops didn’t grow, there was famine and the dark ages and the plague occurred during this time, there were terrible winters during the American Revolution. There is much discussion as to what caused this little ice age, and no one seems to be able to pin point any one cause. Increased volcanic activity could have been the cause, but there have been increases in volcanoes before and after, that didn’t cause a little ice age. There is an odd fact that during this time period the sun was in an unusually quiet stage. Usually there is an 11-year cycle for sunspots, going from no sunspots to many. During this time, there was a 50 to 70 year period where there weren’t any sunspots. This is called the Maunder Minimum.

The year without a summer

Near the end of the little ice age, the summer of 1816 has gone down in history as the year without a summer. It snowed during the summer in New England and the weather was gloomy across the planet and colder then normal. This part of the little ice age does have a known reason and that was the major eruption of Mt. Tambora in Indonesia on April 5, 1815. It erupted for four months and was the largest volcanic eruption in history.

In 1991, Mt. Pinatubo in the Philippines erupted; it was the largest eruption in the 20^th century, throwing out 30 trillion pounds of rock, liquid dust and gas into the atmosphere. The years of 1992 and 1993 were cooler in the interiors of the continents and weather patterns did change.

Now in January 2009 there have been swarms of earthquakes in Yellowstone National Park in Wyoming. In prehistoric times Yellowstone has erupted with 1,000 times more power then the 1980 eruption of Mt. St. Helens. Scientists say it is now 40,000 years overdue for an eruption. Will that cause the next ice age?

When will the next ice age occur?

That might be impossible to know, especially since scientist still don’t know what caused other ice ages. Ice ages start slowly, gradually over a long time. The last major ice age might have been caused by changes in the earths CO₂ levels or it could have been caused by a minor shift in the earth’s axis. Although a cataclysmic event such as a large meteor hitting the earth could cool the planted drastically and suddenly. A major volcanic eruption or series of them could also cause another ice age. Sudden shifts in the ocean currents would shift our weather patterns dramatically, which could cause an ice age. Some scientists believe we are overdue for an ice age, but human activities could have stalled it or possibly even eliminated that cycle.

Scientist can predict the earth’s orbit in the past and in the future, according to that school of thought the next ice age will begin in about 50,000 years. As more studies of ice cores are done, scientist will find more information concerning previous ice ages and may be able to predict the next one.

Sam Montana © 10 January 2009

NASA article about the current solar cycle minimum