Could reversing global warming start an ice age?

The last ice age ended about 12,000 years ago.

© iStockphoto.com/AnaPhelps

Back in the early 1970s, when there were several particularly frigid winters in a row, some scientists saw the plunging temperatures as a sign that the Earth was entering a new ice age. Yet by the end of that decade, the predictions had swung the other way, and experts began worrying about rising temperatures. Since then, governments and environmental groups have been pushing for regulations and changes in public energy consumption to reduce greenhouse gases in the atmosphere and help reverse global warming.

As we scramble to change our energy-gobbling ways, some scientists are asking whether global warming might actually be serving a useful purpose. Could it be possible that this warming trend is preventing us from entering another ice age? And if we reverse the process, could we end up covered in ice once again?

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Extremes of cold and warmth are nothing new in the Earth’s history. Throughout the last billion or so years, this planet has experienced a slow seesaw effect in temperatures, drifting through alternating periods of warmth and cold. Scientists aren’t sure exactly why the Earth has swung between these temperature variations, but they believe a combination of factors, including ocean currents, changes in the Earth’s orbit around the sun, and atmospheric composition is involved.

Some of those periods have been more extreme than others. There have been waves of severe cold that we call “ice ages,” in which huge glaciers blanketed much of the Earth. Between ice ages, the Earth has typically entered stretches of relative warmth, known as “interglacial periods,” which is what we’ve been experiencing since the last ice age ended about 12,000 years ago. Now, we seem to be in a warming trend, which many scientists say is the result of greenhouse gases trapping heat in the Earth’s atmosphere.

Could global warming avert or lead to another ice age? Read on to learn what scientists have to say.

How Might Global Warming Affect a Coming Ice Age?

If the Gulf Stream slowed, could Europe be cut off from its warming waters and air?

© iStockphoto.com/Harrycane

According to one school of thought, a warming planet is one that’s less likely to wind up in an ice age. Because the Earth is always going through warming and cooling cycles, and we’ve been in one of the warming cycles for about 12,000 years now, scientists say it’s inevitable that we’ll hit another big chill sometime in the next 10,000 to 100,000 years. If that happens, much of the world — including Europe and North America — would be covered in a thick sheet of ice.

According to some researchers, the heat trapped in the Earth’s atmosphere from the greenhouse effect will offset this cooling — essentially preventing the Earth from entering another ice age [sources: Science Daily, Cosmos]. Though averting an ice age sounds like good news, the researchers caution that global warming isn’t any picnic, either. It could lead to other drastic and unpleasant effects on the planet (think rising sea levels and dwindling global food supplies).

Another school of thought makes the opposite prediction: Global warming might actually lead to another ice age. According to this theory, warming temperatures disrupt ocean currents — particularly the Gulf Stream, the flow that redistributes warm water from the Gulf of Mexico to northern Europe. As the Gulf Stream makes its deposits of warm water along the coasts of Great Britain and northwestern Europe, it keeps the temperatures there warmer than they would be otherwise.

The worry is that, when Arctic ice melts as a result of global warming, huge amounts of fresh water will pour into the North Atlantic and slow down the Gulf Stream. A study of circulation in the North Atlantic has discovered that there already has been a 30 percent reduction in currents flowing north from the Gulf Stream [source: Pearce]. A slowed Gulf Stream could potentially lead to dramatic cooling in Europe.

Will either of these scenarios really happen? It’s hard to say for sure. Climate experts haven’t even come to a consensus about the cause and effects of global warming, let alone whether it might prevent or trigger the next ice age.

The question of whether reversing global warming might lead to an ice age could be irrelevant if it never happens. According to a study by the National Oceanic and Atmospheric Administration (NOAA), the changes in ocean surface temperature, rainfall, and sea level that have already occurred are irreversible for a thousand years after carbon dioxide emissions are completely stopped [source: NOAA]. That means no matter how much we curb our emissions today, we may not be able to undo the damage that has already been done anytime soon.

The one thing scientists do seem to agree on is that another ice age is not likely to occur for thousands of years — not even remotely close to any of our lifetimes.

Lots More Information

Related HowStuffWorks Articles

  • How Glaciers Work
  • How Global Warming Works
  • How the Ice Age Worked
  • What can I do about global warming?
  • The Top 10 Worst Effects of Global Warming

More Great Links

  • Environmental Protection Agency: Climate Change
  • Intergovernmental Panel on Climate Change
  • NOVA: Cracking the Ice Age
  • United Nations Environment Programme
  • U.S. Global Change Research Program

  • Agence France-Presse. “Global warming to stave off next Ice Age.” COSMOS Magazine. Nov. 13, 2008. http://www.cosmosmagazine.com/node/2305/full
  • Chameides, Dean Bill. “Global Warming and Predictions of an Impending Ice Age — Predicting Future Climate.” TheGreenGrok. http://wwww.nicholas.duke.edu/thegreengrok/futureclimate
  • Maasch, Kirk A. “The Big Chill.” NOVA Online. http://www.pbs.org/wgbh/nova/ice/chill.html
  • McGuire, Bill. “Will Global Warming Trigger a New Ice Age?” The Guardian. Nov. 13, 2003. http://www.guardian.co.uk/environment/2003/nov/13/comment.research
  • NOAA. “New Study Shows Climate Change Largely Irreversible.” Jan. 26, 2009. http://www.noaanews.noaa.gov/stories2009/20090126_climate.html
  • Pearce, Fred. “Faltering currents trigger freeze fear.” New Scientist. Dec. 3 – Dec. 9, 2005, Volume 188, Issue 2528, pgs. 6-7.
  • ScienceDaily. “Did Early Global Warming Divert a New Glacial Age?” Dec.18, 2008. http://www.sciencedaily.com/releases/2008/12/081217190433.htm
  • Weaver, Andrew J. and Claude Hillaire-Marcel. “Global Warming and the Next Ice Age.” Science. April 16, 2004. Vol. 304, Issue 5669, pgs. 400-402.

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