An iceberg floats in the bay of Kulusuk, Greenland. The northern ice caps and glaciers are melting.

AP Photo/John McConnico/File

Is global warming irreversible?

By the time Al Gore's award-winning documentary "An Inconvenient Truth" hit theaters in 2006, most of the world had accepted the fact of global warming, if not humanity's causative role in it. But over the last few years, as more and more scientific organizations have backed up the claim that human activity is to blame for rising temperatures, including a United Nations science panel in 2007, government actions attempting to curtail greenhouse-gas emissions have gained even more supporters. Most of the developed world is now onboard in the fight to save the world from warm, certain doom -- but suddenly, it appears all the effort might be futile.

The situation is indeed dire. As factories, cars and power plants emit tons of gases like carbon dioxide, methane and nitrous oxides into the atmosphere, and all the while deforestation activities remove the plant life that absorbs carbon dioxide, lots of those "greenhouse gases" build up in the atmosphere. There, they act like the glass of a greenhouse, allowing sunlight in but trapping it once it's there.

So far, in the last century, Earth's average temperature has increased about 1 degree F (0.6 degrees C) [source: New York Times]. That may not seem like much, but it can have profound effects, like altering weather systems and changing the balance of sea life. Polar bears are looking at possible extinction in the next few decades [source: NGN]. Experts predict that by 2100, sea levels could rise by up to 2 feet (61 centimeters), leaving major coastal areas underwater [source: New York Times].

Most scientists say that an increase of more than 3.3 degrees F (2 degrees C) would be catastrophic [source: SFS].

The world is taking action to curb the danger, like setting limits on industrial CO2 pollution and developing alternative energy sources. But some new research could throw a wrench in the works of ecological optimism: It seems all our efforts may be for naught.

In this article, we'll look at some newer research suggesting that global warming might be irreversible. We'll find out why we may not be able to undo the damage and see if we might as well just emit to our hearts' content.

We'll start with the "why": As it turns out, Earth's bodies of water do not make for quick change.

Carbon dioxide levels at 450 ppm could result in widespread drought and famine comparable to the Dust Bowl of the 1930s in the United States.

Image courtesy of NASA

An Irreversible State of Global Warming: The Cycle

A study published in 2009, led by a scientist with the National Oceanic and Atmospheric Administration, shows that climate change may in fact be irreversible. Instead of it taking a couple hundred years to reverse global warming if we cut emissions right now, it looks like it could take more like a millennium. The issue is the oceans' absorption of atmospheric carbon dioxide.

The world's oceans play a central role in climate control. It's not just plants that absorb CO2; oceans absorb even more of it. Ocean waters absorb CO2 from the air, effectively cooling the atmosphere. The ocean also emits heat from the sunlight it absorbs, warming the atmosphere. This constant cycle of cooling and warming keeps the Earth at a stable temperature. Or at least, that's how it's supposed to work.

The system starts to break down when the amount of CO2 pumped into the atmosphere rises exponentially, as it has in the last couple of centuries. The ocean can only absorb so much CO2 in a period of time: The upper layers of water absorb CO2, and then, as currents move, lower layers of water replace those saturated surface waters, offering new absorption surfaces. The snail-like turnover pace means any actions we take now to curb CO2 emissions won't have any effect for a long, long time.

There are other cycles involved in the problem, too. The loss of sea ice in the Arctic due to global warming creates further warming conditions that are difficult to undo. Sea ice and glacial mass are another big part of the Earth's climate-control system. While water absorbs sunlight, ice reflects it. Glaciers help keep ocean waters at a stable temperature. When glaciers melt, as they've been doing steadily since the United States started recording their levels in 1978, there's less ice to reflect sunlight and more water to absorb it. With more sunlight absorption, ocean temperatures increase. When ocean temperatures increase, more heat is released into the atmosphere, and overall temperatures increase, leading to more melting.

The end result of these combined cycles could be what some experts are calling an irreversible state of global warming. But are we really at that tipping point where there's no turning back climate change?

Have we reached an irreversible state of global warming?

Image courtesy of the U.S. House of Representatives

Global Warming Tipping Point

If climate change is irreversible, does that mean it could take all cars off the road and it would never have an effect?

It's not quite that dire. According to the 2009 study, we could be looking at a thousand years of warmer temperatures even if we make dramatic cuts in CO2 emissions right now. So technically, it's not "irreversible" -- any of our descendants born after the year 3000 will be able to reap the benefits of our CO2 cuts (whew!).

We have apparently made it to the point of no timely return.

In terms of sea ice, that point became apparent years ago when Arctic ice stopped replenishing itself. Usually, ice melts to a certain level in summer months and freezes back to a certain level in winter months. Starting around 2003, the ice stopped recovering [source: Connor]. For that year and each year since, the ice melted more than usual in summer, and froze less than usual in winter, resulting in an overall loss of "permanent" ice. For September, the average sea ice coverage has typically been 2.4 million square miles (7 million square kilometers); in September 2007, sea ice covered only 1.65 million square miles (4.27 square kilometers) of the Arctic Ocean, the lowest point on record [source: USA Today]. Some experts believe there may be no summer ice in the Arctic within 10 years [source: USA Today].

The atmospheric CO2 situation isn't much better. We currently have 385 parts per million (ppm) of CO2 in our air; scientists are pushing for CO2 caps that will get us stabilized at 450 ppm in the next few decades [source: New Scientist]. Many people believe this goal isn't politically feasible, and have set 550 ppm as a more reasonable target [source: New Scientist]. But new research suggests it may not even matter. That 2009 NOAA-led study states that at 450 ppm, we're still looking at severe, unavoidable drought conditions in Africa, southern Europe, western Australia and the American southwest. And if we reach 600 ppm, expanding warm waters could make ocean levels rise by 3 feet (1 meter) in the next thousand years [source: Modine]. That number gets even higher if you take into account melting glaciers.

Scientists aren't proposing we stop buying hybrid cars, though. The faster we act to make huge cuts in CO2, the better the prognosis. If we can make dramatic changes right now, perhaps we could get the atmosphere stabilized at 400 ppm instead of 550 ppm. That would at least increase the chances that the U.S. West Coast will still be above water in 3000. Probably.

For more information on global warming and related topics, look over the links on the next page.

Lots More Information

Related HowStuffWorks ArticlesMore Great LinksSources
  • "Arctic sea ice melts to 2nd-lowest level on record." USA Today. Aug. 27, 2008.http://www.usatoday.com/weather/climate/2008-08-27-arctic-sea-ice_N.htm
  • Connor, Steve. "Global warming 'past the point of no return.'" The Independent. Sept. 16, 2005.http://www.independent.co.uk/news/science/global-warming-past-the-point-of-no-return-507030.html
  • Global Warming. The New York Times.http://topics.nytimes.com/topics/news/science/topics/globalwarming/index.html
  • Harris, Richard. "Global Warming Is Irreversible, Study Says." All Things Considered. NPR.org. Jan. 26, 2009.http://www.npr.org/templates/story/story.php?storyId=99888903
  • Maugh, Thomas H. II. "Study says some global warming now irreversible." SFGate. Jan. 27, 2009.http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/01/27/MNQP15H779.DTL
  • Modine, Austin. "Boffin dubs global warming 'irreversible'." The Register. Jan. 28, 2009.http://www.theregister.co.uk/2009/01/28/global_warming_irreversible/