National Geographic Daily News
A map of Antarctic sea ice.

Sea ice extent around Antarctica on September 26. Yellow line shows median September sea ice extent from 1979 to 2000.

Illustration courtesy Jesse Allen, EO/NASA/NSIDC

Daniel Stone

National Geographic News

Published October 13, 2012

Despite frequent headlines about a warming planet, melting sea ice, and rising oceans, climate analysts pointed to a seeming bright spot this week: During Southern Hemisphere winters, sea ice in the Antarctic, the floating chunks of frozen ocean water, is actually increasing.

In fact, in late September, satellite data indicated that Antarctica was surrounded by the greatest area of sea ice ever recorded in the region: 7.51 million square miles (19.44 million square kilometers), the U.S. National Snow and Ice Data Center announced Thursday. Even so, it's a slow rate of growth—about one percent over last year—not nearly enough to offset melting in the Arctic, which broke records just weeks ago.

National Geographic asked Eric Rignot, a NASA researcher and earth systems professor at UC Irvine, whether the data is good news, and what it means for the rise of global sea levels, which are fueled by melting ice.

This Antarctic record seems counter to what we often hear about sea ice shrinking. How can we explain growing sea ice?

If the world was warming up uniformly, you would expect the sea ice cover to decrease in the Antarctic, but it's not. The reason for that is because the Antarctic is cooler than the rest of the world. It's warming up as well but not as fast as other places.

So you have the warming world and a cold Antarctica, and the difference between the two is increasing. That makes the winds around Antarctica move a little bit faster. There's also a difference that comes from the depletion of ozone in the stratosphere in the Antarctic, which makes the stratosphere colder.

That's the leading explanation for what we're seeing in the Antarctic, but you have to acknowledge that the effect is very small.

How does this news relate to other studies showing that the melting of Antarctic continental ice is contributing to a rise in sea level?

[Growing sea ice] has no effect whatsoever on sea level, because sea ice is already floating on the ocean. It does not displace sea level. It's frozen seawater, so whether it's frozen or liquid, it doesn't change the sea level.

While Arctic sea ice is decreasing, the Antarctic is now slightly increasing. Why is there so much variation between Arctic and Antarctic ice?

Well we have a continent on the South Pole. On the North Pole we have nothing but ocean. In the Arctic you see full-fledged warming of the atmosphere and the ocean, plus increased ice transport [out of the region, which removes cold air and water]. So all of these effects contribute to reduce the sea ice cover in the Arctic.

In the Antarctic, you have to think of it as its own climate system. It's a big continent isolated from the rest of the world. It has ocean all around it. It has wind regimes that blow clockwise around it and isolate it. It acts differently from the Arctic, which is completely connected to the rest of the North Hemisphere.

Considering we regularly hear about the planet's stressed climate system, is this good news?

Really, it's consistent with our understanding of a warming world. Some of the regional details are not something we can easily predict. But the general trends of decay of the sea ice cover and decay of the Greenland ice sheets and ice caps is in line with what we expect.

The Antarctic has not been warming up as fast as the models thought. It's warming up, but slower. So it's all consistent with a warming planet.

Note: Interview has been condensed and edited.

More on Melting Ice and Antarctica

6 comments
Kim Harper
Kim Harper

Is it possible that melting glaciers *ON* Antarctica could belaying a wider swath of freshwater on the surface of the surrounding oceans....freezing faster/longer than salt water?


Jeff MacLeod
Jeff MacLeod

Rune: By 'less weather' I suspect you mean less storms. Weather is governed by the amount of energy in the system. as energy retention continues to increase weather will become more chaotic. As the water cycle is intensified precipitation and droughts will increase. these aspects of weather have and are being recorded and are following the trend.


CO2 has been known to lag changes in temperature specifically because of what is known as Le Chatelier's Principle. That is, when a change in temperature, concentration, partial pressure, and so on occurs on one side of a system the other side of the system must change in order to keep the system in equilibrium. This is why CO2 outgasses from the ocean during warming periods and is absorbed by the ocean during cooling periods. However, this does not mean that CO2 has no effect on the climate. Rather it has historically been a positive feedback. And the last peak of the last Milankovitch cycle, that which controls the ice age, is not now. According to the data and measurements the peak occurred 8000 years ago and we have been in a slow cooling trend since then that was offset at the beginning of the industrial revolution.


Venus did not become a runaway greenhouse planet primarily due to increases in CO2. It did so as a consequence of increasing solar intensity as the Sun grew and an eventual change in temperatures to not allow the liquid water that existed on the planet to condense and form clouds. Rather that water vapour disassociated high up in the atmosphere and the hydrogen molecules continued onward while the oxygen molecules either did the same or were trapped in the atmosphere. The only way Earth could become like Venus is through increases in solar forcing.


And polar bear numbers are currently declining. they are not thriving. Polar bear numbers increased from the 1950s, though, primarily due to hunting restrictions. nothing to do with changes in climate.

Rune Østergren
Rune Østergren

Poles warming faster then equator leads to less weather not more...

Co2 has been repeatedly found to lag behind changes in temprature, not lead them...

The grap of known iceages shows cyclical iceages roughly 100 000 years appart, we are at a top now, with less temp. then the last tops on the graph, humanity couldnt have caused the former tops, so what makes this one our fault..

The co2 levels are nearing 400 ppm, history shows levels upwards of 4000, without Earth turning into Venus or its cyclical iceage/warmth behaviour ending...

Al Gores "Desserts are growing" and polarbears dying out...from what i can gather from scientiffic reports, even Sahara is growing green and lessening in zize probably due to more co2 in the biosphere and atmosphere, and polarbears are thriving not going extinct...

I could go on writing until it reminded of dickens collected works, but i guess we can say that things has happened that disproves AGW, if the political agenda will change so that it gets accepted is another question!...

Rune Østergren
Rune Østergren

Poles warming faster then equator leads to less weather not more...

Co2 has been repeatedly found to lag behind changes in temprature, not lead them...

The grap of known iceages shows cyclical iceages roughly 100 000 years appart, we are at a top now, with less temp. then the last tops on the graph, humanity couldnt have caused the former tops, so what makes this one our fault..

The co2 levels are nearing 400 ppm, history shows levels upwards of 4000, without Earth turning into Venus or its cyclical iceage/warmth behaviour ending...

Al Gores "Desserts are growing" and polarbears dying out...from what i can gather from scientiffic reports, even Sahara is growing green and lessening in zize probably due to more co2 in the biosphere and atmosphere, and polarbears are thriving not going extinct...

I could go on writing until it reminded of dickens collected works, but i guess we can say that things has happened that disproves AGW, if the political agenda will change so that it gets accepted is another question!...

John Hooper
John Hooper

Is there anything that could happen that would disprove Global Warming?

 It's starting to sound awfully like God.

Share

How to Feed Our Growing Planet

  • Feed the World

    Feed the World

    National Geographic explores how we can feed the growing population without overwhelming the planet in our food series.

See blogs, stories, photos, and news »

The Innovators Project

See more innovators »

Latest News Video

See more videos »

See Us on Google Glass

Shop Our Space Collection

  • Be the First to Own <i>Cosmos: A Spacetime Odyssey</i>

    Be the First to Own Cosmos: A Spacetime Odyssey

    The updated companion book to Carl Sagan's Cosmos, featuring a new forward by Neil deGrasse Tyson is now available. Proceeds support our mission programs, which protect species, habitats, and cultures.

Shop Now »