12. Why is Arctic sea ice decreasing while Antarctic sea ice is not?

Sea ice extent is affected by winds and ocean currents as well as temperature. Sea ice in the partly-enclosed Arctic Ocean seems to be responding directly to warming, while changes in winds and in the ocean seem to be dominating the patterns of climate and sea ice change in the ocean around Antarctica.

fig5-smallFigure 5. The Arctic summer sea ice extent in 2012, (measured in September) was a record low, shown (in white) compared to the median summer sea ice extent for 1979 to 2000 (in orange outline). In 2013, Arctic summer sea ice extent rebounded somewhat, but was still the sixth smallest extent on record. Source: National Snow and Ice Data Center (larger version)

Sea ice in the Arctic has decreased dramatically since the late 1970s, particularly in summer and autumn. Since the satellite record began in 1978 (providing for the first time a complete and continuous areal coverage of the Arctic), the yearly minimum Arctic sea ice extent (which occurs in early to mid-September) has decreased by more than 40% (see Figure 5). Ice cover expands again each Arctic winter but the ice is thinner than it used to be. Estimates of past sea ice extent suggest that this decline may be unprecedented in at least the past 1,450 years. The total volume of ice, the product of ice thickness and area, has decreased faster than ice extent over the past decades. Because sea ice is highly reflective, warming is amplified as the ice decreases and more sunshine is absorbed by the darker underlying ocean surface.

Sea ice in the Antarctic has shown a slight increase in extent since 1979 overall, although some areas, such as that to the west of the Antarctic Peninsula, have experienced a decrease. Changes in surface wind patterns around the continent have contributed to the Antarctic pattern of sea ice change while ocean factors such as the addition of cool fresh water from melting ice shelves may also have played a role. The wind changes include a recent strengthening of westerly winds, which reduces the amount of warm air from low latitudes penetrating into the southern high latitudes and alters the way in which ice moves away from the continent. The change in winds may result in part from the effects of stratospheric ozone depletion over Antarctica (i.e., the ozone hole, a phenomenon that is distinct from the human-driven changes in long-lived greenhouse gases discussed in this document). However, short-term trends in the Southern Ocean, such as those observed, can readily occur from natural variability of the atmosphere, ocean and sea ice system.

Questions and answers

Read short summary answers

1. Is the climate warming?
2. How do scientists know that recent climate change is largely caused by human activities?
3. CO2 is already in the atmosphere naturally, so why are emissions from human activity significant?
4. What role has the Sun played in climate change in recent decades?
5. What do changes in the vertical structure of atmospheric temperature – from the surface up to the stratosphere - tell us about the causes of recent climate change?
6. Climate is always changing. Why is climate change of concern now?
7. Is the current level of atmospheric CO2 concentration unprecedented in Earth’s history?
8. Is there a point at which adding more CO2 will not cause further warming?
9. Does the rate of warming vary from one decade to another?
10. Does the recent slowdown of warming mean that climate change is no longer happening?
11. If the world is warming, why are some winters and summers still very cold?
12. Why is Arctic sea ice reducing while Antarctic sea ice is not?
13. How does climate change affect the strength and frequency of floods, droughts, hurricanes and tornadoes?
14. How fast is sea level rising?
15. What is ocean acidification and why does it matter?
16. How confident are scientists that Earth will warm further over the coming century?
17. Are climate changes of a few degrees a cause for concern?
18. What are scientists doing to address key uncertainties in our understanding of the climate system?
19. Are disaster scenarios about tipping points like ‘turning off the Gulf Stream’ and release of methane from the Arctic a cause for concern?
20. If emissions of greenhouse gases were stopped, would the climate return to the conditions of 200 years ago?

Your questions

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