It seems that many scientists are mystified by the fact that the measured
temperature increases near the North Pole have recently been several times
faster than the temperature increases measured in other places on Earth.
No one seems to know why. It is actually pretty simple. There are actually
TWO different reasons, one which is really obvious and the other a
little more obscure.|
Prior to around 1990, essentially the entire North Polar region was covered in permanent ice and snow, both water and land. According to Liu and Jordan Solar Energy, 1963, the reflectance of snow is around 0.7. That means that of the minimal solar energy that would directly have come to the North Polar region, after getting through the effectively thicker atmosphere (due to the low angle of incidence of the light in passing through it), 70% of that remaining light was getting immediately reflected back out toward outer space by the snow and ice. Only 30% of that rather small amount of incoming energy was actually available to be absorbed, regarding providing heat to keep that region warm. The entire polar region therefore remained very cold.
Now consider the situation since part of the North Polar Cap has melted. Some estimates are that 1/3 of it has already melted (by 2005). And that by September of 2013, the ENTIRE Arctic Ocean is expected to be ice-free. This leaves both open ocean and open land to now be exposed to the sun's light and heat. In other words, the high reflectivity of the snow and ice no longer reflects such a high percentage immediately back out into space. Liu and Jordan give a reflectance of 0.2 for open land. Open water is relatively comparable.
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We have included some arrows at the top of this graph, which require some explanation! Any object that is heated releases RADIATION to get rid of some of that heat. The wavelength of the radiation is dependent on the temperature of the source. Scientists including Planck, Wein, Stefan, and Boltzmann developed equations that describe those effects.
Since the Sun's surface is around 5760°K, the wavelength of the MEDIAN radiation which comes IN is around 0.709 micron, a reddish color. This is represented by the LONGER downward (orange) arrow. There is also a different wavelength which is the one that is most intense, which is at 0.503 microns (a greenish color), which is represented by the attached shorter arrow to the left in the graph. Collectively, this results in the Sun appearing to be yellowish to us.
That INCOMING heat from the Sun easily gets through our atmosphere, and we can see that the left part of this graph shows that carbon dioxide essentially does not absorb any of that incoming sunlight.
Different parts of the Earth are at different temperatures, so they radiate at different wavelengths. We show the MEDIAN (13.2 microns) and peak (9.3 microns) wavelengths for the radiation from the hotter Equator regions (as red arrows), and also for the radiation from the colder Polar regions (16.1 microns and 12.4 microns) (as blue arrows).
It happens that carbon dioxide has extreme absorbtivity of such wavelengths of radiation from the polar regions, ENTIRELY DUE TO THE TEMPERATURE OF THE GROUND DOING THE RADIATING, as seen toward the right in the graph. Unfortunately, carbon dioxide has an absorption peak which is very close to the wavelengths that the Earth radiates, especially from the poles. That was great in the past, as in increased the Earth's original Equilibrium Temperature from around -5°F up to the current 59°F. No life was possible long ago, since all the water would have generally been ice! But now that we have decided to add spectacular amounts of carbon dioxide to the atmosphere by burning fossil fuels, the same characteristic now represents a dreadful problem.
It might be noted that SOME of the radiation from the Equator regions has a chance of escaping, as the absorbtivity of carbon dioxide is not quite as high for some of those wavelengths. But the absorbtivity of carbon dioxide for the Polar regions is consistently near 100%. Many scientists seem mystified as to why the North Polar region is warming up several times faster than the rest of the planet. Part of the explanation seems pretty obvious when this differential energy absorption of carbon dioxide is considered.
|Use the slider in the interacitve animation above to see the decline in Arctic sea ice mass between 1979 and 2005. Don't see anything? Get Macromedia Flash!|
SATELLITES CONTINUE TO SEE DECLINE IN ARCTIC SEA ICE IN 2005|
Researchers from NASA, the National Snow and Ice Data Center and others using satellite data have detected a significant loss in Arctic sea ice this year. On Sept. 21, 2005, sea ice extent dropped to 2.05 million sq. miles, the lowest extent yet recorded in the satellite record.
Incorporating the 2005 minimum using satellite data going back to 1978, with a projection for ice growth in the last few days of this September, brings the estimated decline in Arctic sea ice to 8.5 percent per decade over the 27 year satellite record.
Scientists involved in this research are from NASA's Goddard Space Flight Center, Greenbelt, Md., NASA's Jet Propulsion Laboratory, Pasadena, Calif., the National Snow and Ice Data Center at the University of Colorado, Boulder, and the University of Washington, Seattle.
Satellites have made continual observations of Arctic sea ice extent since 1978, recording a general decline throughout that period. Since 2002, satellite records have revealed early onsets of springtime melting in the areas north of Alaska and Siberia. In addition, the 2004-2005 winter season showed a smaller recovery of sea ice extent than any previous winter in the satellite record and the earliest onset of melt throughout the Arctic.
With the exception of May 2005, every month since December 2004 has seen the lowest monthly average since the satellite record began, but more data are needed to fully understand this pattern. Sea ice records prior to late 1978, for example, are comparatively sparse, but they do imply that the recent decline exceeds previous sea ice lows.
Arctic sea ice typically reaches its minimum in September, at the end of the summer melt season. The last four Septembers (2002-2005) have seen sea ice extents 20 percent below the mean September sea ice extent for 1979-2000.
Perennial ice cover is ice that survives the summer melt, consisting mainly of thick multiyear ice floes that are the mainstay of the Arctic sea ice cover. "Since 1979, by using passive microwave satellite data, we've seen that the area of Arctic perennial sea ice cover has been declining at 9.8 percent per decade," said Joey Comiso, senior scientist at Goddard.
For the perennial ice to recover, sustained cooling is needed, especially during the summer period. This has not been the case over the past 20 years, as the satellite data show a warming trend in the Arctic, and it is not expected to be the case in the future, as climate models project continued Arctic warming. If ice were to grow back in these areas, the new ice would likely be thinner and more susceptible to future melt than the thick perennial ice that it replaces.
Scientists are working to understand the extent to which these decreases in sea ice are due to naturally occurring climate variability or longer-term human influenced climate changes.
Scientists believe that the Arctic Oscillation, a major atmospheric circulation pattern that can push sea ice out of the Arctic, may have contributed to the reduction of sea ice in the mid-1990s by making the sea ice more vulnerable to summertime melt.
Sea ice decline could also affect future temperatures in the region. Ice reflects much of the sun's radiation back into space. As sea ice melts, more exposed ocean water reduces the amount of energy reflected away from the Earth. "Feedbacks in the system are starting to take hold," says the National Snow and Ice Data Center's lead scientist Ted Scambos.
Claire Parkinson, senior scientist at Goddard, cautions against thinking that Arctic sea ice is gone for good, especially with such limited data. "The reduced sea ice coverage will lead to more wintertime heat loss from the ocean to the atmosphere and perhaps therefore to colder water temperatures and further ice growth," said Parkinson.
There are many factors beyond warmer temperatures that drive changes in the Arctic. A longer data record, combined with observations from additional environmental parameters now available from NASA satellites, will help scientists better understand the changes they are now seeing.
The study used data from the Defense Meteorological Satellite Program Special Sensor/ Microwave Imager and data from NASA's Scanning Multi-channel Microwave Radiometer (SMMR) on the NIMBUS-7 satellite.
The minimum concentration of Arctic sea ice in 2005 occurred on September 21, 2005, when the sea ice extent dropped to 2.05 million sq. miles, the lowest extent yet recorded in the satellite record. The yellow line represents the average location of the ice edge of the perennial sea ice cover for the years 1979 through 2004. Credit: NASA
Arctic sea ice typically reaches its minimum in September, at the end of the summer melt season, and then recover over the winter. The 2004-2005 winter-season showed a smaller recovery of sea ice extent than any previous winter in the satellite record, and the earliest onset of melt throughout the Arctic. This visualization shows seasonal fluctuations in Arctic sea ice derived from the new high resolution AMSR-E instrument on NASA's Aqua satellite. Credit: NASA
Sea ice decline is likely to affect future temperatures in the region. Because of its light appearance, ice reflects much of the sun's radiation back into space whereas dark ocean water absorbs more of the sun's energy. As ice melts, more exposed ocean water changes the Earth's albedo, or fraction of energy reflected away from the planet. This leads to increased absorption of energy that further warms the planet in what is called ice-albedo feedback. Credit: NASA
This text derived from NASA. Images courtesy of NASA Earth Observatory.
This effect shows the multiplication effect that often happens when any natural system is disturbed. Not only are the expected consequences seen, but new consequences that are due to secondary effects.
In this case, it seems reasonably logical that the North Polar region WOULD be heating up much faster than the rest of the planet right now, because that snow and ice cover has only recently been removed. This premise can probably be confirmed by seeing if NO such effect is yet seen in Antarctica. The snow and ice is so very thick there, that the white reflectivity should still be as it long has been, and Antarctica should logically be heating up at approximately the same rate as the rest of the planet. Only the North Polar region should be heating up much faster right now.
In 2008, those same researchers and others predicted that the ENTIRE Arctic sea ice cap will likely be melted and gone in September 2013!
So they are acknowledging that the effects are getting far faster, extremely quickly. Greenland will still have much of its Glacier covering, but other researchers are finding that even that is all melting at amazingly fast rates, where those researchers now feel that Greenland may be ice free within a few decades.
Ice which is IN the ocean does not cause sea level rise when it melts (the water replaces the ice), so much of this Arctic Polar Cap melting is NOT contributing to sea levels rising, yet. But all the glaciers on Canada and Siberia and Greenland and other countries are also melting, and they ARE above sea level! Around 2004. researchers had calculated that if only the ice on top of Greenland all melts, that volume of new water in the oceans will cause a world-wide rise in sea levels of around 22 feet. MOST large cities around the world were built at close to sealevel so they could profit from shipping trade. But if you consider a representative example, New York City, if and when the Atlantic Ocean rises by 22 feet due to Greenland's ice all melting, then the Hudson River and East River will also rise by the same amount. The majority of streets in Manhattan are LESS than 22 feet about sea level now, and so they will all be permanently flooded! Nearly every one of the thousands of buildings on Manhattan will only be approachable by boat, and basically the First Floor will have disappeared under the Ocean surface! Imagine what Property values will do!
Published update from NASA in 2011 Two specific events have been noted by NASA. One was that the largest iceberg ever has recently come loose from Greenland, an iceberg which has an area of 97 square miles! That ice will melt as the iceberg drifts through the North Atlantic Ocean.
NASA also announced that Greenland ice melted MUCH FASTER in 2010 than they have EVER detected before! Researchers and scientists now have no idea what to expect, because the rapidity of the ice melting is far faster than any Model would ever have predicted! They seem very apprehensive, or what I would call, scared.
Antarctica Regarding Antarctica, the fact that the ice there is so very thick, there has not yet been much change in the Earth's albedo due to white ice being replaced by darker water or soil which would capture much more solar energy and magnify these kinds of effects. But we can certainly expect that it is coming. Antarctica has enough ice on top of it to cause the world's seas to rise by around 260 feet (or 78.9 meters) should all that ice melt. The weight of that ice is known to have caused the Earth's Crust there to have subsided (sunk) by around 560 meters, so when the ice melts and that weight is no longer there, the Crust will rebound, likely causing another 560 meters thick of ice to be added to the oceans. (That ice IS currently below sea level, but when the Crust rises, the volume of that ice will be taken up by Crust, meaning the added ice will probably increase the sea level rise problems. Instead of 260 feet, the calculations indicate that the sea level rise due to Antarctica all melting is therefore around 330 feet.
The remoteness of Antarctica seems to have delayed serious attention regarding the melting there, but several extremely large sections of ice have broken off in recent years, one of which was comparable in size to the State of Connecticut. That ice took a few months to melt after it drifted out into the ocean, but it certainly melted. There are other sections near the edges of Antarctica which are also showing signs of rapid melting and fracturing, where additional huge icebergs seem certain to break free each year.
Personally, in examining all the data and the increasing rates that all this is happening, my guess is that nearly all the ice on Antarctica may be melted by 2100 AD. In other words, soon enough that small children today may still be alive to see the total effect. If the oceans DO rise by the cumulative total of around 410 to 450 feet, then Nashville, Tennessee (current altitude, 440 feet above sea level) may have Atlantic Ocean beaches! Florida and several other States may not even exist at all in just 100 years! Look at a map of the US to see how terrifying that thought is of a Nashville ocean beach!
C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago