Temperature anomalies averaged from 2000-2009 show Polar amplification of global warming. Graphic courtesy of NASA.
Global warming is real. But not all places are warming at the same rate. The Arctic has warmed by more than two degrees Celsius (3.6 degrees Fahrenheit) since the beginning of the industrial revolution, while during that time the average temperature rise over the whole earth is about one degree Celsius.
The reasons for this so-called Polar Amplification (also called Arctic Amplification) are straightforward.
It is natural for land temperatures to warm faster than sea surface temperatures, given water’s ability to absorb and distribute solar radiation. So then why is the mostly H2O north pole warming at more than twice the rate of the rest of the world?
The answer lies in albedo and geometry.
Albedo: Reflection Of Solar Radiation
When a light ray (an electromagnetic wave carrying energy) strikes an object, solid or liquid, it can be absorbed, reflected, or refracted. When sunbeams strike the surface of the earth, the percentage that are absorbed, reflected or refracted, depends on the type of surface they strike:
When a ray of light strikes the solid earth, it is often absorbed in the very top layer of sand, soil, rock, or vegetation and the energy of the light ray is turned into heat. The temperature rises during the day because sunlight is absorbed by the surface of the earth and some of this heat is conducted into the adjacent air. Since most solid substances are poor conductors, very little heat from the absorbed light is conducted deeper than a few inches into the ground. Dig a hole ten feet deep and the temperature doesn’t change from day to day or year to year. At 20 feet below most surfaces in mid-latitudes, the difference between maximum and minimum temperature during the year is about one degree Celsius. Compare this to the average difference between the morning low air temperature and the afternoon high of about ten degrees Celsius (16 degrees Fahrenheit).
Light rays can also be reflected back to space. The percentage of the incoming radiation that is reflected is called the albedo, normally expressed as a decimal between zero and one. Snow has an albedo of 0.9; ice has an albedo of 0.5; and open ocean has an albedo of 0.06. Ice reflects half of the incoming radiation, while open ocean reflects only about one-seventeenth.
Sunlight can also be refracted (bent) when it strikes the ocean. Since light waves travel at different speeds in different mediums, the light changes direction when it strikes the sea, but it keeps on going. A small amount of energy is absorbed at the surface; the rest of the half of the radiation that is not reflected is re-directed downward and absorbed below the surface.
Temperatures north of sixty degrees north latitude have risen about twice as fast as those in the rest of the world. Graphic courtesy of NOAA.
As the planet warms, ice melts.
In the Arctic, this has the effect of significantly lowering the albedo: Instead of reflecting 50% of incoming radiation when it is ice-covered, the water reflects only six per cent.
The heat absorbed and spread throughout the ocean eventually warms the surface layer and reinforces the warming.
The Earth Is Not Flat
The fact that the earth is round has implications beyond prospects of falling off the edge.
The amount of solar radiation striking the earth per unit of surface area varies with the latitude as the angle of the sun varies. On the other hand, the outgoing microwave radiation is the same all over the world.
Arctic temperatures fluctuate wildly during winter, almost entirely above the long-term average. Graphic courtesy of Danish Meteorological Institute.
At the pole, where there is only a modest amount of sunlight in the summer and none at all in the winter, the effect is to give the contribution of the outgoing radiation a comparatively much bigger role in the temperature balance than it has nearer to the equator — and bigger in the winter than summer. The temperature record makes this effect clear.
The Danish Meteorological Institute has made arctic temperature measurements for 57 years, These measurements show that in the summer months, the temperature is fairly near the long-term mean; but as soon as the dark months arrive, there are wild fluctuations in temperature and they are almost all on the warm side.
Past Episodes Of Polar Amplification
The record of historical warm periods on Earth shows that Polar Amplification is not confined to the present warming. Historical periods of enhanced atmospheric carbon dioxide, due to increased volcanic activity and the ‘carbon cycle,’ show much the same effect — arctic warming up to three times that of the rest of the planet.
Ramifications Of Polar Amplification
The results of global warming generally, and Polar Amplification in particular, will be mixed. As the Arctic becomes ice free, shipping goods by sea will become much cheaper. Residents of Moscow and Manitoba will welcome the warmth.
On the other side are the not-so-good effects, some of which are already with us: As polar ice melts, sea level is rising; Island nations are being submerged and coastal cities are increasingly subject to flooding. And just as Polar Amplification warms the Arctic at an increasing rate, other feedback mechanisms, some that we likely do not recognize at present, could bring disastrous climatic changes.
One such feedback is already in evidence: A change in the position and strength of the jet stream. As the pole warms more than the equator, the temperature differential that drives the jet stream as a west-to-east current of air is weaker. The jet stream has begun to meander more and get stuck in place. Record rainfall, drought, and heat have increased in recent years.
Another potential feedback mechanism: melting permafrost could release locked-up carbon dioxide and methane, the two major greenhouse gases.
On a more global scale, new research indicates that during the past hundred thousand years, periods of increased atmospheric greenhouse gases have led to rapid changes (on a scale of tens of years) in ocean currents. A breakdown of the Gulf Stream, for example, would have a dramatic influence on the weather of Europe. Examination of ice cores from the South Atlantic Ocean indicate that worldwide changes of this magnitude have taken place in the past.
Playing With Fire
The current rate of global warming is clearly unsustainable in terms of a livable earth several hundred years from now.
Since the warming is a result of anthropogenic activity (burning of fossil fuels), it is up to human civilization to deal with the problem. The earth has been both much colder and much hotter than it is now. The surface of Venus illustrates what can happen when the greenhouse effect gets out of control: Surface temperatures over 410 degrees Celsius (approximately 800 degrees Fahrenheit). This will not happen on Earth, but scientists have warned that a warming if two degrees Celsius (3.6 degrees Fahrenheit) will pose a substantial risk of catastrophic climatic effects — and we’re about half way there, with carbon emissions still increasing.
The political leaders who will convene at the UN-sponsored conference in November to try to rein in carbon emissions would do well to study the past and the ramifications of Polar Amplification.
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