Some fairly basic physics made a decades-old prediction that Arctic warming would outpace warming elsewhere on the globe a relatively easy one. That prediction has been verified … and then some.
Unlike Antarctica, Arctic sea ice is just that, floating on water, while a large portion of Antarctic ice sits on top of a vast continent. Ice has high reflectivity, known as albedo. Where there is ice and a high albedo, much of the sun's energy including heat is reflected back into space.
Where the ice has melted, there is a dark sea surface which does just the opposite. It absorbs much of the solar energy, and the water heats up. That, in turn, slows the refreezing process, results in thinner new ice during refreezing, and releases more water vapor into the atmosphere during the warm season.
All the processes have been sped up in the last nine months, owing to two incredible warm spells this past winter and exceptionally warm temperatures earlier this month.
More rapid melting and gusty winds have led to first breakup of the thick ice north of Greenland since satellite records began in the 1970s. This ice normally has been fixed in place. However, this summer the thick ice became more vulnerable to winds and has been blown away from the coastline.
Once exposed in open sea water, even this thick ice is subject to more erosion. This previously compacted ice was given the nickname "the last ice area" because it was thought to be the most resistant to the warm Arctic climate. Here is a Reuters image from an article in The Guardian this week of just such a huge iceberg dislodged due to mild temperatures and wind.
In the last century, the global average temperature has risen about 1 degree C. But in the Arctic, the warming has been much greater, as expected in earlier climate models. In some locations, the rate of warming has been astonishing. At Barrow, the temperature is now running 5.5 C higher than in 1979. During the extreme warming this past winter, the warmest on record in the Arctic, some locations ran 20 C higher than their respective averages.
Some scientists believe the data now supports the establishment of a warmer "new normal" in the Arctic. NASA satellite imagery since 1979 shows irrefutable evidence that Arctic sea ice is declining at a rapid pace, running about 13 percent per decade. The Norwegian Ice Service reports ice cover in the Svalbard region is running 40 percent below its average since 1981.
The erosion of sea ice has left exposed coastlines where wildfires have actually increased this year. So, it's been a very bad year, but not the all-time worst year on record. Some pockets of cold weather have kept overall Arctic ice cover from setting an overall new record low, despite the warm spikes.
Previous predictions of almost iceless summers on the Arctic Ocean have been premature and, when sometimes manipulated by advocacy groups, alarmist. However, there is reason to believe new shipping passages will could open up at some future point. That is good news for shipping and commerce, amidst the bad news. On the other hand, there are already indications such passages may be a point of geopolitical conflicts between the United States and Russia.
There is also growing evidence that Arctic warming is having several climate and weather impacts elsewhere in the Northern Hemisphere. The warming may be weakening the polar jet stream which can allow it to buckle into a "blockier" pattern of more ridges and troughs more often locked in place for weeks and months at a time. When a blocking pattern develops, parts (not all) of the globe can have longer periods of drought, or cold, or heat, or wet conditions. This is a theoretical impact, subject to more research. Nonetheless, observations already taken in recent years lend at least some preliminary credence to this theory.
Amidst the mean warming may yet come some regional cooling due to another phenomenon which has occurred in the past. Lower salinity in the North Atlantic due to freshwater ice melt, especially from Greenland, can weaken the Gulf Stream. There is good evidence this has happened long before humankind had an impact on hemispheric climate, and some evidence from sediment studies it has happened with great rapidity when some unknown threshold in lower salinity was reached.
Current climate models are not forecasting such an extreme event, but the lead author in a study in the journal Nature is not so confident the models will be right. His and another study show the current Gulf Stream is at its weakest in the last 1,600 years based on extensive sediment analysis and is continuing to weaken.
Part of the great unknown will be the rate and extent of future weakening. One study relates most of the Gulf Stream weakening to natural variability following the "Little Ice Age," aided and abetted by the more recent warming climate. The other study fixes the accelerated weakening as tied mostly to our warming climate. Both studies show a virtual shutdown of the Gulf Stream brought cooling of 5 to 10 degrees C in as short a period as one to three years on land masses bordering on the North Atlantic during the last Ice Age. So much for fine French wine!
On a serious note, that unlikely event would produce drastically colder winters in northeastern North America and western Europe.
At this time, the overall consensus among climate scientists and oceanographers is this worst case scenario, while very high impact, is a "low probability" event. There is good agreement among the many climate models on the probability. Let's hope the good agreement is a good call.