It’s happening again.
A story that starts in the Arctic where abnormally warm temperatures for this time of year are in the process of disrupting the polar vortex, shoving its node out of the Arctic Ocean and pushing it all the way south over Hudson and Baffin Bay. The result is a core of extreme cold shoved much closer to related warmer, southerly regions. A highly unstable event that is likely to spawn extreme weather for the US and UK yet again.
This polar heat amplification and related extreme weather is a signature of human-caused global warming. And though it wears a grotesque mask of what some would call a normal Arctic oscillation, it is anything but.
Our rapid production of greenhouse gasses since 1880 has caused the Arctic to warm, on average, by about 5.3 F (3.0 C). This rapid increase in warming is nearly 4 times that of the global average and resulted in temperatures for the Arctic, during the 20th Century, reaching a range not seen in at least 44,000 years and likely 120,000 years. Since warming has continued well into the first and second decades of the 21rst Century, Arctic temperature excursions are likely outside even that extreme range and may well now be approaching averages when parts of today’s Arctic first began to freeze and glaciate.
The causes of this rapid Arctic amplification are manifold. First, human greenhouse gas emissions added more heat to the oceans and atmosphere. The polar sea ice, sitting atop a warming ocean went though a period of recession from the 1920s through the 1950s, hovered in about the same zone during the 60s and 70s and then commenced a more rapid melt phase from the 1980s onward.
Loss of Sea Ice and a Changing Jet Stream
Loss of sea ice reduced northern polar albedo (reflectivity) by a total of 4% since 1980 which increased Arctic heat capture by an amazing 6.4 watts per meter squared (more than 4 times that of human CO2 forcing over the entire globe). As a result, the seas under the Arctic ice cap began to even more rapidly warm. By 2012 the warming was intense enough to have reduced end-summer sea ice volume by 80 percent since 1979. Now, during winter time, a perforated and much diminished sheet of sea ice bleeds ocean heat into the Arctic atmosphere. As a result, cold air tends to be shoved out of the Arctic Ocean basin more and more often.
This bleeding of oceanic heat has bent the Jet Stream ever northward over two zones — one over Svalbard and one over Alaska. And both these Jet Stream weaknesses allow warmer air to rush into the Arctic from the south. These various heat forcings cause the winter time polar vortex to wobble uneasily over a warming Arctic Ocean even as it is more frequently ripped apart by warm air incursions through the oceanic weak points. Meanwhile, these vortex disruption and collapse events spill cold air southward over the continents and into the Atlantic Ocean.
Yet one more Polar Vortex Disruption
And for this winter, such Arctic heat driven polar vortex disruption and collapse events have been the norm. This week is featuring yet one more — sparking extreme weather that will revisit both the US and UK over the coming days.
(Climate Change Institute Map Showing Arctic Heat Anomaly 2.68 C above the, already warmer than normal, 1979 to 2000 average. Image source: Climate Reanalyzer.)
Today, the Arctic temperature anomaly was 2.68 degrees Celsius above the, already warmer than normal, 1979 to 2000 average. Areas near Svalbard, Alaska, and Baffin Bay showed extraordinary temperature departures in the range of 15 to 20 degrees Celsius above average. Meanwhile a zone of cold, Arctic air has been shoved southward over the US, setting up extreme temperature differentials over a relatively small area and putting in place conditions ripe for extreme weather.
A Tale of Three Storms
A large Pacific storm now in the process of leaping over the west coast blocking pattern is forecast to dump up to 5 inches of rain on a parched California before injecting itself into the highly unstable atmosphere over the central and eastern US. Areas in the center of the US such as Oklahoma may experience a range of weather from thunderstorms to tornadoes and precipitation running the gambit between snow, hail, ice, and rain. This system is predicted to spread out, covering a massive swath from Texas to Maine and incorporating at least two low pressure systems. It will draw in a deep flow of warmth and moisture from the Gulf of Mexico and this warm and moisture laden air will abruptly collide with the much colder Arctic air to the north. Extreme rain, ice and snowfall are certainly possible as this intense event is expected to last from Saturday through Monday.
Across the Atlantic, as the Jet Stream invades southward and picks up speed, a gale formed to the south of Greenland and Iceland before barreling on into the storm ravaged shores of England and France. The gales and storms this winter for the region have been relentless, resulting in the stormiest winter ever on record for England and creating conditions so battering and exhausting that more than 21,000 sea birds are thought to have tragically lost their lives in at sea before washing up on French shores.
Now a strong double barrel low pressure system is bringing gale force winds and heavy rains back to a United Kingdom that has suffered an almost constant assault of storms since the middle of December. Flood warnings have again been issued for multiple counties and regions just north of London, which experienced 60 degree temperatures earlier this week, are expected to see snow. The storm is expected to sweep through the UK on Friday and Saturday before exiting Sunday. A storm of similar intensity is then expected to return to the UK on Monday where the process of gales and floods are likely to again repeat.
(Sediment outflow from the swollen rivers of England and France on January 26 as yet another storm encroaches. Image source: Lance-Modis.)
In total, this worst continuous period of storms in UK history, has resulted in over a billion dollars in damages. Meanwhile, the storms are expected to continue through at least early March.
Overall, these extraordinary conditions cannot be entirely separated from the still-high temperature deviations occurring in the Arctic. Usually, by this time of year, the ice is solid enough and the warm air incursions are weak enough to allow at least some minor re-establishment of the polar vortex. Not so for 2014. The above average temperatures throughout the Arctic continue and show little sign of abatement as we head into March and the end of sea ice freeze season.