Archives For Arctic sea ice

Spring 2013 across much of the northern hemisphere mid-latitude landmasses has been notable for extreme cold, record breaking snow falls and severe winter storms.  Northern Europe, Scandinavia, Russia, Western and North Canada, North and Eastern USA and NE China and Northern Japan have all been exposed to many more prolonged incursions of cold air from the Arctic than in “normal” years.  The blue and green colours on the temperature anomaly map above show areas experiencing a record breaking March of well below average temperatures (“anomalies”), some exceeding an average of 10°C below the temperature expected.  The map for 2013 year-to-date looks very similar, so the whole of late winter has been colder.  The satellite photo shows widespread snow across the whole northern hemisphere mid-latitudes: a good indication of how extra-ordinary this late winter has been.

So, what is responsible for this extreme late winter weather?   Here is a fun round-up of some of the main “suspects” on the Climate Cluedo board: which of them killed Spring 2013?  Click on each (as posted!) and find a quick judgement on their culpability in the death of Spring 2013! 

  1. Blocking high pressure / weaker jet stream
  2. Loss of Arctic sea ice
  3. Solar activity: sunspot cycles
  4. Volcanic eruptions
  5. El Nino / La Nina / ocean currents
  6. Long term climate change and orbital cycles
  7. Sudden Stratospheric Warming (started January)
  8. Human activity (to be dealt with later!)

Thought of some more suspects? Please leave a comment to add them!

Update 23/04/2013: UK Met Office now backtrack on loss of Arctic Sea Ice as a possible cause. Read it here. Nevertheless, Arctic Sea ice loss could be a future cause of climate change so we will leave it here as a suspect!

Scientists have been monitoring the shrinking mass of sea ice which covers the Arctic Ocean.  Arctic sea ice shrank by 2.7%per decade between 1979-2006 and continues to do so at a faster rate now.  The 2013 ice maximum was reached on March 15 and was the sixth lowest on record at 15.13 million sq km, 733,000 sq km below the 1979-2000 average.  The lowest maximum extent occurred in 2011.  Sea ice naturally expands during winter as more sea freezes over. By March it is at its maximum size, extending furthest from the North Pole. The ice naturally shrinks to a minimum area around the Pole by late summer / Autumn which is when scientists usually take another measurement of sea ice extent.  The Arctic has warmed TWICE as fast as the rest of the northern hemisphere (Arctic Amplification) and the Arctic sea ice has shrunk in area.  In summer 2007 the North West Passage north of Canada became ice free for the first time. Sea ice has a high ALBEDO which means it is bright and white and reflects solar energy (the Arctic gets 24 hours of sunlight during the summer). Most sunshine is reflected back into space off the ice and does not heat the atmosphere or the sea, the energy is more or less “lost” from the earth-atmosphere system.   Less sea ice means more dark ocean water is exposed and, with a lower albedo, this readily “absorbs” solar energy i.e. warms up.  The Polar atmosphere is warmed up by this extra heat flux from the ocean. The “warmer” atmosphere contains more energy and water vapour and this could potentially deliver more humid Polar air carrying more snow to mid-latitudes.
There is a final twist to this theory: warmer Arctic air reduces the difference between Polar temperatures and those further south. This reduced “thermal gradient” weakens the jet stream which feeds off big differences in temperature. A weaker jet stream is less able to BUST the blocking HIGH pressure built by Polar air.  All this adds up to slower moving weather systems in the mid-latitudes which prolongs any extreme weather: the cold gets further south and lasts longer.  There are many factors which control climate but loss of Arctic sea ice and the almost prophetic predictions made by scientists studying the effects it would induce, seems to keep Arctic Sea ice as a key suspect! The video below concerns all types of ice loss in the Arctic: land based and sea ice.

http://www.theweathernetwork.com/news/storm_watch_stories3&stormfile=Winter-time_Arctic_ice_cover_was_fifth_lowest_on_record__NASA_07_04_2013?ref=ccbox_homepage_topstories

Climate Cluedo!

SUSPECT #1: HIGH PRESSURE OVER THE NORTH POLE

global atmospheric circulationCold air sinks and this builds HIGH pressure over the Polar regions as part of the “normal” global atmospheric circulation.  Hot air rises over the Equator creating LOW pressure.  Tropical and Polar air flows in a series of complex but fairly predictable patterns in between.  These cells power global weather.  Polar air meets Tropical air in the mid-latitudes at the Polar Front.  Fronts, low pressure systems and jet streams are all a product of this unhappy meeting of two the different air masses.  The jet stream (fast flowing ribbons of westerly winds at altitudes of 15 km) usually acts like a belt and keeps the Polar air inside the high latitudes.  The mid-latitude jet usually sits somewhere near the UK during “normal” winters and brings in relatively mild westerly winds circulating around depressions with rain and wind.  2013 has seen higher than usual pressure over the Polar regions and these have pushed the jet stream and attendant LOW pressure systems further south than usual, somewhere over the Mediterranean which has seen more rain and wind than usual.  Winds blow from HIGH to low pressure and, without the belt-like effect of jetstreams to keep them in, frigid polar air has flooded out across the mid-latitudes.

blocking highs and AO

Anywhere located north of the jetstream has been left exposed to these incursions of the Arctic air mass.  Winds from the Pole tend to blow from the NE or East rather than straight from the North to South because the spin of the Earth deflects them to the right … the coriolis force.  Hence, “the Beast from the East” in the UK.

 

 

 

Arctic Oscillation NAOThe index measuring the balance between HIGH pressure in the north and LOW to the south is called the Arctic Oscillation and this has been at record breaking negative figures this Spring: meaning the pressure over the Pole is unusually high compared to the low pressure over the mid-latitudes.  Blocking HIGH pressure prevented warm air getting to the UK on several occasions this Spring and, with this fresh in our minds, we must consider BLOCKING HIGHS as “caught red handed” in the act of causing our cold spring.  However, it seems that there is always a bigger fish and we must find the master criminal controlling the BLOCKS to get nearer the real killer of Spring2013!  We must find the cause behind these increased heights over the Pole? The answer might be the loss of Arctic sea ice.

Climate Cluedo!