Archives For causes of cold

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!

Climate change is the natural state of the planet. The Earth’s climate has changed dramatically throughout all timescales: the longest geological timescale measured in thousands of millions of years shows frequent dramatic swings between extremely cold ice-house phases and much warmer-than-present greenhouse phases. Over the 4.5 billion years of Earth history there have been five big ice-house epochs where cold conditions have dominated.

Snowball Earth

BIG cold snap

The most extreme example was around 700-800 million years ago when the Earth was totally covered by ice, the so-called “snowball earth”.  Volcanic eruptions probably released the planet from this particular predicament by ejecting vast quantities of CO2 which warmed the atmosphere.  Despite these dramatic deep freeze episodes, for 85% of geological time the Earth has been warmer than it is right now and with much higher levels of carbon dioxide.  For example, 70 million years ago CO2 was eight times higher than now and shortly before that it was twelve times higher.  Only 15% of Earth history has seen cold ice-house conditions.  So the last 2 – 3 million years has been much colder than “average” for planet Earth.  During this time there have been several fluctuations into and out of cold conditions called glacials that have typically lasted 100,000 years.  The interspersing warmer periods are called interglacials and these have usually lasted about 10,000 years.  The cold period of the last 2 million years is popularly known as the Ice Age and more technically termed the Pleistocene.

Dinosaurs: mean but warm

Dinosaurs: mean but warm

The Ice Age itself has been subject to warmer and colder times.  The last really cold snap ended about 10,000 years ago.  Modern human existence has developed entirely in this warmer interglacial period over the last 10,000 years but technically we are still living in an “Ice Age” period, merely a warm bit of it, called the Holocene interglacial.  Until the 1970’s this warm period was expected to be nearing its end, being about 10,000 years since the last glacial ended, and global cooling was the concern in many climate books of the time e.g. Nigel Calder: “The Weather Machine and the Threat of Ice” BBC 1974.
Orbital cycles are one of the possible causes of regular long-term swings in global climate. The orbit of the Earth wobbles and stretches which affects seasons and energy receipt from the sun. These wobbles occur regularly over 100,000 years. Orbital cycles are the “pace-makers” for temperature change and could be argued to trigger change when other factors coincide with it (like location of continents over polar regions, volcanic eruptions, etc).

Pinning one cold Spring on such large scale cycles would be stretching the evidence somewhat: one cold snap certainly doesn’t prove the climate is changing. Nevertheless, when the Earth’s climate decides to change to another phase, the rate of change is often rapid (called step functions). Spot the steep lines in all of the climate charts: these show how temperature change, once underway, can accelerate and “change gear” quite rapidly.   It is the RATE of change happening now that seems to show the Earth’s climate is possibly moving towards a new phase and scientific monitoring seems to suggest this. Moving into a new climate phase could herald a time of more frequent extreme weather like the unusually cold Spring 2013.  Whilst blaming “climate change” for “changing weather” is arguably a tautology and not especially useful, climate change, regardless of the cause, must surely be another prime suspect in the death of Spring 2013!  At least, there is enough uncertainty not set this prime suspect free just yet!

http://m.guardian.co.uk/uk/2013/apr/07/science-behind-britain-coldest-easter

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!