Archives For March 2013

28-03-2013 14-36-39RGS weather blog is closing for Easter week.  While we are off-air please remember that the best view is often up, be inspired by the clouds and atmosphere around you and wonder at the record breaking Spring 2013 weather…continuing cold and dry through next week, at least!

In the meantime, please read our “Climate Cluedo” posts investigating “Who Killed Spring 2013?” to get more details and a more convincing explanation than our word-cloud above on what has caused the extraordinary spring weather.  Comments via this blog or @RGSweather on Twitter are, as always, most welcome.

Happy Easter!

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!

Climate Cluedo!

Changes in ocean circulation, especially perturbations and regular large scale changes like El Nino and La Nina, are significant in controlling climate and weather systems around the planet.  How El Nino Southern Oscillation (ENSO) events influence European weather is still not entirely clear.  Nevertheless it is known that Europe is not nearly as impacted by ENSO events as other large land masses.  In any case, the entire mid-latitude belt around the northern hemisphere has suffered a cold 2013 Spring so it seems unlikely that ENSO or other circulation perturbations in different oceans could alone be to blame for the cooling of the whole Northern Hemisphere.  In addition, the current ENSO status is in “neutral” which means we are between La Nina and El Nino events … blaming either would be churlish, so ocean circulation does not seem to be a prime suspect for killing Spring 2013… so we should set El Nino and La Nina free!
Nevertheless, it is interesting to note that, whilst Europe and North America have frozen, the North Atlantic has experienced higher than “normal” temperatures. So, whereas it could be partly to blame for the European Little Ice Age, this time the North Atlantic Drift warm ocean current also seems to be entirely innocent of killing off Spring 2013.

point to note: additional considerations regarding longer term thermal changes in oceans such as the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) are currently controversial, though widely used by global warming sceptics to indicate the relative importance of cycles in ocean circulation over CO2 contributions to climate change on a human time scale.  Sceptics consider Arctic ice loss and CO2 to be insignificant in comparison to orbital wobbles and ocean circulation cycles.  THIS is an excellent website which debunks many of the climate skeptic arguments.

Climate Cluedo!

Volcanoes erupt ash and gas high into the atmosphere. A volcanic dust veil injected into the atmosphere can reduce solar radiation receipt at the surface for a few years and lower global average temperatures sometimes by a few degrees.  A cooler atmosphere also tends to sink and create high pressure at the surface, a prolonged feature of our 2013 winter. Finally, sulphuric acid from volcanic eruptions can get into the stratosphere where it is particularly effective at reflecting solar radiation which would induce cooling.  So, volcanic eruptions near Polar regions could produce cooler winters for a few years and several high latitude volcanoes have erupted fairly recently: Kasatochi in Alaska in 2008, Mt. Redoubt in Alaska and Sarychev in Russia in 2009 and Eyjafjallajokull Iceland in 2010.

volcanic eruptions and global temperatureHowever, none of these have been terribly big eruptions, Eyjafjallajokull was only VEI4 (volcanic explosivity index).  In fact, this eruption was insignificant compared to super-eruptions of the past which did have a climatic cooling effect: Tambora was 10,000 times bigger!  Hekla in Iceland is rumbling right now but that, along with these other examples, seems too little and too late to be a true suspect in the crime of Spring 2013!

Climate Cluedo!

Whilst the output of the sun varies very little (it is called “solar constant” for good reason), various other measurable factors such as solar magnetic activity, sunspot cycles and irradiance have all been raised as possible suspects for the crime of killing Spring 2013 across the northern hemisphere. Low solar energy receipt has been correlated with a colder northern hemisphere by influencing northern blocking.  A low point in sunspot activity called the “Maunder Minimum” has been closely associated with the onset of the Little Ice Age when the Thames regularly froze over every winter. Solar flares have been associated with warming of the upper atmosphere which has, in turn, been linked to higher pressure in the polar regions.
Links (correlations) have also been found between sunspot cycles and the extent of sea ice in the North Atlantic. Nevertheless, correlating solar activity and the climate on Earth has been surprisingly difficult to pin down.  Importantly, correlating sunspot activity with any climatic variable does not indicate a causal link. Wiggly lines on graphs may coincide but does one cause the other?  It is all still full of controversy. Even the IPCC recognise that, whilst there is some evidence to suggest a link between warming and increases in solar activity between 1750 and 1950, the measurable increase in global warming far exceeds any change in solar output. Since 1979, when measurements of sun output started in space, there has been no long-term significant increase in solar energy.  Sunspots are frequently hauled in to account for weather and climate changes but the evidence is hard to pin on them and almost entirely circumstantial!  Sunspots are intertwined with the greatest driver of our weather, the Sun, however, with such flimsy evidence the jury is still out on this suspect. With other major suspects under questioning it seems reasonable to let solar energy go free.

Climate Cluedo!

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.

Climate Cluedo!


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!

Quick update Tuesday: This LOW is not now predicted to trouble UK Fri – Sat: it will not be the BLOCKBUSTER  we hoped might break through and bring milder conditions.  Instead, it’s a near miss to the South as the LOW skirts thru NFrance pushed aside by the Icelandic HIGH building once again to the North of UK. LOW to south WILL drag in more cold / cool easterlies through much of next week; so start of April will be cool but should be not quite so cold as now with daytime Tmax +6-7°C for Reigate.  Nights still frosty.  Mostly dry, poss of snow showers. No dramatic snow on the charts for Reigate at the moment. Point to note: Hekla volcano in S Iceland is seismically active: heightened eruption possibility. Hekla is not usually a show-stopper for air traffic and winds would blow ash away from Europe!

How and when will this record breaking cold weather end?  Models suggest the first week of April will still be cool but not quite as cold as now. The latest UKMO chart for the end of the week shows mild SW winds developing around a huge Atlantic depression and squeezing up against the cold air towards Southern England. The leading edge of fronts pushing up the Channel into southern England could bring snow for a time to the south, and possibly lots of it, as cold air undercuts the warm and forces it up.  The snag will be if these fronts stall for a while: the chart shows fronts parallel to isobars which usually means they are slow moving and could stick around, thus increasing any precipitation over areas underneath. Later models also show this LOW slipping to the south of the UK which will drag in more cool Easterlies for the start of April. Too early for details, could change… but this LOW may not be the blockbuster we all hope for to sweep away the cold!

A medley of photos showing Reigate today: heavy snow in the morning melted rapidly as air and surface temperatures remained above freezing most of the day.  Colder air is on the way overnight and tomorrow.  Read on to find out why…

Here is the weather synopsis for this week: HIGH pressure to the north, LOW pressure to the south and a weak jetstream well to the south of the UK: result = POLAR NORTH EASTERLIES flood across the UK…again! Crazy low temperatures for March are forecast early/mid week with 850hPa temps at 1500m as low as -8°C over Reigate and surface temps struggling above freezing: wind chill as low as -9°C possible at night, daytime wind chill as low as -5ºC with winds up to 20mph feeling outrageously cold for this time of year, or any for that matter!

Sunday: watch out for snow streamers developing across the SE and East Anglia as the cold easterly wind crosses a comparatively warm North Sea. The 12°C difference between sea surface temps (+6°C) and air mass temps (-6°C at 1500m) could cause instability on decaying fronts lingering near the SE. This could cause the formation of perky showers in “lines” (snow streamers) which could mean some areas get prolonged snow whilst others, a few miles away, see none at all.
Monday and Tuesday: colder, drier, brighter; but snow showers always possible.

update Sunday 24: Big uncertainty about the end of the week: less uncertainty now: COLD set to continue: snow storm for Easter? 😦