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Weather is chaotic and numerical weather models are not perfect. The forecast for Reigate today went rather awry, though not completely.  It was forecast to rain heavily, perhaps on and off, but the forecast was for heavy rain more or less throughout the day. Check UKMO forecast from yesterday below.  Some models brought 24 hour totals of 20-30mm to SE at points on the lead up to the event.  The cause of the forecast deluge: a small scale low tracking NW to SE with a tightly wrapped occluded front crossing the area once, then lingering nearby to deposit more rain during the day before drifting off southeast. Once the front had passed through early am, it turned out to be a splendid day with sunshine and bright spells throughout, until rain later.  So what went wrong/right?

The front passed over as forecast during early am dropping 6mm on Reigate before 8am.  It then sat N of London most of the day while further south convection over Sussex caused significant Cb clouds and showers (some thundery) to spark off from midday.  For us in Reigate, we had a splendidly bright day with glorious sunshine by 8am and bubbly cumulus clouds thereafter, the odd spot of rain but nothing significant until early afternoon when the front migrated south east.  So for most daylight hours Reigate was dry, quite the opposite of the forecast.

The photos above and graphics below suggest a possible reason for this.  Reigate sat in a sort of “Goldilocks Gap” between the persistent frontal rain further north and convective rain nearer the LOW further south. It is notable that the convective showers built mostly over the land, showing almost April-shower tendencies to build on warmer land surfaces than the now-cooler sea. The occluded front sat close to Reigate, frontal wave clouds and cirrus were visible above and to the north for most of the day.  This may have helped suppress convection.  As warm tropical air is lofted over an occluded front it spreads out and forms a cirrus veil, this often suggests a broad inversion of warmer air aloft that effectively suppresses uplift of thermals: the cirrus acts like a lid.  So cumulus clouds over Reigate and the N Downs stayed small and harmless.  Not far south, in Sussex, thundery downpours developed as the buoyant air lofted uninhibited by any inversion.  You can see this on the radar image below.

Reigate was therefore dry for most of the day perhaps because of our location in a sort of Goldilocks Gap (our word) that was just far enough from the occluded front to avoid persistent rain and just near enough to benefit from the inversion to prevent convective showers. Met-Magic!  The graphics and photos try to explain this further.

This is just one possible reason why slight changes in the tack of a LOW will render a forecast completely wrong, even in the middle of a LOW pressure when all hope of a nice day might be thought lost.  Further ideas are most welcome to extend this.

A wild meridional loop in the jet stream on 14-15 Feb injected a cool pool of air over NW Africa that created unsettled conditions, cloud, cold temperatures, rain, snow and dust storms over Morocco and parts of North-Western Sahara. RGSweather went to Morocco to investigate the effects of this African storm and bring you the experience of an unusual African cut-off low first hand! (well, we were going there on an expedition anyway, so why not?!).

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A cut-off low is a depression, usually associated with mid or high latitudes when a meridional (bendy) jetstream loops down and leaves a cool pool with a resultant low pressure system “cut-off” as the jetstream returns to a more northerly latitude.  Cut-off lows sometimes barely show up on pressure charts but are often persistent features that introduce unsettled weather: often associated with showers as convective activity warms through the atmosphere and gradually “fills” the LOW.

The Moroccan cool pool caused winds to circulate around the low and drag dust and sand over the High Atlas for a period as easterlies blew in across the Sahara as the low moved north and then east.

Snow is common across the Atlas mountains during winter but temperatures fell unusually low and snowfall across the Atlas fell below 1000m.

Gradually, as the cut-off low filled and moved NE, pressure built and skies cleared and, at low altitudes, temperatures rose.  Dew points fell as humidity fell and nights remained exceptionally chilly!

The animations below show the cut-off forming and cool-pool with showers and frontal precipitation (snow in mountains) over NW Africa and Morocco. Probable influence of sub-tropical jetstream too but information not available on this at the moment.

Reputedly, the first snow for over 100 years has fallen on the Sphinx but several photos on the web are actually of a model in Japan!  Anyhow, snow certainly fell across Cairo, N Egypt and even deeper snow has fallen over Israel, including Jerusalem and more widely across the Middle East and Turkey.  The upper air temperatures across Israel and Egypt are cold, of course, but only -2c or -3c at 850hPa which, in the UK is common and rarely produces snow for us… as a rule of thumb our 850hPa temps need to be at least -5c or lower to deliver much snow to the UK, especially the south away from hills.  So why did it snow on the Sphinx when the airmass was not really that cold?  BTW check this link for the sphinx in the snow pic

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Cold, but not like the UK!

Well, it looks like the snow in Israel and Egypt is what meteorologists call “Lake or Sea Effect snow” and is quite common near the Great Lakes in the USA and across Japan but of course rather more unusual in the warmer Middle East. A deep LOW pressure (Winter Storm Alexa) swept across to the north of Israel dragging in bitterly cold strong N winds across Egypt and Israel and the Middle East as a whole.  The air originated from further north over continental Asia, where winter temperatures are extremely cold. The strong wind has crossed the Med (still fairly warm of course) in a wide arc across the warm sea surface which has allowed a good deal of moisture to evaporate, adding humidity and instability to the air mass.  A temperature difference of at least 13c is required to produce the greatest evaporation and moisture input required to produce plenty of “sea or lake effect snow”. SST across the Med off Israel is currently over 20c and this air mass had a temp of -3c at 850hPa and around freezing at sea level.

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On hitting land the strong wind experiences friction and literally “piles up” against the coast causing convergence and uplift.  The uplift, especially pushed up over the heights of Israel, causes cooling in the frigid polar air and, eventually, precipitation in the form of snow. Ingredients for sea effect snow were therefore all met in this case:

  • deep polar air mass
  • strong winds
  • temperature difference between the water and the air at 850hPa must be at least 13c for significant lake/sea effect snow
  • hills near the sea to encourage uplift

More pics here

Elsewhere in the region, winter storm Alexa has caused flooding in the Gaza strip

The 2013 December 5-7 North Sea storm caused “the biggest UK storm surge for 60 years” (UK Environment Agency).  With associated gales across Scotland, coastal flooding in North Wales, Merseyside and the UK East coast, tidal river flooding in Hamburg, the closure of all major North Sea coastal surge barriers and disruptive snow further south in Europe, this storm system was arguably more powerful than StJude back in October.  Thankfully, this storm only killed 7 people across Northern Europe (

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Essentially a storm surge is a higher-than-normal sea surface caused by low air pressure coinciding with high tides which, when thrown into shallow coastlines by winds, can produce exceptional coastal flooding.  A surge can also include associated lower-than-normal water levels with off-shore winds pushing water away from the coast at low tide.

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This post outlines the factors that makes the North Sea so vulnerable to storm surges and, further down, there is a summary of some impacts and a quick resume of the successful responses to this hazard event with some useful links.  Finally, before we get too smug and chill out entirely about future storm surge hazard…will development land lapped-up on exposed coasts, for example in the Thames Gateway, increase our future vulnerability in the face of sea level rise and climate change?  Is it sensible to build in these locations?

Animation shows storm surge rolling round the coast and into the North Sea.


The North Sea is particularly vulnerable to storm surges because of an unlucky combination of factors that come together to occasionally make the “perfect storm”.  Fortunately, not every North Sea storm produces a surge!  Remember that Tacloban in the Philippines was hit by an even bigger storm surge generated by Typhoon Haiyan due to similar forces and a funnel shaped bay.  Compare videos on this blog to see the difference between Tacloban and North Sea surges. So what comes together to produce the most significant storm surge hazards in the North Sea? There are at least 6 factors that combine to produce the biggest storm surges: here they are:

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1. Sea shape and low lying coastlines: The North Sea is particularly prone to dramatic storm surges because it is open to the North Atlantic and then tapers towards the south in a funnel shape. This funnel shape has the effect of allowing strong northerly winds to direct storm surges towards cities like London, Amsterdam and Hamburg and surrounding vulnerable low lying coastal areas including Norfolk, Lincolnshire, Essex, Kent and the Netherlands. Some of these areas are at or below sea level and require sea walls and dykes and barriers to protect them during storm surge events otherwise they will be flooded. The 1953 storm surge broke the rather primitive sea walls of the time and flooded large areas of Essex and even more of the Netherlands causing the worst European peace-time disaster since the war and killing 307 people in the UK and thousands in the Netherlands (see you tube documentaries below)


2. Sea depth/ bathymetry: the North Sea gets shallower towards the bays and wetlands towards the south.  These shallows have the effect of increasing the height of tides and surges as they are forced up over submerged shelves into narrowing bays.  This is possibly why Boston, Lincs and Hamburg suffered some of the worst flooding because surges were forced up bays and rivers.

3. Intense low air pressure: A 1 millibar reduction in air pressure allows sea level to rise by 10mm.  This effect can be replicated by sucking water up through a straw. The storm that crossed to the north of Scotland on 5 December had a central pressure of 976mb that deepened to 968mb over the North Sea. This is a similar central pressure to the storm that caused the 1953 storm surge that killed 307 people in the UK and 1800 people in the Netherlands.

4. Storm track: the LOW pressure has to track east over north of Scotland, which will drive a surge of water into the North Sea that is then pushed south by vigorous onshore Northerly winds into the low lying east coast of UK.  Ideally, the storm should deepen on its’ track across the North Sea, thus allowing northerly winds to gain in strength driving the surge and associated wind waves south.

LOW track

LOW track

5. High tides: high spring tides are the final requirement for the biggest surges.  Tides migrate as a bulge of water around the coast and, for the worst impacts, any surge travelling south down the North Sea must match the dome of the highest tide to produce the highest water levels in any one place. Since high tides occur twice a day it is quite likely that high elements of the surge will match a high tide level somewhere down the east coast.

6. Wind driven waves: Finally, surge and tide heights can be increased yet further by strong on-shore winds producing locally high wind driven waves that can over-top sea walls.

Warnings and impacts

The impacts of the 2013 storm surge included flooding in coastal towns on the east coast of the UK with perhaps worst hit being Boston in Lincolnshire. Houses on some vulnerable stretches of coasts such as Hemsby were washed into the sea as waves eroded sand dunes.  There was also significant flooding in Rhyll, North Wales and along the Merseyside coast at New Brighton (note: not Brighton!) where a Morrisons supermarket was flooded. The worst impacts on major populations and cities were avoided by the raising of the Thames Barrier to defend London and the closure of the flood gates on the Delta Scheme in the Netherlands.

The storm was modeled over a week prior to impact.  Initially GFS and UKMO models were seeing a cold surge as the main factor bringing possible snow across the UK but from about 6-7 days out it became increasingly obvious that the exact track and orientation of the LOW meant that powerful northerly winds and a possible storm surge were the greatest risk.  The UK Met Office, with Environment Agency, then started preparations for warning those at risk from flooding.  Most news channels were airing significant coverage from 24 hours out.


Significant flooding did occur along the East coast, notably in Scarborough in Yorks, Boston in Lincs and Hemsby in Norfolk. In Hemsby some vulnerable houses located on the sand dunes were washed into the sea. Bridges near the sea were shut for a time, like the Humber Bridge; and rail services in some eatern counties were disrupted for a time.  Power was cut to homes in Scotland due to high winds.  Hundreds of residents were evacuated prior to the floods in various locations but some claimed to have little warning.

The worst impacts were successfully controlled by the massively impressive engineering schemes built since the devastating 1953 floods.London has nearly 200 miles of flood walls and 8 barriers holding back the tidal Thames. The Thames Barrier was opened by the Queen in 1982.

The Eastern Scheldt storm barrier was closed for the first time since the 1970’s.  The Netherlands barriers are built to withstand a 1 in 10,000 year storm surge event so it is perhaps unsurprising that they easily saw off this event.  It is also noteworthy that the Dutch have great faith in their storm surge protection barriers.

These measures, along with warnings and on the ground assistance for places that were flooded, proved extremely effective.

Further useful links on 1953 and 2013 storm surges:

1953 storm surge: original newsreel and timewatch documentary

The sting in the tale?

London is sinking into clay and, along with the rest of the SE, it is tilting into the sea partly due to an epeirogenic / isostatic adjustment taking place since the glaciation released the north of the country from the burden of millions of tonnes of glacial ice causing positive isostatic rebound in the north and related subsidence in the south.

Flood plains and reclaimed land exposed to storm surges are still being lapped up by hungry developers as places ripe for building, like the Thames Gateway in London.  But is it sensible to concentrate massive new urban development in low lying areas vulnerable to coastal flooding when we have sea level rise and climate change?

The Greenland ice sheet always melts in summer.  Snow and ice especially melts around the lower altitude edges, coastline and often the “saddle” region between the north and south ice caps. The ice sheet snow cover always reaches a maximum at the end of winter when the entire land mass is covered in snow, 100%. The minimum snow cover reached by late summer (i.e now) is of greatest interest to climate scientists because summer snow cover varies each year and is therefore a more critical indicator of climate change. While the Greenland 2012 melt season was intense, the 2013 melt started late (May). Greenland currently has a greater coverage of snow than average for this time of year.

Of greater interest is the longer term trend. This is more of a climate paradox. While the cover of Arctic SEA ice in summer is reducing in extent and thickness, the snow cover over Greenland at the end of summer appears to have increased since satellite measurements began in the 60’s. Note the downward spikes on the graph… they have reduced in size showing a greater cover of snow over Greenland surviving and occasionally falling during summer. 

So… paradoxically, whilst summer minimum Arctic Sea Ice cover is reducing, the cover of snow over Greenland in summer appears to be increasing. Nevertheless, before we consider this as an indicator of less global warming (AGW), a glance at a global map of 2013 snow cover departures from the average shows that Greenland is alone amongst snowy parts of the globe in this increasing trend of summer snowiness.  Most high mountains which hang onto snow through the northern hemisphere summer are showing markedly LESS snow than average: Himalayas, Rockies, Alps and Pyrenees are all displaying lower than average snow cover for July.  This paradox of more summer snow cover in Greenland while summer Arctic Sea ice reduces in extent and thickness is another illustration of the complexity of global climate and how easy it is to pick out data to suit any agenda.

Meanwhile, forecast for today: Greenland ice cap today light winds, snow, cloudy, -25ºC; Reigate +22ºC, sunny, light winds.

greenland temp


The jetstream meanders like a river of air in the high atmosphere. Much of the time the jetstream blasts pretty straight west to east, at other times it loops wildly north to south. This week the jetstream is due to loop wildly, like a meandering river and threatens to form a special weather feature called a “cut-off low”.

How do cut-off lows form and why are they special?

1# A loop of the jetstream descending over the UK is forecast to form a TROUGH of low pressure over Europe this week. The southward limb of the jet directs cool polar air towards Europe and LOW pressure.

2# The loop becomes so sinuous (bendy) that, like a meandering river, the neck is cut-off as the jetstream re-forms to the north.  The LOW to the south becomes “cut-off” as HIGH pressure builds to the north.

3# The cut-off LOW over Europe is left as an “ox-bow” of cool unsettled weather, especially near the centre of the low pressure.

4# The surface warms and CONVECTION occurs through the cool air: air rises forming big convective storms.  These are forecast to migrate from the continent and effect especially the South and SE of England.  Higher pressure should keep the north more settled. 

5# Cut-offs fill gradually as warm air convects aloft, reducing instability.

6# The rest of May looks to have more rain and cool unsettled conditions as LOW pressure dominates.

(pics courtesy of netweather)

What makes a thunderstorm?

The conditions for lightning occur when powerful updrafts in cumulonimbus clouds force water droplets and ice crystals to rub against one another, creating massive amounts of positive- and negative-charged particles. The updrafts cause these two types of charged particles to separate, with the top of the thundercloud usually becoming positively charged as the lower part becomes negatively charged.

Here are the ingredients which formed the heavy “April showers” and first thunderstorm (TS) of 2013 over Reigate on Friday afternoon, 12 April 2013.  Whilst only a minor storm, it possibly still contributed to a multi-vehicle non-fatal accident on the M25, closure of the motorway for several hours, poor visibility, local flooding and hail across the area. Convective isolated rainfall events like these are important but tricky to forecast accurately: predicting exactly how much rain will fall, what type and precisely where and when isolated showers and thunderstorms will take place has a lower success rate than other elements of forecasting, like temperature predictions, for example.  Here is a round-up of the key indicators that enabled @RGSweather to issue a forecast for possible thundery activity more than 4 days before and monitor it’s development thereafter and issue a local forecast warning of a thunderstorm risk with very marginal low level tornado risk on the morning of 12 April.

A single relatively minor thunderstorm developed mid-afternoon with hail and lightning crossing north of Reigate on April 12, following a line roughly along the M25 between Leatherhead and Reigate.  The morning saw scattered and heavy showers but little organised severe weather.  Skies darkened over Reigate by 3pm under thicker cumulonimbus cloud and this thunderstorm caused some hazardous driving conditions on the M25 and a non-fatal multi-vehicle accident coincided exactly with the time the storm passed over the M25 which was closed clockwise for several hours thereafter.

Synoptic Situation: An upper trough over the UK and surface low (pictured) across southern UK moved slowly east during Friday, with an unstable airmass building cumulonimbus and increasingly heavy showers during the day as April sunshine heated the surface and increased instability. Here are the figures for yesterday and brief analysis…

LAPSE RATES: +29°C: Cold temperatures at 500mb heights and warming at the surface in the April sunshine caused steep LAPSE RATES of 29ºC. Lapse rates are the drop in temperature with height usually measured between 850hPa (1500m) and 500hPa (5000m). Steeper lapse rates indicate an unstable airmass where parcels of warm air heated at the surface in spring sunshine will rise rapidly and remain warmer than the environmental air surrounding them. Such air parcels will condense, releasing latent heat, which causes further rapid uplift and potential for the formation of cumulonimbus clouds given the absence of any inhibiting factors, like a cap (inversion or isothermal layer… see link below).

CAPE and Lifted Index: 378j/kg; LI -1: Convective Available Potential Energy (CAPE) is a measure of the energy in the atmosphere for convection (j/kg).  Figures in MidWest USA approaching 6000 j/kg cause tornadoes. Here in the UK, CAPES above 300j/kg can cause thunderstorms.  Lifted index is the difference in temperature between the environmental air at 500hPa and a parcel of air lifted to that height: a negative LI indicates buoyancy in rising air parcels and instability and significant convection.

Vorticity at 700hPa: upper air velocity at mid levels means that air is rising. April 12 has UVV: upwardly mobile air at mid-levels.

PWAT: 20mm: Precipitable water is the amount of water that would fall to the surface if all the moisture in the atmopshere rained or hailed out.  Relative humidity is a measure of how saturated the air is at various levels in the atmosphere.  100% means saturated: most levels were at least 80% RH.

TTI index

Total Totals Index (TTI): 60: this is a forecasting index used to measure potential storm strength.  It is calculated using the difference in dew point and temperature between 850hPa (1500m) and 500hPa (5000m).  TTI’s in the MidWest of >60 can yield severe tornadic supercells.

Wind shear: this means change in speed and direction of winds with height.  April 12 saw little deep layer wind shear: winds were blowing at similar strength and direction throughout the atmosphere so little rotation or organisation into severe storms could develop.  Nevertheless, slow moving storms deposited a lot of rain locally and caused minor localised flooding.

WAA: warm air advection: introduction of warm air at the surface increases lapse rates and can increase likelihood of severe TS: 12 April saw little WAA and this inhibited the development of any organised severe weather.

Towards the evening warmer air moved in aloft and, along with the removal of surface heating as the sun set, rapidly reduced lapse rates and inhibited convection causing towering cumulus clouds to melt away leaving a clear night.

So, several ingredients were present to create a marginal storm risk but the absence of some other critical factors like WAA and wind shear kept a lid on the severity and distribution of thundery activity yesterday.  Hopefully, this brief round-up of key storm indices relevant for SE England should help in predicting more severe weather in our region in the future.

Tornado Titans posted this on the CAP and skew-t charts. v helpful. If this is all too much then watch this instead…!

Polar Continental (Pc) air is most common in winter as HIGH pressure forms over cold northern continental interiors and pushes out freezing air to mid-latitudes.  In summer, when it does occur, Pc brings dry stable and warm conditions to the UK as the continents warm up.  Pc has been an unusually frequent visitor this March and effectively reversed our usual south westerly prevailing wind. As Spring sunshine warms the surface and Atlantic LOW pressure systems edge closer to the UK next week dragged by a more northerly migrating jetstream, we can be assured that moist maritime air will be making a return and any remaining incursions of polar continental air will increasingly lose their frequency and ferocity, Russia has to warm up sometime!
air masses UKMOBefore we bid “farewell” to the freezing Polar Continental air until next winter it is worth remembering the good times.  Pc has occasionally brought crystal clear skies with excellent visibility and dramatic views of the sky both day and night (as anyone staying up to see the ISS will testify). The long picture series shows Cumulus Congestus building over Stratford on Avon last week and an unusual Pileus Altocumulus Lenticularis veil forming over the dramatic rising thermals. Pileus is a fleeting, ephemeral cloud type and forms as convective up-draughts in the cumulus force upper winds over the rising congestus, just like air being forced to rise over a mountain range.  Moisture in the air condenses, or sublimes into ice, and forms a beautiful veil called Pileus.  The photos were taken over just two minutes and then the Pileus melted away.  Pileus is a beautiful cloud but has a darker side because it sometimes forms above rising nuclear mushroom clouds and volcanic eruptions.

Cloud streets, lines of Stratocumulus, were also a feature of the easterly winds: where an isothermal “cap” (temperatures staying the same with increasing height) kept a lid on rising thermals and clouds remained flat and formed lines in the airstream.  Cloud streets seem to urge us to follow them, pointing the way to something important over the horizon.  Finally, the “sundog” (mock sun) was another fleeting feature of polar continental air, though not exclusive to it: apparently only 5/100 people have ever seen a sundog, so here is a picture of one in case you haven’t caught one yet.  They occur as low-angled sunlight refracts through hexagonal ice crystals.

Pc air wasn’t all as beautiful as this of course: freezing grey blankets of dull stratocumulus dominated the weather for days in the south east and deposited icy snow grains right through to Friday.  Nevertheless, I do hope you had the time to look up and admire the best of the Polar air show this March.  So, Polar Continental may crack our cheeks and rage and blow but we’ll kind-of miss it… won’t we?  “Adieu, adieu, adieu… remember me.” Exit Ghost of Pc! (The photos above were all taken along the Stratford canal last week, the statue is William Shakespeare in Bancroft Basin).

n.b. March summary for Reigate coming soon!

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!