Air Pollution - A National Failure

'The UK faces fines of up to £300m a year and embarrassing court appearances after the European commission launched legal proceedings against it for failing to reduce "excessive" levels of nitrogen dioxide (NO2) air pollution from traffic, despite 15 years of warnings and several extensions and postponements granted to the government', stated the opening paragraph of a recent Guardian article on the UK's poor record on air pollution.

Since the 'Great Smog' of London claimed over 4000 lives back in 1952, regulations have been tightened ever since. But today's pollution is different from the smoke induced smog's of the past, which resulted from the burning of coal - the predominant fuel back then. 

In this article I'll examine the types of air pollution that typically affects a country such as the UK and what's being done to improve it and what the health affects are. The current regulatory framework will also be considered.

The EU legal action stems from a Supreme Court ruling that the UK is in breach of the EU Air Quality Directive and “the way is open to immediate enforcement action at national or European level”.

So what are the effects of NO2 on health and what is the source of 
NO2 and other pollutants? The EU lists the following urban air pollutants:

Exposure times can vary for different pollutants. This is reflected in the Average period.
*Member state can apply for 5 year extension.
**Specific extension criteria available at discretion of EU Commission.
***New standard.
The Air Quality Directive (Directive 2008/50/EC ) was adopted in 2008 and came into force in 2010. But as noted above states can apply for an extension. The problem with the UK is that it has failed to take steps to implement the Directive, hence the legal action.

I'm not going to delve into the specifics of the Directive here (see below). But the first two paragraphs set the scene:

1. The Sixth Community Environment Action Programme adopted by Decision No 1600/2002/EC of the European Parliament and of the Council of 22 July 2002 establishes the need to reduce pollution to levels which minimise harmful effects on human health, paying particular attention to sensitive populations, and the environment as a whole, to improve the monitoring and assessment of air quality including the deposition of pollutants and to provide information to the public.
2. 
   In order to protect human health and the environment as a whole, it is particularly important to combat emissions of pollutants at source and to identify and implement the most effective emission reduction measures at local, national and Community level. Therefore, emissions of harmful air pollutants should be avoided, prevented or reduced and appropriate objectives set for ambient air quality taking into account relevant World Health Organisation (WHO) standards, guidelines and programmes.

The next step in the legislative process is for member states to implement domestic legislation. In England The Air Quality Standards Regulations 2010 came into force, with equivalent regulations established by the devolved administrations in Scotland, Wales and Northern Ireland. 

As the EU Directive has stated, the international regulatory framework is based on WHO standards and guidelines. It is this source that I will focus my analysis on.

Although the main emphasis of this article will be on the UK, the WHO guidelines apply on a global extent. 

The key pollutants
There are two types of air pollution; Primary (emitted direct into the atmosphere) and Secondary (formed within the atmosphere). Primary air pollutants include sulphur dioxide, oxides of nitrogen, carbon monoxide, volatile organic compounds, and carbonaceous and noncarbonaceous primary particles.  Secondary air pollutants arise from chemical reactions of primary pollutants in the atmosphere, often involving natural components of the environment such as oxygen and water. Secondary pollutants include ozone, oxides of nitrogen and secondary PM.

PM10,PM2.5, and ultrafine particles (PM1 or less) are typically measured within the atmosphere and monitored. The following diagram shows the size range of airborne particles (WHO):

Oxides of nitrogen (NOx) are prevalent in high concentrations in urban areas - especially during busy periods. These are formed during high temperature combustion. From a human health perspective nitrogen dioxide (NO2) is of concern. This is formed via a reaction of nitric oxide (NO) with ozone (O3): 
NO + O3 → NO2 + O2.

Carbon Monoxide (CO) is formed from the incomplete combustion of petrol. Full combustion would generate CO2.

The WHO report sums up the issues: 'Emissions from road vehicles are typically thought of in terms of the exhaust, though this is only part of the story (see below). Combustion of petrol or diesel fuel leads to the production of exhaust gas containing a range of potentially harmful pollutants. In many modern vehicles this passes through a control device, such as a three-way catalytic converter, before emission to the atmosphere. Pollutants emitted from the combustion of petrol or diesel fuels typically include carbon monoxide, oxides of nitrogen, VOC and suspended particles. Some countries still use lead additives in petrol and this generates an important air pollutant emission.

Exhaust emission standards are set as limits in grams per kilometre or grams per mile of pollutant emitted over a standard driving cycle...

'While exhaust emissions are often the most important emissions from a vehicle, they are far from being the only ones. Evaporative fuel emissions can also be important, especially from petrol vehicles, and these are measured and included in inventories of emissions. Far more difficult to account for, however, are the

other non-exhaust emissions of PM from road vehicles that arise from sources such as the wear of brake components and tyres and the attrition of the road surface itself. Crude estimates have been made of the magnitude of these sources, which are included in many emissions inventories. However, road vehicles also cause the emission of particles by suspending particles from the road surface into the air, either through the turbulence in the wake of the vehicle or by the shear forces between the tyre and the road surface. These are far more difficult to account for and are not widely included in emissions inventories'.

Emissions inventories are compiled by countries from air pollution data that has been measured and collected from relevant sources. WHO explains the general process: 'In the case of road vehicles, the vehicle fleet will need to be subdivided according to the type of vehicle, the fuel it uses, and its age or any abatement technology fitted. Emission factors are developed specifically for each of these elements. In conducting calculations for an inventory, it will be necessary not only to know the type of vehicle in each category but also the annual mileage of that type of vehicle or the proportion of the total mileage that it represents on a given road link. Inventories are becoming increasingly sophisticated in disaggregating vehicles according to their age and mileage, and also in allowing for high-emission vehicles with faulty abatement devices. It is not feasible to take data directly from type approval testing and assume that a vehicle that has been operating for, say, 100 000 km produces the same emissions as a new vehicle on a dynamometer test. Test cycles, although aiming to reflect the real world, do not always do so very well'.

Receptor modelling is another method of analysing air quality. 'This method uses the measurements of air quality itself, often in combination with simultaneously measured meteorological data, to recognize and quantify the contributions of specific characteristic source types to air pollutant concentrations. In the case of PM, multi-component chemical analyses of consecutively collected air samples allow recognition of components that co-vary in time and therefore have the same source. Typically some 6–10 individual source types can be identified through their chemical profiles'.

Exposure to air pollution
WHO defines exposure as 'the event when a person comes into contact with a pollutant of a certain concentration during a certain period of time'. This follows a distinct pollution pathway: 
Source → Emissions → Concentrations → Exposure → Dose → Health effects.

Exposure also depends on location. Pollution can form in micro-environments, which may not be picked up by a stationary air monitor. So levels of exposure can vary depending on the place and time and how long the exposure lasts for. The effects of the later will depend on the pollutant and the health effect under consideration.

It should be particularly noted that exposure levels can be much higher in vehicles. For example, 'in a study of taxi drivers in Paris, the average nitric oxide concentration in the taxi was more than 11 times higher than at a city background measuring site, whereas the level of nitrogen dioxide was only twice as high. Black smoke concentrations (8-hour average) in taxis were on average almost four times higher than those at a city background site. In general, cyclists and pedestrians tend to be somewhat less exposed than people in buses and cars, although this difference can be offset by longer journey times. In addition, increased breathing rates while bicycling and walking may mean that larger volumes of pollutants are inhaled'. 

PM exposure tends to be lower indoors because of the physical barriers to the outside.

There are several ways to determine pollution levels and exposure. Effectiveness and accuracy can vary. The following table summarises the approaches to exposure assessment:

The use of personal air monitors can offer a more representative estimate of individual exposure to pollutants.

Historical monitoring of individuals and/or sites may reveal a pattern of pollution levels and exposure and might be useful in determining disease patterns related to exposure to air pollution. It is therefore important that policy makers respond accordingly to air pollution data. The following table details possibilities for policy action in relation to indoor and outdoor sources and personal activity:

It is incumbent on policy makers to establish air quality standards that take account of potential impacts on public health and the environment. However WHO notes that 'For most air pollutants, no “safe” levels have been found whereby no health effects are observed following exposure. In fact, for many pollutants, adverse effects have been associated with low, almost background levels of exposure. Since the process of setting air quality guidelines and standards aims at defining levels that do not pose adverse effects on health, how can such levels be determined when the scientific evidence indicates that no thresholds exist?'. In other words it boils down to risk assessment and what should be regarded as an 'acceptable' range of standards. Here in the UK that is determined by the EU.

WHO observes that 'Public opinion can be an important factor in influencing decisions, as the political capability of decision-makers is directly proportional to the interests and concerns of their constituents. Research has found that resources will often be directed to where the public perceives risks to be large, whether or not they represent the most serious hazards to society. When people understand the importance of air quality, they can demand action and be more receptive in complying with control measures. It is therefore in the interest of environmental and health authorities to ensure that the public is informed and educated about air pollution levels, sources, health impacts and possible solutions.
 
Maintaining an active communication strategy throughout the whole air quality management process may also help prevent crises, conciliate interests, provide advance notice for the implementation of control measures and inform stakeholders on compliance status. For these reasons, the development of communications tools that are understandable and accessible to the public is an important part of air quality management'. So the message is - if policy makers aren't getting it then its time to put the pressure on. 

I'll now examine how the UK is implementing air pollution policy within the context of the WHO report and the EU Framework.

The Department for Environment Food & Rural Affairs (DEFRA) website offers guidance and links to air pollution monitoring. As part of this process, DEFRA along with the devolved administrations use air quality projections. These are models that attempt to predict future patterns of air quality. These comprise of background maps up to the year 2030. The maps consist of Excel datasets and can be referenced to any local authority in the UK.

The Community Multi-scale Air Quality (CMAQ) modeling system is used to forecast daily projections of air pollution. It was developed by the U.S. EPA Atmospheric Science Modelling Division. Other models are used, which are defined on the DEFRA website.

Other useful sites include:

• Air Pollution Information System (APIS). APIS provides a comprehensive source of information on air pollution and the effects on habitats and species.
• National Atmospheric Emissions Inventory. The NAEI compiles estimates of emissions to the atmosphere from UK sources such as power stations, traffic, household heating, agriculture and industrial processes. 
• UK-AIR: Air Information Resource. Run by DEFRA. Current state of play and forecasts for air quality. There are also sites covering Scotland and Wales.

The Health Effects of Air Pollutants

The Committee on the Medical Effects of Air Pollutants (COMEAP) is an expert Committee that provides advice to government departments and agencies, via the Department of Health's Chief Medical Officer, on all matters concerning the effects of air pollutants on health.

They have produced several publications in recent years on air pollution and health. Cardiovascular Disease and Air Pollution is an important paper published in 2006, which I'll go through briefly here. Its worth noting that there is a lot of medical based information and data detailed within the report.

In defining cardiovascular disease (CD) the report states that it 'includes all diseases of the heart and blood vessels including stroke. It accounts for 40% of deaths in the United Kingdom and a large proportion of hospital admissions.

'The most common [form] ...is coronary artery disease (CAD), also known as ischaemic or atherosclerotic heart disease. Coronary artery disease is the most frequent single cause of death in the UK and is caused by atheromatous plaques occurring in the walls of the coronary arteries, the arteries which supply blood to the heart. These plaques appear first in young people and are widely distributed in the large and medium sized arteries of the body. The occurrence of plaques in the coronary arteries is particularly important as growth of these lesions can lead to progressive narrowing and eventually obstruction of the vessels in some cases. In addition, the plaques may rupture or fissure leaving an ulcer in the wall of the artery on which a thrombus (blood clot) forms. This may lead to complete blockage of the artery (coronary thrombosis or heart attack)'.

The report followed two research criteria:

• A time-series approach, 'investigates whether air pollution is accompanied by short term changes in the incidence of cardiovascular events such as heart attacks. This method generally uses available data on daily counts of deaths or hospital admissions and relates these to ambient concentrations of air pollution on the same or previous days, measured by monitors situated in the study area – usually a city. Evidence from a large number of time-series studies show very clearly that, with few exceptions, all of the commonly measured pollutants (particles, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide) are positively associated with increased mortality and hospital admissions for cardiovascular disease.
• 'Compar[ing] the incidence of cardiovascular diseases between populations with different long-term exposures to pollution. These studies usually follow groups of subjects (cohorts) for a number of years and provide important information about the amount of life lost due to air pollution. Because large numbers of subjects are required and because the cohorts must be followed up for a number of years, few cohort studies have been done. The evidence from two American studies suggests that cardiovascular deaths are increased by living in areas with higher levels of particulate air pollution. This effect seems to be modified by socio-demographic and regional factors'.

Here I'll present a brief summary of the mechanisms involved after a subject is exposed to air pollution. The following diagram outlines the toxicological process:

The above diagram considers two mechanisms that may contribute to CD. The report explains each in more detail:

• Inhaled particles, especially very small particles, may set up inflammation in the lung and that this can trigger changes in the control of blood clotting. It is also suggested that changes in chemical factors in the blood can affect the stability of the fatty deposits (atheromatous plaques) found in the walls of arteries in many people – especially those in the walls of the arteries which supply blood to the muscle of the heart itself. If this is true then a link between inhalation of particles and the likelihood of, for example, heart attacks will have been established.
• The inhalation of particles and perhaps some pollutant gases may trigger a reflex that leads to a subtle change in the rhythm of the heart. The triggering of a reflex begins when some stimulus is detected by a receptor, a message is sent along nerves to the spinal cord or brain and a response follows. Well known reflexes include the production of saliva on smelling appetising food and the forward kick of the leg when the tendon below the knee-cap is tapped smartly. Coughing is also a reflex: in this case the receptors are in the airways and the trigger is an irritant: perhaps a crumb of food. Air pollutants may stimulate receptors in the airways and though coughing may not be produced, reflex changes in the rhythm of the heart may occur. Such changes may lead to the heart being more susceptible to dangerous changes in rhythm: such changes can cause sudden death. Evidence for and against this theory is also presented in this chapter. Interestingly, this hypothesis links with the one above: inflammation may be involved in the early stages of both.

The above is a very brief summary of the mechanisms involved in CD. There are other health effects related to air pollution including asthma and other respiratory diseases. To engage with the overall topic in greater depth would require two separate posts. But I hope I've covered the necessary ground in this article. If I've missed anything, do let me know!

Tuesday, 18 February 2014

The jet stream is changing

I'm sure wherever you are in the world, you're probably thinking the weather has been going crazy lately. In the northern hemisphere in particular we have been enduring some very unusal weather. 

Here in the UK, we've been battered by one storm after another almost relentlessly since December, whilst in North America, Siberia arrived.

The one thing that stands out - certainly here in the UK - is the total lack of preparedness. In part that's due to the remarkably nonchalant inclination to build on flood plains without due consideration to the blatantly obvious fact that flood plains actually flood! With climate change heralding even worse flooding of the sort we're witnessing now it would appear that the current Government has been caught with its pants down.

But there's more. The Guardian reports that 'The money spent on preparing the UK for the impacts of global warming has almost halved since the environment secretary, Owen Paterson – widely regarded as a climate change sceptic – took office. Critics called the cuts "shocking" and "complacent".

Figures released under freedom of information rules show annual spending falling from £29.1m in 2012-13 to £17.2m in 2013-14. The drop in funding follows a previous slashing of staff working on the issue from 38 to six in May 2013'.

Paterson has always been blasé about climate change, so he must have been surprised when he found his boss recently saying 'Colleagues across the House can argue about whether that [the floods] is linked to climate change or not. I very much suspect that it is'.

But as the crisis verges on the catastrophic, the Government has been found wanting. It has been exposed for what it is - anti-environment, negligent and effectively hopeless. An article from a world to win sums up the sentiment nicely: 'The current weather crisis has shown up the illegitimacy of politicians in charge of a system that is unable and unwilling to act for the common good. They greatly fear this exposure – it's the reason for the tide of government rhetoric about "money no object" and promises of future help.

In 2010, government chief scientist Sir David King warned of the need to plan for increased floods resulting from climate change. He proposed pulling flood defences inland, sacrificing some areas to the sea, establishing flood plains at the heads of rivers, modernising weirs, widening bridges and replacing sewers to separate sewage and floodwater.

This is the current policy of the Environment Agency and it has a backlog of hundreds of measures based on this approach. It can't complete them because of cuts and a Treasury rule that they can't invest more than £400,000 in any one project. The government's fantasy was that business and the insurance industry would step up as co-funders. As a result, of course, nothing happened'.

The fact that nothing has happened is a sad reflection on the fact that over 25 years of warnings have been totally ignored and that political ideology is paramount to science. Indeed the script was written in 1987 with the release of the Report of the World Commission on Environment and Development: Our Common Future. This document formed the foundation for the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro, 1992 (the Earth Summit). This led to the formation of The United Nations Framework Convention on Climate Change (UNFCCC). And since then the UNFCCC Conferences of the Parties have been taking place on a regular basis. It led to the adoption of the Kyoto Protocol in 1997, but since then nothing concrete has emerged from negotiations.

Now, nearly 30 years after a common future, it appears that we have stepped backwards rather than forwards. We are now witnessing the sort of extreme weather that we have been waiting for, for the past 25 years or so.     

So how are the floods and the other weather events around the globe linked to climate change?

The answer lies in the melting Arctic sea ice and its effects on the jet stream. Although the science behind this is relatively cutting edge is does offer insights into the extreme weather we are witnessing.

The following excellent video looks at recent extreme weather events and features Prof. Jennifer Francis from Rutger University, Institute of Marine and Coastal Sciences: 

To give a brief explanation of the phenomonon, essentially the jet steam is a current of air that marks the boundary between warm air masses to the south and cold air from the north. The confluence of these air masses coupled with the spin of the Earth drives a river of air around the globe. There is a southern equivalent. The spin of the Earth creates a force known as the Coriolis effect, which causes winds to deflect to the right in the northern hemisphere and to the left in the southern hemisphere. This is why the wind-flow around low and high-pressure systems circulates in opposing directions in each hemisphere.

Typically the temperature gradient between north and south of the jet stream is considerable. However to due accelerated warming in the Arctic, the gradient has been diminishing causing the jet stream to slow down. This causes the jet stream to meander. In so doing it forms ridges and troughs.

One of the effects of a slow meandering jet stream is a tendency for weather patterns to get stuck in a rut. This means that a pattern of weather may persist for a number of months. This is precisely what has been happening over the UK during the past couple of months.

However due to the high temperature gradient over North America, the jet stream has accelerated over the Atlantic, increasing the severity of the storm systems heading towards the UK. This can make the dynamics of the jet stream difficult to predict. Depending on location it can speed up, slow down or disappear altogether. The National Oceanic and Atmospheric Administration (NOAA) has an excellent introductory article on the topic.

Within the jet stream there are ribbons of accelerated winds called jet streaks. These tend to form the boundary's of low pressure zones. The winds leaving the jet streak are rapidly diverging, creating a lower pressure at the upper level (tropopause) in the atmosphere. The air below rapidly replaces the upper outflowing winds. This in turn creates the low pressure at the surface. This surface low pressure creates conditions where the surrounding surface winds rush inwards. The Coriolis effect creates the cyclonic rotation that is associated with depressions. The strongest surface winds in any developing depression are normally seen at the left exit point of the jet streak, where the jet streak is strongest:

The black oval indicates a jet streak, the purple square indicates entry winds into the jet streak and black box indicates rapidly diverging exit winds (Source, netweather.tv).

In The Big Chill, I detailed the wider dynamics of atmospheric change in the Arctic relative to circulation patterns elsewhere around the globe. The following diagram from the NOAA article simplifies the circulation patterns that are present reletive to the northern hemisphere:

It's the Polar Jet that affects our weather.  According to the IPCC AR5 Working Group 1 report, there is evidence of a polar shift in the jet stream with a likely intensification of North Atlantic storm systems. In addition, blocking activity is more frequent at the exit zones of the jet stream and shows appreciable seasonal variability in both hemispheres, reaching a maximum in winter - spring and a minimum in summer - autumn. Blocking is caused by persistent areas of high pressure. There is also evidence that there may be links with the El Nino Southern Oscillation (ENSO) and other global oscillations. 

At the time of writing, the UK Met Office has just released a new report The Recent Storms and Floods in the UK. The report examines the statistics and evidence of the recent flooding events. It then considers the Global context of weather patterns and whether climate change is a contributing factor.

One of the key issues pointed out in the report is the combined vulnerability of the south of England to sea level rise caused by global warming and isostatic adjustment, i.e. 'the rise of land masses that were depressed by the weight of ice during the last glacial maximum. For the UK this is seen in increasing land heights over Scotland and northern England and falling land heights (sinking) over southern regions'.

The report notes that 'UK rainfall is increasing in intensity. This increase in the frequency/intensity of extreme daily rainfall events, as the planet warms and the atmosphere can hold more water, has been discussed in the literature for a number of years, and robust evidence for this is increasingly seen around the world.'

Climate models form a vital role in determining climate change attribution - the science of determining the causes of unusual climate trends and climate-related events. Models are becoming increasingly powerful and more reliable. The current climate model used by the Met Office is the HadGEM3. A modified version of Met Office climate models have been used successfully in a project designed for PC use. 

How does this all fit in with global patterns? Well, the report covers the issues already noted above with regards to the unusual jet stream patterns being observed and the impacts of this here in the UK and elsewhere. It links the storms in the UK with the exceptionally cold weather in North America: 'These extreme weather events on both sides of the Atlantic were embedded in a persistent pattern of perturbations to the upper tropospheric jet stream. The climatological distribution of the winter jet streams shows the well-known Asian-Pacific jet stream, which extends across North Africa and out into the North West Pacific, close to Japan. A second jet stream forms over the US, extending in a north-easterly direction across the North Atlantic towards the UK. The North Atlantic jet stream acts to steer weather systems towards the UK, but there also exists a symbiotic relationship between the jet stream and the depressions that form on its flanks. The jet stream provides the atmospheric conditions that are favourable for cyclogenesis (the formation of depressions), but it also depends on the momentum from the depressions to maintain its own strength. So it is possible on occasions to observe a strengthening of the jet stream when there is a particularly active sequence of depressions, as was the case in December 2013 and January 2014. 

During December and January 2013/14 the pattern of winds over the North East Pacific and North America was very disturbed. The North Pacific jet was deflected a long way north, with a secondary branch extending southwards into the tropical Pacific accentuating the separation of the Pacific and Atlantic jet streams. The effects of this over North America and into the North Atlantic were profound. The deflection of the jet to the north led to colder air being carried south over Canada and the northern US to enter the North Atlantic jet and establish a stronger than normal temperature gradient at the entrance of the North Atlantic Jet. This acted to strengthen the jet and provide the conditions for active cyclogenesis, which in turn led to a sequence of strong storms across the UK throughout December and January'. 

Certain weather patterns tend to be associated with ENSO events. However the report points out that 'neither El Nino nor La Nina were active, with temperatures in the equatorial East Pacific Ocean being close to normal. The West Pacific remains anomalously warm, as it has done for much of the past decade. Elsewhere in the Pacific the patterns of sea surface temperature anomalies still display elements of the negative phase of the Pacific Decadal Oscillation (PDO) that has contributed to the recent pause in global surface warming. Likewise the very warm waters in the North Pacific are a result of the systematic weakening of the Aleutian Low during the last decade, driven by the negative phase of the PDO'. 

The higher temperatures in the West Pacific have caused higher than normal rainfall in the region. These anomalies appear to be feeding into the wider climate system as 'the ‘buckling’ of the jet stream over the Pacific and North America became much more pronounced during January 2014, as the precipitation anomaly over Indonesia and the West Pacific strengthened. A notable feature of this anomalous area of tropical precipitation is its northwards extent into the winter hemisphere where it is able to interact with the North Pacific jet and generate Rossby waves that propagate along the jet and act to reinforce the huge meander of the jet stream off the west coast of North America. At the same time, Rossby waves propagate along the southern branch of the jet stream and enter the tropical East Pacific through the westerly duct, creating weather disturbances that can then get caught up in the entrance region of the Atlantic jet stream'. Rossby waves describe the large scale meanders in the jet stream, and are due to the variation in the Coriolis force as air moves north and south. They are fundamental to understanding the global circulation and its natural variability. It has been known for some time that variations in tropical heating associated with anomalous rainfall acts as a source of Rossby waves. Furthermore, theory says that Rossby waves can only propagate where the ambient flow is westerly. It seems that Rossby wave patterns are a crucial influence in the weather patterns that have unfolded this winter.

In addition to terrestrial weather influences, new research is revealing stratospheric influences on weather. The report states that 'westerly winter winds in the polar night jet stream were very strong during December and January. The polar night jet exceeded twice its normal strength at times during the winter, reaching speeds in excess of 100ms-1 in the upper stratosphere. A strengthening of the polar night jet often precedes periods of a strong Atlantic jet stream below and a positive North Atlantic Oscillation pattern, as was seen during the whole December to January period and consistent with the increased winter storminess this year.

Although internal fluctuations in the strength of the polar night jet cannot be excluded, there has also been an external factor in the current winter, again in the tropics, that has helped to precondition the system for a strong polar night jet. In the tropical stratosphere the winds circulate around the globe from west to east in some years and from east to west in others. This cycling of the tropical winds occurs roughly every two years - hence its name, the Quasi-Biennial Oscillation (QBO). Although it may seem remote from the North Atlantic, historical records show that when the QBO winds are westerly, this increases the chance of the positive phase of the North Atlantic Oscillation and a strong jet stream. The QBO has been in an unusually strong westerly phase throughout this winter, and this factor was cited in the Met Office October long-range outlook for the November to January period, which pointed out the risk of increased storminess in early winter this year'.

The Polar night jet is a river of strong winds that form around the polar vortex in the upper atmosphere, due to the strong thermal gradient created by the large cooling over the pole during the polar night. As such, it is only present during winter. With respect to the recent cold spell in North America, the jet stream formed a trough which flowed around the southern US before turning north again. This caused frigid air from the Arctic to move south. This was due to a stronger than normal Polar vortex. This caused 'the increased winds in the polar night jet; the structure of the vortex has also been stretched with the core of the vortex extending southwards over Canada. The extent to which this temporary deformation of the polar vortex played a role in the recent extreme cold temperatures over North America is unclear at present. In terms of the UK weather, the stronger than normal polar vortex throughout the winter is an indication of a less variable and colder stratosphere than normal and a strong polar night jet. This predisposes the circulation towards the positive phase of the Arctic Oscillation with more stormy weather conditions over the North Atlantic'. Combined with continental cooling the result was Siberian like conditions. The following diagram shows the phenomenon:
Further research on this topic by Jennifer Francis, was presented at the annual meeting of the American Association for the Advancement of Science (AAAS) in Chicago. Although scientists are not totally committing to saying that climate change is the definite cause of recent weather anomalies, they do however fit the pattern. What ever way you look at it the evidence is pointing towards climate change and it is highly likely that challenging weather patterns in the future will become the 'new normal'. 

If you want to monitor atmospheric air currents yourself, the picture at the top of the page is a snapshot of a real time interactive earth-wind map. The background to the project can be found here.