Cool temperate western maritime climates (CTWM) are found in several countries worldwide, all of which are bordered immediately to their western seaboards by oceans which moderate the climate typical of their latitudes. These countries include Chile, the UK, New Zealand and Western Canada (British Columbia) all of which are classified as MDC's. These countries enjoy climates with a limited range in temperature, significant extremes are rare and the climate is well suited to agriculture and aquaculture. Their populations have made use of these benefits particularly the UK by progressing through their agricultural revolutions, and the demographic transition early in their history. It can be argued that this early development is a product of a temperate climate, however this may be altered by global climate change which poses a significant risk to all these regions. However, this moderated climate is punctuated by extremes in weather conditions, though by definition, the CTWM is changeable on both a short term basis with the passage of anticyclones and depressions, and a significant yearly variation with seasons, when these extremes do occur, their infrequency places both industry and population at risk as these countries are poorly equipped and unused to more climatic events as has been observed in the UK during the 1987 storm, the 2003 heatwave and the two recent severe winter anticyclones.
The CTWM is found across the UK, and is a climate controlled by its location in reference to the tri-cellular model. This country sits beneath the boundary of the Ferrel and polar cells, and as such endures the influence of the jet streams and the Rossby waves created by their undulating path around the northern hemisphere. These high altitude waves direct the path of high and low pressure systems on the surface, predominantly anticyclones and depressions. The degree of sinuosity, either a high zonal flow with few waves, or low zonal flow with a significant north south movement, determines the location of these different pressure systems which bring considerable variations in weather.
The first of these systems, anticyclones, bring different conditions depending on seasons. During the winter months, the descending air brings clear, cloud free skies, very little precipitation and low temperatures. In the UK these temperatures rarely drop below 2 degrees, and during a typical winter anticyclone the hazards for these events are manageable. To the general population the main social hazards are to drivers, black ice and radiation fog are common, particularly during the cold nights, and are the cause of many accidents. They can pose a risk to infrastructure and property with frozen pipes and potholes which are both caused by the expansion of water by 9% as it freezes. The elderly can be at risk from illnesses such as pneumonia, and particularly with rising fuel costs, this risk may be set to increase. In general, these events cause few hazards to industry, and offer the benefit of tourism in Scotland such as ice climbing and associated tourism, the roads are easily managed through gritting and the public is used to these conditions.
There have recently been examples of severe anticyclones over our winters that have brought significant risks. The winter of 2010 saw a significant snow storm followed by a sustained blocking anticyclone that kept temperatures in some regions of the South West as low as -10, and in Scotland a new record of -27 was set. This anticyclone restricted temperatures and allowed the snow and ice to persist to depths of several centimetres. As the country is unused to this, there were numerous impacts on society. There was sustained criticism of the government as we ran out of grit and salt for the roads, the airports were closed for several days creating loss through trade, and the airports were filled with many international students, ranging in age from 10 to 18 for up to four days. This prompted the Chinese government to consider sending a dedicated plane to retrieve children stranded in the UK. The novelty of ice over lakes in the UK caused some people to venture out onto the thin ice which collapsed, killing five, often as a result of attempting to rescue others or animals. The UK does not have a significant number of snow ploughs, our infrastructure is not set up to cope with cold weather, hence many of our major transport lines around the country are closed, including our roads, railways and shipping lanes. This isolates the UK from our international links, and as we are not self sufficient in either food, energy or labour, anticyclones represent a potentially significant impact to our economy.
In the summer months, extreme anticyclones represent significantly different hazards, but also some considerable benefits. During our summer, an anticyclone again brings clear skies, with cool nights, and heat wave type conditions. Daytime temperatures can exceed 30 degrees, which poses the most damaging risk to our population. Intense insolation causes high risk of sunburn and heat stroke, often people do not follow safe guidelines for sitting in the sun and the combination of dehydration and beach weather encourages people to go swimming when they are weakened, which has led to many deaths, particularly during the 2003 heatwave where 23000 people died across Europe. As with winter anticyclones, the demographic most at risk are the elderly, and the very young.
The potential implications from intense heating of the surface are wide spread, and in terms of environmental impacts, could cause widespread damage. Ice caps and glaciers melt at a faster rate in mountainous regions, rivers and lakes that are not glacially fed can dry up, causing widespread drought and hosepipe bans. However, due to the high levels of development, countries can afford to import water, hence comparatively, the disasters could have a more significant impact in regions such as sub-saharan
It can, however, make a positive economic impact. Particularly in the South West if the UK, heat waves bring about a boom in local tourism, especially around honeypot sites such as Lyme Regis and Newquay, creating demand for jobs in the service sector, and helping to encourage re-investment and redevelopment of older coastal engineering schemes, and possibly ensuring that these new schemes are more sustainable and ecologically friendly than more traditional concrete based walls and groynes. Lyme Regis is an excellent example, showing how natural processes can be developed in the form of the new shingle beach, to dissipate the wave energy, whilst appearing to be very much a natural feature that encourages tourism. Summer Anticyclones also increase the yield of certain crops within the UK, particularly our higher value crops such as English strawberries, and encourages high levels of attendance and associated spending at some of the UK's biggest summer events such as Wimbledon and Glastonbury. The final hazard these systems bring, is to create convectional thunderstorms, the precipitation form which is often channelled directly to surface runoff across the baked ground surface, such as the floods in Boscastle in 2003, where steep topography at the edge of the Dartmoor batholith created significant flash floods and caused over £12 million in damages.
The other significant weather system, a depression, is formed by the slow mixing of two air masses, the tropical maritime and the polar maritime. The differing conditions of the two, combined with the coriolis effect create an anticlockwise rotating system that always moves NE across the country. Where the air masses meet, fronts develop that bring frontal rainfall, and the rising of the warmer air creates low pressure and unstable atmospheric conditions. These systems are normally associated with higher wind speeds, blowing across the pressure gradient and towards the centre of the depression. When these systems are relatively small, they bring our much needed rain, and do so throughout the year, this enables successful agriculture, water supply to populations and industry, and keeps our reservoirs and lakes topped up. They rarely represent hazards, besides sustained precipitation can cause flooding, and deep depressions are rare, and often blown off course towards Iceland, or loose all excess moisture by the time they reach the south east due to the orographic influence of higher ground in the west.
When these systems are very deep, such as during both 1987 and 2008, they are very hazardous. The 1987 storm cost £3 billion in damages by todays estimates, and had a significant impact on our biodiversity and ecosystems. This storm had a low pressure centre of 963 millibars, and winds speeds approaching hurricane strength. Many lightweight coastal tourist centres such as caravan parks and chalets suffered almost total devastation, and over 15 million of the UK's trees were lost in one night. In addition to several fatalities, there was extensive damage to property and infrastructure, and again transport routes and trade were affected. It is rare for a storm to persist for so long overland, but this event affected nearly the entire country, and with restricted emergency services, recovery was slower than many would have liked. In 2008, another severe depression occurred in March, just before the start of the tourist season, damaging coastal regions, including some defences which a an impact on tourism that year.
These events raise the question of funding for new coastal defence projects, as with rising sea temperatures and a predicted increase in extreme weather, our coastal towns are both the UK's biggest tourist resource, and the most vulnerable areas of the country. Low pressure systems also pose the risk of a significant storm surge which when combined with high tides raises the risk of overcoming coastal defences.
These events must be placed in context, by comparing them to other climate regions and associated hazards. Our level of development ensures we are able to recover faster from any hazard than a developing country, and all of our most hazardous weather systems are short-lived. The benefits of our climate certainly outweighed the hazards early on our development, as they ensured we could feed our populations and not suffer water stress which would have limited our ability to develop. In comparison to a failed monsoon in India, or another category four or five hurricane in Louisiana, these impacts are certainly manageable, and with the advent of better weather forecasting and prediction, the hazard can be mitigated. However, this situation may change over time as the predicted patterns of global warming play out. As a country we are kept warmer than we should by our proximity to the ocean, and the influence of the gulf stream. Should a large volume of freshwater enter the North Atlantic, and the Gulf Stream shut down (or the North Atlantic Deep Water), we would loose this influence, and be subjected to an icy and far colder yearly temperature which would restrict future growth. Should the number of extreme events per year increase, our older defences will be overwhelmed, we have cut our spending on these as a country, and we will have to adapt to a new climate, which could bring benefits, but will enhance the risk posed by the CTWM.
Overall, the threats to population and industry are rare, and uncommon, but significant when they occur. The benefits of the CTWM are felt year round, and have brought all these regions economic and social prosperity. The threat posed by global climate change is one that can be addressed through research and development into predicted changes and patterns, and given enough time, which may be the issue, developed countries may well be able to managed sufficiently under their new conditions. The two main weather systems are therefore both important, when extreme both are potentially damaging, but represent a manageable risk.
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