Wednesday, 7 March 2012

Where would the British be without the Gulf Stream!?

Hello everyone! Hopefully everyone is enjoying the new climate module! Millie has written a very useful and succinct summary (something I never manage to achieve!) post on all the basics we have covered so far so there is no point me doing it to......instead I am going to write a little about the ocean circulation. After a polite reminder that Geography is the study of peoples interaction with the environment I am going to focus on the impact that the Gulf Stream has had on our development and the way society functions; projecting this into the future to examine how we would cope without it; rather than focusing on the science (although this is incredibly interesting, for the exam, unfortunaltely we do not seem to need to know that much - however feel free to ask lots of questions as this links with my EPQ topic).
I will get the sciency bit out of the way first....
This is a graphic I produced as part of my EPQ and so perhaps goes into a little two
 much detail but the image in the top left hand corner illustrates really well the role of the
Gulf Stream in heat transfer
- Continents divide the oceans up into basins and so this complicates the direction of currents which are already inlfluenced by Coriolis in the same way as winds
- Gyres (large circular) form and move clockwise in the Northern Hemisphere
- Currents are driven by winds, Coriolis and the sinking of cool water near the Poles
- Antarctic Cirumpolar Current is the only current that goes right the way around Earth, preventing icebergs from entering the oceans - this is important when analysising possible threats capable of perturbing the ocean circulation
- Gulf Stream is initiated as water moves across the Atlantic from Africa to the Carribean. As it travels close to the Equator is gets heated. It then gets deflected by landmasses, Coriolis and other factors and so flows along the Florida coast. As it reaches higher latitudes it gets colder and saltier (we say salinity increases) as when ice forms, salt is removed from the fresh water and left behind in the ocean (brine rejection). This makes it more dense so it sinks.
- The Gulf Stream is a surface current but there are also other currents than flow deeper in the oceans. Together they connect all of the world's oceans, transporting heat, and forming the Global Conveyor Belt

I will get into trouble if I talk anymore about the theory but just a quick mention for the deep water circulation (just ignore the next paragraph if you don't want to know anything more than we strictly need to - the bit after is very relevant though)......
Another graphic I made for my EPQ - atleast they are coming
 in handy!
All the currents are linked in a complicated way and are dependent on each other. The sinking of Gulf Stream waters at high latitudes, feeds the crucial Thermohaline Cirulation (THC). Due to the combination of high evaporative salt enrichment and Gulf Stream presence, THC is best developed in the Atlantic. The Gulf Stream transports warm, salty water to the north-east of the Atlantic where it cools, mixing with the cold Arctic Ocean waters. This causes it to become dense enough to sink, both to the south and east of Greenland. The resulting current is part of a larger system that connects the North Atlantic to the rest of the Atlantic, Indian, Pacific and Southern Ocean, where the two main sinking regions spread out in the subsurface ocean, thereby able to influence the world’s oceans from depths of 1000m and below, before the cold, dense water gradually warms and returns to the surface. Basically, the Global Conveyor Belt consists of surface and subsurface currents, sinking regions and return waters which interlink to form a closed loop. The conveyor starts in the Atlantic where salty water proceeds northwards to Iceland, is thermally densified, and thus sinks through the interior to form the conveyor’s lower limb. There are also deep-water flows such as the North Atlantic Deep Water (NADW), which have great influence on our lives. THC is very important. THC engages the entire ocean into the climate system by permitting ocean water to directly interact with the atmosphere (over a timescale of 100-1000 years), ergo, via the Gulf Stream and NADW, moderates the UK’s climate – one that is, consequently, on average, 5°C warmer than countries of similar latitude. On a more global scale, THC influences biome distribution, NPP, sea level, ITCZ movement and productivity of oceans whilst individual currents themselves allowed for the early navigation of the oceans, thus aided development. However, the present pattern has not always existed and is vulnerable to many external factors and cyclic atmospheric changes. Even a significant weakening would have multiple detrimental impacts, with the effects being globally experienced and, as the oceans control the Earth’s climate over decades to centuries, understanding how they are likely to change is crucial in selecting how to appropriately mitigate and adapt to future climate change.

Why is the Gulf Stream important for the UK?
Raises air temperatures, thereby helping to deliver mild winters and cool summers to the British Isles. The warmer waters have a significant impact on North Atlantic temperatures as they give up about one-third of the energy they had previously stored from the sun. The extent of the warmth provided by the Gulf Stream can be seen by comparing the climate of countries at a similar latitude to Britain's - i.e Canada which is a bit colder! It is believed that the UK climate is 5°C warmer than it would be without the Gulf Stream. Warming effect of Gulf Stream prescence enabled agricultral productivity to increase, permitting an acclerated transition through the early stages of the Rostow Model of Development. 
Perhaps the easiest way to understand the benefits of having the Gulf Stream nearby is to summarise the impacts on society if it was absent. Whilst there are many extrinsic forcing factors capable of shutdowning THC, thereby causing a southward shift or even complete shutdown of the Gulf Stream, the most likely is a large freshwater input at high latitudes due to melting ice, consequential to global climate change.........

How would the UK cope without the Gulf Stream?

This area is currently recieving a lot of attention (this is what I focused on when at the Met Office) and model simulations suggest that freshwater forcing of a shutdown, as a result of global climate change, could cause:
- 8C cooling
- Increase in wind speed
- Precipitation reduction
- Storms tending further north so hitting UK with increasing frequency
- 1-2 months additional snow cover
- 80cm sea level rise
- 2% reduction in the UK's GDP
Sea level rise is potentially worrying for the UK as factoring in isostatic readjustment, population growth forcing more onto marginal lands and £130 billion worth of assets currently at risk of coastal flodding, greater than 10% as present, of our coastline would need to be protected. Even factoring in global climate change, the UK would still see reduced precipitation and 3C reduction in temperature. Increased snow cover would drastically decrease mobility, isolate people from an alrady straioned health care amongst other amenities, instigate higher living costs due to restrictions on agriculutre and issues with transporting food (in 2010 one milk company had to throw away 100,000 litres of milk) and cause huge disruption to education (altough, I don't think us students would mind a few more snow days!!!). Lower temperature and prolonged snow cover could cause issues for the UK's ageing population, with 1/4 in the southwest unable to heat their homes, possibly initiating greater urbanisation with cities able to offer facilities in close proximity, more likely to recieve greater funding for protection and the urban heat island effect warming, on average, summar and winter by 5C and 2C respectively. Consequently, a shift in employment could be experienced, with construction work becoming more seasonal and people looking for office-based work that can be completed from home during winter moths. Restricted agricultural and inducstrial productivity, fewer TNC's attracted whose presence stimulats cumulative causation and reduced touristic value, amongst other factors, is projected to generate a 2% reduction in the UK's GDP (-0.1% of global economy) with politicians put under increasing pressure to develop effective contingency plans to prevent societal collapse during protracted snow cover, minimise economci impacts and provide sufficient protection in coastal areas.

Global Impacts???
The two hemispheres and the atmosphere and oceans are coupled in a way we don't need to understand but this means that, despite centralisation of impacts in the North Atlantic, impacts would be globally experienced. A 1C temperature increase in projected in the Southern Hemisphere, which would only be accentuated by global warming. A southward shift in the ITCZ would occur, reducing monsoon intensity/duration over India - worrying as India's water security is already poor, their rivers are reliant on glaciers, sea-level is threatening to displace millions thus increasing population density and India's population is expected to exceed China's by 2030. A 5% reduction in global NPP would be accompanied by alterations in temperate biome distribution and ecosystem disruption whilst with 20% of the world's fisheries dependent on upwelling systems and risng SST's futher reducing ocea oxygen content, food scarity would become prevalent especially with the global population soaring to 9 billion by 2045.

As you might have guessed, I find all of this stuff really interesting but I get the impression all you really need to know is the basic's of the Gulf Stream formation, a bit about how it has helped the UK and, just that society would struggle to sustain current livestyles without it -  so hopefully this all made sense!


4 comments:

  1. Replies
    1. Thanks, I think it is a very interesting topic although the possibility of a future thermohaline circulation is a worrying one!!! Once I start my degree I will be able to write about this a lot more, and in more detail which may be of interest to you to!

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  2. that's everything I needed! May I speak to you via email and ask some questions?

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    Replies
    1. Glad it is helpful! Of course you can; there is a contact address on my blogger profile.

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