Met Office Work Experience - Day 5 (for 25-08-2011)

I realise that these posts on what I did at the Met Office are like a week late but I thought that, because I had such a great time and learnt an incredible amount, I would still write them! Well, what did I get up to on my last day with the Met Office?

First up was a very interesting discussion with a researcher about ice sheets. There is currently a lot of uncertainity about ice sheets and their stability, with much of this uncertainity stemming from a lack of understanding of the mechanisms for ice sheet melt. Currently, it is believed that Antarctica is the most likely to experience significant melt and this is because much of it is under the sea. If the proportion that lies below sea-level was to melt, which scientists think could occur over the next few hundred years (although this may sound quite slow, it is considered to be rather rapid!), it would raise global sea-level by 6 metres!!! Greenland melting is an area that often recieves much attention, perhaps becuase we are unsure just how much freshwater could be released or how quicly it would occur, but for now alteast, many feel that a large freshwater input is unlikely. Before this discussion, I had never really given much thought to the influence that the angle of the bedrock, upon which the ice sheet lies, on melting but it does, in fact, seem to play quite a large role. The bedrock that the Greenland ice sheet lies upon slopes away from the sea, whilst that in Antarctica slopes towards the sea and thus making runaway melting possible. When the Laurentide Ice Sheet existed it was sat upon 'flat' bedrock, something that many considered essential for the occurence of Heinrich events. Due to this, depsite the fact that models currently cannot replicate Heinrich events, it is believed that this current climatic state cannot provoke Heinrich events. The fact that surprised me the most was that increased surface air or sea surface temperatures, as a result of global climate change, are not the biggest threat to the stability of ice sheets and would not be responsible for instigating the greatest volume of melt. Instead it is increased wind speeds.....but why?

This is a bit of an exaggeration of what happens but
hopefully you get the general idea....

Well, increased wind speeds would raise the height of local sea-level and increase Ekman Pumping. Increased Ekman Pumping would provoke old warm waters from the deep ocean to be dragged closer to the surface and over the terminal morraine, which marks the end of glaciers or ice sheets, and towards the base of the ice sheet, thus causing melting to occur. This is believed to be responsible for more melting than raised surface air/sea temperatures. One thing that scientists are unsure of though is what happens to the warm water once it passes the terminal morraine. Does it hit the base of the ice sheet and then continually circle, gradually melting away the base or does it bounce back off and return to the rest of the ocean? Understanding this is, again, crucial if predictions of ice sheet melt are to become more cetain.....

Anyway, all of this 'stuff' is important if scientists are to make more certain predictions of the future of the MOC and there is a lot of debate over just how much of an impact melt of Greenland or Antarctica would have. Most focus is placed on Greenland, as a result of its location. Some feel that perhaps, if enough of Greenland melted, it could significantly reduce the MOC intensity whilst others believe that, due to existance of sinking sites either side of Greenland, that Greenland melt could provoke a switch in sinking sites to the western side of Greenland - a switch that could have the potential to actually warm the UK during winter. There are a couple of other quite specific topics that we covered but I think I will leave them for another blog post.

After this I attended a Modelling Team meeting which was quite interesting as it provided an insight into some of the work that researchers at the Met Office are currently doing and some of the problems they are facing at present. Following this I had a chat with someone regarding ENSO, a topic that fascinates me, and as, again, there was lots that we covered,and I am a bit more confident about talking about ENSO, I am going to write another post solely on this. The afternoon was finished off with a chat about the relationship between the ocean and atmosphere and how this relationship is replicated in models. The relationship between the ocean and atmosphere is really really complex and I literally touched the very very basics. The ocean is sort of like the memory of the Earth climate system. The atmosphere cannot store things, like signals or changes in climate, and so instead it passes the signals on to the oceans. The oceans can store this information for hundreds and hundreds of years, whilst it circulates them around the world, and then passes the signal back to the atmosphere where it provokes a short term, but rapid, response. This coupling is crucial for many things such as ENSO. It is tricky to model all of the processes that link the oceans and atmosphere and all of the exchanges that happen between them (I am in the process of writing a post on the real basics of climate modelling as it is like a whole new science).

I apologise as I realise that all of my posts regarding my time at the Met Office have been a bit all over the place but I honestly learnt so much and I am not that great at explaining things. Despite this, I still hope they have been interesting to read and have given you a bit of an insight into the work done at the Met Office and some of the things I was fortunate to do whilst up there. I really cannot thank the people who made this whole experience possible enough - I learnt an unbelievable amount, gained some invaluable advice universities courses and careers etc, got to meet some great and highly intelligent people and simply had just an amazing time!!!

The race for a million year old ice sample

Around every 100,000 years the Earth enters an Ice Age but it hasn't always been this way...... Up until about a million years ago the Earth swung between glacial and interglacial periods a lot faster, with this switch occuring every 40,000 years. However, no one knows why the time taken for Ice Age's to occur slowed and this is why scientists are so eager to find a million year old ice sample.



Axial Precession



At present, the switch between glacial and interglacial periods is believed to be influenced by three cyclical changes to the Earth's motion known as the Milankovitch Cycles, which were named after the Serbian astronomer who is credited with discovering their magnitude. The first of these cycles is called Precession and relates to the wobble of the Earth as it spins on its axis provoked by the gravitional interaction between the Sun, Moon and Earth. Precession occurs on a 26,000 year cylce and there are two forms - axial and apsidal precession. Axial precession is linked with the tilt of the axis in relation to the fixed place of the stars Vega and the North Star as the Earth wobbles from pointing to the North Star to pointing at Vega. If the axis tilts towards Vega then then the winter solstice in the Northern Hemisphere will coincide with the aphelion (point at which the Earth is furthest away from the Sun) and the summer solstice with perihelion (the point at which the Earth is closest to the Sun) thereby creating the greatest seasonal differences. When this occurs, the Southern Hemisphere experiences warmer winters and cooler summers and so a smaller seasonal difference. However, when the tilt of the Earth allows for the aphelion and perihelion to, respectively, occur near the autumn and spring equinoxes, the seasonal contrasts experienced in the Northern and Southern Hemisphere become similar.  At present, the perihelion is closer to the Northern Hemisphere's winter solstice therefore meaning a small seasonal difference in the Northern Hemisphere. Apsidal precession occurs when the Earth's orbit, as a result of the influences of the Moon, Jupiter and Saturn, starts to precess in space. This movement is known as the precession of the equinoxes and it effects the intensity of the seasons. So, in summary, Precession does not effect the amount of solar energy recieved by the Earth but the way it is distributed between the two hemispheres, therefore altering the seasonal differences experienced.



Apsidal Precession

 

Obliquity

The second cycle is the tilt of the Earth's axis which, I think, is normally known as Obliquity or the Angle of Inclination. Currently, the axis lies at a 23.4 degree angle and over a 41,000 year period this varies between 22 degrees and 24.5 degrees, thereby altering the latitundinal distribution of solar energy. This fluctuation in the angle of incidence causes changes in the intensity of the seasons experienced. As the angle of incidence increases, during summer, areas at high latitudes experience more solar energy whilst in the winter they experience a decrease in insolation (insolation is a measure of solar radiation energy recieved on a given surface area in a given time). This allows for permanent snow fields to form in the Northern Hemisphere.  In relation to low latitudes, changes in Obliquity have little effect as the strength decreases the closer you get to the equator. Therefore, changes in Obliquity alter the strength of the latitudinal temperature gradient. When the axial tilt is lower the Sun's solar radiation is more evenly distributed between the seasons but the difference in radiation recieved between the equator and polar regions is greater. A smaller degree of axial tilt would provoke the formation of ice sheets because warmer winters would result in more warm air, which has the potential to hold more moisture and so produce more snowfall. Ontop of this, milder summers would mean that less of the ice formed over winter would melt.



Circular orbit

 


Ellipictal orbit 

 

The third, and final, cycle is known as Eccentricity which is the shape of the Earth's orbit around the Sun. The changes in Eccentricity occur due to the gravitional influences of Jupiter and Saturn and the shape of the Earth's orbit around the sun changes from being ellipictal (eccentricity of 0.0607) to less ellipictal/more circular (eccentricity of 0.0005) on a cycle of around 100,000 years. This is of great importance to climate and glaciation as it alters the distance between the Earth and the Sun, thereby changing the distance that the Sun's radiation has to travel before reaching the Earth. This subsequently reduces or increases the amount of radiation recieved on the Earth in different seasons as this variation has a direct impact on the amount of solar energy recieved at perihelion in constrast to aphelion. Currently the Earth's Eccentricity is 0.016 which results in a 6.4% increase in the level of insolation recieved in January in comparison to July. This increase has been provoked by the 3% difference in the distance between perihelion and aphelion. When the Eccentricity is higher (so a more ellipictal orbit) the difference between the solar energy recieved at perihelion can be anything between 20% to 30% greater than that recieved at aphelion. The variations in Eccentricity also impacts on the length of the seasons and, at present, in the Northern Hemisphere, summer is 4.66 days longer than winter and spring is 2.9 days longer than autumn. Overall, Eccentricity influences the amount of solar radiation that reaches the Earth and so the fluctuations in Eccentricity play a key role in determining climate and the occurance of glaciation. 

So, a short summary about Milankovitch cycles......  basically the changes in Procession, Obliquity and Eccentricity alter the intensity and distribution of solar radiation hitting the Earth which then affects the climate, with particular reference to the extent of glaciation. Milankovitch used these variations to develop a mathematical model which linked insolation to the corresponding surface temperatures and from this model he came to the conclusion that variations in insolation at high latitudes were responsible for the increase and decrease in the size of the ice caps at the poles. One crucial thing that I have yet to mention is the importance of landmass when talking about the Milankovitch cycles as it helps to explain why fluctuations in Precession, Obliquity and Eccentricity are harder to locate in older records. The Northern Hemisphere is known as a Milankovitch sensitive region and, as mentioned above, the effects of alterations in the three cycles decreases as you get closer to the equator and lower latitudes - which don't lie in Milankovitch sensitive latitudes. Therefore, when Pangea existed, which was centred around the equator, the cycles did not have such a prominent effect............. and so the question is, what did? 

This is perhaps the most puzzling question surrounding the shift to a slower pace, by the Earth, around a million years ago as records suggest that their was no obvious change to any of the three cycles and this is yet another reason as to why finding a million year old ice sample is so important. Understanding this shift would enable us to understand why we have the climate we do today and, perhaps, even help us make better predictions for the future climate. One of the most common possible explanations for this shift, at present, is the idea of the slow decline in concentration of the carbon dioxide in the atmosphere that is believed to have started to occur around 3 million years ago. This would have reduced the greenhouse effect and, possibly, cooled the Earth to the extent that the tilt of the Earth towards the Sun, every 41,000 years, was no longer able to provide sufficient heat to melt the glaciers that formed in between.  Confirmation of this is required though and is dependent on the finding of a direct record of the ancient atmosphere. This can only be uncovered from the analysis of the air that became trapped in tiny bubbles within ice as the snow it formed fell to Earth. In 2005, the European Consortium for Ice Coring in Antarctica discovered, to date, the oldest ice core which has stretched our records of the ancient atmosphere back 800,000 years - however, this is short of the crucial time period in which the key transition from a 40,000 year ice age pulse to an 100,000 year one occured.  And so, the race is on to find this crucial million year old ice core........

The EPICA have been joined in the race by an Australian Antarctic Division, an American contigent and a research team from the Chinese Arctic and Antarctic Administration. The Chinese have already secured a location in east Antarctica but have been set back by the discovery that the ice sheets in this chosen location are growing from the bottom up which means that the ancient ice has most likely melted or been replaced already. The Australians are close to securing a site in the Aurora basin, also in east Antarctica, which is believed to be home to the thickest ice in Antarctica, however research needs to be done to ensure that they too don't experience the same set back as the Chinese. Despite this, climatologists remain optmistic that a million year old ice core will be found eventually as it is one of those things that is going to take time. Current drilling methods, which are very similar to those used in the oil industry, mean that to reach this million year old ice core, which is hoped to lie at around 3000 metres deep, will take three summer seasons due to the remote locations of potential sites, but advances in technology mean that this process could be sped up.

This race for the million year old ice core is clearly no where near finishing and, despite the competition that exists between the four teams, the international collaboration that exists will hopefully allow for this increasingly important clue, that will be provided by this crucial ice core, to be uncovered and consequently provide information as to why the climate we presently experience exists and perhaps even how and why, due to physical influences, it could change in the future.

Ice

I am not quite sure what to call this post as it is likely to end up jumping all over the place but seeing as ice should feature in all of the things I am going to try to explain I thought that it would do.

Firstly I am going to discuss albedo. Albedo is a measure of the reflectivity of different objects and surfaces on the earth and the lower the number the more energy that is absorbed, which is believed to contribute to global environmental climate change (or what ever the new term for global warming is). The most reflective surfaces are snow and ice, which have the ability to reflect as much as 90% of the sun's energy back to space. Black carbon (I think it is practically that same as soot) is considered to be one of the largest contributors to climate change, even though unlike all of the other polluntants it is not a gas and it is the shortest lived as once we stop emitting it, it would stop trapping heat in the atmosphere within a couple of weeks. If this is true, then why is black carbon emissions so potentially problematic and what is its link to albedo? Well, black carbon has been closely linked with the acceleration of the melting of ice and snow around the world and thereby a reduction in albedo. The largest source of black carbon is from the burning of biomass which occurs a lot in Brazil, Indonesia, Central Africa and this accompanied with the black carbon produced in Siberia and Eastern Europe by forest fires and the seasonal burning of ground cover has contributed greatly to the progressive disappearance of the Arctic's sea ice cover, as the prevailing winds have carried this polluntant to the Arctic. This is also effecting the Himalayan glaciers. It is believed that 20% of the black carbon in the atmosphere is the result of burning wood, dung and crop residues for household cooking and heating in India. The increasing use of coal-fired power stations in China has added to the black carbon that it produced in this region and, due to the seasonal weather patterns experienced, black carbon poses a particular threat to both India and China. The Indian subcontinent normally experiences 6 months lacking in rain surrounded either side by monsoon seasons and this temperature inversion (a situation where the temperature of the air in the lower troposphere (the lowest layer of the earth's atmosphere) increases with height), which forms over much of South Asia during that period, traps the black carbon above the glaciers and snow of the Himalayas and the Tibetan Plateau. When the black carbon falls on the glaciers, it darkens their surface which causes the snow and ice to absorb the sunlight instead of reflecting it (basically it reduces its albedo) which accelerates the rate of melting. Not only is this likely to present huge issues surrounding water supplies for countries like India, Bangladesh and China who rely on the seasonal melting of the glaciers, for example 70% of the water flowing in the Ganges comes from the melting of ice and snow in the Himalayas, but also that it is reducing the earths natural ability to reflect the sun's energy. The results of a 30 year study of the Northern Hemisphere's albedo was recently published and it suggests that the reduction is albedo due to snow and ice loss is more than double than previously thought. The study involved comparing the model estimates of changes in the Northern Hemisphere's cryosphere (portions of the earth where water is in its solid form e.g sea ice, glaciers, permafrost etc.) with the changes in actual snow, ice and albedo measurements over the same period. The study concluded that, during the 30 year period, cryosphere cooling in the Northern Hemisphere declined by 0.45 watts per square metre and that, on average, for every degree of warming 0.6 fewer watts of solar radiation, per square metre, are reflected to space due to reduced snow and sea ice coverage. The reduction in albedo across the global is increasingly worrying scientists who have seriously considered proposing that all building roofs should be painted white to try and imitate the role that ice and snow play in reflecting solar energy to accompany plans to reduce black carbon emissions. However, as densely populated countries such as India and China continue to develop reductions in the global emissions of black carbon are going to be increasingly hard to meet because the burning of coal and biomass are the largest contributors to the production of black carbon.

I am going to go back to the Himalayan glaciers again but this time in reference to the recent publication of research that suggests that debris on the Himalayan glaciers may be helping to keep them intact. The new research suggests that debris such as rocks and pebbles may help to shield glaciers in the Himalayas from the solar energy and therefore slow the rate at which they are melting. The research that was carried out between 2000 and 2008 on 286 glaciers between the Hindu Kush on the Afghanistan-Pakistan border and Bhutan, disovered that half of the studied glaciers in the northwestern regions of the Himalayas were stable whereas two thirds, elsewhere in the region where in retreat. Retreat rates were also found to be high on the Tibetan Plateau, an area that lacks in debris. The scientists have attributed this difference to the amount of debris present on glaciers and they concluded that debris, in the form of rocks and pebbles, has the opposite effect on glaciers to black carbon and dust. It is hoped that this research could help to explain why glaciers in the Himalaya's haven't all responded in the same way to rising atmospheric temperatures and therefore possibly make it easier for us to predict how glaciers are going to respond to changes in atmospheric temperatures in the future which may enable us to predict the impact that the melting of the Himalayan glaciers will have on the people of China and India.

It is a well known fact that the melting of earth's ice sheets could play havoc with sea levels but to what extent has often be debated. The most recent report (sorry - I realise that this post has involved lots of 'recent reports') by the Intergovernmental Panel on Climate Change suggested that sea levels, before taking into account the Greenland and Antarctic ice sheets, could rise by between 18 and 59 centimetres by 2100. Another report, that did include the ice sheets of Greenland and the Antarctic claim that sea levels woudl rise globally by 56 centimetres by 2100. This prediction was calculated by using NASA satellites to estimate the changes in the ice mass by measuring earth's gravity field over Greenland and Antarctica (the gravity field is apparently affected by changes in ice mass - don't ask me how) and by using monthly measurements of glacier movement and ice thickness. Both reports seemed to produce similar predictions and they also noth agreed that the rate of loss of ice is increasing by 36 gigatonnes a year which is roughly three times as fast as the rate of loss from mountain glaciers and ice caps. However the melting of glaciers and ice caps should not be overlooked as it is estimated that melt from mountain glaciers and ice caps will contribute around 12 centimetres to global sea levels by 2100.

From all of the above I think that it is clear to see that the melting of ice has the potential to have catastrophic human consequences from displacing millions due to rising sea levels and hugely influencing th ewater supply of the most densely populated countries in the world and that little is still known about patterns to glacier melts and why some respond differently to changes in atmospheric temperatures.

Sorry it is all over the place and a bit brief but I hope some of you might have found it vaguely interesting. I am ensure as to whether or not it links to any of the Geography ones or not - perhaps one to do with climate change - but even if it doesn't I think it is quite interesting to see what research is being conducted in terms if ice sheets and glaciers and the effects that human activities have on them.