Tim O’Hare
observations, thoughts and useful stuff…Archive for oceanography articles
Time for Plan B – Geoengineering
There has been a huge amount of coverage of the need to cut Greenhouse Gas emissions as the primary route to slow down, halt and eventually reverse the current global warming trend and rightly so. However, in the background there have been a number of suggestions for actions that mankind could take to directly counter-act global warming. Such measures are collectively known as geoengineering and include such things as the direct removal of carbon dioxide from the atmosphere (e.g. by planting trees or fertilising the oceans) and reflecting incoming solar radiation away from the Earth (e.g. by using mirrors in space or changing the land surface to make it more reflective). These measures have not recevied much public attention, partly because they are all really, really expensive, partly because no-one knows how effective they would be and partly because by discussing the ideas in public we might distract attention from the goal of reducing Greenhouse Gas emissions.
Now, the tide has turned a little. A recent report produced by the Royal Society has highlighted the need to urgently begin considering geoengineering as a Plan B to reducing emissions. The report works through various geoengineering ideas examining their affordability and effectiveness and suggests that there should be a major shift of funding into geoengineering research. The report was widely publicised in the media at the beginning of September and the geoengineering debate is nicely summarised in New Scientist, Issue 2724 [05 September 2009].
Marine life mixes oceans
One of my colleagues carries out research examining the small scale mixing processes that go on in the oceans. He uses a complicated camera system with lasers and holograms and maps out the swirling motion of the water by tracking particles in the water [see here]. In the past he has ended up with some interesting pictures of little (microscopic) creatures in the water and he has begun to think about how these creatures stir up the oceans as they move around.
So, it was interesting when news of some research conducted in California broke recently. The work has measured the effect that jellyfish swimming in weater have on the mixing of the water water itself. Jellyfish were used because they are relatively simple and can be simulated in models quite well but the principle of ocean mixing by organisms is being considered more widely. In fact, the idea was suggested by Charles Darwin’s grandson some time ago. It turns out that the new research suggests that the mixing could be significant although the extrpolation to all ocean-going organisms, in particular the really small ones (of which there are huge numbers) is a rather uncertain process. It has been suggested that this organismal mixing could be as big as that produced by the other key mixing processes – wind and ocean tides. The result won’t change the results of ocean models because these work by adding in as much mixing as is necessary to get the “right” results but it may point a way to understanding global ocean mixing more thoroughly and it suggests that my colleague’s potential to view the water motion around smaller organisms might be a really fruitful direction to go in.
The research is reported in New Scientist, Issue 2719 [01 August 2009] and also on the BBC Website [29 July 2009].
Sea level rise – it just goes on and on…
New Scientist, Issue 2715 [04 July 2009] contains a substantial article on sea level rise which sets out the latest findings on rates of sea level rise and puts these into the context of past changes in sea level. It seems that a rise of 80cm by 2100 is a pretty standard projection, a rise of ~2m by 2100 is within the realms of possibility and even bigger rises cannot be discounted. An important point to bear in mind is that when projections are given for 2100 it is important not to forget that this isn’t the end of the story and that sea levels will continue to rise after this point and also that although much greater changes have occurred earlier in the Earth’s history we need to remember that humans weren’t around then…
From World War II to surf forecasts
My favourite reference in my PhD thesis (1992) was to a paper from the 1940s which was titled “On determining the gradient of enemy held beaches”. I liked the way that the title gives an explicit description of what the paper is about and I also liked the way that it seemed so far removed from the time and purpose of my own study.
In reality though, a great deal of the modern-day research done on waves and beach processes has its roots in the work of scientists in the 1940s associated with predicting wave and beach conditions for Allied Forces landings in north Africa and Normandy. One such piece of work that anyone who studies waves to a reasonable level will come across is the SMB-method for predicting waves. The abbreviation SMB represents the names of the three protaganists in the development of the method – Sverdrup, Munk and Bretschneider – and the method uses a knowledge of three parameters, wind speed, duration for which the wind has been blowing and the fetch (distance) over which the waves are being built up by the wind to predict the significant wave height and peak wave period. It is based on a special diagram which cleverly combines all of the variables and presents the outputs in a graphical form called a nonogram.
So, given my own use of research originating from the World War II era, it was interesting to read an historical piece in New Scientist, No 2714 [27 June 2009] about how Walter Munk (now aged 91) became involved in wave prediction in relation to Allied Forces landings and how this work subsequently spawned the surf prediction industry. It’s a good example of how widely applicable research can be triggered by a specific requirement and how it is not always possible to spot the full value of research (Munk missed out on making money from surf prediction).
A tale of two oceans – the seas in 2050
Last weekend The Times newspaper carried various reports publicising The Times Cheltenham Science Festival. One of these focussed on the major threats to the world’s oceans including CO2 emissions, warming and acidification and carried a plea for immediate action. The report was accompanied by a nice graphic showing two versions of the seas in 2050 side-by-side. In the first of these, the major problems had been tackled and the oceans and the ecosystems they contain had “revived” and in the second, problems had not been solved and the oceans and ecosystems are “collapsed”. For each version of the oceans there are 15 or 16 points of note, either positive in the case of the “revived” seas or negative in the case of the collapsed” ones. The article is available online (The Times [06 June 2009]) and pleasingly, so is the colour graphic (either via the link in the article or directly via this link).
Sink or sink – there’s little choice in the Maldives
The Maldives are a set of low-lying islands in the Indian Ocean. 80% of the islands are less than 1 metres above sea level and the highest point is only 2.3 metres up. But sea level has risen 52 millimetres in the last 15 years, the Intergovernmental Panel on Climate Change has predicted a rise of up to 59 centimetres by 2100 (not including glacial melting) and the most extreme predictions put sea level at 25 metres above current levels by 2100. So, it doesn’t take a genius to work out the for the Maldives it is not a cae of sink or swim but rather a case of sink – the only uncertainty relates to how long it will take to go under. It could be 50-100 years (IPCC) but it could be much, much sooner. What is to be done? There are various plans afoot that range from building artificial sea walls or a raised island to house the population or puting buildings on raised platforms. An article in New Scientist, Issue 2707 [09 May 2009] discusses the problem facing the Maldives and reveals that the current government there is also contemplating what, to me, seems like the most logical approach, namely to divert a large amount of the islands’ income from tourism into a fund to buy land elsewhere in the world to which the Maldive islanders can relocate at an appropriate time int he future.
Green conflict
I grew up in Bridgwater, Somerset, a town on the muddy banks of the River Parrett that flows out into the muddy expanses of the Severn Estuary. The Severn Estuary is famous for its huge tidal range (peaking at 13m) and for it tidal bore and consequently the Parrett also has a high tidal range and its own (somewhat smaller) bore which I did actually get to see once. Even when I lived in that region (and I am talking 25-30 years ago) there was talk of building a tidal barrage across the Severn to generate electricity and although no such barrage has been built, the idea of building one resurfaces from time to time and is particularly topical in our current fossil fuel dependent world.
Predictably, the idea of building a tidal barrage across the Severn is controversial, particularly in terms of the impact of any such scheme on wildlife and ecosystems and so whilst the environmental lobby might be expected to support such a scheme to generate energy from a renewable source, the environmental lobby might also be expected to oppose a scheme. This conflict is nicely set out in a recent article in New Scientist, Issue 2704 [18 April 2009]. Do we go for large schemes that generate lots of power but have obvious big impacts on the environment or do we stick with small schemes to minimise impacts but end up without much gain in energy generation or is there a middle ground? This is a question that is going to keep cropping up and my gut instinct is that there isn’t a one-size-fits-all answer.
Down down, deeper and down
There’s a report on the BBC website about a new robotic submarine that is currently undergoing final preparations ahead of an attempted dive to the deepest part of the world’s oceans, The Challenger Deep in the Mariana Trench (~11,000 metres down). This depth is deeper than Mount Everest is high (incidentally, did you know that George Everest’s name was actually pronounced Eve-Rest rather than the Ever-Est that we now use to describe the mountain that was named after him?). The robotic submarine has been developed by scientists and engineers at the Woods Hole Oceanographic Institution in the USA and is named Nereus (after the son of Pontus [the sea] and Gaia [the Earth] in Greek mythology). Challenger Deep has previously been visited only twice before, both times by human-operated vehicles, so there is plenty of potential for Nereus to turn up some interesting information. The Challenger Deep is part of a major subduction zone in the western Pacific in which oceanic crust that forms the base of the Pacific Ocean is forced down and underneath the oceanic crust that neighbours the Asian landmass and for this reason it is a major earthquake region. At this kind of depth the pressure experienced due to the weight of water supported is over 1000 times greater than the pressure we experience at sea level (due to the weight of the overlying air in the atmosphere).
The Arctic time bomb
It is becoming common knowledge that sea-ice is melting at increasing rates in the Arctic with predictions now suggesting that the region might be ice free in the summer by 2030. The question is, should we really be worried about this, and if so, just how worried should we be? Much of the media attention on the Arctic region is focused on how melting sea ice might alter ocean currents in the north Atlantic, but the real danger lies in what might happen as more and more of the permafrost (permanently frozen soil, water and rock) melts. Locked up in the permafrost are large quantities of carbon (which could be released to the atmosphere as carbon dioxide gas) and, particularly worrying, given its potency as a greenhouse gas, methane. If the permafrost all melts (which apparently could happen within the next 100 years) then the addition of so much carbon dioxide and methane to the atmosphere could lead to an additional increase in global temperatures of 10 degrees Celsius. Put bluntly, that would just about blast humans off the planet. Another key aspect of this issue is that it’s not a tap that can be turned on or off. If temperatures rise enough to melt all of the permafrost then the additional release of greenhouse gases will mean that there’s nothing that can be done to reverse the process. The only hope then is to try to limit the temperature increases that are already in the pipeline to prevent this runaway gas release from occuring. There’s a detailed article on this topic in New Scientist, Issue 2701 [28 March 2009] .
Power from seawater
A few weeks ago I wrote an entry about generation of electricity from the temperature differences that exist between seawater at the surface and at depth (OTEC) and it is common knowledge that it is feasible to generate power from waves, tidal currents or tidal water level changes. However, it is less well known – by which I mean that I had never ever heard of the idea – that it is possible to generate power from the difference in salt content between freshwater and typical seawater. An article in New Scientist, Issue 2697 (28 February 2009) introduces this idea, the basis of which is some kind of cell in which freshwater and seawater are separated by a special membrane. There are two ways that this arrangement could then lead to the generation of electricity depending on the set-up and the membrane used. First, the process of osmosis (in which water moves from a weak solution to a strong one across a semi-permeable membrane) can lead to water molecules from the freshwater side crossing the membrane into the seawater and thereby causing an increase in its pressure that can drive the water through a turbine. Alternatively, a more complex arrangements of membranes can be created that allows the salt ions to move in different directions (e.g. positively-charged sodium ions one way, negatively-charged chloride ions another way) so that the positive and negatively charged ions move towards a cathode and an anode respectively producing a voltage across the cell (basically a big battery). There are plans for a prototype power plant to be up and running soon but it does seem that this technology would only ever be a minor/local player in global power generation (despite figures that suggest it could provide 40% of the world’s electricity demands), especially as any such power plants could only ever be cited in regions where this is ample supply of both seawater and freshwater – namely large estuarine systems that are almost always both environmentally sensitive and quite highly developed already.
