Archive for September, 2013

Weighing the perfect pumpkin

September 30, 2013
A 124 kg pumpkin and me.

A 124 kg pumpkin and me.

Every job has its ‘perks’. And being asked to help Andrew Hanson adjudicate at the weigh-in of the pumpkin competition of the Royal Paddocks Allotment Society in Hampton Wick is definitely a ‘perk’. It might even be an honour.

Normally we put the pumpkins into a large ‘IKEA’ bag and lift up the bag with two luggage scales – each capable of weighing 50 kg. We then add the results together to find the total weight.

This year we were faced with an unprecedented challenge which we met with a combination of new technology and ingenuity. The new technology was some 100 kg parcel scales with a remote readout. These were fantastic and very easy to use.

But we knew we had a problem when the first large pumpkin weighed in at 24 kg. Then the next two ‘biggies’ weighed in at 87 kg and 95 kg respectively. All this made it obvious that the ‘Great White Pumpkin’ was going to weigh more than 100 kg. We tried it, and sure enough, the scales overloaded and switched themselves off. So how could we weigh the ‘Great White’?

The pumpkin in teh wheelbarrow at the back weighed 25 kg. Teh two 'large' orange pumpkins weighed 85 and 95 kg. But how  could we weigh the big one?

The pumpkin just visible in the wheelbarrow at the back weighed a  very creditable 25 kg. The two ‘large’ orange pumpkins weighed 87 kg and 95 kg. The ‘Great White Pumpkin’ obviously weighed more than 100 kg But how could we weigh it?

The solution was to combine the new parcel scales with the old luggage scales and team of expert lifters. We first manouevered ‘Moby kin’ onto the luggage scales in its large bag. We then slid an IKEA bag underneath and completed a belt around the beast’s underbelly with a camera strap. We then attached the luggage scale to the strap.

A carefully synchronised procedure was then implemented:

  • First the luggage scale was switched on, zeroed, and left unstressed on the top of the beast.
  • Then the expert lifting team raised ‘Moby kin’ off the scales allowing them to be zeroed
  • The team then lowered the weight onto the scales until the weight read approximately 90 kg.
  • Then two people gradually took the residual weight of the pumpkin with the luggage scales.
  • Then the two scale were read simultaneously, and the sum was our estimate for the weight of the pumpkin.

The uncertainty of measurement was larger than for the other pumpkins – probably around 2 kg –  but it was still pretty clear which pumpkin had won. And then we all had some tea and cake. All in all a very pleasant Sunday lunchtime.

How to weigh a large pumpkin.

How to weigh a large pumpkin.

Beethoven’s ninth: My first: A scientific analogy

September 28, 2013
The Royal Albert Hall

The Royal Albert Hall

Some years ago we made a family list of ‘things to do before the children grow up’.  This evening we headed off to the Royal Albert Hall to listen to Beethoven’s Ninth Symphony performed by the Royal Philharmonic Orchestra. And when we got home we ticked  ‘Attend a classical music concert’ off our list.

I was familiar with the work because my elder brother had a record of it and I had listened to it several times as a teenager. But watching it being performed was enormously more pleasurable in a way I find I hard to describe.

One feature of ‘attending a classical music concert’ is that for a brief while, you can’t do anything else. It thus creates a meditative arena within which one’s thoughts and anxieties flow and ebb with the music. And in this meditative state I reflected on the fact that what I heard was an orchestra, and not the sound of individual instruments.

Each of those musicians would probably have studied their instrument for at least 10 years – and probably twice that. Each one by themselves would probably be the best player of that instrument I had ever encountered! And yet the result of their virtuosity was not that we could hear them individually. Instead, we got to hear their collective creation – the sound of an orchestra.

And as I wondered how that must feel, I reflected that the situation was in some respects like a large scientific project. Highly-trained scientists add their skills and expertise together but while the overall work benefits from the attention to detail of each contributor, the individual components should not distract from the overall result.

For example, thousands of scientists are involved in work at CERN (at least 3000!) and every year hundreds of PhD students complete theses studying the behaviour of components of the experiments conducted there. But in the big performances – the particle discoveries for example – their work contributes only as a harmonious overtone to the overall result. And the ‘conductor’ and the principal ‘violin’ get to bathe in the fame and glory.

And I reflected that I particularly appreciated the self-effacement involved in both these activities – creating music and creating science. The musicians and scientists will generally not find great fame or wealth. But they do get to earn a living doing something they love. And then occasionally, they get to take part in something really big and grand and inspiring.

Is the IPCC report ‘News’?

September 27, 2013
For a couple of hours this was the headline at the BBC News Web Site. By the evening it was the fourth story after a 'Tax Break for Married Couples'.

For a couple of hours this was the headline at the BBC News Web Site. By the evening it was the fourth story after a ‘Tax Break for Married Couples’.

Why do I find myself unmoved by the release of the fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC)? Because despite the epic scale of the report, on my quick perusal of the summary, I see nothing ‘new’.

And the BBC seems to concur. Although it made the lead story on the BBC web site for a couple of hours, it was down to fourth position by the evening and made only the third story on the television news. At least it was ahead of the inane story about why ballet dancers don’t get dizzy. [Aside: since when was that considered ‘News’?].

One aspect of the news did make me smile. Because of the ‘pause’ in rise of the average air temperature above the land surfaces of the Earth, sceptics are now saying that our understanding of climate change must be fundamentally flawed. This made me smile because while the ‘temperature curve’ was rising the sceptics were arguing that the data could not be relied upon. Now that it has slowed down, the data is all of a sudden more trustworthy!

But levity aside  the report is grim. It reads like a list of battle casualties where new intelligence reveals that those previously listed as ‘missing in action’ are now confirmed as ‘fatalities’ or ‘injured’. The report list each casualty detailing our state of knowledge of the extent of their injury. I have included a couple of snippets below.

So the report is as clear as it can be, but it leaves one basic question unasked, and of course unanswered:

What are we going to do about all this?

Snippets

  • The atmospheric concentrations of carbon dioxide (CO2), methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years.

  • CO2 concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions.

  • The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification

  • Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence)

  • Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence). It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971.

  • Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years (medium confidence). 

  • The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence). Over the period 1901–2010, global mean sea level rose by 0.19 [0.17 to 0.21] m

Slow…Slow…Slow Slow… Quick

September 11, 2013
The Queensland University PItch Drop Experiment. The pitch has been 'dripping' out of the funnel for the last 83 years. So far only 9 drops have formed.

The University of Queensland PItch Drop Experiment. The pitch has been ‘dripping’ out of the funnel for the last 83 years. So far only 9 drops have formed.

In general human beings are unable to pay attention to things which don’t change: try looking at a wall if you want to see what I mean. Human beings are not fascinated by stasis, but by change.

However some changes are so rapid that we just don’t notice them. For example you are probably unaware of the rapid flickering of the screen on which you are reading this.

And some changes are so slow that we think: “Nothing’s happening”. But exactly what we mean by ‘slow’ depends on context and experience.

  • For a child “slow” could refer to a process taking longer than a few seconds.
  • For an adult “slow” might refer to changes taking place much longer periods of time – possibly even years.
  • For a geologist “slow” might refer to a process taking a million years.

In each case the changes are real, even though it can be almost physically painful to consider such slow rates of change.

And it is in this context that I would like to draw your attention to a fascinating experiment situated in the foyer of the Physics Department of the University of Queensland in Australia: It is called the ‘pitch drop’ experiment and it involves the flow of a near-solid sample of pitch – roughly speaking the ‘tar’ that we use in ‘tarmac’ roads.

In 1927 Professor Parnell heated a sample of pitch and poured it into a glass funnel with a sealed stem. Three years were allowed for the pitch to settle, and in 1930 the sealed stem was cut. From that date on the pitch has slowly dripped out of the funnel – so slowly that now, 83 years later, the ninth drop is only just fully formed.

There are three things I really like about this experiment:

  • The forces involved are constant, and there is no mystery at all as to what is happening, and what has happened.
  • The second is that although all the forces are all constant, the response is not. This is like many processes in nature, but it seems an especially apt analogy for climate change.
  • And finally the recent death of the experimental custodian, Professor John Mainstone shows that physical timescales pay no attention at all to human timescales.

Ocean Heat Content: How do you measure that?

September 11, 2013
Typical profiles of temperature and salinity measured as a function of depth by an ARGO probe.

Typical profiles of temperature and salinity measured as a function of depth by an ARGO probe. (From Wikipedia). Notice the interesting behaviour (called the thermocline) about 100 metres below the surface. Measurements such as this enable us to understand where heat is stored in the oceans.

Where does all the Sun’s energy go when it reaches Earth? We obviously need to be able to answer this question if we want to fully understand what is happening to Earth’s climate.

Because roughly two-thirds of the Earth’s surface is covered in water, we can make a first guess that the main effect of solar energy is to warm the oceans.

The mass of water in the oceans is 280 times larger than the mass of air in the atmosphere and so we can guess that the temperature of the atmosphere is then determined by exchange of heat with the oceans.

Of course it is all more complicated than I have implied. But even so, it is clear that one question that needs to be answered is this:

  • Is the amount of heat energy stored in the oceans changing?

To answer this we just need to measure the temperature of the oceans and see if the answer is changing.

We have a records of the temperature of the atmosphere above the land surfaces of the Earth that extend back over some parts of the globe for around 150 years. And we even have some records of the temperature of the atmosphere above the sea surfaces too. And through careful analysis we have been able to detect a temperature rise of about 1 °C over the last century or so.

However records of ocean temperature are much much poorer. In fact until the turn of the 21st Century – the measurements were really inadequate to detect changes in ocean temperature. The reason is that in order to detect changes one needs to measure the temperature of the entire column of water in the oceans. In lots of places. Over a long period. And one needs to make measurements very accurately.

The reason one needs measure the ocean temperature accurately is because of the contrasting properties of water and air.

  • Water is nearly a thousand times denser than air.
  • If you give equal amounts of energy to equal volumes of water and air, then if the air warms by one degree, then the water will warm by the less than one thousandth of a degree.

As a consequence, vast amounts of energy can be stored in the ocean without the temperature of the water rising  very much. I won’t go in to the fascinating details of this measurement covered in a recent paper, but simply tell you that  a solution to this problem now exists. and the answer is a network of more than 3000 ingenious ‘ARGO’ probes busy measuring the temperature of the ocean right now.

Schematic diagram of an ARGO probe

Schematic diagram of an ARGO probe

Each ARGO probe is fiendishly clever. Once deployed from a research vessel, the probe sinks to a depth of 100 metres, and waits for 10 days. It then adjusts its buoyancy to sink to 2000 metres depth and then ascends smoothly to the surface recording the pressure (from which the depth is deduced), the temperature and the salinity of the water. When it reaches the surfaces, it establishes a connection to one of a variety of satellites and sends its data back to base along with its location deduced by GPS. It then sinks to 100 metres depth again, drifts with the currents and repeats the whole exercise 10 days later.  It can keep going for 5 years or more.

Importantly the temperature probes are carefully calibrated so that their uncertainty of measurement is only 0.002 °C, and so even small changes in ocean temperature can be sensitively detected. Additionally the network of more than 3000 probes enables fair sampling over most of the world’s oceans. The data from the network is freely available and over the coming decades it is likely to reveal hitherto unmeasurable details about heat storage in the oceans.

Deployment Sites of Argo probes colour-coded by the country that deployed them. All the data is openly accessible.

Deployment Sites of Argo probes colour-coded by the country that deployed them. All the data is openly accessible.

And I take a personal lesson from the ARGO project too: just because something has always been done badly is no reason not to start doing it better. Or at least to try to.


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