July 2, 2017

SI Units

Welcome to the Interregnum.

At midnight on the 30th June 2017 the world stepped over the threshold into a new domain of metrology.

It is now too late to ever measure the Boltzmann constant or the Planck constant 😦

What do you mean?

Measuring is the process of comparing one thing – the thing you are trying to measure – with a standard, or combination of standards.

So when we measure a speed, we are comparing the speed of an object with the speed of “one metre per one second”.

  • The Boltzmann constant tells us (amongst other things) the amount of energy that a gas molecule possesses at a particular temperature.
  • The Planck constant tells us (amongst other things) the quantum mechanical wavelength of a particle travelling with a steady speed.

To measure these constants we need to make comparisons against our measurement standards of metres, seconds, kilograms and kelvins.


But actually we think that quantities such as the Planck constant are really more constant than any human-conceived standard. That’s why we call them ‘constants’!

And so it seems a bit ‘cart-before-horse’ to compare these ‘truly-constant’ quantities to our inevitably-imperfect ‘human standards’.

Over the last few decades it has become apparent that it would make much more sense if we reversed the direction of comparison.

In this new conception of measurement standards, we would base the length of a metre, the mass of kilogram etc. on these truly constant quantities.

And that is what we are doing.

Over the last decade or so, metrologists world-wide have made intense efforts to make the most accurate measurements of these constants in terms of the current definitions of units embodied in the International System of Measurement, the SI.

On July 1st 2017, we entered a transition period – an interregnum – in which scientists will analyse these results.

The analysis is complicated and so for practical reasons, even if new and improved measurements were made, they would not be considered.

If the results are satisfactory the General Conference on Weights and Measures, a high-powered diplomatic meeting, will approve them. And on May 20th 2019 the world will switch to a new system of measurement.

This will be a system of measurement which is scaled to constants of nature that we see around us.

And afterwards?

The value of seven ‘natural constants’ including the Boltzmann Constant and the Planck Constant will be fixed.

So previously people placed known masses onto special ‘Kibble balances’ and made an estimate of the Planck constant.

By ‘known masses’ we mean  masses that had been compared (directly or indirectly) with the mass of the International Prototype of the Kilogram.

After 20th May 2019, people carrying out the same experiment will already know the value of the Planck constant: we will build our system of measurement on that value.

And so the results of the same experiment will result in an estimate for the mass of object on the Kibble balance.

What difference will it make?

At the point of the switch-over it will make no difference what so ever.

Which begs the question:Why are you doing this?”

The reason is that these unit definitions form the foundations for measurements in every branch of every science.

And the foundations of every complex structure – be it a building or the system of units – needs occasional maintenance.

Such work is often expensive and afterwards there is nothing to show except confidence that the structure will not subside or crack. And that is the aim of this change.

The advances in measurement science over the last century have been staggering. And key developments would have been inconceivable even a few decades before they were made.

Similarly we anticipate that over future centuries  measurement science will continue to improve, presumably in ways that we cannot yet conceive.

By building the most stable foundations of which we can conceive, we are making sure that – to the very best of our ability – scientific advances will not be hindered by drifts or inconsistency in the system of units used to report the results of experiments.


What is Life?

June 28, 2017
Royal Trinity Hospice

A pond in the garden of the Royal Trinity Hospice.

On Monday, my good friend Paula Chandler died.

It seems shocking to me that I can even type those words.

She had cancer, and was in a hospice, and her passing was no surprise to her or those who loved her. But it was, and still is, a terrible shock.

It is unthinkable to me that we will never converse again.

How can someone be alive and completely self-aware and witty on Saturday; exchanging texts on Sunday evening; and then simply gone on Monday morning?

Her body was still there, but the essential spark that anyone would recognise as being ‘Paula’, was gone.

As I sat in the garden of the Royal Trinity Hospice, I reflected on a number of things.

And surrounded by teeming beautiful life, the question of “What is Life?” came to my mind. Paula would have been interested in this question.

What is life?

In particular I tried to recall the details of the eponymous book by Addy Pross.

In honesty I can’t recommend the book because it singularly fails to answer the question it sets itself.

In the same way that a book called “How to become rich” might provide an answer for the author but not the reader, so Addy Pross’s book was probably valuable for Addy Pross as he tried to clarify his thoughts. And to that extent the book is worth reading.

Life is ubiquitous on Earth, and after surveying previous authors’ reflections, Addy Pross focuses the question of “What is Life?” at one specific place: the interface between chemistry and biology:

  • In chemistry, reactions run their course blindly and become exhausted.
  • In biology, chemistry seeks out energy sources to maintain what Addy Pross calls a dynamic, kinetic stability.

So how does chemistry ‘become’ biology?

In the same way that a spinning top is stable as long as it spins. Or a vortex persists in a flowing fluid. Similarly life seems to be a set of chemical reactions which exhibit an ability to ‘keep themselves going’.

What is life?

Re-naming ‘life’ as ‘dynamic kinetic stability’ does not seem to me to be particularly satisfactory.

It doesn’t explain how or why things spontaneously acquire dynamic kinetic stability any more than saying something is alive explains its aliveness.

I do expect that one day someone will answer the question of “What is Life?” in a meaningful technical way.

But for now, as I think about Paula, and the shocking disappearance of her unique dynamic kinetic stability, I am simply lost for words.

Measuring the Boltzmann constant for the last time

June 27, 2017
BIPM gardens

The gardens of the International Bureau of Weights and Measures (BIPM) in Paris

If you were thinking of measuring the Boltzmann constant, you had better hurry up.

If your research paper reporting your result is not accepted for publication by the end of this Friday 30th June 2017 then you are out of time.

As I write this on the morning of Tuesday 27th June 2017, there are four days to go and one very significant measurement has yet to be published.

UPDATE: It’s arrived! See the end of the article for details

What’s going on?

The Boltzmann constant is the conversion factor between mechanical energy and temperature.

Setting to one side my compulsion to scientific exactitude, the Boltzmann constant tells us how many joules of energy we must give to a molecule in order to increase its temperature by one kelvin (or one degree Celsius).

At the moment we measure temperatures in terms of other temperatures: we measure how much hotter or colder something is than a special temperature called the Triple Point of Water.

And energy is measured quite separately in joules.

From May 2019 the world’s metrologists plan to change this. We plan to use our best estimate of the Boltzmann constant to define temperature in terms of the energy of molecules.

This represents a fundamental change in our conception of the unit of temperature and of what we mean by ‘one degree’.

In my view, it is a change which is long overdue.

How will this changeover be made?

For the last decade or so, research teams from different countries have been making measurements of the Boltzmann constant.

The aim has been to make measurements with low measurement uncertainty.

Establishing a robust estimate of the measurement uncertainty is difficult and time-consuming.

It involves considering every part of an experiment and then asking two questions. Firstly:

  • “How wrong could this part of the experiment be?”

and secondly:

  • “What effect could this have on the final estimate of the Boltzmann constant?”

Typically working out the effect of one part of an experiment on the overall estimate of the Boltzmann constant might involve auxiliary experiments that may themselves take years.

Finally one constructs a big table (or spreadsheet) in which one adds up all the possible sources of uncertainty to produce an overall uncertainty estimate.

Every four years, a committee of experts called CODATA critically reviews all the published estimates of fundamental constants made in the last four years and comes up with a set of recommended values.

The CODATA recommendations are a ‘weighted’ average of the published data giving more weight to estimates which have a low measurement uncertainty.

In order to make their consensus estimate of the value of the Boltzmann constant in good time for the redefinition of the kelvin in 2019, CODATA set a deadline of 1st July 2017 – this coming Saturday.

Only papers which have been accepted for publication – i.e. submitted and refereed by that date will be considered.

After this date, a new measurement of the link between temperature and molecular energy will be reflected as a change in our temperature scale, not a change in the Boltzmann constant, which will be fixed forever.

The NPL Boltzmann constant estimate.

Professionally and personally, I have spent a decent fraction of the last 10 years working on an estimate of the Boltzmann constant – the official NPL estimate.

To do this we worked out the energy of molecules in a two-step process.

  • We inferred the average speed of argon molecules held at the temperature of the triple point of water using precision measurements of the speed of sound in argon gas.
  • We then worked out the average mass of an argon atom from measurements of the isotopic composition of argon.

Bringing these results together we were able work out the kinetic energy of argon molecules at the temperature of the triple point of water.

When we published our Boltzmann constant estimate in 2013 we estimated that it had a fractional uncertainty of 0.7 parts per million.

Unfortunately it transpired that our estimate was just wrong. Colleagues from around the world helpfully highlighted my mistake. That led to a revised estimate in 2015 with a fractional uncertainty of 0.9 parts per million.

At the time I found this cripplingly humiliating, but as I look at it now, it seems like just a normal part of the scientific process.

The source of my error was in the estimate of the isotopic content of the argon gas we used in our experiment.

Since then I have worked with many colleagues inside and outside NPL to improve this part of the experiment.  And earlier this month we published our final NPL estimate of the Boltzmann constant with a fractional uncertainty of… 0.7 parts per million: back to where we were four years ago!

Our estimate is just one among many from laboratories in the USA, China, Japan, Spain, Italy, France, and Germany.

But at the moment (7:30 a.m. BST on 27th June 2017) the NPL-2017 estimate has the lowest uncertainty of any published value of the Boltzmann constant.

The NPL 2017 estimates of the Boltzmann constant is very close to CODATA's 2014 consensus estimate

The history of NPL’s recent estimates of the Boltzmann constant. The NPL 2017 estimate of the Boltzmann constant is close to CODATA’s 2014 consensus estimate

The LNE-CNAM Boltzmann constant estimate.

However my Frieval – i.e.friendly rival – Dr. Laurent Pitre from LNE-CNAM in France reported at meeting at BIPM last month that he had made an estimate of the Boltzmann constant with a fractional uncertainty of just 0.6 parts per million.

WOW! That’s right. 0.1 parts per million more accurate than the NPL estimate.

Dr. Pitre is a brilliant experimenter and if he has achieved this, I take my hat off to him.

But I have been looking daily at this page on the website of the journal Metrologia to see if his paper is there. But as I write – the paper has not yet been accepted for publication!

So after working on this project for 10 years I still don’t know if I will have made the most accurate measurement of the Boltzmann constant ever. Or only the second most accurate.

But I will know for sure in just 4 days time.


The article arrived this lunchtime

New Measurement of the Boltzmann Constant by acoustic thermometry in helium-4 gas

The paper reports a measurement of the Boltzmann Constant with a fractional uncertainty of just 0.6 parts per million.

The  measurements are similar in overall quality to those we published four years ago, but the French team made a crucial advance: they used helium for the measurements rather than argon.

Overall measurements are technically more difficult in helium gas than in the argon. These difficulties arise from the fact that helium isn’t a very dense gas and so microphones don’t work so well. Additionally the speed of sound is high – around three times higher than in argon.

But they have put in a lot of work to overcome these difficulties. And there are two rewards.

Their first reward is that by using a liquid helium ‘trap’ they can ensure exceptional gas purity. Their ‘trap’ is a device cooled to 4.2 degrees above absolute zero at which temperature every other gas solidifies. This has allowed them to obtain an exceptionally low uncertainty in the determination of the molar mass of the gas.

Their second reward is the most astounding. Critical uncertainties in the experiment originate with measurements of properties of helium gas, such as its compressibility or thermal conductivity.

For helium gas, these properties can be calculated from first principles more accurately than they can measured. Let me explain.

These calculations assume the known properties of a helium nucleus and that a helium atom has two electrons. Then everything is calculated assuming that the Schrödinger Equation describes the dynamics of the electrons and that electrons and the nucleus interact with each other using Coulomb’s law. That’s it!

  • First the basic properties of the helium atom are calculated.
  • Then the way electric fields affect the atom is calculated.
  • The the way two helium atoms interact is calculated.
  • And then the way the interaction of two helium atoms is affected if a third atom is nearby.
  • And so on

Finally, the numbers in the calculation are jiggled about a bit to see how wrong the calculation might be so that the uncertainty of the calculation can be estimated.

In this way, the physical properties of helium gas can be calculated more accurately than they can measured, and that is the reward that the French team could use to overcome some of their experimental difficulties.

Is it hotter than normal?

June 21, 2017

This map shows how the average of the maximum daily temperature in June varies across the UK.

It was hot last night. And hot today. But is this hotter than normal? Is this global warming?

Human beings have a remarkably poor perspective on such questions for two reasons.

  • Firstly we only experience the weather in a single place which may not be representative of a country or region. And certainly not the entire Earth!
  • And secondly, our memory of previous weather is poor. Can you remember whether last winter was warmer or colder than average?

Personally I thought last winter was cold. But it was not.

Another reason to love the Met Office.

The Met Office have created carefully written digests of past weather, with month-by-month summaries.

You can see their summaries here and use links from that page to chase historical month-by-month data for the UK as a whole, or for regions of the country.

Below I have extracted the last 12 months of temperature summaries. Was this what you remembered?

  • May 2017: UK mean temperature was 12.1 °C, which is 1.7 °C above the 1981-2010 long-term average, making it the second warmest May in a series from 1910 (behind 2008).
  • April 2017: UK mean temperature was 8.0 °C, which is 0.6 °C above the 1981-2010 long-term average.
  • March 2017 :UK mean temperature was 7.3 °C, which is 1.8 °C above the 1981-2010 long-term average, making it the joint fifth warmest March in a series since 1910.
  • February 2017: UK mean temperature was 5.3 °C, which is 1.6 °C above the 1981-2010 long-term average, making it the ninth warmest February in a series since 1910.
  • January 2017: UK mean temperature was 3.9 °C, which is 0.2 °C above the 1981-2010 long-term average. It was a cold month in the south-east but generally milder than average elsewhere.
  • December 2016: UK mean temperature was 5.9 °C, which is 2.0 °C above the 1981-2010 long-term average, and the eighth warmest December in a series from 1910.
  • November 2016: The UK mean temperature was 4.9 °C, which is 1.3 °C below the 1981-2010 long-term average.
  • October 2016: The UK mean temperature was 9.8 °C, which is 0.3 °C above the 1981-2010 long-term average.
  • September 2016: The UK mean temperature was 14.6 °C, which is 2.0 °C above the 1981-2010 long-term average, making it the equal second warmest September in a series from 1910.
  • August 2016: The UK mean temperature was 15.5 °C, which is 0.6 °C above the 1981-2010 long-term average.
  • July 2016: The UK mean temperature was 15.3 °C, which is 0.2 °C above the 1981-2010 long-term average.
  • June 2016: The UK mean temperature was 13.9 °C, which is 0.9 °C above the 1981-2010 long-term average.

So all but one month in the last year has been warmer than the 1981 to 2010 long term average. It is almost as if the whole country were warming up.

But UK mean temperature is not we feel. Often we remember single hot or cold days.

So I looked up the maximum June temperature recorded in England or Wales for every year of my life.

Each point on the graph below may have occurred for just a day, or for several days, and may have occurred in a different place. But it is broadly indicative of whether there were some ‘very hot days’ in June.

June Maximum Temperatures

The exceptional year of 1976 stands out in the data and in my memory: I was 16. And 2017 is the first June to come close to that year.

But something else stands out too.

  • From 1960 to 1993 – the years up until I was 34 – the maximum June temperature in England and Wales exceeded 30 °C just 6 times i.e. 18% of the years had a ‘very hot day in June’.
  • Since 2001 – the years from age 41 to my present 57 – there were 10 years in which the maximum June temperature in the England and Wales exceeded 30 °C i.e. 63% of the years had a ‘very hot day in June’.


  • From 1960 to 1993 there were 6 years when the maximum June temperature fell below 26 °C  i.e. 18% of the years didn’t have any very hot days.
  • Since 2001 the maximum June temperature in the England and Wales has always exceeded 26 °C.

Together these data tell us something about our climate – our average weather.

They tell us that weather such as we are experiencing now is normal. But it didn’t used to be: our climate – our average weather – has changed.

Is this global warming?

Broadly speaking, yes. In our new warming world, weather like we are experiencing now is likely to be become more common.

More technically, global warming is – obviously – global and requires the measurement of temperatures all around the world. It also refers to climate – the average weather – and not individual weather events. So…

  • The fact that this year we have had exceptionally hot days this June is not global warming: indeed 1976 was hotter!
  • But the fact that exceptionally hot days in June have become more common is a manifestation of global warming.

P.S. This Met Office page shows all the weather ‘records’ so you can check for when new ‘records’ are likely to be set.

Be kind

May 16, 2017


Dear Reader,

Last week I attended a lunchtime seminar on ‘Imposter Syndrome‘.

The specifications of the syndrome seem to be rather broadly drawn, but roughly speaking, it involves ‘successful people‘ who are ‘unable to internalise, or feel deserving of, their success‘.

The seminar leader had many good quotes, but somehow missed out the genre-defining Groucho Marx quote:


I should have felt more surprised that anyone turned up! But feeling persistent and unquenchable self-doubt is the ideal mental disposition for a person interested in precision metrology.

So it might not surprise you that the session was attended by some of the best scientists at NPL. At least, I think they are some of our best scientists. They might not feel the same way.


I came across the following tale from Neil Gaiman on Twitter.

“… Some years ago I was lucky enough to be invited to a gathering of great and good people: artists and scientists, writers and discoverers of things. And I felt that at any moment they would realise that I didn’t qualify to be there, among these people who had really done things.

On my second or third night there, I was standing at the back of the hall, while a musical entertainment happened, and I started talking to a very nice polite elderly gentleman about several things, including our shared first name. And then he pointed to the hall of people and said words to the effect of “ I just look at all these people and I think, what the heck am I doing here? They’ve made amazing things. I just went where I was sent.

And I said, “Yes, But you were the first man on the moon. I think that counts for something”

And so…

It is clear that “Imposter Syndrome” is a common cognitive bias in which people whom most people would consider to be “successful”, are unable to feel the positivity which we imagine would accompany such a designation.

Like most cognitive biases, this is something we can become aware of and transcend.

I am aware that I am ‘successful’. Indeed I am more “successful” than I ever aspired to be.

It would be invidious to list my own ‘successes’. Indeed, I put ‘successes’ in quotation marks, because what I think other people might imagine to be ‘my successes’ feel to me either like ‘good fortune‘ or ‘a narrow escape from failure‘.

I know I ought to feel successful. But that is not what I actually feel.

What I learn from this.

At the height of his Nobel-prize winning powers, Bob Dylan wrote:

There’s no success like failure, and failure’s no success at all

(Taken from the Book of Bob, Subterraneans, 19:65)

What I think his Bob’ness means by this is that the very idea of a person being “successful” is nonsense.

As we each travel the path from our birth to our death, to call people following one path ‘successful’ and people on other paths ‘failures’ would be bizarre.

Compassion for one’s fellow travellers should outweigh any illusion of success or failure.

And thinking of: my colleagues; acquaintances; the more senior and the more junior; the faster and the slower; women and men; even managers. And thinking of all their situations in life, and of how quickly our lives pass, I am reminded of another quotation:

Each person you meet is carrying a heavy load. Be kind. 

Perhaps this should read:

Each person you meet, even apparently successful people, may be carrying a heavy load. Be kind.

Wishing you every success.

With kind thoughts.


Reasons to be cheerful

May 6, 2017

My Grid GB 28 daysWhen everything feels rubbish, it is sometimes calming to remind oneself that progress in human affairs is possible.

Solar Energy in the UK!

Looking at the MyGrid GB site I notice that the longer brighter days are leading to significant solar power generation every day – the yellow in the figure above and below.

My Grid GB 48 hours

Over the last month, solar power has contributed more than 5% of the UK’s electricity supply. I find this truly astonishing.

The electricity comes from solar panels on people’s rooftops, and from large solar ‘farms’ – which can still be used to graze sheep!

It is clear that solar energy generation is well matched to the demand for electricity – peaking every day at around 1:00 p.m. BST.

Storing the energy

We could certainly generate two or three times as much solar energy as this with relatively low impact. But imagine how cool it would be if we could store some of that energy as it was generated, and then release it exactly when we most needed it.

Over the last year I have noticed that ‘energy storage’ has gone from being ‘a great thing if it existed‘ to ‘a reality on a small but ever-growing scale‘.

Here are five ideas I have seen recently. They don’t have much in common, but I am collecting them together simply to hearten myself.

One of the ideas pumps water as an energy storage medium, one compresses air, one uses ice, and another is just a big battery! And one is just a cool idea whose point I don’t quite understand!

Pumping Water

At the Dinorwig power station (earlier blog) water is pumped uphill at night and released at times of peak demand to generate electricity. Dinorwig stores approximately 10 GWh of energy with approximately 75% efficiency – enough to generate 1.8 GW of electricity for approximately 6 hours.

But sites such as Dinorwig are rare. What if the same trick could be done in a more mundane way?

Ars Technica describes a sweet idea in which 30 metre diameter concrete spheres – each containing a pump-generator set – would be placed deep underwater.

Positioned near a wind farm, wind-generated electricity could be used to pump water out of the sphere against the enormous head of a few hundred metres of water. When electricity was required, water could be let back in, generating electricity.

They report that each sphere could generate 5 MW for 4 hours. So a Dinorwig-scale installation would require 500 spheres – which would probably occupy about 1 square kilometre of sea bed.

German Undersea Spheres

Less practically, The Independent have a story describing an artificial island in the North Sea that could form a hub of a renewable energy facility.

NOrth Sea Island

I don’t quite know what the point of the island would be, but I love the sheer chutzpah of the proposal.

Compressing Air

Much more practically, the Hydrostor Terra company have a plan to store energy as compressed air in scale-able plants built by a lakeside.

Interestingly – and showing a reassuring contact with reality – they separately store and recover the heat generated  when the air is compressed. This is the key to getting a reasonable efficiency.

It would take perhaps a thousand of these systems to create a Dinorwig-scale storage facility. However, because the system is scale-able, small systems could be built and put into operation quickly, with the revenue being used to fund the creation of expanded storage over the coming decades.

This ‘scale-ability’ avoids the need for billions of pounds to be invested up front and is important for demonstrating new technologies.

Ice Batteries

In the here and now, I love this idea of power companies subsidising the purchase of equipment which will lower demand for electricity rather than simply building more capacity.

In this scheme, air conditioning plant is run off-peak to create a store of around 2 cubic metres of ice. The ice is then used to chill air at times of peak demand.

In a way this is really ‘demand management’ rather than ‘energy storage’, but it achieves the same effect.

Ice Storage

Tesla Batteries

And finally, the obvious idea of storing electricity in batteries! This story reports on an an actual real functioning 80 MWh storage facility in California that can deliver 20 MW of electricity for 4 hours.

It would take 120 of these installations to create a Dinorwig Scale facility, but because each unit can be built independently, it does not require investment at the same scale and risk as that required to build a Dinorwig.

Energy Storage has arrived

The problem of grid scale energy storage has many solutions, and they are available now using current engineering practices.

My hope is that the growth of energy storage will surprise me in the same way that the the growth of solar energy has suprised me.

I hope that one day soon I will look at the chart on MyGrid GB and see that the wind supply is smooth not spiky – and that solar power is supplying electricity after the sun has gone down!

How is knowledge lost?

April 20, 2017

At some point in the 1950’s the physics of the Greenhouse Effect was so uncontroversial in the United States that it was the subject of a children’s song. A really great song.

WARNING: This song contains a BANJO accompanimentWARNING

The song is on the You Tube link above and the lyrics are at the end of this article.

Written by folk-singer Tom Glazer, the lyrics show an excellent appreciation of the physics of the greenhouse effect.

After first describing how a greenhouse works, the song describes how the Earth is warmed by solar radiation

The atmosphere is like a greenhouse too
It lets most of the solar rays through
The surface of the Earth absorbs these rays
And re-radiates them as long heat rays

And then, in very sophisticated terms it describes the role of water vapour in the atmosphere

There’s vapour in the air, What does it do?
It doesn’t let the long heat rays pass through
Trapped by the vapour they bounce back and forth,
Re-radiated and re-absorbed

Did you read that?

re-radiated and re-absorbed

Tom Glazer is describing the basic physics of the MODTRAN model of atmospheric transmission! (Link).

Can you imagine a world where it is OK to say “re-radiated and re-absorbed” to primary school children?

Children who learned this song would have a better operational understanding of the physics of the greenhouse effect and global warming than a fair fraction of the population of this country or the USA!

But the terrible truth is that 60 years after it was written, this song and the knowledge it embodies has been lost to popular culture and become – apparently – controversial.

How did we lose this collective knowledge?


What does the glass of a Greenhouse do?
It lets the short solar rays pass through
The objects in the house absorb these rays
And re-radiate them as long heat rays

What does the glass of a Greenhouse do?
It doesn’t let the long heat rays pass through
Trapped by the glass they bounce back and forth,
Re-radiated and re-absorbed

Stay Stay, you long heat rays, Warm up the house on cold cold days
Stay Stay, you long heat rays, Warm up the house on coooooold cold days

The atmosphere is like a greenhouse too
It lets most of the solar rays through
The surface of the Earth absorbs these rays
And re-radiates them as long heat rays

There’s vapour in the air, What does it do?
It doesn’t let the long heat rays pass through
Trapped by the vapour they bounce back and forth,
Re-radiated and re-absorbed

Stay Stay, you long heat rays, Warm up the house on cold cold days
Stay Stay, you long heat rays, Warm up the Earth on cooooooold cold days

Weather Songs

Not everything is getting worse!

April 19, 2017

Carbon Intensity April 2017

Friends, I find it hard to believe, but I think I have found something happening in the world which is not bad. Who knew such things still happened?

The news comes from the fantastic web site MyGridGB which charts the development of electricity generation in the UK.

On the site I read that:

  • At lunchtime on Sunday 9th April 2017,  8 GW of solar power was generated.
  • On Friday all coal power stations in the UK were off.
  • On Saturday, strong winds and solar combined with low demand to briefly provide 73% of power.

All three of these facts fill me with hope. Just think:

  • 8 gigawatts of solar power. In the UK! IN APRIL!!!
  • And no coal generation at all!
  • And renewable energy providing 73% of our power!

Even a few years ago each of these facts would have been unthinkable!

And even more wonderfully: nobody noticed!

Of course, these were just transients, but they show we have the potential to generate electricity which has a significantly low carbon intensity.

Carbon Intensity is a measure of the amount of carbon dioxide emitted into the atmosphere for each unit (kWh) of electricity generated.

Wikipedia tells me that electricity generated from:

  • Coal has a carbon intensity of about 1.0 kg of CO2 per kWh
  • Gas has a carbon intensity of about 0.47 kg of CO2 per kWh
  • Biomass has a carbon intensity of about 0.23 kg of CO2 per kWh
  • Solar PV has a carbon intensity of about 0.05 kg of CO2 per kW
  • Nuclear has a carbon intensity of about 0.02 kg of CO2 per kWh
  • Wind has a carbon intensity of about 0.01 kg of CO2 per kWh

The graph at the head of the page shows that in April 2017 the generating mix in the UK has a carbon intensity of about 0.25 kg of CO2 per kWh.

MyGridGB’s mastermind is Andrew Crossland. On the site he has published a manifesto outlining a plan which would actually reduce our carbon intensity to less than 0.1 kg of CO2 per kWh.

What I like about the manifesto is that it is eminently doable.

And who knows? Perhaps we might actually do it?

Ahhhh. Thank you Andrew.

Even thinking that a good thing might still be possible makes me feel better.


25 years ago…

April 4, 2017

25 years ago, the atmospheric concentration of carbon dioxide was 350 ppm  – just 70 ppm higher than its pre-industrial concentration.

Oh yes. And I got married.

Objectively, I can describe this elapsed time as 9131 days. Or almost 789 million seconds.

And I can describe the way in which the atmospheric concentration of carbon dioxide has changed since then by more than 50 ppm.

And I can even describe the wonder of seeing two new human beings come into the world and evolve from being babies to being adults.

But subjectively, words fail me.

Version 2

But it is a fact that on this date, 25 years ago, friends and relatives gathered and supported Stephanie and myself as we got married.

And this post is just to say ‘Thank you’ to everyone who was there that day, and whose good wishes felt like a very tangible blessing. Our aim this year is to try to visit each of you. We have a list and you have been warned!

But whether you were there or not, I leave with you the Epithalamion written by my brother Sean and read by him at the wedding.

Epithalamion for Michael and Stephanie

Young people dance and drink a lot,
Draw close in metaphysical discussion,
Make light of commitments in making love
Celebrate the sadness of casual encounters,
Make art from them, and then repeat them.
Moments exhilarate; memory excruciates; the future’s a dream.
Years pass; what was painfully beautiful becomes untenable.
There comes time to move from testing the limits of resilience
To exploring the possibilities of permanence

Flitting is fine for adolescents and Peter Pan,
But now this woman is a woman, and this man a man.

Michael played guitar and sang a lot.
Went with women, but not a lot;
Sought the wrong thing in the wrong places,
And thus made the necessary errors;
Skirted sanity’s edge and touched insanity’s terrors.
I knew him as an orphaned six-year old; I have known
the need, and comfort of, his hand.
I have sought the warmth of his palm; welcomed his embrace;
Suffered the full force of his anger
— And see! Here I am unharmed.
And here is the baby I held in my arms
Become an adult who,
In looking for his mother, found a lover;
And in loving a lover, found a wife;
And, after a long search,
The needed even tenor of a stable life.

In seeking after women, he was never a Don Juan;
But now the child whose hand I held is become a man.

I don’t know Stephanie’s past;
However I strongly suspect
That happy women don’t jump from Aeroplanes;
And I know for a fact
That Ireland is the best
But least happy nation to stem from;
And that an uncertain constitution of your blood
Doesn’t do your humour any good.
This is not to carp, but just to establish
A youth that was below emotional perfection,
So that future adventures – this moment –
Might allow scope for improvement.
How sad, if all her relations, now full-stomached and dyspeptic,
Were also silently lamenting her deteriorating spirit,
Her vanished prospects,
The poor calibre of chap who’s landed in it!
To them I would say:
“The Chosen Path is the best!
And this is it!”

Today Stephanie puts on her Bridal Gown
To follow a dream that is her own.
Today good faith and trust may light hope’s flame;
She thus assumes perfection and a woman’s name.

Today is the ceremonial,
The tip of the huge and hidden thing to come;
The speckle and glass-glint of sun on the sea’s surface,
Eye-pleasing and transient, above depths that would terrify.
Today is about sex and the containment of sex;
About fear and the overcoming of fear;
About flesh and the fact flesh is fertile;
And the fact flesh decays;
And the fact flesh is human and lovely.
Today, too, is about family,
About what your Mother and Father do to you,
And for you;
It is about fertility and the bearing of children,
About the repetition of familiar things — and old errors;
The discovery of particular new joys,
New ways of two people meeting,
The miracle, perhaps, of new human beings.
Today is about what — what no ceremony could proclaim —
Informing the mundane with a proper focus,
With the laser intensity of life, and making it last;
About enlivening the drudge of living,
The dulling-ness of day to day.

It is about making do, and doing the best you can.
It is about Stephanie being a woman, and Michael a man.

If that’s all, then what’s the point?
Why are we here?
Why not reach for our revolver
And place it in our ear?
Because… because there’s more.
Today is about this…
We need each other;
We are nothing if connected to nothing.
Today we celebrate connectedness;
Cutting the crap we acknowledge love,
And the power of love to sustain.
And love is a light thing —
Not just the fleshly decaying ponderousness of sex,
But the shock of seeing, and then seeing afresh.
Today we dignify love,
Erecting a social carapace to protect it,
To allow it, in the private vision of two lovers.
We try to fix a hope — that love is not a flimsy.
Can such a light thing — love — though ever be strong enough?
All brides and all their grooms are optimists or fools.
But. Imagine egg-shell-skating carefulness; Consider how caution kills.
Let’s learn, and be thankful for the lessons of these optimistic fools;
Aristocrats of human risk, they let love open the future.
To feed hope’s flames, their noble folly’s fuel.

Come, then let us thank them; let us now applaud;
Today, this woman is a lady; and this man a lord.

Sean de Podesta , 1992

Global Warming: we were warned.

April 2, 2017

Human beings – including the one writing this – often find it hard to grasp the rates of processes involved in Global Warming.

When thinking about the physics, there are three important rates to consider.

  • The rate at which human emissions have taken place.
  • The rate at which the emissions affect Earth’s temperature.
  • The rate on which human emissions will dissipate.

But we also need to consider one other ‘rate’:

  • The rate at which humanity can respond to a warning after it has been given.

Let’s look at each of these ‘rates’ in turn:

Rate of Emissions

We are emitting carbon dioxide into the atmosphere at an astonishing rate: about 33 billions tonnes of carbon dioxide every year.

Humanity's Cumulative Emissions of Carbon Dioxide expressed in two ways. The left-hand axis shows the data as a fraction of the emissions. The right-hand axis shows the data as billions of tones (i.e. Gt) of carbon.

The graph above shows data from the Carbon Dioxide Information Analysis Centre. It shows humanity’s cumulative emissions of carbon dioxide expressed in two ways.

  • The left-hand axis shows the data as a fraction of the emission up to 2013 (100%)
  • The right-hand axis shows the data as billions of tonnes (i.e. Gt) of carbon. Multiply this number by 3.67 to convert it to billions of tonnes (i.e. Gt) of carbon dioxide.

From the graph we can see that:

  • 80% of the carbon dioxide we have put into the atmosphere has been put there in my lifetime. I am 57.
  • Although climate emissions have stabilised in the last three years, this only means that the slope of the graph has stopped increasing.
  • Continuing at the current rate, every 7 years we will emit carbon dioxide equivalent to the entirety of human emissions from the dawn of time to the date of my birth.

Climate Impact

Below is the estimate of the Earth’s average surface temperature made by the team at the NASA GISS laboratory. Alongside the data is a trend-line smoothed over a 10 year period.

The temperature rise is shown relative to the average temperature over the period 1951 to 1980.

Global Land Ocean 10 year smoothing

  • The graph shows that since 1980, the temperature trend has been rising roughly linearly at about 0.02 °C per year i.e. 0.2 °C per decade, or 2 °C per century.

Carbon absorption

The 33 billion tonnes of carbon dioxide we emit annually into the atmosphere corresponds to about 9 billion tonnes of carbon – these are the units used in the info-graphic below.


This image is from Wikipedia and was adapted from U.S. DOE, Biological and Environmental Research Information System. –, Public Domain, Link All the numbers are in billions of tonnes of carbon (Multiply by 3.7 to obtain the numbers in billions of tonnes of carbon dioxide). Figures in red are human emissions.

Natural processes remove about 2 billion tonnes of carbon from the atmosphere each year by dissolving it in sea water. And a further 3 billion tonnes of carbon a year is removed by increased plant growth.

If we stopped emitting carbon dioxide now, then these processes would the lower the carbon dioxide concentration in the atmosphere back to 1960’s levels in about 100 years.

As a consequence of these slow rates of removal, we are already committed to many decades of further warming at a rate similar to that which we are experiencing already.


  • The bulk of human emissions have occurred relatively recently.
  • We are now in an era when the Earth’s surface is definitely warming.
  • When we eventually take action we will still experience warming for many decades more.

But we have known all this for a long time: at least 36 years

The process which limits our rate of response. 

Arguably, the emergence of ‘popular’ appreciation of the effect of carbon dioxide emissions can be timed to 1981, when James Hansen and colleagues published a landmark paper in Science 

The paper is complex, but readable. But in case you are busy, here are some extracts.

A 2 °C global warming is exceeded in the 21st century in all the CO2 scenarios we considered, except no growth and coal phaseout.

This is happening now.

Floating polar sea ice responds rapidly to climate change. The 5 °C to 10 °C warming expected at high northern latitudes for doubled CO2 should open the North-west and North-east passages along the borders of the American and Eurasian continents. Preliminary experiments with sea ice models suggest that all the sea ice may melt in summer, but part of it would refreeze in winter. Even a partially ice-free Arctic will modify neighbouring continental climates.

This is happening now well before CO2 concentrations have doubled.

The global warming projected for the next century is of almost unprecedented magnitude. On the basis of our model calculations, we estimate it to be ~2.5°C for a scenario with slow energy growth and a mixture of nonfossil and fossil fuels. This would exceed the temperature during the altithermal (6000 years ago) and the previous (Eemian) interglacial period 125,000 years ago, and would approach the warmth of the Mesozoic, the age of dinosaurs.

This is happening now, but the warming is faster than the ‘worst case’ scenario they envisaged.

Political and economic forces affecting energy use and fuel choice make it unlikely that the CO2 issue will have a major impact on energy policies until convincing observations of the global warming are in hand.

How true! And even after the observations have become convincing, ‘political and economic forces‘ are still resisting a change in fuel use.

In light of historical evidence that it takes several decades to complete a major change in fuel use, this makes large climate change almost inevitable. However, the degree of warming will depend strongly on the energy growth rate and choice of fuels for the next century. Thus, CO2 effects on climate may make full exploitation of coal resources undesirable.

An appropriate strategy may be to encourage energy conservation and develop alternative energy sources, while using fossil fuels as necessary during the next few decades.

In retrospect, we could not have asked for a clearer or more accurate warning or better advice.

As I look at it now, the physical rates of processes make this problem really difficult

But it is our inability to respond to warnings which makes this potentially insoluble.

All the warnings above have come to pass: Let’s hope the paper’s warnings about sea level rise prove to be less accurate.

Danger of rapid sea level rise is posed by the West Antarctic ice sheet, which, unlike the land-based Greenland and East Antarctic ice sheets, is grounded below sea level, making it vulnerable to rapid disintegration and melting in case of general warming.

The summer temperature in its vicinity is about -5°C. If this temperature rises ~5°C, de-glaciation could be rapid, requiring a century or less and causing a sea level rise of 5 to 6 m (55). If the West Antarctic ice sheet melts on such a time scale, it will temporarily overwhelm any sea level change due to growth or decay of land-based ice-sheets. A sea level rise of 5 m would flood 25 percent of Louisiana and Florida, 10 percent of New Jersey, and many other lowlands throughout the world.

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