Archive for August, 2012

If Global Warming is happening, when will I be able to notice?

August 27, 2012
Probability of June, July and August average temperature anomalies in Moscow, Russia since 1950. This image shows that the average temperature in Moscow for summer 2010 was significantly hotter than in any year since 1950. Credit: Claudia Tebaldi and Remik Ziemlinksi.

Probability of June, July and August average temperature anomalies in Moscow, Russia since 1950. This image shows that the average temperature in Moscow for summer 2010 was significantly hotter than in any year since 1950. Credit: Claudia Tebaldi and Remik Ziemlinksi. From Climate Central

What Is The Climate? A Science Song by Tom Glazer

Climate Change is slow on the scale of a human lifetime, and small in comparison with day-to-day and season-to-season variability. A change of average summer temperatures by 1 °C over 10 years is small compared to a day-to-day variability of typically ±5 °C in the course of a typical summer.

So we rely on meteorologist, and climatologists and statisticians to tell us when ‘something is happening’. However many people are understandably sceptical of the opinion of ‘experts’. In many areas – for example in the field of human nutrition – expert opinion is fickle and changeable. So at what point can we expect to be able to make up our own minds using our own senses?

That is the question addressed by James Hansen in a paper (Perception of climate change: pdf: open access) published by the National Academy of Science (of the United States of America).The paper considers extremes of weather and in particular, hot summer events in the Northern Hemisphere. I am not sure that the paper completely answers the question it sets out to answer, but nonetheless is it is very readable.

The conclusion of the paper is shocking. Compared with a reference period from 1950 to 1980, extremely hot summers in the Northern Hemisphere land area are now more than ten times as common. In a typical recent summer, these anomalous conditions now exist over 10% of the Northern Hemisphere land area, compared with a few tenths of a percent in the reference period.

Hansen concludes that these events (e.g. the current US drought , the Russian heatwave in 2010) are now so commonplace that they can they can definitely be said to be due to a changed climate. The extreme summer events arise not just from the warming trend, but also an increase in climate variability – essential extreme weather – compared to the locally-expected average weather. NASA have prepared a nice animation here.

Hansen is clearly convinced, and he convinces me. But other aspects of the changed climate conspire against the perception of change. For example if cold dry winters are replaced by not-so-cold but snowy winters, then people perceive those as being ‘worse’, even if the actual temperatures are higher.

Hansen is addressing this issue for a reason. It is not until the majority of people in a democracy become personally convinced that the Climate really is changing, that it will become inevitable that politicians will do something. Reducing greenhouse emissions – mainly carbon dioxide – is not fun for anyone. But if the US loses a significant fraction of its corn crop for more than a year or two in a row, then even the denialists and contrarians may think again.

Correlation and Causation

August 20, 2012

Estimate of the annual and decadal land surface temperature from the Berkeley Earth average (black line) , compared to a linear combination of volcanic sulfate emissions and the natural logarithm of CO2 (red line). It is observed that the large negative excursions in the early temperature records are likely to be explained by exceptional volcanic activity at this time. Similarly, the upward trend is likely to be an indication of anthropogenic changes. The grey area is the 95% confidence interval.

‘Your Majesty, during the course of a long academic career, I have observed that I can become inebriated by imbibing scotch & soda, brandy & soda, and gin & soda, but I have not concluded that soda is intoxicating.’

Thus Sir Edward Appleton explained to the King of Norway that correlation did not prove causation. It is a fair point, and is the main cause of criticism amongst Climate Sceptics of a recent paper from the Berkeley Earth Surface Temperature team.

Their novel analysis of the surface temperature records basically agrees with the other three estimates and confirms that the Earth appears to be warming by around 2.5 °C per century. In their latest paper, they go further, and assert that this warming can be explained as the sum of just two effects:

  • a warming effect associated with anthropogenic emissions of carbon dioxide, and
  • a periodic cooling caused by volcanic emissions.

Their analysis is admirably simple, but is not based on a physical model: they just tried different mathematical functions and found that these ones matched the data. In other words they are a reporting a correlation and using this as evidence for causation. This was too much for Berkeley team member Judith Curry, who refused to have her name on this paper:

If determining attribution is as simple as comparing a couple of curves, why is everybody else wasting their time with sophisticated modelling and analyses?

In this case I am with Judith Curry and Sir Edward Appleton. Despite the neatness of the fit, without a physical model to explain why the fit works, this is nothing more than an interesting coincidence.

However, if the Berkeley team had bothered to try, they could have run numerical models and compared their record with the predictions of models based on real physics. They just chose not to do that. This kind of weakness may be one of the reasons that none of the groups five papers have yet passed through the peer review process.


The same data as shown at the head of the article, but now showing data averaged over one year rather than over a decade. This shows the way in which the effect of named volcanoes has been modelled.

A message from Mars

August 12, 2012
Curiosity on Mars looking at the rim of Gale Crater

Curiosity on Mars looking at the rim of Gale Crater. Picture from NASA.

The pictures from Mars take my breath away. I am lost for words to describe the bravado and brilliance of the engineers and scientists who placed this robotic laboratory so gently onto the surface of Mars.

NASA should be very proud. Americans should be proud too: they paid for it -around $10 per head. And we should all reflect on just what human beings can achieve when we put our minds to something.

The brilliantly-conceived mission has revived talk about a possible manned mission to Mars. And I have even heard people talk again about the possibility of colonising the Moon or Mars. While such extrapolations are understandable I think it is important  to understand that human beings cannot live anywhere except planet Earth.

This is not fundamentally true. It is conceivable that we could create ‘bubbles’ of survivability far distant from the Earth. Overlooking the many challenges (e.g. the increased radiation doses; the atrophy of muscles in reduced gravity; and the creation of a stable microbial population etc.), I will concede that it  is possible that we could create ‘bio domes’ in which relatively large groups could live for extended periods away from the surface of Earth. But there is one problem that any colonists will not easily overcome: energy.

Curiosity is nuclear-powered which will allow it to operate through the Martian winter and at night when solar power is weak. Our putative colony might be nuclear-powered too, but for how long? Let’s say (optimistically) that the initial colonists brought with them enough nuclear power to last a century. In that century the colonists would undoubtedly achieve great things. But after the nuclear power station was shut down, what would they do? It is unlikely that a colony could develop the capability to build and fuel a new nuclear power station in just a century. Even if they struck oil on Mars – and refined hydrocarbons flowed easily from the rock – they would be of little use because there is no oxygen in the atmosphere with which to burn the fuel. Ultimately, the colonist’s engineers would find that the only sustainable method of generating energy was solar power.

Back on planet Earth we are in a similar position to our putative Mars colonists. Using fossil fuels we have achieved great things. But our use of fossil fuels is now affecting the flow of energy on and off the planet. Worryingly, the evidence that this is happening is becoming irrefutable. We could use nuclear power for a century or two. But if we want to replace all current energy use with a sustainable source then we have no choice: we need to capture 0.01% of the solar energy which reaches Earth’s surface. Yes. We need just one ten-thousandth part of the 123 000 000 000 000 000 watts of solar energy that constantly warms the Earth’s surface.

Earth is a ‘bio-dome’ driven by solar power. The flow of energy on and off our planet allows plants to thrive – and they provide us with the food and resources we need to live from day-to-day. It is the only place in the Universe where humans can live sustainably. If we want to avoid disturbing the climate that creates this home to which we are uniquely adapted, then we need a truly sustainable energy source. And there is only one

If our planet’s engineers and scientists can put the Curiosity rover onto Mars, and if taxpayers can fund this noble mission, then surely we can collectively decide to live sustainably on Earth and ask our scientists and engineers to make it possible. Can’t we?


Earth. The only place in the Universe in which human beings can live. But can we live here sustainably? Picture from Apollo 17 courtesy of NASA.

Back to reality

August 9, 2012
View from VIlla Monastero to Villa Cipressi in Varenna. This postcard view is one of a thousand which assaulted me at every turn.

View from VIlla Monastero to Villa Cipressi in Varenna. This postcard view is one of a thousand which assaulted me at every turn. Click to view all the pixels my iPhone can muster.

Friends, I have returned to reality (a.k.a. Teddington) from the earthly paradise of Varenna where I gave a presentation at the Enrico Fermi Summer School on Metrology. I arrived in Varenna with my head still buzzing with things I should be doing back at NPL. But after spending a few hours writing my presentation I began to calm down. And 24 hours later – after a few more hours on my presentation – I had slowed down to match the pace of the school. And then I began to learn things…

Talking with colleagues from metrology institutes around the world:  from Australia to South Africa and, from Kenya to Belarus, I was reminded of just how much metrology matters. It matters not just at the level of parts per million of fundamental constants – the focus of much of my own work. But even in developing countries – it matters that people calibrate instruments which deliver doses of radiation in cancer treatment. At all levels, measuring things accurately brings benefits

And over the next few days, the talks reminded me of areas of ignorance of which I had been previously unaware.

  • Steve Choquette from the American National Institute for Standards and Technology (NIST), told us about the desperate need for improved standards in biotechnology – particularly in the identification of cells.
  • Michael Stock from the International Bureau of Weights and Measures (BIPM) told us about the latest results from Watt Balance experiments around the world. These experiments aim to replace the unique kilogram artefact – currently the basis of every measurement of weight or mass made on planet Earth – with a phenomenon that could in principle be reproduced by anyone.
  • Patrizia Tavella from the Italian National Measurement Institute (INRIM) told us exactly how clocks from different measurement institutes are harmonised at the BIPM to create Universal Coordinated Time (UCT) – the time which we share around the world.

Varenna is every bit as beautiful as the pictures imply. And being in the presence of this transcendental beauty was constantly arresting – and imbued each moment and conversation with a numinous intensity. And perhaps it was because of this – in spite of having been invited there as an ‘expert’ – the talks intensified my own sense of profound personal ignorance.

This sense of my own ignorance – and of uncertainty about everything I think I know – is very familiar to me. And I was reminded of it again recently while reading the excellent Atmospheric Turbulence: A molecular dynamics perspective by Adrian Tuck. At the end of the book – after many technical chapters – is a chapter of quotations, of which the following quotation struck me as being profoundly true:

To be uncertain is to be uncomfortable, but to be certain is to be ridiculous.

The quotation is from Arthur Holmes (quoting Goethe) on receiving the Wollaston Medal of the Geological Society for dating the origin of the Earth via isotope ratio measurements. It is a paradox and a truth that in order to obtain the most certain results, one must concentrate with all one’s energy on the areas of which one is most uncertain. It is most definitely uncomfortable – but I will always choose that over the alternative


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