Leap Seconds and Blue Moons

The phrase 'once in a blue moon' is commonly used to refer to something that doesn't happen very often. I have long assumed that the phrase originates from a second full moon occurring in a single calendar month, this is backed up by Wikipedia although why 'blue' should be the colour of this moon I don't really know. Wikipedia has a fairly convoluted explanation as to why this might be the case but it sounds a bit dubious to me. Craig Bohren, in his book 'Clouds in a Glass of Beer' seems pretty sceptical of the double full moon origin as well, describing an event witnessed in the 50's in Edinburgh in which an actual blue Moon and Sun were observed. This was analysed by Robert Wilson, a staff astronomer at the Royal Observatory, who concluded that the event was due to ash particles in the air originating from a wildfire in Canada. This is a far more rare event than the now commonly accepted double full moon, which occurs every two or three years.

Despite some dissention in the camp regarding the origination of the phrase, it seems fairly well accepted now that a 'blue moon' is the second full moon occuring in a calendar month. While this is at best only a moderately interesting fact, it does reveal something deeper about the way in which most of the world has decided to live. Our calendar and general method of timekeeping is, at the most rudimentary level, based upon the movements of the celestial bodies which make up our most local universe. The Earth spinning on its axis has given us the day, the Earth revolving around the Sun has given us our year and the Moon revolving around the Earth has defined the month, at least, that's the common explanation. The fact that we can see two full moons in a single calendar month every once in a while kind of undermines that explanation. If you have a particularly good grasp of celestial dynamics, you might realise that the Moon is revolving around the Earth at the same time that the Earth is revolving around the Sun. This means that, relative to the Earth, the Moon might be turning 12 times in a year, while relative to the Sun itself (or a distant star) it is turning more (13 times in fact). I'm in danger of a digression here so I'll leave that where it is and let you figure it out or google it if it's not obvious to you.

So... back to the original thread, if we can see two full moons in a single calendar month, even if only rarely, it should be fairly obvious that, even if the length of the month was originally tied to the rotation of the Moon, it isn't any more. As for where weeks, hours and minutes come from, I'm not even going to begin to try and address that. Although I will say that it's less than obvious (or even accepted) that our current system is optimal or natural in origin.

I'm bringing all this up because there is a formal proposal on the books, at the ITU (International Telecommunications Union) World Radiocommunication Conference next year to scrap the leap second. This ambiguously^* named unit of time is added (or occasionally subtracted) from our clocks and calendars on our behalf by various organisations around the world on a not-very-regular basis. I played a very small role in implementing one such unit of time when working at a telescope in the US. The prospect that this would bring the entire observatory system crashing down around us induced a mild state of panic but the transition was smooth in the end. A significant, ever-increasing, number of organisations that rely on precise timing go through similar contortions of their computer systems every time a leap second is implemented. No doubt bringing great stress to the workers at those organisations but remarkably little anxiety to the rest of the world.

The truth is that very few people have ever noticed, let alone worried about leap seconds. If you're not involved with satellite communications in some way (even tangentially) then I wouldn't be at all surprised if you weren't even aware that they existed. However, the proposal to scrap them still has some far-reaching implications. This might seem a bit dramatic, after all, do you really care if you are a second early or late? Even if you were a full 25 seconds late for a meeting (the cumulative total of all leap seconds since their inauguration in 1972), would anyone notice or care? There is a more philosophical point underlying this though - for the first time in history there are serious suggestions that we should cease to follow the motion of the Earth around the Sun and in its celestial path when setting our clocks.

The way in which we would define time, should the proposal be accepted, would likely rely upon atomic clocks, which are no less 'natural' as a timekeeper, although their nature is somewhat different and of a massively different scale to planetary orbits. This would be almost imperceptible for some time, at least a year or two, when we would inevitably become out of sync with our planetary orbit by a second or so. Give it a century or so and we might be a full minute behind our garden sundial.

This still seems like a fairly trifling matter, that is of course unless you're interested in increasing the length of time over which we consider human affairs. The Long Now Foundation has as its mission to 'creatively foster long-term thinking and responsibility in the framework of the next 10,000 years'. They are therefore understandably interested in how we keep time over long periods and are working to come up with a mechanical solution to that problem.

Personally, you may feel that we could let our clocks slip for a century or so before updating them with a full minute. After all, many of us cope with an hour more or less each time daylight savings is imposed upon us (to the chagrin of some). After all, as has been pointed out by the Long Now blog linked above, by the time it's really important, we may well have found a new, more accurate way of telling time. Possibilities abound when you think that far ahead, so why worry about it now?

The problem with this of course is that we need to define time accurately in some way. Even if you or I don't feel so in our day to day lives, an air traffic controller would probably have rather strong feelings about how precisely their systems are calibrated in time. The practical need for accurate timekeeping is undeniable.

Accepting the real practical need for precise time-keeping, is there a more philosophical angle? Certainly the National Measurement Office seems to thinks so; looking at the guest list for their recent meeting on a public dialogue about leap seconds reveals what must be one of the most varied audiences ever assembled.Representatives from national air traffic control services, navigational institutes and the National Physics Laboratory were in attendance, as were the British Bankers Association who likely had more financial than academic concerns that led to them being invited. There are those for whom the issue would be central to their work, although ultimately unlikely to change things too much, like the timekeeper for Big Ben, the British Horological Institute or the intriguingly named Worshipful Company of Clockmakers. Then there are those less involved in the technical implications of the leap second and more concerned with the human side of things, such as the Board of Deputies of British Jews, the British Muslim Forum and the Hindu Forum of Britain. In fact, there are only slightly more representatives invited from the technical and academic sector than from the loosely defined 'faith' sector.

Clearly, the way in which we track the passing of our days is seen as more than formal timekeeping but also something central to our humanity. I can appreciate this, there is a sense that we live our lives by a natural clock, that waking with the dawn and so on is how things should be. There is also a feeling of continuity in knowing that our ancestors were connected to a natural calendar, possibly more so than our current society. After all, the construction of Stonehenge may well indicate that we were using the Sun for our calendar thousands of years ago. The winter and summer solstices have been recognised as cultural events since ancient times, with the winter solstice likely setting the timing of our Christmas celebrations.

What is lacking from this ancient connection is any precision to our circadian rhythms, many experiments have been run to determine what the 'natural' length of the human day is and, while there have been a multitude of answers, the most conclusive would appear to be '24 hours or so'. Left to our own devices, without mobile phone alarm clocks, we tend to gravitate towards a regular schedule, rising and sleeping around the same time each day. However, this certainly will not be the exact same time each day. If you've had the discipline, good fortune, or whatever to rise whenever you feel like after waking naturally you probably found that this time varied by 15 minutes or so around a regular time. Maybe more on occasion, maybe less. If you're anything like me I doubt that you found this lack of precision in any way affected your day-to-day life.

Just as the occasional double full moon in a calendar month doesn't really affect you (and I'd be very surprised if more than 5% of the population even noticed it!) I suggest that measuring our civic timekeeping by an atomic clock rather than by the orbit of the Earth won't really affect anyone. Let those who need to worry about the precision of their computer systems and let the rest of us carry on regardless. I, for one, would be very happy if our society paid a little less attention to the clock on the wall, watch on our wrist and phone in our pocket. Measuring our days in ever-smaller chunks is vital when it comes to guiding aeroplanes and financial transactions, it is far less so when it comes to what time I should be waking up or be getting to work. After all, regardless of your actual beliefs, it is worth remembering that while God used to be in the details, that position has now been taken over by the Devil.

^*leap years are longer by a day than other years, leap seconds are the same length as a normal second

Who’s to Blame for our Changing Climate?

The term 'smoking gun' is often brought up in reference to climate change, a quick google search reveals that this phrase has been thrown around in climate circles at least for the last 20 years or so. Often, the 'smoking gun' is a reference to some single, unrefutable piece of evidence that might finally silence climate change deniers, such as the rising levels of CO₂ (e.g. by Julia Slingo, Chief Scientist of the Met Office). However, for most people carbon dioxide levels in the atmosphere are not particularly tangible while, for example, the floods afflicting the south-west of England last winter or the record summer seen in Austria and Slovenia are much more visible and closer to our everyday experiences. Attributing events like these to climate change is not always simple though; after extreme weather events there may be debate regarding whether the event (or the scale thereof) can be attributed to the effects of climate change; perhaps these might just be part of natural climate variability? Such discussions rarely result in any kind of satisfactory answer for the media and, I suspect, the general public. The reason for this is not, as commonly claimed, that a single event cannot possibly be attributed to any root cause (although this is largely true) but rather that natural climate variability and climate change are not separate. Any trend in overall climate variables (e.g. temperature) will underlie the natural variability and it is this that makes global warming so dangerous. It has been repeatedly said (largely as a joke) that an extra degree or two might make the weather in [insert country/state/county here] more bearable. However, this simplification of the global warming trend discounts the variation which has existed and would exist without any warming (or cooling) trend.

An increasing temperature moves climate variability with it.

In this image (taken from climatecommunication.org) you can see how temperatures vary around a central, average temperature^*. A shift in average temperature (which is what climate change/global warming implies) shifts the entire distribution to the right, i.e. towards hotter temperatures. That means that weather events that might exist in this portion of the plot...

  ... which were once the extreme end of the distribution, now become far more common. So attributing a weather event to climate change means that we are saying it falls in the red part of this inset plot, rather than the orange. We are not able to definitively do that. What we can do is measure the number of times that extreme events occur and see how that compares with our plot of variability. A new record temperature is bound to occur at some point, when a record temperature is reported as being a 1-in-1000 year event, that means we only expect a temperature that high to occur once every thousand years. If a temperature that high were to happen tomorrow, it is possible (likely even) that it was just random chance that it occurred when it did. However, if it happened again the month after, that looks a little suspicious. If we were to reach that temperature again in two years, then again in another 10, then we begin to cast real doubt on our definition of 1-in-1000 year event. Either our statistics and/or model were wrong in the first place, or the system has changed.

The evaluation of how often certain weather events should occur is a type of risk analysis. By analysing the number of times that events occur, we can say how likely they are to happen in the future. Given enough data, we can even say what the contributing factors to those events are. For example, the NHS and other medical institutions can evaluate the risk of developing lung cancer. Given data about the lifestyles of the people who do develop it, it is possible to draw correlations between factors such as smoking and the incidence of the disease. After further investigation it is possible to more firmly establish these links and therefore we can say that there are different risks of lung cancer for smokers vs non-smokers and what these risks are. The important thing to remember here is that these are probabilistic risks, we have all had a great aunt or other relative who smoked 80-a-day and lived to a ripe old age. At the same time, there are many unfortunate people who live exemplary, healthy lives, who will contract lung cancer nonetheless. These people represent the natural variability of this system, while the people who smoke have shifted the distribution of probability towards contracting lung cancer.

Having described this kind of analysis in perhaps too much detail, I can get to the point of this post - the study by Sophie Lewis and David Karoly, researchers at the University of Melbourne in the overwhelmingly appellated 'School of Earth Sciences and Australian Research Council Centre of Excellence for Climate System Science'. They have performed an analysis like that I've described for the extreme summer of 2013 in Australia. I'll link to the paper itself here, published in the journal Geophysical Review Letters, although I'm not sure about paywalls, etc. - apologies if it's not readily available to you.

Lewis and Karoly performed an extensive analysis using suites of models to determine exactly how likely the extreme heat seen in the summer of 2013 in Australia would be in the natural (no human contribution) course of events and then again with human contributions included. They extended this further to include the RCP8.5 emission scenario (covered in a previous blog here) running forward to 2020.

The Australian 'Angry Summer' of 2013 saw record-breaking temperatures on a daily, as well as seasonal basis with the all-time record holders for hottest day and hottest month occurring. By running large numbers ('ensembles') of climate models, some of which included human contributions to emissions and some which didn't, Lewis and Karoly were able to evaluate the probability that these contributions would result in such an extreme summer. In addition to their paper, the authors have published two blogs which sum up their findings very well here and here. Here they publish their plots which illustrate their findings that human contributions have increased the likelihood that the 'Angry Summer' would occur by a factor of five. The plots below show how models incorporating natural as well as anthropogenic contributions reveal dramatically increasing probabilities of raised temperatures when evaluated from 2006 onwards.

Probability distribution of average temperaturevariations across Australia in summer from observations (dashed line) and climate model simulations (solid line) for 1910-2005. The vertical lines mark the temperature departures for 1998 summer (the second hottest) and 2013 (the hottest) summer across Australia/ Lewis & Karoly

As above, but showing the shift in the probability distribution for 2006-2020 from climate model simulations including increasing greenhouse gases and other human influences on climate. Lewis & Karoly

It is worth digging into these results a bit, they are explained thoroughly by the authors in the paper and summarised well in their blog postings so I'm not going to repeat what they say. What is worth showing here is the spread of their model results. I think the plot below shows something that is often missing from statistical reports, climate or otherwise.

Australian annual temperature changes (relative to 1911-1940 average) for observations (dashed black) and model simulations with natural influences only (green) and with both human and natural influences (red). The grey plumes indicate the range of values simulated across nine global climate models used. Average Australian temperature anomalies are indicated for 2013 and the previous hottest year on record in 2005. David Karoly & Sophie Lewis

What this plot shows is not only the results from the various models (green showing climate variability arising from natural contributions only, red including human emission contributions) but also what the spread in those models looks like (in grey). This is very important as it is easy to see from the variation in observed temperatures that, for any given year, the red line and green line aren't really separated by more than we might expect from natural variations anyway. The grey spread of model results shows us that the green line, representing the 'natural' state, is now right on the edge of the feasible range predicted by our models. This means that we are now entering a period in which it is impossible (statistically) to account for current weather trends without incorporating the influence of human emissions. Australian Prime Minister Tony Abbott is fond of quoting the poet Dorothea Mackellar in her description of Australia as 'a land of droughts and flooding rains' in dismissing possible climate change. However, it has become completely untenable to ignore the changing climate in that country. Climate change deniers, who once might have charitably been called skeptics have descended into the realm of conspiracy theory. I won't link to any sites because I'd rather not give them any traffic but it is all too simple to search online (or simply look in the comments of legitimate blog posts) for climate change in Australia and find sites, no longer able to refute scientific findings, which now simply accuse scientists of falsifying data, proactively as well as retroactively.

One of the more legitimate plausible explanations for high temperatures in Australia is the El Niño Southern Oscillation (ENSO), which has been regularly linked to higher than average temperatures in the Pacific. It is true that the second hottest summer in Australia to date (1998) may well owe some of its heat to ENSO. However, 2013 was essentially an 'ENSO - neutral' year and so the record temperatures were almost certainly unaffected by it.

One last thing to mention about Australia's extreme climate (changing or not) is the absolutely phenomenal amount of rainfall experienced there in the last few years. In the two years preceding the 'Angry Summer' Australia was subject to exceptionally heavy rainfall, this time perhaps linked to an El Niño/La Niña event. While attributing this heavy rainfall to human influences is more muddled than with the record temperatures, I reiterate my earlier point that we can no longer take 'natural variability' in isolation from anthropogenic global warming. My main reason for bringing the rainfall is that I was struck by the fact that so much water fell on Australia in those two years that sea levels ceased to rise. Andrew Freedman blogs here in detail about this topic, the main gist being that the 3.2 mm/year sea level rise that has been observed for decades plateaued for an 18 month period correlating with the rains falling in Australia. The explanation posited in this study is that the particular geography of Australia prevented much of this water returning to the oceans on short timescales - therefore taking water from the oceans without returning it.

^*This is a bit simplified, this temperature distribution shows an essentially Gaussian distribution. There are good reasons why real temperature distributions might not be Gaussian but that's another story for another time... The general principle here will still stand.

Solar Panels and Tofu

Just a quick post today, it would be nice to pretend that I can contribute to this blog often and regularly but that's not always possible. Heard this neat story on Inside Science and so wanted to throw it up on the blog as it doesn't seem to have been very widely reported anywhere else.

Solar panels have, in theory at least, the potential to have a massive impact on our renewable energy consumption. While solar panel efficiencies have been climbing fairly steadily over the last few decades concerns have been raised regarding the toxic materials used in the manufacture of the solar cells. There are actually several areas in which the environmental impact of the life-cycle of solar panels may be less than ideal, as outlined here. However, the toxicity of some of the components (or materials used in the manufacture thereof..) seems to have been cause for widest concern, especially when it relates to the disposal of old solar panels.

There was good news on Wednesday for those of us who worry about such things when Jon Major of Liverpool University published a paper in Nature (link here, not sure about paywall access, etc). The paper claims that the toxic cadmium chloride used to 'activate' the solar cell (increasing the energy efficiency from less than 2% to more than 10%) can be simply and easily replaced with magnesium chloride, a compound typically used bath salts and in the manufacture of tofu.

Jon Major himself is quoted here as saying “The problem is cadmium telluride [sic]* itself is a highly toxic compound," Major said. "It’s been linked to genetic defect, and if it gets into the water supply, it can poison fish for generations.” The toxicology report for cadmium, which includes reports on cadmium chloride, makes for some fairly scary reading, detailing interstitial pneumonitis, diffuse alveolitis, fibrosis, increased lung weight, reduction in body weight, focal interstitial thickening, oedema, pulmonary haemorrhage and emphysema in rats exposed to cadmium chloride.

Not only is a reduction in the overall toxicity of the solar cell production process good news for the environment but, by using a naturally-occurring substance which will allow for a significant reduction in the costs of handling and disposal of materials, the overall cost of production will be brought down.

While there are still other environmental problems relating to the use of solar panels, including other toxic/hazardous materials, it is cheering to see that progress is being made. It is good to remember that many renewable energy sources are still in relatively early days as far as development is concerned. Ongoing research is constantly improving the methods and materials used in solar, wind and water power (not to mention fusion reactors).

A small aside I wanted to mention, having heard it reported recently (seems like a lot of my posts recently have been inspired by Radio 4, I'm clearly of a certain demographic these days!) is the rather strange legal situation home-owners might find themselves in in the UK. It is now fairly common for people to effectively lease their roof to a solar panel company in return for free electricity and installation of the solar panels, which remain the property of the company that market them. These sounds like a pretty good deal to begin with. However, there are rather harsh ramifications when it comes to re-mortgaging or selling the home, given that the solar panel company is now effectively a tenant on your roof! Certainly not a reason to not get some solar panels installed but good to be aware of.

*not sure if this is a typo/misquote or perhaps Jon Major simply mis-spoke, cadmium telluride is actually rather stable and not very soluble. Provided that it is disposed of correctly, it's pretty safe and, given the context I believe he meant cadmium chloride not telluride.

D-Day and the Met Office

If I were being glib (and I often am) then I might have titled this post 'How the Weather Won the War'. However, I find it hard to be glib about war, particularly World War II. Perhaps it's memories of my grandfather, who fought a role in the war that went far beyond the stories he told me as a child. More likely it is simply the staggering loss of life that I am now better able to comprehend. Certainly, I am sobered by the realisation that the work I now do may once have contributed to one of the most important battles ever fought.

If ever there was an example of high-pressure meteorology then it must have been the weather forecasts made by the chief meteorological officer for Operation Overlord, Group Captain James Stagg on and around June 4th 1944. Though, to see a picture of the guy, he looks like he could probably handle it. That steely glare was presumably captured at some other time than the 4th of June though when he wrote in his diary 'I am now getting rather stunned - it is all a nightmare'.

Stagg was responsible for advising Eisenhower when D-Day (variously referred to as the largest seaborne, the largest amphibious and the largest just plain old invasion of human history) would go ahead. The requirements placed upon Stagg were that the day be close to a full moon and that low tide be at or around dawn. So far, so good, a reasonable almanac and/or calendar would be able to supply that information. However, it was also necessary that winds be light, that conditions be no worse than slightly cloudy (30% coverage below 8,000 feet) and that visibility be more than three miles. These conditions are considerably harder to predict and forecasting them, particularly 70 years ago, is an error-prone business.

Sian Lloyd has written a great piece at the Huffington Post which lays out the order of events which came from James Stagg's predictions, including his advice that the operation not go ahead on the 5th, as planned. Instead, on the night of the 4th, Stagg told Eisenhower that there should be a break in the otherwise unsettled weather on the morning of the 6th. This break in the weather was not predicted by the Germans and so German intelligence had decided that a landing would be unlikely on that day.

It is likely that James Stagg would have known that the Germans failed to predict the break in the weather as he had access to observations coming from the Germans themselves. Weather reports originating from German U-boats were encoded by the Enigma machine and, thanks to the deciphering done by Bletchley Park these reports were now readable by Allied forces. An intriguing sidenote, given the meteorological theme here, is the vital role that weather reports played in the Allied capture and decoding of the Enigma code. It was Harry Hinsley, working at Bletchley Park, who reportedly realised that German weather trawlers must be able to decode Enigma messages and so must have code books aboard. This realisation led directly to the attack of one of these trawlers and the capture of a code book.

The fact that Group Captain Stagg had access to German weather reports may well have led directly to the success of the Normandy landings. However, it was weather coming from the west that was most crucial to the D-Day landing decision and so it certainly helped that an observation network was in place providing data from reconnaissance aircraft as well as ships at sea. While ships were supposedly restricted by a radio silence order, it has been speculated that weather reports were sent in via messenger pigeon. All of these observations contributed to the hand-drawn charts used at the time for forecasting. The chart from the day itself is available (upon request) at the Met Office library and is a remarkable piece of scientific history. Seeing the chart, which admittedly looks like almost any other synoptic chart, makes one feel the weight that history placed on that single sheet of paper. Not only that but the responsibility that those scientists that drew the chart bore for being absolutely correct in their determinations. Quite frankly, I think I would prefer the astronomical observations I'm more familiar with, I am unable to think of a single situation in which anyone's life has been placed at risk due to my mis-calibration of GBT data!

Weather charts from both the Allied and Axis forces for June 6th, 1944 are shown below. Note how the Allied chart contains observations covering Germany while the German chart contains none of Britain. The entire outcome of World War II may well have come down to the simple superiority of our knowledge about the weather.

Allied weather chart for 6th of June, 1944

Axis weather chart for 6th of June, 1944

There is a webpage hosted by the Met Office itself with some embedded videos which go into detail regarding the interpretation of the weather charts and what the contributing factors were at the time. If you are interested in some of the finer details of the meterology involved here then I advise you to go here.

I think it is worth pointing out the role that women meteorologists played in these predictions. Although there were no women forecasters until 1947 Wren meteorologists were stationed with the other navy staff at Portsmouth collectively responsible for drawing the D-Day planning charts and other work. It was often roles such as these chart-drawers and the 'Harvard Computers' that were 'allowed' to be filled by women and lay the groundwork for a future which includes female Lego scientists(!) While I have mainly focussed on James Stagg in my post, it should be remembered that there were other contributors to the forecasts that decided that the Normandy invasion should go ahead. They too, must have surely felt the gripping tension James Stagg did when he wrote 'Fair interval confirmed, invasion put on "Final and Irrevocable Decision". Whatever the outcome the decision is taken.'

The next possible window for the planned invasion was to be two weeks later, at the next suitable tides. Stagg later wrote to Eisenhower that, had the landing been delayed until that day, the troops would have met the worst weather in the region for 20 years. Eisenhower wrote back - 'Thanks, and thank the Gods of war we went when we did'.

Why the world cup will/won't be predicted by computer modelling.

You may have recently heard about attempts to predict the results of the upcoming World Cup in a scientific way. Although it's not mentioned explicitly the calculations by Stephen Hawking and Goldman-Sachs (GS) are the results of statistical modelling. Fortunately for me, this ties in well to a blog post I already wanted to write about just this subject.

The online betting company Paddy Power has employed Stephen Hawking for a month in order to calculate the probability that England will win the world cup. A more general aim of evaluating the overall outcome of the world cup has been undertaken by GS. I heard Peter Oppenheimer of GS interviewed last Thursday morning by John Humphrys and the interview in general was a really good example of the problems with the public perception of probability and statistics. The interview should be available for the next few days at least here and the bit I'm referring to was slightly before 7 am if you're trying to pinpoint it.

The interview consisted largely of Peter Oppenheimer explaining the details of their model, which include the past goal-scoring history of each team (as might be expected). Some more subtle analysis included the under- or over-performance of those teams at previous world cup tournaments as well as home vs away games. Hawking's analysis allowed for more intricate inputs, such as the height above sea level for the match. However, Hawking was approaching the problem from a different perspective, analysing the prospects of a single team, while GS were modelling the entire competition and the relative placings of every team.

  What I found particularly blog-worthy about the Radio 4 interview was the attitude of John Humphrys. Humphrys, along with his radio 4 compatriot Melvin Bragg are exceptionally intelligent men and yet they are often dismissive of vital aspects of the scientific method. I am dragging Bragg into this because I have heard several episodes of In Our Time which have a scientific theme in which he happily confesses his ignorance of maths and science to his guests. This disregard would be very poorly received if it related to a knowledge of British history, for example. However, numerical and scientific theorems do not appear to warrant the same level of esteem.

  I digress, in the interview Humphrys was incredulous of Oppenheimer's World Cup predictions. Notably he said something like 'I don't even follow football, yet I can probably tell you the four teams that will end up in the semi-finals' (apologies if this is horribly paraphrased, I am unable to listen to the interview again at the moment). Implying perhaps that the work by GS was worthless as it only told us something that could be guessed at by a layman anyway. There are two important points here. Firstly, I think that this misses the point entirely. The phrase that springs to mind is 'when you do something right, people won't be sure you've done anything at all' (if anyone can trace this quote back further than the Futurama link I've pasted please let me know!).  Humphrys statement actually shows us that there is really an intuitive element to probability which isn't always evident, especially when it comes to some of the more esoteric results of probability theory, such as the still-argued-over Monty Hall problem. If a layman can predict the four teams to reach the semi-finals of the World Cup 2014, why scoff at attempts to do the same thing in a numerical, analytical manner? Why does John think he can predict the semi-finalists? Because he is aware that Brazil, Germany, Argentina and Spain are probably the best teams in the world, even if he gained this awareness through osmosis, something very easy to do, at least in the UK. Why are these teams the best (or perceived to be so)? Because they win a lot, meaning that they have good, measurable goal scores and differences - exactly the kind of variable that is input into the GS model. Even I, as a complete football luddite, know that Brazil are extremely likely to beat the U.S. at 'soccer' (no offence U.S.). This is because I have been brought up with images of Pelé as the messiah of football while there's only a grudging willingness to acknowledge the participation of the U.S. in the same sport because, you know, at least they give it a go.

  The second point I want to make is that I think Humphrys misunderstands the language of probability that Oppenheimer is using. I think that this represents a fundamental lack of public understanding of probability. Scientists understand that very few hypothesis can ever truly be ruled out completely and so may appear vague or uncertain about their findings. This allows scientific theories to be cast as 'doubtful' when they are, in fact, remarkably certain.

  We (or at least John Humphrys) seem to have some inbuilt desire for our models to be 'deterministic', meaning that there will be an exact, predictable outcome. The alternative being presented by GS is for a 'probabilistic' result. The difference between these two interpretations is rather philosophical and so somewhat loosely defined, this is probably (heh) why it's not easily digested by the public at large. A glib explanation of this difference comes from the Terry Pratchett book 'The Colour of Magic' in which a character flips several coins. The deterministic philosophy would lead us to expect that half of the flips land on heads while half land on tails, in the book what happens is that four of the coins land on the coins' edge while another turns into a caterpillar. While it's unlikely that a probabilistic analysis of coin flipping could predict these outcomes, it may be able to account for a very slightly weighted coin, or perhaps a coin flipper who consistently puts the coin a particular way up before flipping. Either of these elements (and more) could contribute to the outcome of a coin flip being other than 50:50. This might actually be important to you if you really care about the outcome of 1,000 coin flips. Worse, you might care about the outcome of the World Cup, particularly where England are involved. That might mean you care about El Niño and its intensity this year, not because there's some spooky coincidence between that intensity and how well England perform but because a strong El Niño might make it hot and dry in Brazil during the competition, probably not a good thing for footballers who are used to playing in the cold and wet.

Our ability to model things like El Niño or, heaven forfend, the entire Earth climate, depend on things that have far more effect on outcomes than a slightly weighted coin or a sneaky flipper. They depend on things like knowing the sea temperature in the middle of the pacific and how exactly that temperature varies with the depth of the ocean. Even our best measurements of such quantities are subject to errors as banal as being mistyped by a sleepy meteorologist or as sophisticated as rounding error in a big-endian vs little-endian machine. These errors have the potential to grow and lead to larger and larger effects. When climate modelling reveals emergent properties that have large effects, such as hurricanes, it becomes vitally important that those properties are not being unduly amplified by errors in your inputs. For an excellent overview of how climate modelling works in just this context see Gavin Schmidt's TED talk, 'The Emergent Patterns of Climate Change'. Of course, when running models as complex as climate modelling, essentially trying to recreate the entire Earth system with computer simulations we have to bear in mind that 'garbage in = garbage out' and that if our measurements are not at least correct on average then our model is likely to be meaningless (though possibly still informative). Knowing that it is perfectly possible that errors do creep in though, enables us to be probabilistic about our analysis. For example, we want to be absolutely sure that, when we are looking at our climate model we are not looking at that tiny fraction of coin flips that land on the edge (or turn into a caterpillar). We can do this by running our climate models again and again and then analysing the results of all of the different simulations in a statistical way. It is for this reason that scientists cite a percentage likelihood that an event will occur. Rather than hedging their bets, they are simply telling you how many times a certain event will occur, given certain conditions. This may be seen as dodging the question but it is actually an attempt to be utterly transparent and honest about results.

The statistician George E.P. Box wrote that 'essentially, all models are wrong, but some are useful'. This summarises beautifully our inability to fully recreate complex systems in simulations, we can only extrapolate and interpret.

Something in the Air

A lot happens at the Met Office that goes largely unreported upon. For example, planting transmitters on seals to measure sea temperature might not be the first thing to cross your mind if you were asked what the Met Office actually does. As I listened to a talk this week about tracking the spread of atmospheric particles I realised that this was something else that would fall under this umbrella. Time for a blog post!

The talk was by the Atmospheric Dispersion and Quality (ADAQ) group who are responsible for some very interesting aspects of the MO services like supporting the emergency services in the event of civil contingencies like chemical fires, radioactive accidents, volcanic ash and animal and plant health. This is achieved through the use of NAME - the Nuclear Accident ModEl, one of the more outrageous examples of acronym abuse I've come across.

NAME was developed by the MO following the Chernobyl disaster in 1986 when weather conditions conspired to spread the released radioactive particles across Europe, including the Welsh hills. How exactly this happened can be seen in the model image below.

Since then, NAME has been through multiple iterations, capable of predicting the transport, dispersion and chemistry of atmospheric particles. If you're interested in the gritty (haha) details then I can tell you that it does this through the modelling of core atmospheric processes such as turbulence, deep convection, deposition & sedimentation^* and chemistry. If you want to know exactly how it does that then here would be a good place to start.

^*material removed from atmosphere by transport to, and uptake by the ground. Gravitational settling, rain 'washout' (material is brought down to ground by rain), rain absorption (precipitation forms around particles directly).

The latest generation of NAME is NAME III and this has been used extensively in recent times to track the effects of the Fukushima Daiichi nuclear disaster, the second event ever to reach the highest rating of 7 on the International Nuclear and Radiological Event Scale. Research into the health effects of the Fukushima disaster is ongoing, incorporating the results of NAME's model analysis.

NAME is supported by many tools which work over different scales, interesting in various ways. In order of increasing scale over which they function:

• PACRAM (Procedures And Communications in the event of a release of Radioactive Material) gives little information generally but the main priority is to be fast so as to advise emergency services, etc. on possible hazardous directions or areas to avoid in the event of a UK nuclear power plant event.

• RIMNET (not sure if this is a really convoluted acronym or just a name...) a Met Office-managed project in partnership with DECC and DEFRA. A country-wide network of gamma radiation detectors (isn't this a plot device from the Avengers?!) which allow the UK to monitor background radiation levels. All measurement and reference data is stored in the UK National Nuclear Database.
• Regional Specialized Meteorological Centers and the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) give the international radiological response. The CTBTO (actually a preparatory commission as the treaty is not yet law) are tasked with establishing and developing a worldwide network which monitors the planet for nuclear explosions. This network is reportedly 85 percent complete at the time of writing.

One of the more useful aspects of atmospheric modelling is that it can be run backwards to establish the source of an atmospheric feature. For example, if a non-reported nuclear event were to occur, this can be traced back to its source through inputting current observations into the NAME model.

This feature has proved particularly useful in disease control such as in the outbreak of  Legionnaires Disease in Edinburgh in 2012. Not only can the model predict the spread of airborne bacteria and so inform the public and authorities if certain areas are at particularly high risk but, once an infection has been found, the model can be run backwards to see where the bacteria might have originated from in the first place. Useful again in the case of animal and plant health. The Met Office has been researching the spread of Foot and Mouth Disease since the 1960s, again through the dispersion in the atmosphere of airborne particles originating from infected pigs.

There is more use to this than might be immediately obvious, vaccines are often limited in amount, especially in the case of a sudden outbreak. By identifying the likely spread of diseases, the vaccines can be distributed in a targeted way.

There are yet more applications of this technology and, to be honest, I wasn't particularly familiar with them before the talk. I'd heard of 'Ash dieback', apparently spread on the small scale (up to 10s of miles) by windborne spores but what has apparently been called the 'polio of wheat', UG99, is also the subject of Met Office research.

The front line of the climate change battle, as viewed from a safe distance…

Since starting to work for the Met Office I have been able to have a front row seat when some interesting new science is announced. Recently the Intergovernmental Panel on Climate Change (IPCC) released their fifth assessment report. This was reported pretty widely in the Guardian, the BBC and various other places and so I'm probably not bringing much to the table in talking about it now. However, the announcement and its content relates well to some of the wider themes I'm trying to explore in this blog and, as I'm experiencing some of the science first-hand I thought that I could write something worthwhile about it.

In case you want to go and read the original report, it is here. This is actually only one of four reports coming from each of three working groups and a synthesis report. The report I'm referring to is the WGI report which focusses on the physical science behind climate change and this is arguably the most important as it is this science which the other working groups build on. WGII concentrates on 'Impacts, Adaptation and Vulnerability' while WGIII takes on the problem of climate change mitigation.

The fact that the report exists at all (the IPCC AR5 WGI report to give it its full name) is amazing to me. The entire report is summarised in a trifling 14,000 word Summary for Policy Makers, in which every single sentence has been agreed upon by all 101 countries in attendance. Having spent literally months in meetings of five people simply trying to decide whether or not to buy a treadmill for the work gym I would be stunned if you told me that 101 countries had managed to agree on what time to have lunch.

One of the messages climate scientists are told to convey to the public is that there is an extremely strong consensus amongst scientists regarding the science behind climate change. I think that, if anyone truly still believes that human-driven climate change is a contentious subject, they should reflect on the fact that 101 countries could all agree on a report that unequivocally states that this is the case.

Not only does the report's existence refute the idea that intergovernmental bodies are unable to make any progress, it is also a remarkable testament to the power of peer review. In my last post I gave an example of peer review that shows how it can be a time-consuming, unsatisfactory process for all involved. That was for a paper involving only five authors and three referees. The WGI report involved 259 authors covering 14 main chapters utilising 1,089 reviewers who gave 54,677 comments.

The summary of the report, the Summary for Policy Makers, contains only robust science, agreed upon by all the attendees as well as the relevant scientists. I have it on good authority that there was less political motivation involved than might be expected. Certain oil-producing countries did apparently make every effort to stress the uncertainties inherent in the science of the report. However, while this is presumably politically/economically motivated, it can only lead to more robust findings. These findings have been boiled down to a single page (well, two sides) of the headlines which are kept here but, in case that still seems like a bit much, the climate scientist Professor Thomas Stocker has boiled these down to three main messages

• The evidence for climate change is unequivocal
• The role of human influence in climate change is clear
• The limiting of climate change will require substantial carbon reductions

If you're the kind of person who likes plots and can interpret them easily then this one should give you a fairly hefty amount of information.

  What this shows is how much warming we might expect (y-axis) as a function of how much CO₂ eventually ends up in the atmosphere (x-axis). This is presented for multiple potential scenarios referred to as 'RCP's. 'RCP' stands for Representative Concentration Pathway and relates the emission of greenhouse gases to the 'radiative forcing' that would result from that emission. There's a pretty good summary with all the detail you could probably ask for here but I'm going to leave 'radiative forcing' very loosely defined here as the difference between the heat energy received by the Earth (from the Sun) and the amount of energy radiated back into space. In a system in equilibrium this would be zero, with no overall warming or cooling resulting. We know that this value is not zero for the Earth at the present time and that is why it is warming. What the different trajectories followed by the different RCPs can tell us is what the eventual extent of the warming will be. The RCPs can also allow us to plan our emissions so as to take this into account. For example, the Copenhagen Accord (2009) stated that a temperature rise of 2°C or above would lead to 'dangerous climate change'. Of our four presented RCPs, the only one which would allow us to stay below a rise of 2°C (by the year 2100) is the RCP2.6. It is pretty much accepted that this is not going to happen. To follow RCP2.6 all man-made carbon emissions would have to cease today, a scenario I think we can all agree is unlikely (I apologise if this is hyperbole or a gross oversimplification, I am attempting to keep things non-technical and reasonably concise). Further, if you're sharp-eyed you may notice that the RCP2.6 pathway on the inlaid plot in the above figure goes into negative numbers meaning that, not only would carbon emissions have to decrease substantially, we would have to actually start removing carbon from the atmosphere via carbon capture or geoengineering. Scenarios which are now reportedly accepted by those within the UK government.

At the other extreme is RCP8.5 pathway, generally known as the 'business as usual' pathway. This is the scenario under which we continue to burn fossil fuels with absolutely no mitigation whatsoever. As you can see from the plot, this would lead to the Earth exceeding the 2°C milestone in something like 25 years. Whether we even have the resources to continue burning fossil fuels at our current rate for that long is a separate question but, as oil and gas become more scarce, they become more expensive leading to the techniques used to acquire them becoming more cost-effective, fracking being a case in point.

While it is somewhat unsettling to accept that climate change is now unavoidable, even at dangerous levels, I have found that scientists in the field are, if not upbeat, then at least somewhat positive. This positivity appears to be more of a recent development and it appears to be due to the fact that governments are actually listening these days. The fact that the IPCC AR5 reports even exist are a testament to that. At the Met Office I have been pointed towards five key components of our communications regarding climate change

1. Climate change is happening
2. This is largely due to us
3. Overall it will be bad
4. Scientists overwhelmingly agree on above
5. There are many things we can do about above and we're free to argue about what

It is this final point that I think is responsible for the trend towards positive attitudes in the climate science community. The government department responsible for energy is now also responsible for our actions on climate change and it is their mission to take action on this front. Their stated vision is for the UK to have made a safe and secure transition to a low carbon economy. Take that with as many pinches of salt as you wish but I believe that there is at least an attempt to take the issue seriously. I think that it also helps that the projected scenarios regarding climate change are veering away from the drastic and towards the affordable. While accepting some warming and slowly weaning ourselves away from fossil fuels is not the ideal solution for many people, it is far more palatable to government ministers who have to soothe the worries of economists and energy companies.

The framing of climate change mitigation as 'affordable' and, more importantly, possible, may not place enough emphasis on the dangers of global warming and exaggerate our ability to deal with them. However, it does allow those in power to do something, which is always preferable to nothing.