Seals as Probes - Revisited

As per my last post, I was very happy that Chris Benjamin wrote up a considerably better researched version of my very first blog post for Science Friday last year regarding the use of seals in climate and weather monitoring/research. As I recently was able to attend a seminar on the updated results from the seal project I thought this would be a good opportunity to explore the subject a little further.

  Something that was perhaps missing from my original post is the importance of monitoring ocean conditions. Ocean observations are very important in terms of measuring their heat uptake. According to the IPCC Assessment Report 5 the top 700m of the oceans take up 93% of global warming heat content (see below).
 
Given this, you can perhaps see why it might be interesting (and important) to study the Antarctic circumpolar current (ACC). This is the most important current in the Southern Ocean and the only current that flows completely around the globe. Incidentally, it was discovered by Edmund Halley, the British astronomer (who says astronomers have no real-world use?). The ACC is equivalent in flow to all of the rivers in world combined (Chidichimo et al, 2014).

Measuring the temperature and salinity of the water in the ACC, in addition to other, less well-travelled water has become easier and more widespread with the ARGO float system. However, in order to take the same measurements beneath the variable sea ice which extends beyond the land it is necessary to recruit the services of seals, as covered by myself and Chris Benjamin.

The seal measurements allow forecasts to be made for the Antarctic area, this is particularly useful for military pilots who, under certain circumstances, must where survival 'dry suits' when flying. These suits are very uncomfortable, particularly in cramped cockpits and so knowing whether or not they are necessary is useful information for the pilots!

Mapping ocean currents, particularly in a predictive sense, can be immensely useful in a 'man overboard' search and rescue mission. The disappearance of flight MH370 last year is another example of the importance of this information.

The measurements made by the seals, or rather by the instruments attached to the seals, are made on the upward portion of the seals foraging dives. The data loggers consist of a pressure sensor (in addition to other sensors) which is on constantly, this notes when seals begin to ascend from their dive and alerts the other sensors to turn on and begin measurements. The record dive of an Elephant seal is over 2000 metres, over four times the average of 500 metres. It's not really understood how such deep dives are possible, although the seals have ribs made of cartilage which means that they can collapse their chests, the impact on the seals' blood chemistry is still very significant.

Dive profiles consist of seventeen points which are split into four messages, the transmission of which is attempted when the seal surfaces. A minimum of 160 seconds is needed to send these four messages via the Argos satellite tracking system, unfortunately the mean elephant seal surface period only lasts for 130 seconds, meaning that transmissions are often incomplete, resulting in poor positional information and/or incomplete profiles of the water temperature and salinity. An alternative to transmit the messages via the Iridium satellite constellation exists but depletes the data logger batteries at an increased rate.

  By running reanalysis experiments of past weather conditions the usefulness of the seal observations can be evaluated. It turns out that incorporating the temperature and salinity measurements tends to lead to an overestimation of the water salinity. This is difficult to verify without independent observations (of which there are none) but in the Kerguelen region where there is some overlap between ARGO floats and seal data it was found that the ARGO floats had the opposite bias - where the sea measured fresher than predicted by the ocean model.

  It is notable that the primary difference in instrumentation between the floats and the seal data loggers is that the former use capacitance to measure salinity while the latter use inductive conductivity sensors. The seal sensors are found to have a high bias (as seen) when the sensor is close to any surface (like a seal for example...). This effect can be accounted for by calibrating the sensor for each individual seal, unfortunately this requires a long data baseline of around a year. At which time the sensors are falling off the seals in any case!

  All this means that the salinity profiles obtained from the seals are partially useful for research purposes but can't really be used for meteorological forecasting.

  What is lucky is that even incorporating only the temperature profiles from the seals data loggers results in a significant improvement for temperature and salinity forecasts, as well as improvements in estimates of global temperatures, extending far beyond the regions sampled by the seals.

It has been noticed that the location and strength of ocean fronts are impacted in models by the seal-measured temperature. However, without good quality independent observations it is difficult to assess whether this is a beneficial change or not.

Seal Blog makes it to Science Friday!

So, after I wrote my first ever post on this blog (Resistance is Futile), my friend Chris Benjamin picked up on the story and asked for contacts to follow up for a potential Science Friday article. That article has now been published and is available here!

This is what 50 years of satellite technology development will get you...

Courtesy of NASA's Earth Observatory

Ada Lovelace Day Blog! Sophie Germain

Today is Ada Lovelace Day (much info and other stuff at findingada.com), an international celebration of the achievements of women in science, technology, engineering and maths (STEM). As I'm a fan of Ada Lovelace (particularly as told in steampunk style!)(http://sydneypadua.com/2dgoggles/lovelace-the-origin-2/) I thought I'd like to join in the event and write about a woman in STEM that I personally have found inspiring.

  Normally, if I was trying to write about an interesting, inspiring woman in STEM, I would probably have gone straight for Ada Lovelace. That seemed a bit 'on-the-nose' for Ada Lovelace Day though, so instead, I'm going to write about Sophie Germain.

  I first read about Sophie in the book 'Fermat's Last Theorem' by Simon Singh, in which the work she did towards the theorem is highlighted. I later was reminded of her through some lines in a play I was in, 'Proof', in which she was used as an example of how you just can't keep a good mathematician (a woman one at that!) down.

  The basic details of Sophie Germain's life are fairly well reported - she was part of a family pretty low down in the bourgeoisie stratum. They were, however, of sufficient standing that, come the French Revolution, Sophie was largely confined to the house in order to avoid the chaos that ruled the streets. She used this time to study the books on mathematics in her father's library, going well beyond what I might consider a 'casual interest', reportedly teaching herself Greek and Latin so that she might be able to read the works of Newton and Euler. If Sophie had made no further progress than this she would still be utterly remarkable, Newton's Principia Mathematica is not exactly an easy read, even in English.
  Supposedly Sophie was drawn to mathematics by an apocryphal story of how Archimedes was slain by a Roman soldier while distracted by a mathematical diagram, thinking that something that can cause someone to ignore a man with a sword must be pretty interesting! She went on to become immersed in mathematics, using lecture notes from the École Polytechnique which she was either allowed or begged, borrowed or stole from students. She herself was denied entry on the basis that she was, you know, a woman. Later, she assumed the identity of a male student and began sending her work to Lagrange, a faculty member. The story of her later meeting with Lagrange, his support of her and how she developed mathematics and earned the respect of (some of) her mathematical peers is well documented.

Rather than repeat the facts of Sophie's life which are well explored elsewhere, I'd like to write about why I find her interesting and inspiring.
  Firstly, she's interesting because reading about her is like reading a who's who of mathematics. Looking around different sites about her brings up the names Lagrange, Gauss, Legendre, Navier, Poisson and Laplace. These names would be familiar to anyone with a career or extensive education spent in the mathematical and physical sciences and some of them would be likely candidates for this blog post if I were instead writing about inspiring men in STEM. I love the way that the theorems and mathematical devices that I've used in my work become part of a larger world of actual people when you start to see the links between someone like Gauss and someone like Sophie. These were living, breathing people with feelings, ideas and politics and that is all too rarely remembered.
  Secondly, I find Sophie's life inspiring because she wasn't normal. The truth is that I would likely never have heard of Sophie if she had been a man, her accomplishments were in fields that I have never had much interest in. What has really brought Sophie to the attention of most people, including myself, is the story behind her work. The struggles that she went through to be able to be a 'mathematicienne', her subterfuge in pretending to be male in order to converse with Lagrange and Gauss and her battles against a hierarchy determined to ignore her.

It is quite possible that, had Sophie been a man, I would never have heard of her. However, the truth is that Sophie Germain is a difficult person to play 'what if' with. No doubt, if a man had produced the work she had, this would be just as important for people in those fields. However, for those of us outside of those fields, we probably would never have come across it. A young man would likely have been encouraged in their pursuit of mathematics, instead of denied candlelight and bedding to try and crush the love of the subject, as Sophie was. A man would have been able to attend the École Polytechnique, had tutors and opportunities to work alongside other mathematicians.
  Had Sophie been given these opportunities, she would have been taught in much the same way that others were taught at the time and that is what makes the hypothetical 'male Sophie' so hard to imagine. One of the main criticisms of her work was that it lacked rigour. No doubt this rigour would have been taught to her had she been taught in the traditional fashion. At the same time, it is possible that this may have driven some of the fascination from her or robbed her of the originality that her work had (for example, the work that she eventually won the prize for).

 Her work was important because of the insight that she had and I doubt that this would have been easily removed simply by a more traditional education. In fact, I expect that the truth is more likely that society has been denied the even greater work and insights that Sophie might have had if she had simply been encouraged to reach her full potential. Louis Bucciarelli and Nancy Dworsky, who were biographers of Germain's, wrote 'All the evidence argues that Sophie Germain had a mathematical brilliance that never reached fruition due to a lack of rigorous training available only to men.'

  While Sophie Germain struggled to find recognition in a field of work which she was truly passionate about and then died at a young age from breast cancer, she was fortunate in other ways. Her father was wealthy enough that she was supported by him throughout her adult life. In fact, if it had not been for a somewhat privileged background, Sophie would never had access to the materials and opportunities that inspired her in the first place. While we can at least recognise today that society suffers when people are denied opportunities based on gender, we still have a long way to go before we can hope for anything approaching real equality. I hope that Ada Lovelace Day will inspire young girls and women to see the potential and enjoyment in the STEM subjects. At the same time, I hope that one day we will actually provide the resources and true opportunity for everybody who is inspired by people like Sophie Germain, male, female or trans, rich, poor or underprivileged.

  Finally, while reading around for material for this blog, I found this amazing quote from a textbook that I struggle to believe even existed. At the time that Sophie Germain was working, women were not expected to be completely ignorant of mathematics. In fact, they were encouraged to know a little so that they could discuss the topic, should it come up in dinner conversation or wherever. To this end, Francesco Algarotti wrote 'Sir Isaac Newton's Philosophy Explain'd for the Use of Ladies'. This book attempted to explain the Principia through a romantic (naturally) relationship, describing the inverse square law of gravitational attraction thus - "I cannot help thinking ... that this proportion in the squares of the distances of places ... is observed even in love. Thus after eight days absence, love becomes 64 time less than it was the first day."
  I wonder whether Sophie Germain found this interpretation any less bewildering than the Latin she read it in?

India's Mars Mission Envy

India's Mangalyaan (Mars Craft) spaceship and its successful insertion into Mars' orbit is exciting on so many fronts. What I'm most excited about is that one of its instruments is searching for methane. The Mars Express mission detected raised levels of the molecule way back in 2004. This discovery was heralded as being a possible indicator of microbial life on Mars, or maybe the marker of geological activity on the planet (admittedly less exciting but not a bad consolation prize!). While the NASA Maven mission entered Mars orbit rather more quietly a few days ago it has mission objectives focussed elsewhere, on the passing of a nearby comet and then the upper atmosphere of Mars. I can't seem to find a way of constructing a sentence about the Maven mission that doesn't seem patronising or dismissive but the truth is that I'm more excited by far about India's mission. Not only am I looking forward to the methane detection experiment results, this is a great accomplishment for India.

I haven't read a single news article yet that hasn't drawn attention to the notion that India would have been better off redistributing the $75 million it spent on the mission (around a tenth of what the Maven mission cost!) on feeding and clothing hungry citizens. There are even snarky digs at the fact that the country receives aid while having the audacity to perform science. This seems to me to completely miss the point. India has pulled off a fantastic feat of engineering here, for a bargain no less! How can this possibly be anything other than good for their economy and standing in the world? If we are worried about the poverty in the country then surely it is more helpful to improve the industry, infrastructure and reputation of the country. The Mangalyaan mission will do all of those things, even if indirectly. The western world has been driving for years towards the notion that science must always be directly practical in its application, otherwise it is somehow unworthy and wasteful. I'm glad that India at least can overcome this lack of vision and I hope that they, as a country, can make great accomplishments in areas where we must now rely on private citizens and companies.

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.