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.

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.