Deadly Swiss Avalanches, in Charts

Snow-covered mountains are one of the most beautiful sights in nature, but in the wrong circumstances they can kill you. Skiers and other mountain enthusiasts sometimes refer to avalanches as the “white death”, and for good reason. Hundreds die in avalanches every year, and a great deal of effort is spent on trying to understand the factors that cause avalanches in the hope of decreasing this toll.

Located in the Alps and a mecca for winter sports, Switzerland takes avalanches seriously. The Swiss Institute for Snow and Avalanche Research  (SLF) monitors snow conditions, issues warnings, and collects data on avalanches. Their web site is very interesting for those interested in winter sports in the Alps. I find the snow maps particularly useful. But for this post I will use their data on fatal Swiss avalanches in the last 20 years to experiment with different ways to visualize some patterns and relationships.

The dataset includes information on the date, location, elevation, and number of fatalities, in addition to the slope aspect, type of activity involved (e.g. off-piste skiing), and danger level at the time of the avalanche. Over the last 20 years there have been 361 fatal avalanches in Switzerland, for a total of 465 deaths. Most avalanches killed only one victim.

Because I wanted to experiment with radial plots, I’ll focus on the variable of slope aspect in this post. Aspect is the compass direction that a slope faces. In this case we’re looking at the slope where the avalanche occurred. In Switzerland, the majority of avalanches occur slopes facing NW – NE, as you can see from this plot:

rose

The gaps at NNE and NNW are probably artifacts of how the aspect data was reported.

This pattern is common in the temperate latitudes of the northern hemisphere. Avalanches are more common on north-facing slopes because they are more shaded and therefore colder, which allows snowfall to remain unconsolidated for longer. When more snow falls, these unconsolidated layers can act as planes of weakness on which snow above can slide. It’s much more complicated that that, with factors like wind and frost layers coming into play. To learn more about how aspect and avalanches, see here. The pattern is unmistakable, but does it hold all year long? I separated the data by month to find out:

rosefacet

Fatal avalanches occurred in all months, but are much more common December – April

A few interesting insights emerge from this plot. First, February is clearly the most deadly month for avalanches.  In December there are actually quite a few avalanches on SE facing slopes, but by January the predominate direction is centered around NW. In February, and to some extent in March, it changes to N-NE. In April it’s NW again, but by then there are significantly few avalanches. So there are some monthly patterns, but I’m not exactly sure what the explanation is. Of course to really nail this down we’d want to do some statistics as well.

One pattern I expected, but did not see, was a decrease in the dominance of northern aspects later in the spring. I expected this because as the days get longer, the shading effect of north facing slopes decreases. It’s important to remember that these are fatal avalanches, and a dataset of all avalanches would look different. For example there are probably a lot of wet avalanches on southern slopes in the spring. But these are much less dangerous than the slab and dry powder avalanches, and therefore not reflected in the fatality data.

The rose style plots above are useful, but I wanted to try to illustrate more variables at once. So I tried a radial scatter plot:

Fatal Swiss avalanches 1995 - 2016: Slope aspect, elevation, and activity

Click on the image for the interactive Plot.ly version

This plot is similar to the previous ones in that the angular axis represent compass direction (e.g. 90 degrees means an east-facing slope). The radial axis (the distance form the center) represent the elevation where the avalanche occurred. And color represents the type of activity that resulted in the fatality or fatalities. Each point is one avalanche. The data are jittered (random variations in aspect) to minimize overplotting. This is necessary because the aspect data are recorded by compass direction (e.g. NE or ESE). The density of the points clearly illustrates the dominance of north-facing aspects. It’s also clear that most avalanches occur between 2000 and 3000 meters (in fact the mean is 2507 m). In terms of activity, backcountry touring and off-piste skiing and boarding dominate. And avalanches at very high altitudes are mostly associated with backcountry touring, which makes sense, as not many lifts go up above 3000m. Perhaps especially perceptive viewer can make out some other patterns in the relationships between variables, but I can’t. Any thoughts on the usefulness of this plot for the dataset?

Finally, I want to share a couple graphics from SLF (available here). Here is a timeline of avalanche fatalities in Switzerland since 1936:

The average number of deaths per year is 25, but this has decreased a bit in the 20 years. There were also more deaths in buildings and transportation routes prior to about 1985. Presumably improvements in avalanche control and warnings reduced fatalities in those areas. And what happened in the 1950/51 season. That was the infamous Winter of Terror. The next plot shows the distribution of fatalities by the warning level in place when the avalanche occurred:

Interestingly, the great majority of deaths happened when warning levels where moderate or considerable. There were significantly fewer deaths during high or very high warning periods. One reason must be that high/very high warnings don’t occur that frequently, but it’s also likely that skiers and mountaineers exercise greater caution or even stay off the mountain during these exceptionally dangerous times. There’s probably some risk compensation going on here. To really quantify risk, you have to know more than just the number of deaths at a given time or place. You also have to know how many people engaged in activities in avalanche country without dying. One clever approach is to use social media to estimate activity levels, as demonstrated in this paper.

Have fun in the mountains and stay safe!

Data and code from this post available here.

All data from WSL Institute for Snow and Avalanche Research SLF, 25 March 2016

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Illustrating the Arc of European Colonialism Using a Dot Plot

A while back I was thinking about European colonialism and the enormous impact it’s had on world history. Wouldn’t it be nice to have a simple visualization to illustrate colonization and decolonization around the world? It occurred to me that a dumbbell dot plot would work well for this task. Here’s what I came up with:

colonial2

The chart shows the dates of colonization and independence of 100 current nations. The countries are organized into broad regions (Asia, Africa, and the Americas), and sorted by date of independence. Color represents the principal colonial power, generally the occupier for the greatest amount of time.

There are many interesting patterns visible in the chart. For example, you can clearly see Spain’s rapid conquest of Central and South America, and then even more rapid loss of its colonies in the 1820s. The scramble for Africa in the late 19th century stands out well, as does the rapid decolonization phase of the late 1950s through early 1970s.

About the Data

To reduce complexity to a manageable level, I set some limitations on what countries to include. First, the chart shows only those countries victim to Western European colonialism. I don’t include Ottoman, Japanese, Russian, American, or other colonial empires. I also don’t include territories that are still governed by former colonial powers (e.g. Gibraltar). This gets controversial and complicated. Countries that were uninhabited upon discovery by colonial powers are also not included. The same with countries that later gained independence from a post-colonial state (e.g. South Sudan).

The dates of independence come from the CIA World Factbook (here). Dates of colonization were derived by my own research, mostly from Wikipedia country pages. I quickly found that establishing a date of colonization is a somewhat subjective decision. Do you choose the date of first European contact? Formal incorporation of the territory into the colonial empire? For the most part, I chose the date of the first permanent European settlement. Notes on the rationale for the date chosen are include in the data spreadsheet (below). In looking at the chart, it’s important to remember that in many cases colonial subjugation was a long process, moving from initial contact, to trade, conquest, settlement, and incorporation.

Constructing the Plot

I wanted to make this plot using ggplot2 in R, but was not sure about best approach. So I reached out on Twitter to dataviz guru and dot plot enthusiast @evergreendata

The response from the #rstats and dataviz community was extremely constructive and useful. Users  @hrbrmstr@jalapic@ramnath_vaidya, and @plotlygraphs all provided great examples (here, here, here, and here, respectively). In the end, I chose to adapt the approach taken by @jalapic.

A quick note on color: I choose colors from the flags of the principal colonial powers to represent them on the plot (except for the Netherlands for which I picked orange). The idea is to make it easier for the viewer to match the color with the country without having to always go back to the legend. I’d be interested in any reactions to this approach. In general, I’d be thrilled with any feedback on how to make this plot better.

Data and code for the plot:

The 1960 Chile Earthquake Released Almost a Third of All Global Seismic Energy in the Last 100 Years

I just saw a trailer for the movie San Andreas. It looks preposterous but I love geology disaster movies, so I’ll probably see it. In the film, a series of earthquakes destroy California, culminating with a giant magnitude 9.5 quake. Fortunately the Rock is on scene to help save the day.

The largest earthquake ever recorded in real life struck central Chile on May 22, 1960. With a magnitude of 9.6 (some estimates say 9.5) this was a truly massive quake, more than twice as powerful as the next largest (Alaska 1964), and 500 times more powerful than the April 2015 Nepal quake. The seismic energy released by the 1960 Chile quake was equal to about 20,000 Hiroshima atomic bombs. Thousands were killed. It also triggered a tsumami that traveled 17,000 km across the Pacific Ocean and killed hundreds in Japan.

But I think the most striking thing about this quake is that it accounts for about 30% of the total seismic energy released on earth during the last 100 years. To illustrate this, I calculated the seismic moment (a measure of the energy released by an earthquake) of all earthquakes greater than magnitude 6 and plotted the global cumulative seismic moment over the last 100 years.

Global Cumulative Seismic Moment 1915-2015

Click for interactive version

This plot clearly shows how the 1960 Chile quake (and to a lesser extent the 1964 Alaska event) dominates the last 100 years in terms of total energy released. This is not always obvious as the earthquake magnitude scale is logarithmic. So a magnitude 9.6 releases twice as much energy as a 9.4 and 250 times as much as an 8.0.

Technical notes: To make this plot I downloaded from the USGS archive data on all the earthquakes greater than magnitude 6 from 1915-2015. There are about 10,500 of them.

I calculated the seismic moment for each quake relative to a magnitude 6 (the smallest in the database) using

\Delta M_{0} = 10^{3/2(m_{1}-m_{2})}\

Where m1 is the magnitude of each quake and m2 = 6.

So a mag 9.6 is about 250,000 times more powerful than a mag 6.0. (Note that this refers to energy released, not necessarily ground shaking, which is influenced by many factors, such as earthquake depth).

Then I summed all the relative moments, normalized to 1, and plotted the cumulative seismic moment over the time period.

A few caveats. First, the quality of the magnitude measurements has improved over time, so that the data from the earlier part of the 20th century is not as reliable as the more current data.

Second, this analysis only looks at earthquakes larger than magnitude 6.0. Of course there are many, many smaller earthquakes. However, the cumulative amount of seismic energy released by these smaller quakes is very small compared to the larger ones (again, remember the logarithmic scale).

Third, the magnitudes listed in the USGS archive are calculated in different ways. The majority are moment magnitude or weighted moment magnitude. The equation above is meant for these types of magnitude. Other magnitude measurements, such as surface wave magnitude, have slightly different ways of calculating total energy release. This may introduce some inaccuracies, However, they will be small compared relative to total energy release.

If any seismologists would like to weigh in, I would be most grateful.

More information on calculating magnitude and seismic moment here and here.

Data and R code here. Graph made with Plot.ly.

Hurricanes and Baby Names

Recently there has been bit of buzz about a study claiming that female named hurricanes cause more fatalities, on average, than male ones. The authors suggested that the discrepancy is attributable to gender bias. Female named hurricanes do not seem as threatening to people, so presumably they take fewer precautions. From the start this seemed pretty far-fetched, and in fact a number of problems have been found with the study.

But it got me thinking about hurricane names. A more likely effect of a hurricane’s name would be to discourage parents from giving their children that name, if the hurricane is associated with death and destruction. Fortunately, there is readily available data with which to test this hypothesis. For hurricanes, I used the same data as the hurricane gender study described above (they may have had some problems with their methodology, but at least they released their data). It contains data on 92 Atlantic hurricanes that made landfall in the U.S. since 1950*. For baby names I turned to the Social Security Administration. There is a great R package called babynames that makes the yearly SSA data available in a readily accessible format for use in R. As an aside, the SSA baby names data is the source of all sorts of interesting visualizations and analyses, such as the baby name voyager and this article from fivethirtyeight.com on predicting a person’s age based on their name.

The tricky part of this analysis is deciding how to define a decrease in name usage after a hurricane. The simplest way would be to look at how many times a name was given in the year of a hurricane versus how many times that name was given the following year. For example, how many baby Kartrinas were there in 2005 versus 2006. However, this method does not take into account that most names are either decreasing or increasing in popularity as part of a longer-term trend. So you have to look at how the popularity of a name was changing before the hurricane as well. To see why, look at this plot of the number of babies named Katrina over time.

katrina

Katrina peeked in popularity in in 1980 and has been declining ever since. But from 2004-2005 the number of Katrina’s actually increased about 13%. From 2005-2006, however, it decreased dramatically – by 26%. It’s a pretty good bet that this rapid decrease was due to the hurricane.

To quantify the change in a name’s usage after a hurricane, I made the assumption that the best predictor of how a name’s popularity will change in a given year is how it changed last year. To calculate the post-hurricane change in name usage I subtracted the percent change in name usage in the year before the hurricane from the percent change after the hurricane. In the Katrina example the post hurricane change would be (-26%) – (13%) = -39%. This post-hurricane percent change value is what I use in the analysis below.

Before we get to the results, let’s take at look at the fascinating case of Carla:

carla

Hurricane Carla was an extremely intense storm that hit Texan in 1961, killing 43. The name “Carla” had been surging in popularity,  but after 1961 it started a decline in popularity from which it never recovered. It seems a pretty good bet that the hurricane had a major role in Carla’s decline. Interestingly, the first live television broadcast of a hurricane was of Carla, with a young Dan Rather himself reporting from Galveston. Could the shock of the American TV-viewing public seeing footage of the storm in their living rooms have contributed to the demise of Carla as a name?

Back to the analysis. Indeed, the hurricane baby name effect seems real. After running the numbers, I found that names associated with a landfalling hurricane were about 15 percent less common in the year after the hurricane. Out of the 93 hurricanes in the data set, 65 were associated with a decrease in the popularity of their names, and only 21 were followed by increasing name usage. (Seven hurricane names were not found in the SSA data in their landfall year).

So far this is pretty intuitive. Of course people are less likely to name their dear infant after a natural disaster. Based on this reasoning, you’d expect that the more fatalities caused by a hurricane, the greater the baby name effect. Let’s test that.

names.fatal

The effect is quite small. When we take Katrina out (a massive outlier in terms of fatalities), it’s smaller still:

name.fatal.ex.kat.rug

So the correlation between change in baby name usage and hurricane fatalities is quite weak. Finally, I had to see if the gender of the hurricane name affected this relationship. Were more deadly female-named hurricanes more or less likely than male names to affect baby name popularity? Maybe I’d even find that male baby name usage goes up with hurricane fatalities because parents associate the names with strength? I can see the Slate headline now! Alas, there is no significant difference:

names.fatal.ex.kat.bysex

By the way, there are more female names because from 1950 – 1979 all Atlantic hurricanes were given female names.

There’s an almost endless amount of interesting things to glean from the baby names data. My ultimate dream is an algorithm to determine the perfect name for your baby based on a number of criteria chosen by the expectant parents. It would really take the stress out of the naming process. One of the criteria would certainly be that the name is not on the World Meteorological Association’s list of tropical storm names!

Data and code available on github.

* The authors of the hurricane fatalities study did not include Katrina in their data set. I added it in with data from Wikipedia.

 

Graphics for Fitness Motivation using Plot.ly

This post is intended to illustrate the cool things you can do with plot.ly’s API for R. Plot.ly is a web-based tool for making interactive graphs. It uses the D3.js visualization library, and lets you create very attractive plots that can be easily shared or embedded in a web page. With the R API you can manipulate data in R and then send it over to plot.ly to create an interactive graph. There’s also a function that let’s you create a plot in R using ggplot2, and then shoot the result directly over to plot.ly (summarized nicely here).

I have great little free app on my iPhone called Pedometer++ that keeps track of how many steps I take each day. I exported the data, plotted up a time series with ggplot2, and used the API to make the graph in plot.ly. It worked quite nicely. The only hiccup was that plot.ly did not recognize the local regression curve, so I had to add that separately.

You can see from the plot that I’m not consistently meeting my 10,000 step goal. In fact, I averaged 7,002 steps over this period. That still comes out to a total of 1,470,463 steps. From October through February my step count was trending slightly downward, but since then it’s picked up. Maybe that had something to do with the cold winter. Hopefully as the weather (and my motivation) improves, I’ll hit my goal.

steps_taken_per_day_october_2014_-_november_2014

Click to see the interactive version

Any here’s a bonus box plot showing steps taken by day of the week (also using the R API):

steps_per_day2c_october_2013_-_may_2014

Click to see the interactive version

If there are any pedometer users out there who are interested, let me know and I can post the code.

Updated Global Mercury Pollution Viz and Graphics

One of the first posts on this blog was about using Tableau to visualize data on global emissions of mercury.  I’ve gotten suggestions from a few people and given the graphic a bit of a face lift. Click on the image to see the interactive viz:

Dashboard_1 (3)

Click for interactive graphic

I also used the same dataset to make some static graphics using ggplot2 and the ggthemes package. I’d love any input on how to improve the the look and feel of both these and the Tableau viz. I’ve always found picking good colors very challenging, so thoughts on the palettes are especially welcome.

hg.emissions.bysec

The 8 industry sectors with the highest global mercury emissions. Data for 2010 from the 2013 UNEP Global Mercury Assessment.

hg.emissions.bycty_fewm

Countries with the highest mercury emissions. Data for 2010 from the 2013 UNEP Global Mercury Assessment.

Getting to Know the Worldwide Governance Indicators

A while ago I wrote a post suggesting that Ukraine’s propensity for revolution might have something to do with its high level of government corruption in combination with its relatively well-developed civil society. As evidence for this, I showed that Ukraine (together with Kyrgyzstan and Moldova, two countries that have also recently experienced political unrest) was an outlier among post-Soviet states with respect to the relationship between corruption perceptions and authoritarianism. This finding was interesting, but by no means robust enough to warrant broad generalizations about corruption and democracy and revolution.

Since then, a few others chimed in with some ideas. Ben Jones suggested looking at corruption and authoritarianism in countries that experienced revolutions over time. Cavendish McCay looked at corruption and authoritarianism data from the same sources but over the entire globe, and produced a very cool visualization. He also pointed me to the World Bank’s Worldwide Governance Indicators, which contains measures of democracy, corruption, and political stability. Perhaps it would be possible to test my hypothesis empirically using these data. This could be done for individual regions or for the whole world, and could also have a temporal component (the indicators have been published since 1996).

In order to determine if such an analysis is feasible, I decided to take a closer look at the dataset (which is free and downloadable from the website). The Worldwide Governance Indicators (WGI) project is an ambitious one. The authors compile data from 31 different sources (such as think tanks, NGOs, private firms) and produce annual scores for every country for six indicators of the quality of governance. The indicators are:

  • Voice and Accountability
  • Political Stability and Absence of Violence
  • Government Effectiveness
  • Regulatory Quality
  • Rule of Law
  • Control of Corruption

First off, we can look at the data on a map. Fortunately the WGI website has a series of nice Tableau interactive graphics, including maps:

Screen Shot 2014-04-27 at 2.17.49 PM

Looking at the indicators geographically is helpful. But to evaluate whether they can be used to test the hypothesis, I want to see how each indicator is correlated with all the others. For this, we’ll turn to R. Here is a correlation matrix of the six indicators as calculated for 2012. Positive correlations are reflected as positive values. The closer the the number to one, the stronger the correlation. wgi.corrplot As you can see, all the indicators are positively correlated to each other, some very strongly. This is not surprising. We would expect well-governed countries to get high marks for rule of law, regulatory quality, control of corruption, etc. One interesting observation here is that Control of Corruption actually has the lowest correlations of all the indicators. A scatter plot matrix is a good way to look at the data in more detail:
wbi.splom.plot

The idea for this variation on the scatter plot matrix comes from Winston Chang’s R Graphics Cookbook. Its structure is similar to the correlation matrix in that all of the indicators are plotted against each other. The lower panels show scatter plots with LOESS regression lines for each indicator pair. This plot has some extra bells and whistles thrown in – histograms of the distribution of each in indicator in the diagonal panels and correlation coefficients (just like the correlation matrix) in the upper panels. The scatter plots show the strong to moderate correlations that we already saw in the correlation matrix, but allow us to make out some curious features of the data, like the non-linear relationship between Voice and Accountability and many of the other indicators.

The indicator values are in units of a standard normal distribution. A value of zero is the mean, while a value of one is one standard deviation higher than the mean. Given the distributions,  the indicator values range from about -2.5 to 2.5.  Positive values represent better governance, negative represent worse. Because each indicator is measured on the same scale, we can simply sum all six to determine the overall “best governed” country. The top six are:

Country     sum
FINLAND     11.19
SWEDEN      10.94
NEW ZEALAND 10.83
NORWAY      10.67
DENMARK     10.59
SWITZERLAND 10.57

And the bottom six:

SOMALIA              -13.65
CONGO, DEM. REP.     -9.76
SUDAN                -9.74
SYRIAN ARAB REPUBLIC -9.53
AFGHANISTAN          -9.48
KOREA, DEM. REP.     -9.35

I got a bit carried away examining the correlations between the governance indicators, but in a subsequent post I hope to look closer at the democracy – corruption – stability hypothesis. I’m still not quite sure what statistical tests to use and how to apply them, and I’d welcome any ideas. Data and code are posted on Github (github.com/caluchko/wgi)

 

Another Way to Look at Mercury in Seafood

In the previous post, I used Tableau Public to create a visualization of the Seafood Hg Database. That graphic showed the mean mercury content and number of samples by seafood category. But there are several other dimensions in the database, including the year of the study and the particular species of seafood sampled. I couldn’t resist playing around with the data a little more, this time using the lattice package in R.

The plot below shows the mean mercury concentration (y-axis) in studies of the 12 seafood categories with the highest median mercury concentration. The x axis shows the date of the study. I’ve also plotted a trend line for each panel. This is a nice way to visualize the data, but I wouldn’t read too much into this plot. For one thing, many of the seafood categories contain multiple species, some of which are higher than others in mercury. Also, this plot does not account for the geographical region where the fish were sampled.

fish.hg.latticeplot
We can tease a little more from the dataset by looking at the individual species within a seafood category. Here is a plot of the six tuna species with the greatest number of studies. The larger species, like bluefin, seem have higher mercury contents than the smaller ones, like skipjack. One curious feature of the dataset is also visible here: there were very few studies of mercury in seafood in the 1980s.
fish.hg.tunaplot

Is Artisanal Gold Mining Driving the Price of Mercury?

This is the second in a multiple part series on mercury. In the last post, we explored global mercury prices and production over the last century. In this post, my aim is to answer the following questions: Is is possible to resolve a signal in the price of mercury that is attributable to its use in gold mining? Could the price of mercury be used as a predictor of the amount of gold produced using mercury?

First, some background.  Mercury has a very interesting property in that it forms amalgams with other metals.  A silver dental filling is an amalgam of mercury and silver. If you add mercury to ore or sediment containing gold, the mercury will suck up some of the gold into an amalgam. Then you can heat the amalgam to evaporate the mercury, leaving you with just gold.

This method was used for centuries to recover gold and silver. Today, large-scale industrial mines use other methods that are more efficient and do not release persistent, toxic, and bio-accumulative mercury into the environment. However, mercury is still widely used in artisanal and small-scale gold mining (ASGM). In fact, mercury use in this sector is probably increasing, and is now believed to be the largest source of mercury pollution in the world. The recent spike in gold prices is often cited as a cause of increased ASGM and associated mercury use.

Because ASGM activity is decentralized, often illegal, and commonly occurs in hard to reach parts of developing countries, it is very difficult to estimate the magnitude and trends of mercury use. But we do have data from the USGS on the prices of gold and mercury. In the last post we looked at the time series for mercury prices since 1900. Here, we are only going to look at the period from 1980-2011. (The modern ASGM period really started around 1980.) The chart below shows the inflation-indexed prices of mercury and gold. I’ve normalized them to an index where the 1980 price equals one so that I can show both series on one plot.hg.auMercury and gold prices appear to be closely correlated. The high correlation coefficient (0.89) confirms what we see in the plot. The series only diverge significantly after 2009, and we’ll look at that period more closely at the end of the post.

But the close correlation of mercury and gold prices is not enough to conclude there is a causal relationship. Perhaps there is a lurking variable that is correlated with the prices of both metals. Mercury and gold are certainly not substitutes for each other. No one buys mercury when they are worried about inflation, for example. But maybe mercury and gold prices are both are correlated to overall commodity prices. To find out I plotted an index of metals prices from the IMF (also normalized to one and corrected for inflation) together with the metals prices:hg.au.inThe correlation looks close, and indeed the the correlation coefficients of  the metals price index with the prices of  gold and mercury are both about 0.8. This is not quite as close as the correlation of gold and mercury prices to each other, but it’s too close to conclude that either time series is all that different from the overall trend in commodity metal prices.

Now is a good time to point out that mercury has other uses besides to gold mining, such as in certain products (like thermometers) and industrial processes (like making chlorine). Demand from these other uses is going to affect the price. Of course, the supply of mercury will also have an affect on price. In attempting to see a signal in the price of mercury caused by gold mining, the implicit assumption is that other factors affecting the price of mercury (the supply and demand) remain relatively constant with respect to each other over the time period. This is not a terrible assumption. In general both non-ASGM demand for mercury and mercury supply have been decreasing over the last 30 years. But the assumption does introduce some real uncertainly into the analysis. It is difficult to correct for because we don’t have good data on mercury use by sector over the time period.

There’s one more problem. Recall that the hypothesis is that mercury use in ASGM affects the price of mercury. We were using the price of gold as a proxy for mercury use in ASGM. That sounds like a reasonable assumption. High gold prices should mean more gold being extracted, and greater demand for mercury to extract the gold.  But what really determines mercury use is the amount of gold produced, not the price. And we actually have data on global gold production. It tells a different story:au.qIf anything, global gold production is negatively correlated with gold price over the last ~30 years! I don’t know why this is. One possible explanation has to do with the lag time of starting a mining operation. Perhaps the record high gold prices of the late 1970s and early 1980s caused a wave of exploration and new mines. Once those mines were developed, they could produce gold economically even at low prices. Perhaps technology improved so that it was cheaper to find and develop gold deposits.

This leads to one more complicating factor. Most gold is produced by large scale mines (which do not use mercury). Common estimates suggest that only about 12-20% of gold is produced by rough artisanal miners. Another implicit assumption in this analysis has been that the fraction of gold produced by ASGM has remained constant over time. But this may not be the case. Small-scale miners are likely to be able to take advantage of high gold prices more quickly than the majors, where exploration, permitting, and construction can mean many years before a mine becomes operational. Small-scale miners can often start mining almost immediately. This would mean than gold and mercury prices would be more closely correlated than one would expect when looking at global gold production. On the other hand, work by the Artisanal Gold Council has shown ASGM prevalence is “sticky” with respect to gold prices. That is, once they start mining, artisanal miners are likely to continue their operation even after the price of gold drops. 

Finally, let’s reexamine the period from 2009-2011, when the price of mercury rises much more rapidly that the price of gold. I don’t think there’s an obvious explanation for this. Perhaps mercury use in ASGM really takes off in this period. Another wrinkle is the establishment of bans on mercury export in the EU (took effect in 2011) and the U.S. (took effect in 2013). Maybe buyers were trying to purchase European and U.S. mercury ahead of the ban, driving up the price. We could look at export data to find out.

As you can see, this is an extremely complicated issue. Without better data, it is not possible to resolve a signal in mercury prices that can be attributed to gold prices or gold production. Even though this exercise did not yield a clear result, I think it is important to document the effort. In data analysis (and science in general), the lack of a clear conclusion is in itself  an important piece of information.

In the next mercury installment we’ll travel to Ukraine and Kyrgyzstan to learn how the elusive metal is wrested from the earth and what sorts of environmental, economic, and social impacts this mining brings.

From Miracle Metal to Global Health Risk: A 100-Year History of Mercury Prices and Production

I want to write a series of posts about mercury production, prices, and trade. Although this may seem like a rather esoteric subject, I hope to convince readers that it’s actually pretty interesting. I have a professional interest in mercury as a global pollutant, having worked on negotiations for the Minamata Convention. These posts will also be good opportunity to practice data manipulation, graphics, and analysis in R, a powerful programming language for statistical computing.

Mercury is a pretty amazing substance. It’s the only metal that is a liquid at room temperature, a property that has long been a source of fascination to people, and led to a wide range of applications in industry. Unfortunately, mercury is also a toxin that has harmful effects on both people and the environment.

In this post I’ll examine the price and global production of mercury over the last hundred years or so using data from the U.S. Geological Survey. First, let’s look at the price of mercury in constant 1998 dollars since 1900:

mercury price

You can see that prices have fluctuated quite a bit. Let’s examine the three prominent peaks in the time series and try to figure out what caused them. Now, high prices could mean increased demand, tight supply, or a combination of both. We need to look at global mercury production over the same time period to help shed light on the variations in mercury price:
global mercury production
The first price peak occurred in the late 19-teens, around the time of WWI. In fact, I would posit that it is a direct consequence of WWI. Mercury fulminate is an explosive compound that was commonly used in the last century as a primer for small arms ammunition. They probably used a lot of it during the First World War.

Incidentally, you may recognize mercury fulminate from the TV show Breaking Bad. Walt made some and used it to blow up a group of rival drug dealers. There’s even a MythBusters segment about it.

The second price spike occurred during WWII. This was likely a result of increased demand for use in fulminate explosives, and perhaps in switches and other such products for wartime equipment. Mercury production actually increased quite a bit during the war, but it was apparently not enough prevent high prices. In response to the German invasion, the Soviets moved their main center of mercury production from Nikitovka in Ukraine to Khaidarkan in Kyrgyzstan. I’ll talk about both of these places in a later post.

The last price peak occurred in the 1960s. The causes are a bit more complex. My guess is that a combination of industrial and military uses were driving up demand, and production, although increasing, could not keep up. During this time the United States was building up its national defense reserves of mercury, and other countries were probably doing the same. One defense-related use of mercury was to separate lithium isotopes for use in hydrogen bombs. Hundreds of tons of mercury were spilled at Oak Ridge National Laboratory during isotope separation, and environmental contamination remains to this day. Another use of mercury that never came to be was as a coolant (to replace water) for nuclear reactors.

These were heady days in the mercury business, before the human health and environmental impacts were widely know. This fascinating newsreel from 1955 gives you a flavor of what the times were like:

Mercury prices (and production) started dropping in the 1970s as alternatives to industrial uses were found and the health risks started to become clear. But prices have been growing rapidly in recent years. In the next post I’m going to examine this and look at the degree to which artisanal gold mining might be responsible.