I have made a new graph.
Actually its more accurate to say I have collated or perhaps compiled a data set of New Zealand emission unit (NZU) prices from 2010 to 2015.
Although private sector carbon brokers such as OMF and Carbon Forest Services display some current prices and a few historic prices, there is no openly available public data series of the New Zealand carbon price as represented by trading in the domestic New Zealand Unit.
So I decided to make a monthly data series by digitizing images of graphs via the programme G3Data and via the website Web Plot Digitizer.
I took an image of a chart of New Zealand carbon prices, much like this one below, I drew some vertical lines on it and uploaded it to the Web Plot Digitizer webpage, selected some exact points on the horizontal and vertical axes to orientate the chart and then clicked on the intersection of the data series with the axes. That records the data points in the Web Plot Digitizer app.
The values obtained in this way are best thought of as being similar (but certainly not identical) to a monthly mean. The accuracy is perhaps plus or minus 20 or 50 cents. I know that as I did several 'replications' and they varied from each other by 20 to 50 cents. The data file is available as a Google sheet called "NZU-price-data-2010-2015.csv".
The R script for the chart is also available at Ghost Bin and at the Wikimedia Commons page for the graph.
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