Jun 17, 2007
Derek C. points us to this effort by a science journalist to use graphs to help "clarify the concept of climate change". The graph on the left shows that actual greenhouse gas emissions have exceeded the level predicted by the most pessimistic climate models. The 3D bar chart on the right examines which countries had most increased emissions since 1990.
While the bar chart contains many of Tufte's "ducks" (not sorted by percent change, 3D, color, gridlines, sufficiency, etc.), it's the left chart that can be made more powerful.
The casual observer does not need to know which model led to which trajectory of predictions; the graph is vastly simplified, and the message much clearer in the junkart version. (I only included the CDIAC data because I didn't locate the EIA numbers.)
The general point here is recognizing what is foreground, and what is background. Aside from gridlines, data labels, axis labels and so on, some of the data usually constitute background material, often as in this case being used to establish comparability.
One message I got out of this chart is that these climate models have done a good job! (Now, I have no idea if part of the curve included the training period. It is curious that the predictions were very narrowly contained in the early 1990s.)
Source: The Island of Doubt Blog, June 6, 2007.
If I had to guess, I'd say that the models were trained on data up to ~2000 on the EIA data from the top graph. Oddly, there seems to be a much larger range < 2000 in the junkart chart relative to that first chart?
Posted by: Byron Ellis | Jun 17, 2007 at 09:51 PM
The graph on the left shows that actual greenhouse gas emissions have exceeded the level predicted by the most pessimistic climate models.
One might THINK that's what the graph shows, but without prediction intervals around the model curves, how can you tell? Prediction intervals in time-series models expand FAST.
Posted by: Mike Anderson | Jun 17, 2007 at 10:45 PM
I looked for the source of the blog's figures for that bar chart, and found it, eventually, at http://www.panda.org/. It shouldn't have been so hard for me to find.
I discovered that either the blog or the newspaper got the figures wrong, especially for Japan (emissions up, not down) and Britain (emissions down, not up). I also found that the WWF report fails to give emissions either in 1990 or today. lots of normalised measures and percentage changes, but no actual number for emissions.
That's disappointing. I had wanted to turn the bar chart with its percentages into a "cat's cradle" line chart with 1990 and 2005 numbers on the left and right (Kaiser's favourite "bumps charts" :-)
I'm also not impressed by the WWF's fondness for speedometer gauges. A simple traffic light spot would have worked better.
Posted by: derek | Jun 18, 2007 at 09:25 AM
Derek: For some reason, speedometers are all the rage, especially in the business / management world.
Mike: The variability of the forecasts is given by the range of estimates produced by different models. Of course, as you said, each model has its own prediction interval but as a proxy for those, I think the range of estimates is not bad.
Bryon: I eyeballed the range of estimates as I don't have the data for each model.
Posted by: Kaiser | Jun 19, 2007 at 09:40 PM
A little late to the party here, but the range of carbon dioxide emissions are technically scenarios, not models. IPCC researchers used the estimates of carbon dioxide emissions to feed models, which then predicted changes in climate, the results of which were published in 2001 in the Third Assessment Report. The raw data are here:
and the IPCC report is here:
as well as the PNAS paper from which the line graph published here was taken:
Posted by: R Simmon | Aug 11, 2008 at 02:10 PM