Here are two more versions of the greenhouse gas chart.
The first one is a Marimekko which many would consider to be appropriate for this type of data. It is essentially a stacked bar chart where the width of the bar is scaled to the proportion of the type of gas. Here's what one would be looking at:
Merimekkos (also called Mosaic charts) share many of the problems of pie charts. Note the need to use multi-color, the difficulty in comparing the areas of the pieces (even worse than looking at sectors), and the difficulty in comparing across categories since the pieces float in irregular space (take for example the three pink pieces). My rule is: avoid at all costs. (Well, like the pie chart, when the data is sufficiently simple, with very few pieces and with some outliers, these could be acceptable.)
Secondly, here is a recycled junkart chart, with all white space removed from the interior. (Thanks to Derek for the suggestion.)
Depending on what the purpose of the chart is, one can decide what is the base for the proportions. My version preserves equity between the two dimensions. Anything else will require the designer to make a choice. If, for example, the base is 100% for each type of gas emitted, then the reader could not derive from the same chart the proportion of each source of emission (across all types of gases).