Interpreting plume plots
Plume plots illustrate the possible change in a variable across the century at a range of defined probability levels.
Interpreting the graph below
You can interpret plume plots in a couple of ways.
If you want to know when a particular threshold might be exceeded according to the projections, this can be identified from a plume plot. Figure 1 shows that there is a 67% chance of the temperature being below the threshold of 2.5º by the 2040s, a 50% chance by the 2050s, and a 33% chance by the 2060s.
It is also possible to use a plume plot to identify the different likely ranges at different time periods in the century. In Figure 2 the likely range in the 2030s is between 0.6˚C and 3ºC whereas the likely range in the 2050s is between 1.3˚C and 4.5ºC.