Online Briefing report 5.8 Other ways of displaying the projections
The User Interface can also be used to explore how projections change with time over the course of the century, using a plume of probability. Essentially, this takes a number of probability levels from the CDFs for each of the seven future time periods, and presents them as a , with straight lines for each of the probability levels joining the calculated values. We show an example in Figure 19 of changes with time of summer mean temperature in Central London under a High emissions scenario. Thus the top line in the figure shows how the temperature change that is very unlikely to be exceeded increases decade by decade through the century, the middle line shows the , etc.
The User Interface also allows the of changes in some (but not all) combinations of two variables to be calculated. These can be used to explore specific impacts on targets (for example, crops) which are vulnerable to changes in both variables; the User Interface can create plots of these distributions. Figure 20 shows an example for changes in precipitation and in mean temperature. Joint probability values are shown by the red contour lines, and have been multiplied by 1000 to make them more readable. So, referring to the figure, there is a joint probability of about 2/1000 = 0.0002 of a simultaneous change of 1ºC* in temperature and –50%* in precipitation. Similarly, there is a joint probability of about 18/1000 = 0.0018 of the same precipitation change but a 5ºC temperature change, that is some 9 times greater than for the 1ºC change.
* Strictly speaking, the changes would be over small intervals around 1ºC and –50%.