The IPCC says, in its Special Report on Emission Scenarios (SRES, or Report), that modelling “very complex, ill-understood dynamic systems” has three main sources of uncertainties: data uncertainties, modelling uncertainties, and completeness uncertainties (2000: Technical Summary [TS] 2). These uncertainties make predicting future GHG emissions impossible, so a fortiori the eff ects of climate change. These depend on emissions, on poorly understood variables and on completely unknown variables (2000: TS 1), so that “information on the relevant variables is so incomplete that they can be appreciated only through intuition and are best communicated by images and stories. Prediction is not possible in such cases” (2000: 1.2; emphasis added).