At the end of the book, Crichton gives us an author's message. In it, he re-iterates the main points of his thesis, that there are some who go too far to drum up support (and I have some sympathy with this), and that because we don't know everything, we actually know nothing (here, I beg to differ). He also gives us his estimate, ~0.8 C for the global warming that will occur over the next century and claims that, since models differ by 400% in their estimates, his guess is as good as theirs. This is not true. The current batch of models have a mean climate sensitivity of about 3 C to doubled CO2 (and range between 2.5 and 4.0 degrees) (Paris meeting of IPCC, July 2004) , i.e an uncertainty of about 30%. As discussed above, the biggest uncertainties about the future are the economics, technology and rate of development going forward. The main cause of the spread in the widely quoted 1.5 to 5.8 C range of temperature projections for 2100 in IPCC is actually the different scenarios used. For lack of better information, if we (incorrectly) assume all the scenarios are equally probable, the error around the mean of 3.6 degrees is about 60%, not 400%. Crichton also suggests that most of his 0.8 C warming will be due to land use changes. That is actually extremely unlikely since land use change globally is a cooling effect (as discussed above). Physically-based simulations are actually better than just guessing.