Mathematician Safa Motesharrei and his collaborators showed that the use of non-renewable resources such as fossil fuels allows populations to grow to one order of magnitude larger than they would using renewable resources alone and as such is able to postpone societal collapse. However, when collapse finally comes, it is much more dramatic. Tainter warned that in the modern world, if the supply of fossil fuels were somehow cut off, shortages of clean water and food would ensue, and millions would die in a few weeks in the worse-case scenario.