There may be threats that can cause much greater damage than Daesh but these are neither immediate nor very likely. Nuclear war is undoubtedly a massive threat, but we succeeded in getting through 45 years of cold war without these weapons being used so the probability of the threat happening is low. Climate Change on the other hand is less a security issue than an environmental, economic, and societal one. Daesh on the other hand has already struck at western states with the Paris attacks, and has sucked large numbers of western citizens into a war against their own countries in Syria and Iraq. The threat from Daesh is therefore immediate, almost certain, and large.