Andrew, some scientists say that when enough polar ice such as the glaciers of Greenland deposit so much fresh water into the north Atlantic currents changinging pH and salinity, it could trigger the beginning of such global climate change that could lead to a cycle of. planetary freezing conditions.
Another condition could be the magnetic polar flip, a phenomenon that has already occurred several times over the millenia. Evidence of this is seen in the alternating crystal structure of deep ocean crust along the divergent mid Atlantic Ridge.
Either way, another ice age is inevitable but not to fear...the Neanderthals survived 300,000 years over several such climatic changes. If modern man were wise enough to become reconnected with the natural world in such a way as to revive his primal consciousness, I believe we could be as successful as Neanderthals!