I remember hearing that warming in the polar regions will eventually cause a salinity shift that will trigger changes to how the ocean and air currents transmit heat, which will trigger an ice age. That normally takes a bit of time (historically at least a century, IIRC), so I expect us to enter an ice age if we fail to come up with some large scale geoengineering within the next century or so. In the meantime, things are going to be a bit rocky.
However, I could be wrong and I'm happy to have experts weigh in. We could call them scientists and they could study data, and then we could use their conclusions to make policy decisions.