Well there are climatologists and there are climatologists who know what they're talking about.
Think about it, as glaciers melt there is less white to reflect the infra red sunlight creating a positive feedback in the Earth's warming.
Add to that the Earth holds a vast amount of methane in the form of frozen methane and methane is a terrific pollutant causing Global Warming. Now, the methane is beginning to melt but doesn't really go through a liquid phase as it melts. It pretty much has only a frozen or gas phase. So, the more that melts the more it causes melting, creating yet another positive feedback. Once you get those feed backs over a limit all hell breaks loose and there's no going back for the foreseeable future.