Actually, the scientific community does not believe that the habitabilty of the planet is in jeopardy. Not even the most extreme climate models predict that Earth will someday become uninhabitable to humans. It is this sort of careless, hyperbolic, and unscientific rhetoric — most often spouted by politicians — that has caused the climate science community a lot of heartburn.
Additionally, it should be noted that while human activity is largely responsible for climate change, the IPCC AR5, which is seen as the global consensus on climate change, is more measured in its conclusion. It writes (PDF, page 5): “More than half of the observed increase in global mean surface temperature (GMST) from 1951 to 2010 is very likely due to the observed anthropogenic increase in greenhouse gas concentrations.” (By “very likely,” the IPCC means 90+% confident.) More than half is certainly a lot, but it also implies that a substantial proportion of climate change is due to other factors.
Mr. Sanders’ apocalyptic view of climate change makes his opposition to nuclear power particularly inexplicable. One would think that if climate change really is the “most significant planetary crisis that we face,” as Mr. Sanders once said, then the most efficient solution to that crisis should be warmly embraced. Instead, he rejects it because “we do not know how we get rid of the toxic waste from the [nuclear plants] that already exist.”