From Seth Baum:
Global catastrophic risks (GCR) are risks of events that could significantly harm or even destroy human civilization at the global scale. GCR is related to the concept of existential risk, which is risk of events that would cause humanity to no longer exist. (Note that Nick Bostrom, who coined the term existential risk, defines it in a slightly different way.) Prominent GCRs include climate change, nuclear warfare, pandemics, and artificial general intelligence. Due to the breadth of the GCRs themselves and the issues that GCRs raise, the study of GCR is quite interdisciplinary.
According to a range of ethical views, including my views, reducing GCR should be our top priority as individuals and as a society. In short, if a global catastrophe occurs, then not much else matters, since so much of what we might care about (such as human wellbeing, the wellbeing of non-human animals, or the flourishing of ecosystems) would be largely or entirely wiped out by the catastrophe. The details about prioritizing GCR are a bit more complicated than this (and are part of ongoing research), but GCR does nonetheless remain a (or the) top priority from a range of views.
Seth Baum is one of the only academics working on existential risks. Last December I attended the Society for Risk Analysis annual meeting at his invitation, and gave a talk on molecular nanotechnology risk. I also summarized what the Singularity Institute does.
Seth Baum has some attention and interest from a few leading figures in the risk analysis community, but he needs to get more momentum to have a larger impact. If you are an academic you should consider partnering with him. The UK has a nicely established existential risk research group in the form of the Future of Humanity Institute, but the US lacks one. We have SIAI and the Lifeboat Foundation, but SIAI is focused on AGI, and the Lifeboat Foundation doesn't have any research staff.