Definition: Global Catastrophic Risk – risk of events or processes that would lead to the deaths of approximately a tenth of the world’s population, or have a comparable impact.
-- from the 2016 Global Castrophic Risks Report [1]
page 17.
The GCR that have a "higher likelihood over the next five years" and to which we should pay "high attention" are Natural and Engineered Pandemics and Nuclear War.
The GCR that have a "lower likelihood over the next five years" and to which we should pay "high attention" are Catastrophic Climate Change, Catastrophic disruption from AI and Failure of geo-engineering.