You should be able to get it listed in the University and College weekly emails. (Perhaps you already have pet undergraduates to do this for you.) Subject societies will often advertise talks likely to be of interest to their members too. There's also What's On, and the old fashioned approach of taking posters round the departments.
The Centre for the Study of Existential Risk will be holding a public lecture on "Existential Risk: Surviving the 21st Century" in collaboration with 80,000 Hours: Cambridge and Giving What We Can: Cambridge on the 26th of February in Cambridge (United Kingdom).
Lady Mitchell Hall, Sidgwick Site, Cambridge. 5:30pm-6:45pm, with drinks reception to follow.
SPEAKERS:
Lord Martin Rees, Astronomer Royal
Jaan Tallinn, co-founder of Skype
Huw Price, Bertrand Russell Professor of Philosophy at Cambridge
"In the coming century, the greatest threats to human survival may come from our own technological developments. However, if we can safely navigate the pitfalls, the benefits that technology promises are enormous. A philosopher, an astronomer, and an entrepreneur have come together to form the Centre for the Study of Existential Risk. The goal: to bring a fraction of humanity’s talents to bear on the task of ensuring our long-term survival. In this lecture, Huw Price, Martin Rees and Jaan Tallinn will outline humanity’s greatest challenge: surviving the 21st century."
This event is free and open to all.
Facebook event notice is here.
In other news, I hope to be posting a general update on progress with the Centre's establishment fairly shortly for those who are interested, although it's still an ongoing process. Things have become quite busy and there are a lot of opportunities to follow up on, so I'll be taking a leave of absence from the Future of Humanity Institute for 6 months in April to work full-time on the project to establish the centre.