Thanks Aidan. I am sure that I am being ultra dense here 
but where is the cryosphere calendar url? On this page: Cryosphere Working Group Announce - #6 by kdruken
the Cryosphere calendar URL: link
is just a download file as far as I can tell, and not a web url (e.g. I right click it and open in a new tab and it just downloads an ics file). Sorry for being a pain. Thanks for your patience.