Through Türkiye’s e-Visa platform at evisa.gov.tr, using the registration code from your UNFCCC acknowledgement letter. It costs nothing and is issued within seven working days.
The order matters, and it is where most of the waiting actually sits. You cannot start the visa application until your UNFCCC registration is confirmed and you can open your acknowledgement letter, because the form asks for the registration code printed on it. Getting registered in the first place runs through a party delegation or an admitted observer organisation, on a timeline of months, not days. The seven working days quoted for the visa is the short part of the journey.
The application itself is light: a passport-size photograph of no more than 4 MB in PNG, JPEG or JPG, your travel document details, and your intended arrival and departure dates. Once approved you download the visa from the portal, and you can track it under "My Visa Applications". Some applicants are told by a pop-up during the process that they must instead apply for a sticker visa through a Turkish diplomatic mission.
What you get is a multiple-entry visa valid from 1 to 30 November 2026, with a maximum stay of 30 days. Note that the window is the calendar month, not the conference: it covers pre-sessional arrivals in early November, but nothing in October. It cannot be extended and cannot be converted into a residence permit, and the presidency warns that overstaying can mean administrative fines, deportation, or a ban on entering Türkiye again.
Questions about any of this go to the UNFCCC secretariat at visas@unfccc.int rather than to the Turkish authorities.