Gdddk

I need to add to my bibliography (in LaTeX, using Bibtex) an entry for the Paris Agreement (2015):
https://treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-7-d&chapter=27&clang=_en

However, I have been unable to find any BibTeX-style (or, for that matter, any citation format) for how to cite such a UN treaty. What would be the right format?

Short answer: there is nothing exactly on point ready to hand. It can be approximated quickly, though.

Slightly longer answer:

Depends on what information you need to pass on to your reader.

What will come into play is choosing from a combination of already existing biblatex styles and the entry types they support.

For example, for general purposes:

The oxnotes biblatex style has a @legal bib entry type, and piltreaty subentrytype, which handles the legally relevant dates. URLs are not really part of that picture (yet).

RequirePackagefilecontents
beginfilecontentsjobname.bib

@legalparis,
entrysubtype = piltreaty,
title = Paris Agreement,
shorthand = Paris Agreement,
execution = adopted=2015-12-12 and inforce=2016-11-04,
pagination = article,
journaltitle = United Nations Treaty Collection, Chapter XXVII 7. d,
url = https://treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-7-d&chapter=27&clang=_en,
urldate = 2019-03-28


endfilecontents

documentclass[12pt]article

usepackage[english]babel
usepackage[autostyle]csquotes
usepackage[style=oxnotes,
 isourls=true,
 ]biblatex
addbibresourcejobname.bib

begindocument

sectionOxnotes Style, @legal entry type
As stated in the citetitle[Article 4, paragraph 2]paris: ``Parties shall pursue domestic mitigation measures, ...''

printbibliography

enddocument

Result:

The apa style, by contrast, has a @data entry type which looks promising: it does a nice url, but its dates are limited (more publication-related), and there is not a cascade of them.

RequirePackagefilecontents
beginfilecontentsjobname.bib


@dataparis,
title = Paris Agreement,
type = UN Treaty,
entrysubtype = Treaty No. XXVII-7-d,
%shorthand = Paris Agreement,
day = 12,
month = 12,
year = 2015,
organization = United Nations,
 url =https://treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-7-d&chapter=27&clang=_en,
 urlday = 28,
 urlmonth = 3,
 urlyear = 2019,
 author = ,


endfilecontents

documentclass[12pt]article

usepackage[english]babel
usepackage[autostyle]csquotes
usepackage[style=apa]biblatex
addbibresourcejobname.bib

begindocument

sectionAPA Style, @data entry type
As stated in the citetitle[Article 4, paragraph 2]paris: ``Parties shall pursue domestic mitigation measures, ...''

printbibliography

enddocument

Result:

To get an idea of the effort needed to adapt a style, adding a url to the oxnotes legal entry turns out to be a one-line change, since all the heavy lifting and pre-work (field definition, assignment and allocation; date parsing and processing; options processing; string constant definition) has already been done.

We just get the already-formatted and packaged url+urldate and "bung it in" at the end (literally) of the bit that prints the formatted legal entry item in the bibliography (code from the foundational oxref.dbx file and copied into our document tex file's preamble:

DeclareBibliographyDriverlegal%
 usebibmacrobibindex%
 usebibmacrobegentry%
 iffieldequalsentrysubtypeexplanatorynote%
 printfield[default]title%
 setunitaddspacenewblock
 %
 iffieldequalsentrysubtypeparliamentarytype%
 usebibmacrolegal:parliamentary%
 %
 usebibmacrotreatycitation%
 setunitaddcommaspacenewblock
 printfield[default]note
 setunitaddspacenewblock
 setunitbibpagerefpunct%
 usebibmacropageref%
 usebibmacrourl+urldate%=========== this line
 usebibmacrofinentry

MWE:

RequirePackagefilecontents
beginfilecontentsjobname.bib

@legalparis,
entrysubtype = piltreaty,
title = Paris Agreement,
shorthand = Paris Agreement,
execution = adopted=2015-12-12 and inforce=2016-11-04,
pagination = article,
journaltitle = United Nations Treaty Collection, Chapter XXVII 7. d,
url = https://treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-7-d&chapter=27&clang=_en,
urldate = 2019-03-28


endfilecontents

documentclass[12pt]article


%=============================
usepackage[english]babel
usepackage[autostyle]csquotes
usepackage[style=oxnotes,
 isourls=true,
 ]biblatex
addbibresourcejobname.bib



%=============================
DeclareBibliographyDriverlegal%
 usebibmacrobibindex%
 usebibmacrobegentry%
 iffieldequalsentrysubtypeexplanatorynote%
 printfield[default]title%
 setunitaddspacenewblock
 %
 iffieldequalsentrysubtypeparliamentarytype%
 usebibmacrolegal:parliamentary%
 %
 usebibmacrotreatycitation%
 setunitaddcommaspacenewblock
 printfield[default]note
 setunitaddspacenewblock
 setunitbibpagerefpunct%
 usebibmacropageref%
 usebibmacrourl+urldate%=========== this line
 usebibmacrofinentry




begindocument

sectionOxnotes Style, @legal entry type (mod)
As stated in the citetitle[Article 4, paragraph 2]paris: ``Parties shall pursue domestic mitigation measures, ...''

printbibliography

enddocument

Result:

To change the apa style to be able to handle the dates is TML (too many lines) - for me, anyway :) . Doable, certainly. But not a five-minute job.
Although, thinking about it for a moment, the dates could go in as extra, individual fields, and then get formatted, and with bibstrings added. So, six minutes, then.