As material on the internet can be removed or changed, it is important to add the date that you accessed/viewed the information – it might not be there in a few months’ time.
Generally, web pages do not have page numbers. To help your reader locate where you have quoted from, you could number the paragraphs on the page and use this instead of a page number in your in-text citation. You can also use the phrase non-paginated to replace page numbers.
Sneed, A. (2019) The reason Antarctica is melting: shifting winds, driven by global warming. Available at: https://www.scientificamerican.com/article/the-reason-antarctica-is-melting-shifting-winds-driven-by-global-warming/ (Accessed: 23 July 2020).
Section E10.1 in CTR Harvard
United Nations Development Programme (2020) Sustainable development goals. Available at: https://www.undp.org/content/undp/en/home/sustainable-development-goals.html (Accessed: 29 April 2020).
Section E10.2 in CTR Harvard
Cool Antarctica (no date) Antarctica and global warming: the effects of global warming on Antarctica. Available at: https://coolantarctica.com/Antarctica%20fact%20file/science/global_warming.php (Accessed: 23 July 2020).
Section 10.5 in CTR Harvard