How can scientists accurately know the global temperature 120,000 years ago?

Question

Scientist claims that July 2023 is the hottest July in 120,000 years.
My question is: how can scientists accurately and reproducibly state this is [the hottest month of July globally in 120,000 years](https://www.theage.com.au/environment/climate-change/the-hottest-july-in-120-000-years-what-s-in-store-for-australia-this-summer-20230719-p5dpm3.html)?

In: 4028

Answer 1

How can they accurately know it 120 years from now?