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)?
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Buy combining lots of data points. Ice cores can show how much snow fell in that year and since layers of snow formed at different temperatures have distinct chemical properties, all of these layers can give us some insight to the existing temperature conditions of that time.
Tree rings can tell you how much the tree grew that year, the bigger the rings the warmer the year. So a fossil of a tree can tell you about the growing conditions, plus the location of the tree. If you find a tree that will only grow in a range of temperatures in a location, you can assume that location was within those ranges. For example, you might find a tree the only grows in hot climates in the Greenland fossil record, so you can infer that Greenland was a lot hotter in the past.
Sediment on the bottom on lakes may contain shells of small, surface-living animals that are deposited over millions of years. Oxygen isotopes present in these sediments, again provide a range of temperatures
The more datasets that you combine will narrow the range that the temperature could be.
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