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
What Michael E Mann said was, from his Twitter:
> [July will be the warmest month this planet has seen in modern history (and plausibly the past 120,000 years)](https://twitter.com/MichaelEMann/status/1681664587697889282)
It is so far the hottest global average temperature since we have been keeping accurate records using thermometers. That part is certain.
Climatologists have accurate global coverage of temperatures measured by thermometers since 1970, [and thermometer measurements for limited locations (mainly developed nations) since the late 1800s.](https://www.metoffice.gov.uk/hadobs/hadcrut5/)
Earlier than that they have to use things called proxy measurements. They’re “proxy” because they are measurements that are strongly correlated to temperature and they have a good understanding of that correlation.
Others have mentioned isotope records. Oxygen has 2 dominant isotopes, O-16 and O-18. The both occur naturally, and the ratio between O-16 and O-18 is dependent on temperature. So climatologists can measure that ratio inside ancient ice and fossils to determine the temperature. There’s also other chemical-based proxies, called ‘[Paleothermometers](https://en.wikipedia.org/wiki/Paleothermometer#)’ like magnesium-calcium ratios, or TEX86 and UK37 (chemicals in cells).
Glacial ice also preserves bubbles of air from the time the ice solidified. Very carefully they can extract the ancient air and get a measurement of the atmospheric composition from back then. Using the concentration of CO2 and other greenhouse gases they can base a temperature on that too.
[Another proxy is literally tree rings](http://www.climatedata.info/proxies/tree-rings/). Biologists know how wide the gap between rings are for certain environmental conditions, and climatologists look at old trees and measure the gap to get the temperature.
For ocean temperature measurements they can use an “assemblage” proxy. Based on what we know of how different plankton species are distributed across different sea temperatures today, they can search for these plankton fossils in ocean sediments and get an estimate of the temperature then.
Climatologists won’t just rely on a single proxy. All of these have their limits and uncertainties, so they will combine all of them to eliminate errors to get that 120,000 year timespan.
The problem with going back in time is that you lose “time resolution” as the scale gets squished. Most proxies are naturally based on seasons, so you get a one record of winter conditions, and another for summer, at best. So basically beyond what they have directly measured, it’s nearly impossible to be certain whether or not this July is the hottest July in 120,000 years.
But it is definitely the hottest since we kept direct temperature measurements.
https://theconversation.com/is-it-really-hotter-now-than-any-time-in-100-000-years-210126
Latest Answers