Ultimately derived from here: https://journals.ametsoc.org/view/journals/apme/18/7/1520-0450_1979_018_0861_taospi_2_0_co_2.xml?tab_body=pdf https://journals.ame

Ultimately derived from here: https://journals.ametsoc.org/view/journals/apme/18/7/1520-0450_1979_018_0861_taospi_2_0_co_2.xml?tab_body=pdf https://journals.ametsoc.org/view/journals/apme/18/7/1520-04... The equation came later - the output of that article is just a table, and the equation was derived to be a nice fit over the table's values.