Southeastern Brazil inland tropicalization: Koppen system applied for detecting climate change throughout 100 years of meteorological observed data

Many regions around the world are facing climate changes, with substantial increase in air temperature over the past decades, which is mainly related to continental and global warming forced by the higher greenhouse gas (GHG) emissions. The objectives of this study were to use the Koppen climate classification to detect local climate change based on a historical series of 100 years and to assess if such change is related to those that are occurring in other spatial scales as a likely consequence of increasing GHG. This paper brings a content full of innovative results. The study area presented an average annual air temperature increase by 0.9 degrees C between 1917 and 2016, rising from 21.4 degrees C for the first climatological normal (1917-1946) to 22.3 degrees C for the last one (1987-2016). Furthermore, in the summer months, the temperature rose from 24.5 to 25.3 degrees C, and in the winter months, such increase was from 17.1 (1917-1946) to 18.3 degrees C (1987-2016). Our findings showed the subtropical conditions (Cfa in Koppen's classification) in the study area persisted from the beginning of the analysis (1917-1946) until the climatological normal of 1979-2008, with a clear tendency of tropicalization after that with a change in the climate type of Piracicaba from subtropical to tropical, which can now be classified as tropical with dry winter (Aw climate type). The local average air temperature showed concordances with the long-term air temperature anomalies from regional, continental, and global scales, indicating that all of them may be linked with increasing GHG emissions, since well-defined long-term linear relationships (r(2) = 0.99) were observed between continental and global average air temperature anomalies and atmospheric CO2 concentration observed at the NOAA Lab in Mauna Loa in the last 59 years. While the local and regional forcing effects remain to be fully unraveled, our study provided a valid and strong scientific sound evidence that climate change occurred in Piracicaba, southeastern Brazil, in the last 100 years.