Figure 1 shows how the global surface temperature has increased since pre-industrial time.
The blue dots are the monthly temperature anomalies, the blue curve is the five years moving average, and the red line is the trend calculated over the last 30 years. The reference period is from January 1880 till December 1909. The temperature in that period is often considered as the temperature in pre-industrial time, mainly because we do not have reliable global temperature measurements before that. Consequently, the figure shows the warming since pre-industrial time.
The trend line ends at 1.19°C in August 2020. It is reasonable to say that the global surface temperature has increased by that value since pre-industrial time.
|Figure 1: The average of four global surface temperature series. The reference period is from January 1880 till December 1909.|
The temperatures in Figure 1 are the average of the four series NASA GISTEMP, NOAA Global, Berkeley BEST and HadCRUT4 kriging. These series all have global coverage. They were downloaded from their sources in the beginning of October 2020.