Annual mean of GISTEMP global Ts+dSST temperature anomalies relative to 1951-1980.
Annual lo-pass filtered with a 4-yr running-mean filter.
The trends in return times of extremes page always uses the annual mean smoothed version.

Smoothing is done with a 4-year average, where the value of year 3 is given by the average over years 1-4. So GMST_2019 is the average over GMSTs of 2017-2020. For the most recent years this implies the following: assuming we are living in 2021, in the year 2021 there are GMST values available up to 2021. The smoothed GMST is an average over 2019-2021. The value for 2022 is an average over 2020-2021. the last eight values represent conventions for 1.5, 2.0, 3.0 and 4.0 degree worlds relative to pre-industrial and 1880-1900.

data page: GISTEMP