The Version 6.0 Global Average Lower Tropospheric Temperature (LT) Anomaly for January, 2021 has come out at just +0.12 deg. C above the baseline, down 0.03 deg. C from the December, 2020 value of +0.15 deg. C.
[NOTE: Dr Roy Spencer and Dr John Christy –who update the chart at the beginning of every month– have changed the 30-year averaging period used to compute anomalies from 1981-2010 to 1991-2020. They stress, “this change does not affect the temperature trends.”]
Since 1979, NOAA satellites have been carrying instruments which measure the natural microwave thermal emissions from oxygen in the atmosphere.
The intensity of the signals these microwave radiometers measure at different microwave frequencies is directly proportional to the temperature of different, deep layers of the atmosphere.
The global temperature datasets represent the piecing together of the temperature data from a total of fifteen instruments flying on different satellites over the years. The graph (shown below) represents the latest update; updates are usually made within the first week of every month.