Solar Minimum Cooling Accelerates

Pretty much as predicted over the past 5 years, we are seeing lower troposphere temperatures turning south and solar activity declines.

The plot above presents April 2021 data reported from AMSU-B radiometers aboard NOAA satellites. April 2021 dipped -0.05C below the 1991-2000 average.

AMSU-A + AMSU-B have flown together on the 3 NOAA KLM satellites: NOAA-15 (NOAA K), launched May 13, 1998; NOAA-16 (NOAA L), launched September 21, 2000; and NOAA-17 (NOAA M), launched June 24, 2002.

The AMSU was an improvement of the Microwave Sounding Unit (MSU), incorporating capabilities of the Stratospheric Sounding Unit (SSU), both of which had flown on TIROS-N in 1978 and continued on the NOAA-6 through NOAA-14 satellites. The next generation in the family is the Advanced Technology Microwave Sounder (ATMS), first flown on Suomi-NPP in 2011 and now standard equipment on the JPSS series of satellites, the first of which, NOAA-20, launched in 2017.

This technology has yielded the most accurate and reliable atmopsheric data covering the more recent 40 years.

AMSU also casts a shadow on the accuracy and reliability of Earth-based temperature data underlying IPCC’s climate models and the HadCRUT 4 dataset.

As discussed in Steiner et al. (2020):

The results show a robust cooling of the stratosphere of about 1–3 K, and a robust warming of the troposphere of about 0.6–0.8 K over the last four decades (1979–2018). Consistent results are found between the satellite-based layer-average temperatures and vertically resolved radiosonde records.

We see the 0.6-0.8 trend in the AMSU satellite data above. Steiner et al. associates with ENSO the prominent variability in tropospheric data .

But note the stratospheric cooling over the same period. And note the evolution of these trends.

Fig. 3.

Steiner et al. present results consistent with those of Mlynczak et al. (2018). They used SABER satellite data to measure the actual infrared power radiated by atmospheric NO and by CO2 (i.e., “greenhouse warming”). They determined the time series data has a significant dependence on both solar irradiance and geomagnetic processes. As of February, 2018, the thermosphere power is in the lowest quintile of values, to which we assign the level of ‘Cold.’ These empirical findings are at odds with IPCC models to date which assume-away and dismiss TSI effects as inconsequential

As seen below, Mlynczak reports declining greenhouse warming since ~1960, and the lesser peak ~1980.

Fig. 4

As the AMSU record indicates, the stratospheric cooling experienced in the current declining solar period is not impacting tropospheric temperatures.


Mlynczak, M. G., Hunt, L. A., Russell, J. M., & Marshall, B. T. (2018). Thermosphere climate indexes: Percentile ranges and adjectival descriptors. Journal of Atmospheric and Solar-Terrestrial Physics174, 28–31.

Steiner, A. K., Ladstädter, F., Randel, W. J., Maycock, A. C., Fu, Q., Claud, C., … Zou, C.-Z. (2020). Observed temperature changes in the troposphere and stratosphere from 1979 to 2018. Journal of Climate33(19), 8165–8194.

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