How has the Sun’s energy changed over the last 45 years?

For centuries, it has been known that the Sun goes through subtle and not-so-subtle changes over time. For instance, when Galileo Galilei pointed his telescope at the Sun, he discovered that the Sun is imperfect and often blotched by dark areas known as sunspots. We now know that sunspots are very large features – often many times larger than the Earth. However, it was only in 1978, when the first satellite missions to continuously monitor the Sun were launched, that it became possible to directly measure the changes in the Sun’s energy, without the Earth’s atmosphere getting in the way.

Sun-monitoring instruments on satellites describe the energy reaching the Earth from the Sun in terms of the Total Solar Irradiance (TSI). These satellite measurements show that the average TSI reaching the Earth is around 1360-1365 Watts per meter squared (W/m2). They also show the TSI rises and falls slightly over the course of a sunspot cycle (roughly 8-13 years). However, most of the satellite missions only last for around 1 to 2 sunspot cycles. Therefore, in order to study the changes in TSI for longer than 10-15 years, scientists need to composite, or “stitch together”, the TSI measurements from multiple satellite missions.

For more than 20 years, there has been ongoing scientific controversy between rival scientific teams on how to best composite the TSI missions into a continuous record for the entire satellite era, i.e., from 1978 to the present.

For example, the Active Cavity Radiometer Irradiance Monitoring (ACRIM) team in charge of the NASA ACRIM satellite project took the approach of using the data as provided by the satellite mission science teams. In contrast, the Physical Meteorological Observatory in Davos (PMOD) team applied various data adjustments to each of the satellite missions before constructing their composite.

The ACRIM composite suggested that as well as the changes in TSI over the course of a sunspot cycle, there are also long-term changes in TSI between sunspot cycles. It suggested the possibility that these long-term changes in TSI could be contributing to global warming.

However, the PMOD composite suggested that TSI does not change much between sunspot cycles. It ruled out the possibility of TSI changes being a major factor in global warming.

The UN’s Intergovernmental Panel on Climate Change (IPCC)’s latest reports explicitly favored composites like PMOD’s over ACRIM’s.

A major study, led by the Center for Environmental Research and Earth Sciences (www.CERES-Science.com), has just been published that revisits this long-standing scientific controversy and provides important new insights that could change our understanding of the long-term changes in TSI over timescales longer than 10-15 years.

This new peer-reviewed paper was published in the prestigious journal, The Astrophysical Journal, founded in 1895, it remains one of the top journals in astronomy and astrophysics.

The scientists in the team reanalyzed all the available satellite data from the first Nimbus 7 mission to the currently active missions on the Solar and Heliospheric Observatory (SOHO) spacecraft and Total and Spectral Solar Irradiance Sensor 1 (TSIS-1) on the International Space Station (ISS). They updated several of the older composites, as well as developing a wide range of new composites. In total, they found 21 different composites for the satellite era – including the 4 existing composites currently used by the scientific community.

Using common statistical techniques, these 21 composites were sorted into 6 main composite groups – labelled “A” to “F”, as seen in the chart below:

One group (“A”) matches very well to the PMOD composite and to the various solar activity datasets used in the IPCC’s most recent report. This group implies that there has been little or no contribution of the Sun to any of the global warming during the satellite era, i.e., since 1978.

Two groups (“B” and “C”) agree with the original ACRIM composite that had implied that solar activity might have contributed to global warming in the 1980s and 1990s, but that solar activity had since declined.

However, two other groups (“D” and “E”) suggest a new history of TSI variability in the satellite era. They agree with ACRIM that solar activity might have contributed to global warming in the 1980s and 1990s and that solar activity slightly decreased since the early 2000s. But, unlike ACRIM, they suggest that solar activity is still higher than in the 1980s and therefore might still be contributing to global warming.

The sixth group (“F”) – that is the only group that does not include any of the satellite data associated with the original PMOD team – suggests that solar activity has continued to increase throughout all four of the solar minima during the satellite era so far. It also confirms that the current ongoing solar maximum is already higher than the last cycle. If this composite group is correct, it would completely change our current understanding of how solar activity has changed over the last 45 years.

The team behind this new paper were shocked at how many completely different plausible composites could be generated from the available satellite data as provided by the satellite mission science teams.

The lead author of the study, Dr. Ronan Connolly, said, “As we explain in the paper, Group A – the one closest to that used by IPCC and many of the current climate modelling groups – is probably the most unreliable of the six. This is because of the heavy data adjustments and subjective data truncations that were applied to the original satellite mission team’s data.”

However, they have not yet established conclusively which of the six composite groups are most accurate. For this reason, the team have provided all these new, updated and existing composites to the scientific community so that other researchers can work on resolving these new challenges.

The new dataset is freely available through the Supporting Data at the journal website, as well as at the CERES-Science website and the Zenodo dataset repository website.

Citation details for the study:

• Ronan Connolly, Willie Soon, Michael Connolly, Rodolfo Gustavo Cionco, Ana G. Elias, Gregory W. Henry, Nicola Scafetta, and Víctor M. Velasco Herrera (2024). “Multiple new or updated satellite Total Solar Irradiance (TSI) composites (1978-2023)”. The Astrophysical Journal, 975 (1), 102. https://doi.org/10.3847/1538-4357/ad7794