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Claims › How strong would Solar Cycle 25 be? The prediction debate

How strong would Solar Cycle 25 be? The prediction debate

Status: Contested

The claim: Solar Cycle 25 would be a weak cycle similar to Cycle 24 (the 2019 NOAA/NASA/ISES panel consensus). A competing 'terminator' method argued it could be one of the strongest on record.

Why this label: The outcome is now observed, and neither side called it exactly. The smoothed sunspot number peaked at 160.9 (2024-10), well above the panel's 105–125 range but far below the record cycle (smoothed 285.0 in 1958-03). Which forecasting method is best remains an active research question, so the label stays Contested.

Background

Forecasting the strength of a solar cycle is one of heliophysics' hardest problems. In 2019 an international panel combined nearly 50 community forecasts into a consensus of a peak smoothed sunspot number of 115 in July 2025. Two separate approaches disagreed: surface flux-transport modelling (AFT) supported a cycle similar to Cycle 24, while the 'terminator' timing method of McIntosh et al. argued for a very strong cycle. NOAA revised its forecast upward in 2023, and the Sun's maximum phase was announced in October 2024.

Evidence and arguments for

  • 2019 panel consensus: peak of 115 in July 2025 (range 105–125, timing November 2024–March 2026), with the panel describing a cycle of roughly the same size as Cycle 24. [1][2]
  • The AFT surface flux-transport model (Upton & Hathaway 2018) used polar magnetic fields at minimum, among the best-regarded precursors, and predicted Cycle 25 would be similar in strength to Cycle 24. [3]
  • McIntosh et al. (2020) used Hilbert-transform 'terminator' events and concluded that Cycle 25 might rank among the strongest cycles in the sunspot record, a sharp break from the consensus. [4]

Evidence and arguments against

  • Observed: SWPC's smoothed sunspot series peaked at 160.9 in 2024-10, above the panel's 105–125 range. Cycle 24 peaked at 116.4 (2014-04). The panel underestimated the cycle. [5]
  • NOAA's 2023 revised forecast called for a peak between January and October 2024 with a maximum of 137–173, consistent with what was observed. [6]
  • The observed peak is far below the record smoothed value of 285.0 (1958-03), so the strongest reading of the 'among the strongest on record' forecast also did not materialise. [5]
  • NASA and NOAA announced on 15 October 2024 that the Sun had entered its solar maximum period, adding that the exact peak month can only be identified afterwards. [7]

Open questions & what would change the label

Is the terminator method's timing signal a robust physical predictor or a statistical fit? Can flux-transport models improve with better polar-field data? A forecast for Solar Cycle 26 (expected to begin between 2029 and 2032, per SWPC) will be the next real test.

Sources

  1. NOAA SWPC: Solar Cycle 25 Forecast Update (panel consensus) https://www.spaceweather.gov/news/solar-cycle-25-forecast-update consensus
  2. NOAA SWPC: Solar Cycle Progression (panel details and live data) https://www.swpc.noaa.gov/products/solar-cycle-progression data
  3. Upton, L. A. & Hathaway, D. H. (2018). An Updated Solar Cycle 25 Prediction With AFT: The Modern Minimum. Geophysical Research Letters. doi:10.1029/2018GL078387 forecast
  4. McIntosh, S. W. et al. (2020). Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude. Solar Physics. doi:10.1007/s11207-020-01723-y forecast
  5. NOAA SWPC observed solar-cycle indices (JSON, smoothed SIDC sunspot number) https://services.swpc.noaa.gov/json/solar-cycle/observed-solar-cycle-indices.json data
  6. NOAA SWPC: NOAA forecasts quicker, stronger peak of solar activity (2023 revision) https://www.spaceweather.gov/news/noaa-forecasts-quicker-stronger-peak-solar-activity forecast
  7. NASA: NASA, NOAA: Sun Reaches Maximum Phase in 11-Year Solar Cycle (15 Oct 2024) https://science.nasa.gov/science-research/heliophysics/nasa-noaa-sun-reaches-maximum-phase-in-11-year-solar-cycle/ announcement

Interest signal: Wikipedia 'Solar cycle 25' averaged 5,257 views/month and 'Solar cycle' 9,050 (Oct 2025–Sep 2026). Sources were checked against Crossref/publisher pages on 2026-10-21. Labels describe the claim, not the people who hold it. Disclaimer.