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The South Atlantic Anomaly is growing and splitting

Status: Mainstream Verdict: Supported by satellite data

The claim: The weak spot in Earth's magnetic field over the South Atlantic is expanding, deepening and dividing into two lobes.

Why this label: ESA's Swarm mission finds that the region where surface field strength is below 26,000 nT grew by 0.9% of Earth's surface area between 2014 and 2025 (nearly half the area of continental Europe). Its minimum fell by 336 nT, and a second area of minimum intensity southwest of Africa has weakened faster since 2020. ESA first described the possible split into two cells in 2020.

Background

The South Atlantic Anomaly (SAA) is a region stretching from South America toward southern Africa where the magnetic field at the surface is unusually weak. It matters mostly in space: satellites crossing it receive higher radiation doses and are more prone to glitches. ESA says that at ground level it 'presents no cause for alarm'. It is not linked to any known health effect at the surface, and nothing on this page is health or safety advice. BGS also reported a new weak region developing offshore of South Africa in its IGRF-14 update.

Evidence and arguments for

  • Swarm (2014-2025): the area below 26,000 nT grew by 0.9% of Earth's surface area, and the minimum intensity fell from 22,430 nT to 22,094 nT. [1]
  • ESA (2025): a region southwest of Africa has weakened faster since 2020. The lead author links this to 'reverse flux patches' at the core-mantle boundary moving westward under Africa. [2]
  • ESA (2020): from 1970 to 2020 the minimum dropped from about 24,000 to 22,000 nT. The anomaly drifted west at about 20 km per year, and a second minimum emerged, suggesting a split into two cells. [3]
  • NOAA NCEI's 2025 annual report describes the SAA as deepening and reports an 8% growth in size over the past year (by NCEI's own measure). [4]

Evidence and arguments against

  • Whether it fully 'splits' is still developing. ESA's 2020 wording was that it 'could split up into two separate cells'. [3]
  • Growth of the SAA is not by itself evidence of an impending reversal. Paleomagnetic reconstructions show similar structures that recovered. [5]

Open questions & what would change the label

What drives the reverse-flux patches beneath the South Atlantic and Africa, and how long the growth continues. What would change the status: Swarm or successor missions showing the area shrinking or the minimum strengthening.

Sources

  1. Finlay, C. C. et al. (2025). Core field changes from eleven years of Swarm satellite observations. Physics of the Earth and Planetary Interiors. doi:10.1016/j.pepi.2025.107447 data
  2. ESA, 13 Oct 2025: Swarm reveals growing weak spot in Earth's magnetic field. https://www.esa.int/Applications/Observing_the_Earth/FutureEO/Swarm/Swarm_reveals_growing_weak_spot_in_Earth_s_magnetic_field data
  3. ESA, 20 May 2020: Swarm probes weakening of Earth's magnetic field. https://www.esa.int/Applications/Observing_the_Earth/FutureEO/Swarm/Swarm_probes_weakening_of_Earth_s_magnetic_field data
  4. NOAA NCEI news, 9 Jan 2026: 2025 WMM Annual Report (State of the Geomagnetic Field) is released. https://www.ncei.noaa.gov/news/2025-wmm-annual-report-released data
  5. Brown, M. et al. (2018). Earth's magnetic field is probably not reversing. PNAS. doi:10.1073/pnas.1722110115 critic/test

More in this section: Geomagnetic Field & Pole Shift, including the current status of the geomagnetic field.

Interest signal: Wikipedia 'South Atlantic Anomaly' averaged 5,911 views/month (Oct 2025-Sep 2026). Sources were checked against Crossref/publisher pages on 2026-10-22. Labels describe the claim, not the people who hold it. Disclaimer.