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Earth's magnetic field is weakening

Status: Mainstream Verdict: Supported by measurements

The claim: The overall strength of Earth's magnetic field has been falling since direct measurements began in the 1800s.

Why this label: Observatory and satellite records agree that the global (dipole) field has weakened since the 1830s-1840s: about 9% over the last 200 years on a global average according to ESA and NASA, about 10% since the 1830s according to USGS, and about 5% per century since 1840 according to Brown et al. (2018). The decline is uneven: some regions, such as Siberia, have strengthened in the Swarm era.

Background

Earth's main field is produced by moving liquid iron in the outer core, roughly 3,000 km down, and it changes continuously. Since magnetometers were invented, the strength of its dipole part has declined. The decline is real and well measured. What it means for the future is a separate question, covered in Is a geomagnetic reversal overdue or imminent?. For the latest figures, see the status of the geomagnetic field.

Evidence and arguments for

  • ESA, using Swarm and earlier data, puts the global loss at about 9% of field strength over the last 200 years. [1]
  • NASA gives the same figure: about nine percent weaker on a global average over the past 200 years. [2]
  • USGS states that average surface intensity has fallen by about ten percent since magnetometers were invented in the 1830s. [3]
  • Brown et al. (2018) describe a decay of roughly 5% per century since at least 1840, with indirect (archaeomagnetic) evidence that it began earlier. [4]
  • Eleven years of Swarm satellite data (2014-2025) show the weakest-field region over the South Atlantic expanding and its minimum intensity falling from 22,430 nT to 22,094 nT. [5]

Evidence and arguments against

  • The weakening is not uniform. Between 2014 and 2025 the strong-field region over Siberia grew and its peak intensity rose by 260 nT, while the Canadian strong-field region shrank. [5]
  • In context: NASA notes that paleomagnetic studies show today's field is about as strong as it has been over the past 100,000 years, and about twice its million-year average. [2]
  • USGS notes that large intensity changes appear in the paleomagnetic record without leading to a reversal, and that the field could strengthen again. [3]

Open questions & what would change the label

How long the current decline will last, and whether it is a decade-to-century fluctuation or part of a longer trend, cannot be predicted from present data. What would change the status: a sustained global increase in dipole strength in the observatory and satellite record.

Sources

  1. 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
  2. NASA Science (2021): Flip Flop: Why Variations in Earth's Magnetic Field Aren't Causing Today's Climate Change. https://science.nasa.gov/science-research/earth-science/flip-flop-why-variations-in-earths-magnetic-field-arent-causing-todays-climate-change/ background
  3. USGS FAQ: Are we about to have a magnetic reversal? https://www.usgs.gov/faqs/are-we-about-have-a-magnetic-reversal critic/test
  4. Brown, M. et al. (2018). Earth's magnetic field is probably not reversing. PNAS. doi:10.1073/pnas.1722110115 critic/test
  5. 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

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

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