CLIM-03 / SPM.A / Research primer
Do Arctic and Antarctic sea ice tell the same story?
How do seasonal sea-ice changes differ between hemispheres when months, reference periods and measurement definitions are held consistent?
NASA/GSFC/Michael Studinger. The calving front of Gyldenlove Glacier in southeast Greenland, photographed during Operation IceBridge in 2011. Contextual image; not used to estimate a trend. Image credits.
The question
A global sea-ice total can conceal different seasonal histories. This comparison keeps the two poles visible and tests how much the selected month changes the impression.
Why it matters
Hemispheric differences help readers distinguish a regional observation from a global climate argument without treating one pole as a control experiment.
The AR6 anchor
AR6 assesses widespread, rapid cryospheric change and intensification of multiple hazards with additional global warming (high confidence).
AR6 Synthesis Report (2023) / A.2; B.1.
Evidence and comparison
- Unit of analysis
- Hemisphere-month-year, with world-year temperature as background context.
- Baseline and denominator
- Use each hemisphere's same calendar month in 1981-2010; retain absolute extent beside percentage anomalies. Do not compare opposite seasons as equivalent observations.
- First descriptive test
- Compare March and September extent histories separately, then summarize changes between fixed decades with a shared extent scale within each seasonal comparison.
- Deeper analysis
- Test trend sensitivity to start years and individual extreme seasons. Use dependence-aware intervals if fitting trends; a visually chosen breakpoint requires independent justification.
- Attribution status
- descriptive observation
- Uncertainty
- Retain quality flags and distinguish retrieval uncertainty from interannual variability. An extreme minimum alone cannot identify a new regime.
Principal sources
- NSIDC Sea Ice Index v4
Monthly sea-ice extent (million square kilometers); Hemisphere; Quality flags.
Target 1979-2025, Sea Ice Index v4; completeness and release checks pending. Candidate source; import and publication checks are still required. - Indicators of Global Climate Change
Annual observed global temperature anomaly (degC).
Target 1979-2025 from IGCC 2025; compact export verification pending. Candidate source; import and publication checks are still required.
Alternative explanations
- Atmospheric circulation
- Ocean heat transport
- Satellite processing changes
The visual argument
Provisional: seasonal small multiples with a month selector; annotate the reference climatology and selected decade differences, never a combined global cancellation total.
- Monthly climatology comparison
- Absolute versus percentage changes
- Trend endpoint sensitivity
- Separate global-temperature context
What these data do not show
- Extent does not measure ice thickness or volume.
- Co-movement with global temperature is not a new attribution analysis.
Reproducibility and next release
Plan src/build.mjs, immutable data/raw monthly files and data/processed/sea-ice.csv; provenance checks will verify hemisphere-month keys, missing seasons, units, climatologies, version hashes and redistribution terms.
- After approval: two-pole web study
- Article and seasonal methods
- Responsive figures and exact values
- 16:9 hero and LinkedIn launch
- Optional PDF carousel
- Light/dark exports and processed CSV