Definition
Slow change is improvement (or deterioration) that occurs at less than about 1% per year — too gradual to feel year-to-year, too gradual to make news, but cumulatively meaningful over a generation. A steady 1% per year compounds to roughly 35% over thirty years; 0.5% to about 16%.
Rosling argues that most of the big positive trends in human welfare — falling child mortality, rising literacy, lengthening lifespan — are slow-change phenomena, which is why they are systematically under-reported.
Why it matters
How it works
The math: a quantity changing at rate r per year over n years multiplies by (1+r)^n. At r = 0.01, n = 30, the factor is about 1.35; at r = 0.005, about 1.16; at r = 0.02, about 1.81. The corollary: r above ~2% per year is newsworthy and gets covered; r in the 0.5% to 1.5% band almost never does, even though it dominates long-run outcomes.
To see slow change, plot a long series — at least 30 years, ideally 50 — on a single chart. The visual undoes the memory failure: each year looks flat, but the line as a whole has obviously moved. Without that picture, slow change is hard to defend in conversation against vivid recent events.
Note the symmetry: slow deterioration is just as invisible as slow improvement. Sea-level rise, soil depletion, and trust erosion are all candidate slow-change processes whose annual magnitude looks ignorable while their thirty-year accumulation does not. The same chart-discipline applies in either direction.