Bollinger Bands and the Evolution of Global Temperature Anomaly Trends

Since 1970, the global temperature anomaly trend has been locked into a narrow upwards channel between the 20-year rolling mean (orange line) and upper band (green line), representing two standard deviations.

The narrow channel of the temperature anomaly trend and steady bandwidth are sharp departures from pre-1970 behavior. It is not surprising that the temperature anomaly trend remains above the mean for prolonged periods given the steady rise in temperatures over the past five decades. But it is remarkable how range bound the trend has remained for 50 years – stubbornly sticking above the mean after 70+ years of oscillating between top and bottom bands.

That a trend occurring at a global scale, driven by an astonishingly complex interaction between anthropomorphic and natural variables, can behave so dependably is astonishing.

The change in trend behavior does correlate with the steeping of the atmospheric CO2 concentration slope in 1960 (but that doesn’t necessarily equate to causation).

graph with two lines, one showing annual atmospheric carbon dioxide and the other showing carbon dioxide emissions from 1750-2019

One bit of ‘technical analysis’: Narrowing or tightening bands in a low-volatility environment are often regarded by technical analysts as a sign that a sharp move is near. Sure enough, when the bands narrowed in the late 1930s, the temperature anomaly shot up above the upper band for three out of four years.

Chart notes: temperature units are degrees Celsius. Bollinger Band settings – window: 20, standard deviations: 2. Temperature data for Land and Ocean from NOAA National Centers for Environmental Information,
Climate at a Glance: Global Time Series, published May 2021, retrieved on May 26, 2021 from

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