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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Step Function

This animation refutes the myth that the global temperature record is somehow explained by "climate shifts" or "step functions", when in reality the record is physically explained by an underlying long-term trend of increasing temperature (global warming caused by human greenhouse gas emissions) plus the superimposed effects of noise and natural cycles such as the El Nino Southern Oscillation (ENSO) and the solar sunspot cycle.  Using simulated temperature data to illustrate how these physical factors combine to explain the appearance of the real temperature record, the frames show:  1) a 0.2°C per decade global warming trend; 2) two "natural cycles" of amplitude 0.15°C and periods of 10 and 20 years; 3) random noise of amplitude 0.07°C; 4) the sum of the warming trend, cycles and noise (the simulated temperature record); 5) a fit to the sum using a step function given by 3 linear trends from 1950-1963, 1967-1986, and 1987-2003 (light blue); and 6) a linear fit to the entire time period 1950-2010, which has slope 0.21°C per decade (red).  The fit to the complete simulated temperature record in frame 6 is almost identical to the assumed global warming trend of 0.2°C in frame 1, just like the situation in the real world where short-term cycles and noise don't contribute to the long-term global warming trend.


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