[Paper Review] Structural break models of climatic regime-shifts: claims and forecasts

David Stockwell, Anthony Cox|ArXiv.org|Jul 9, 2009

Climate variability and models34 references3 citations

TL;DR

This study uses Chow tests for structural breaks to evaluate claims about climatic regime-shifts in global and Australian temperature data. It identifies significant breakpoints in 1978 (global and Australian temperature) and 1982 (Australian rainfall), supporting the hypothesis that natural oceanic regime-shifts—particularly the 1976–1979 Pacific Decadal Oscillation transition—account for much of the observed warming, reducing the estimated anthropogenic global warming rate to 0.05°C per decade.

ABSTRACT

A Chow test for structural breaks in the surface temperature series is used to investigate two common claims about global warming. Quirk (2009) proposed that the increase in Australian temperature from 1910 to the present was largely confined to a regime-shift in the Pacific Decadal Oscillation (PDO) between 1976 and 1979. The test finds a step change in both Australian and global temperature trends in 1978 (HadCRU3GL), and in Australian rainfall in 1982 with flat temperatures before and after. Easterling & Wehner (2009) claimed that singling out the apparent flatness in global temperature since 1997 is 'cherry picking' to reinforce an arbitrary point of view. On the contrary, we find evidence for a significant change in the temperature series around 1997, corroborated with evidence of a coincident oceanographic regime-shift. We use the trends between these significant change points to generate a forecast of future global temperature under specific assumptions.

Motivation & Objective

• To test the statistical significance of claimed regime-shifts in global and Australian climate data.
• To evaluate whether the apparent flat temperature trend since 1997 is statistically justified or 'cherry-picked'.
• To assess whether structural break models provide a better fit than linear trends for global and regional temperature series.
• To forecast future global temperatures under structural break assumptions, distinguishing between anthropogenic warming and natural variability.
• To examine the role of oceanic regime-shifts—particularly the PDO and related oceanographic changes—in modulating global temperature trends.

Proposed method

• Application of the Chow test (F-statistic) to detect structural breaks in annual temperature and rainfall anomaly time series.
• Use of the R package 'strucchange' to compute F-statistics across all potential break points in the data.
• Analysis of HadCRU3GL global monthly temperature anomalies and Bureau of Meteorology (BoM) data for Australian temperature and rainfall (1910–2008).
• Segmentation of time series into distinct linear trends around identified breakpoints to estimate post-break trends.
• Incorporation of oceanographic evidence (e.g., upwelling changes, sea surface temperature anomalies, volume transport) to corroborate structural break timing.
• Forecasting future global temperatures by projecting post-break trends under assumptions of continued underlying anthropogenic warming and no new regime-shifts.

Experimental results

Research questions

• RQ1 Is the claimed 1976–1979 regime-shift in Australian temperature statistically significant according to structural break analysis?
• RQ2 Does the apparent flat global temperature trend since 1997 represent a significant structural break or is it a result of 'cherry-picking'?
• RQ3 To what extent do oceanographic regime-shifts, such as the Pacific Decadal Oscillation transition, explain observed temperature trends?
• RQ4 How does the estimated rate of anthropogenic global warming change when structural breaks are accounted for versus when linear trends are assumed?
• RQ5 What are the implications for future climate projections when structural break models are used instead of linear trend models?

Key findings

• A significant structural break in global surface temperature trends is detected at 1978 (HadCRU3GL), with a change in slope from a pre-break trend to a steeper post-break trend.
• A significant structural break in Australian rainfall is identified at 1982, with flat temperature trends before and after, suggesting a regime-shift in precipitation rather than temperature.
• The estimated anthropogenic warming rate is reduced from ~0.14°C/decade to ~0.05°C/decade when accounting for the 1978 regime-shift, indicating a major role for natural variability.
• The 1997 breakpoint is statistically significant, supporting the claim that the flat temperature trend since 1997 is not arbitrary but reflects a real climate regime-shift.
• Oceanographic evidence—including reduced equatorial upwelling, altered volume transport, and sea surface temperature changes—corroborates the 1976–1979 regime-shift timing.
• Forecasting under the structural break model projects near-stable global temperatures until ~2050, followed by a rise to ~0.2°C above present levels by 2100, assuming continued underlying AGW and no new regime-shifts.