The Shifts Hypothesis – an alternative view of global climate change

Guest post by Pavel Belolipetsky

The IPCC, Bob Tisdale and others have presented hypotheses to explain 20th century warming. This article presents another. My co-workers and I call it the “Shifts” hypothesis. And we consider it to have advantages over other hypotheses in terms of simplicity, consistency over time, and homogeneity for the two considered regions. It is described in a submitted paper which can be read here

http://arxiv.org/ftp/arxiv/papers/1303/1303.1581.pdf

Its simplicity is that it uses only two factors to obtain an explanation of general features in each considered region. And it displays consistency over time because it provides the same explanation for the warming of the beginning and of the end of 20th century. This consistency enabled a fit of linear regression coefficients of data from first part of century (before 1950) to obtain similar reconstruction for the second part (after 1950). The homogeneity between regions means that shifts occur at similar times in the temperature time series of the tropics and of the north middle latitudes although the two time series differ. This homogeneity provides confidence that the Shifts Hypothesis applies globally.

It is an old idea that climate exists in “regimes” (or states) and that climate variations often occur in the form of shifts between them. Thus, regime shifts are rapid reorganizations from one relatively stable state to another. The idea gained in acceptance in the 1990s.

Many articles have been published [1-20], showing that climate shifts appear to be an essential feature of Earth’s climate system. Yasunaka and Hanawa [20] described a “regime shift” as an abrupt transition from one quasi-steady climatic state to another, and its transition period is much shorter than the lengths of the individual epochs of each climatic state. Kevin Trenberth [15] was among the first to characterize a climate shift and reported a “different regime after 1976”. Douglass and Knox [6] wrote that abrupt shifts in Earth’s climate system are common.

Lo and Hsu [10] provide a good illustration of climate shift in northern extratropical hemisphere at late 80th (Fig. 1)

Fig. 1. Time series of 9-year running-mean surface temperature anomalies (°C) in five chosen regions. Modified from Lo and Hsu (2010).

Importantly, the idea of quasi-stable regimes and sharp shifts between them is very different from the widespread view (e.g. of the IPCC) that the climate system is naturally in equilibrium and passively follows changes in radiation forcing. The existence of regimes and shifts between them suggests there may be strong negative feedbacks and buffering spaces holding the system in each regime. And there should be critical thresholds, after reaching which system moves from one regime to another.

The common feature of all studies concerning climate shifts is that causes of observed shifts are unknown. Or, in other words, there are no outstanding changes in known external forcing which induce climate shifts. For example, what extraordinary changes of forcing to northern extratropical regions are known which can produce the changes shown in Figure 1? And it is clear that IPCC climate models showing near constant feedbacks are unable to reproduce these features.

It seems that the only available mechanisms for the observed shifts are weakening of negative feedbacks or strengthening of positive feedbacks over short periods. Why and how the feedbacks would vary is not known, but there is clear need to determine this.

In our studies of regimes and shifts we considered sea surface temperature (SST) and not combined land-ocean temperatures: this was to diminish the level of variability which may mask the shifts. We compared two important regions; i.e. tropics (30S-30N), and the north middle latitudes (30N-60N). We found that probably there were three climate regimes in these regions from 1900 till now: the detected regimes were before 1926, from 1926 till 1987, and after 1988.

It seems that during each of the 1925/1926 and 1987/1988 shifts, the mean temperature rose to a new level around which natural oscillations occur. This assumption of shifts allows for an easy way to reconstruct SST anomalies at the tropics (30S-30N) and north middle latitudes (30N-60N). Of course there are some residuals between observed and reconstructed values, but they are quite homogeneously distributed during the century. This homogeneity of residuals is not the case for reconstruction by anthropogenic forcing.

Fig. 2. a) Blue line – SST in tropics, red line – linear regression on ENSO and climate regime, studied by 1900-2012 years b) ENSO influence on tropical SST; c) climate regime influence on tropical SST.

Figures 2 and 3 provide very simple linear regression models for SST dynamics in the tropics and north middle latitudes. Quite adequate reconstructions are obtained as linear combination of shifts with ENSO for tropical SST, and shifts with PDO for north middle latitudes SST. Correlation coefficients for monthly mean anomalies are 0.86 and 0.81, respectively. Is this simple? Yes, I think it is.

And the homogeneity is a remarkable feature. The temperature time series of tropics and north middle latitudes are very different, but the way of warming is common: they each exhibit shifts at near the same times.

Fig. 3. a) Blue line – SST in north middle latitudes (30^oN-60^oN), red line – linear regression on PDO and climate regime, studied by 1900-2012 years b) PDO influence on SST in this region; c) climate regime influence on SST in this region.

Symmetry allows fitting linear regression coefficients for data from only the first part of century (before 1950) and obtaining nearly the same reconstruction. In our paper we used the data from 1910 till 1940 (15 years to both side from shift in 1925/1926) and with almost the same quality reproduce the whole period from 1900 till now (Fig. 4).

Fig. 4. a) Blue line – SST in tropics (30^oS-30^oN), red line – linear regression on ENSO and climate regime with training period 1900-2012 years, purple line – the same linear regression with training period 1910-1940 years; b) the same as “a” but for north middle latitudes (30^oN-60^oN).

Various studies have indicated the existence of many shifts in the 20th century. And we are not the first to have observed shifts at 1925/1926 and 1987/1988. However, our working definition of shifts has some differences from that used by Yasunaka and Hanawa and many others. We define a climate regime as a quasi-steady state with known sources of variability. Additionally, we assess a climate regime shift as being significant and systematic changes that separate one climate regime from another and occur besides intra regime variability. For example, a step change of SST in the tropics in 1976 is clearly seen in time series, but the shift in 1987 is not obvious at all (Fig. 2).

The 1976 shift is, in general, associated with ENSO and could be almost reproduced by direct linear association with ENSO Nino34 index (Fig. 1b). Therefore, according to our definition, it should not be considered as a regime shift, because it is described by known intra-regime variability.

This is a fundamental difference between our work and that of, for example, R. Tisdale who considers ENSO to be a part of regime shifts.

We claim that our approach has advantages over others because – using our approach – we have shown that most of temperature anomalies produced by apparent shifts could be explained by known sources of variability (ENSO and PDO indexes) and only the shifts of 1925/1926 and 1987/1988 occur independently of known intra regime variability.

More detailed description of our hypothesis is in our preprints:

Belolipetsky PV, Bartsev SI, Degermendzhi AG, Hsu HH, Varotsos CA (2013) Empirical evidence for a double step climate change in twentieth century. Preprint. http://arxiv.org/ftp/arxiv/papers/1303/1303.1581.pdf

(Now under review in Climate Dynamics)

Belolipetsky PV, Bartsev SI (2012) Hypothesis About Mechanics of Global Warming from 1900 Till Now. Preprint. viXra:1212.0172.

All the calculations used for producing the figures were made in Excel by standard functions. Archive containing these files could be downloaded by following link:

https://www.dropbox.com/s/kmvg6ccjy6iy7q2/Calculations2.zip

I want to thank Richard S. Courtney and Robin Edwards who helped to prepare this post.

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