The Great Climate Shift of 1878

Guest essay by Jeffery S. Patterson

My last post on WUWT demonstrated a detection technique that allows us to de-noise the climate data and extract the various natural modes which dominate the decadal scale variation in temperature. In a follow-up post on my blog, I extend the analysis back to 1850 and show why, to first-order, the detection method used is insensitive to amplitude variations in the primary mode. The result is reproduced here as figure 1.

Figure 1a – First-difference of primary mode Fig 1b – De-trended first-difference of primary mode

We see from Figure 1b that once de-trended, the slope of the primary mode has remained bounded within a range of ± 1.2 °C/century over the entire 163 year record.

The linear trend in slope evident in Figure 1a implies a parabolic temperature trend. The IPCC makes oblique reference to this in the recently releases AR-5 Summary for Policymakers:  

“Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850 (see Figure SPM.1). In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years (medium confidence).”

True enough, but that has been true since at least the mid-1800s. The implication of the IPCC’s ominous statement is that anthropogenic effects on the climate have been present since that early time. Let’s examine that hypothesis.

Up to this point I have been using de-trended data in the singular spectrum analysis (SSA) because de-trending helps to isolate the oscillatory modes of the climate system from the low-frequency trend. We are now interested in the characteristics of the trend itself. Figure 2 shows the SSA trend extracted from the raw Hadcrut4 northern hemisphere data.

Figure 2 – SSA[L=82,k = 1,2] on Hadcrut4

We see the data oscillates about the extracted trend with approximately equal peak –to-peak amplitude until about the year 2000. More about this departure later. The really interesting characteristic of the trend is revealed when we look at the first-difference (time derivative of the red curve of figure 2), shown in figure 3.

Figure 3 – First difference of extracted trend

Any engineer will instantly recognize this shape as the step-response of a slightly under-damped 2^nd order system as described by equation 1.

(1)

where a is the step-size, b the offset, w the natural frequency, z the damping factor and t the offset in time at which the input step occurs. is the unit step function which is zero when its argument is negative and unity elsewhere.

A parametric fit of (1) to the data of figure 3 is shown in figure 4.

Figure 4 – Parametric fit of (1) versus data

I know what you are thinking. That fit is too perfect to be true. It must be an internal response of the SSA filter. We can test that hypothesis by integrating equation (1) and comparing it to the unfiltered data.

Figure 5 – Indefinite integral of (1) versus data

We see the resulting integral fits the unfiltered data, with the residual exhibiting the same oscillatory behaviors as before. The integral of (1) yields eqn. 2 below:

(2)

I know what you’re thinking. We’ve said all along that the AGW signature would show up as a step in in the slope of the de-noised temperature data, precisely what we see in figure 4. Is this the AGW smoking gun? If we plot figure 3 and the raw data on the same graph we see the real smoking gun.

Figure 6 – First-difference of extracted trend versus data

Around the year 1878, a dramatic shift in the climate occurred coincident with and perhaps triggered by an impulsive spike in temperature. As a result, the climate moved from a cooling phase of about -.7 °C/century to a warming phase of about +.5°C/century, which has remained constant to the present. We see that this period of time was coincident with a large spike in solar activity as shown in figure 7.

Figure 7 – Solanki et al, Nature 2004 Figure 2. Comparison between directly measured sunspot number (SN) and SN reconstructed from different cosmogenic isotopes. Plotted are SN reconstructed from D14C (blue), the 10-year averaged group sunspot number1 (GSN, red)

Virtually all of the climate of the last century and a half is explained by equation (2) and the primary 60+ year mode extracted earlier as shown in figure 8b.

Figure 8 – Primary mode SSA[L=82,k=3,5] vs. residual from eqn.(2) (left) Fig. 8b – eqn. (2) + primary mode vs. hadcrut4

As others have observed, this 60+ year mode plotted in figure 8a is highly correlated to solar irradiance.

Figure 9 – This image was created by Robert A. Rohde from the data sources listed below

1. Irradiance: http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant

2. International sunspot number: http://www.ngdc.noaa.gov/stp/SOLAR/ftpsunspotnumber.html

3. Flare index: http://www.koeri.boun.edu.tr/astronomy/readme.html

4. 10.7cm radio flux: http://www.drao-ofr.hia-iha.nrc-cnrc.gc.ca/icarus/www/sol_home.shtml

Note that the reconstruction due to Solanki et al shown in figure 7 disagrees with figure 9 in terms of present day solar activity. The temperature record clearly tracts Solanki, but I’ll leave that controversy to others.

The residual from Figure 8b, shown in Figure 10, shows no trend or other signs of anthropogenic effects.

Figure 10a – Residual from primary mode Figure 10b – Smoothed histogram of residual

A similar analysis was done on the sea-surface temperature record. The results as shown in Figure 11:

Figure 11 – SST (red) vs. Hadcrut4 (blue)

We see the land temperatures follow the ocean surface temperature with a 4-5 year lag.

Conclusion

The climate record of the past 163 years is well explained as the integral second-order response to a triggering event that occurred in the mid-to-late 1870s, plus an oscillatory mode regulated by solar irradiance. There is no evidence in the temperature records analyzed here supporting the hypothesis that mankind has had a measurable effect on the global climate.

Related articles

• Detecting the AGW Needle in the SST Haystack (wattsupwiththat.com)