>Ever since Scafetta and West, in their recent paper “Is Climate Sensitive to Solar Variability?”, March 2008 “Physics Today”, provided the graph of Phenomenological Solar Signal (PSS) from 1950 to 2007, I’ve wanted to see what effect adding other natural climate influences (volcanic aerosols, ENSO, AMO, PDO) would have on the curve. Refer to Figure 1.
Scafetta and West paper:
Estimates of the effects on climate of explosive volcanic eruptions vary greatly. For the Mount Pinatubo eruption of 1992, these temperature estimates range from 0.2 to 0.5 deg C. I’ve elected to use 0.2, which is documented in “Short-term climatic impact of the 1991 volcanic eruption of Mt. Pinatubo and effects on atmospheric tracers”, Pitari and Mancini, Natural Hazards and Earth System Sciences (2002) 2: 91–108.
I’ve also used annual SATO Index of Mean Optical Thickness data, with a scaling factor of 1.65176, to adjust the curve based on the values for the Mount Pinatubo eruption. (0.2 deg C/0.121083 Mean Optical Thickness) Figure 3 shows the effect of volcanic aerosols on PSS.
El NINO/SOUTHERN OSCILLATION (ENSO)
Trenberth et al (2000) in “The Evolution of ENSO and Global Atmospheric Temperatures” identified two impacts of ENSO on global temperatures: the direct year-to-year effect and the impact on the linear trend.
ATLANTIC MULTIDECADAL OSCILLATION (AMO)
From Knight et al (2005) “A Signature of Persistent Natural Thermohaline Circulation Cycles in Observed Climate”, GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L20708, doi:10.1029/2005GL024233, 2005: “The regression of simulated global and Northern Hemisphere mean decadal temperatures with the THC are 0.05 +/- 0.02 and 0.09 +/- 0.02_C Sv_1 respectively, implying potential peak-to-peak variability of 0.1 and 0.2_C.” Peak to peak changes on the AMO are on the order of 0.45 deg C. With a global temperature change of 0.1 deg C and a 0.45 deg C swing in the AMO, the scaling factor would equal 0.22. (0.1 deg C/0.45 deg C)
Since the AMO oscillation splits the period being investigated, there is a time when it adds to global temperature and another when it subtracts. Refer to Figure 5.
A PRELIMINARY COMPARISON TO GLOBAL TEMPERATURE ANOMALY
Figure 6 illustrates where the adjustments to the PSS curve stand now when compared to global temperature anomaly, as represented by HADCrut3GL. It’s not a bad fit. The obvious problem is in the trend line. The global temperature curve trend is significantly higher than the adjusted PSS curve. That appears to be caused for the most part by the variance prior to 1965.
A preliminary “fix” by the Climate Research Unit of the University of East Anglia (CRU) is shown in Figure 7.
PACIFIC DECADAL OSCILLATION (PDO)
The PDO is the only major natural climate phenomenon that hasn’t had its effect on global temperature specifically identified. I’ve been looking on and off for years. If a significant portion of the global ocean surface rises and falls naturally; by thermohaline circulation (THC), by meridional overturning circulation (MOC), by delayed response to ENSO signals, by some other unidentified source, or by a combination of all of the above; temperatures on land masses will change in response. The AMO causes Northern Hemisphere temperature changes, and ENSO causes temperature changes in both hemispheres. These responses have been identified. Why not the global or hemispheric response to the PDO?
The other mystery associated with the PDO is its actual magnitude. The data available from JISAO is standardized. By definition, a standardized value is the distance of one data point from the mean divided by the standard deviation of the distribution. Got that. For some climate data sets, the effect of standardization can multiply the data by a factor of four. For others such as ENSO, standardization might amplify the data by only 5 or 10%. Where does PDO data fall? Without downloading the entire global SST data set and extracting the Pacific Ocean data north of 20N, there’s no way for me to tell.
The annual PDO is illustrated in Figure 8. Based on the smoothed data, it would lower Northern Hemisphere and global temperatures between the mid-1940s and the late 1970s; magically the same period tropospheric aerosols are used by GCMs to lower global temperature.
Any future revisions to SSTs and global temperatures will also cause changes in the AMO, ENSO, and PDO, but the relationship between them will remain the same. It seems as though any attempt to raise the global temperature curve between 1945 and the mid-60s will simply require a smaller PDO scaling factor to make the curves fit.
GISS AND NCDC GLOBAL TEMPERATURE ANOMALY DATA
The following are duplicates of Figure 10, which compares Global Temperature Anomaly (HADCrut3GL) to the adjusted Phenomenological Solar Signal (PSS), but in these I replaced the Hadley Centre data with data from GISS (Figure 11) and NCDC (Figure 12). Due to the differences in SST data sets and in calculation methods, the Scaling Factor for the PDO needed to differ to match the trends. GISS required a much higher scaling factor (0.155), where NCDC require one significantly less (0.065).
NOTES ON THE USE OF PDO SCALING
I do understand that using undocumented PDO scaling to achieve the trend match corrupts the data. But is creating a non-existent tropospheric aerosol adjustment to tune GCMs any different?
I also understand the scaling factor used to calculate the ENSO contribution to annual global temperature may also contribute to changes in the PDO. This is possibly why adding PDO to the curve amplifies the ENSO signal. I have no means of removing the ENSO signal from PDO, to provide an independent contribution for it.
Hopefully, when all data sets are revised to correct the errors in mid-century SST data, the scaling of the PDO will not be required at present levels.
A COMPOSITE GRAPH OF THE ALL THE ADJUSTMENTS
It occurred to me there might be interest in seeing all the adjustments that were made to the PSS curve illustrated on one graph. Refer to Figure 13. I’ve also included before and after linear trend lines.
This morning at Prometheus, Roger Pielke Jr.’s Science Policy blog, in one of his battles with RealClimate, he posted a graph of projected changes to the global temperature anomaly data. Refer to Figure 14.
From the Pielke graph, I revised the global temperature anomaly data set and compared it to the adjusted PSS data. It’s important to note that in this comparison the PDO was not required to make up for any additional decline in the mid-20th century. It has been “zeroed.” Yet even without the PDO, the slope of the PSS trend exceeds the trend of the revised global temperature anomaly curve. Refer to Figure 15.