Guest Post by Willis Eschenbach
In my peripatetic meandering through the CERES satellite data, I’ve been looking at the correlation between the temperatures in the NINO3.4 region and the temperatures of the rest of the planet.
The NINO3.4 region is an area in the equatorial eastern Pacific Ocean. It covers five degrees north and south of the Equator, from 170° West to 120° West. Temperatures in that area are used to measure the strength of the El Nino / La Nina phenomenon.
Now, people often discuss procedures like “removing the effects of the El Nino from the global temperature record”. What they mean is that they have noted the similarity between the temperature of the NINO3.4 region and the global temperature. Figure 1 shows that relationship as seen in the CERES data.
Figure 1. Surface temperature of the globe (blue) and of the central Pacific ENSO3.4 area (red). Note the large “El Nino” event at the end of 2015. Both datasets are normalized (set to a mean of zero and a standard deviation of one).
Seeing this relationship, people have “removed” the NINO3.4 temperature variations from the temperature record. They have done this by subtracting out, in one form or another, the variations that are “caused” by the El Nino swings. However, I have disagreed numerous times with this procedure. Let me propose a more encompassing way to understand the relationship shown in Figure 1.
This is to note that although there are areas of the surface which show a good positive correlation to global temperatures, there are also areas that show a good negative correlation to global temperatures. Figure 2 shows this relationship on a gridcell by gridcell basis. It displays how well the temperatures in each gridcell agree or disagree with the global average temperature variations shown in Figure 1.
Figure 2. Correlation of each gridcell with the global average temperature. Note the large areas of negative correlation (green and blue)
Looking at that, I ask you to reconsider the idea that we can simply subtract out the temperature variations in the NINO3.4 area (blue box) from the global temperature … clearly, the relationships are far from simple. Is the fact that certain areas correlate well with the global variations a sufficient reason to “remove” them from the temperature record?
And if so, why limit ourselves to the ENSO3.4 area of the Pacific? Why not use a much larger area of the Pacific and “remove” half of the Pacific from the temperature record?
Setting those questions aside, the overall pattern in the Pacific is clearly related to the heat which is moved by the El Nino / La Nina pump. These two phenomena act together to pump warm Equatorial water across the Pacific in a westward direction. Once this warm surface water hits the Asian mainland/islands it splits and moves toward the two poles.
Now, many people say that this shows that the El Nino / La Nina is causing the global temperature changes. I say that the causation is going the other way. When the earth warms and excess heat accumulates in the eastern tropical Pacific, it triggers a cycle of the El Nino / La Nina pump. This pump moves warm water to the poles, where it is lost to space. Overall this cools the planet. The results of this pumping action can be seen in Figure 2 as the green areas in the western Pacific heading towards the north and south polar regions.
In other words, the El Nino doesn’t control the temperature—the temperature controls the El Nino.
We can look at this from another perspective. Rather than comparing gridcells to the average global surface temperature as in Figure 2, we can compare gridcells to the average NINO3.4 area temperature. Figure 3 shows that result.
Figure 3. As in Figure 2, but comparing ENSO3.4 area temperatures with gridcell temperatures. Note different color scale than that used in Figure 2.
Again, a most interesting result. It makes the El Nino pattern even clearer. Note that both the Western Pacific and the North Atlantic move in opposition to the NINO3.4 area.
The source of the pattern seen in Figure 3 is clear. It is driven by the El Nino / La Nina pump. When enough heat has accumulated in the eastern Pacific, the El Nino / La Nina pump pushes warm water first westward, then poleward. This cools the eastern Pacific and warms the western Pacific. In the South Pacific, you can see how it goes around Cape Horn at the south end of South America.
The oddity from my perspective is the North Atlantic. It moves in opposition to the NINO3.4 area, but the physical nature of the connection (or teleconnection) between the two is not clear to me.
In any case, I wanted to look at how temperatures in the areas in blue changed with respect to changes in the NINO3.4 temperatures. I restricted the analysis to the areas with a correlation more negative than – 0.3. Those areas are outlined in Figure 4 below. It is the same as Figure 3, but with the most negative areas outlined by the gray contour lines.
Figure 4. As in Figure 3, but with the gray contour line at a correlation of – 0.3.
Note that the North Atlantic is included among the areas with a strong negative correlation to the NINO3.4 area. To see the difference between the positively and negatively correlated areas shown in Figure 4, I graphed them up in Figure 5.
Figure 5. This shows the two areas outlined in Figure 4 above. The red line shows the average of the NINO3.4 area, shown as a rectangle in Figure 4. The blue line shows the average of the areas shown in blue and outlined with a gray contour line.
Dang … I certainly didn’t expect that nearly perfect mirror-image. When the NINO3.4 area warms up the North Atlantic and the other areas cool down, and vice versa.
So this highlights the problem. Given that we have an alternating phenomenon wherein the North Atlantic cools down when the Eastern Pacific warms up, and vice versa … just exactly how should we “remove” this phenomenon from the global record?
And more to the point, why should we remove it? The El Nino / La Nina pump is a central part of the natural thermoregulatory mechanisms that keep the temperatures within a very narrow range (e.g. ± 0.3°C during the 20th Century). The Nino pump kicks into gear whenever excess heat accumulates in the equatorial Pacific waters and moves that warm water to the poles.
As such, “removing” the El Nino / La Nina / North Atlantic signal from the global signal is cutting out a vital emergent climate heat-removing mechanism … I don’t even have a name for what remains once that radical surgery is performed.
Here, I’m putting the finish touches on this post and getting some needed hydration before going back to my current fun … driving a 1.5 tonne excavator, leveling an area on our tilted patch of dirt in order to make a level patio garden … big boys do love our big toys.
A summer’s day, an excavator, and red-tailed hawks circling in the distance … what’s not to like?
Best to all,
PS: If you comment please QUOTE THE EXACT WORDS THAT YOU ARE DISCUSSING, so we can all be clear about your subject.