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Parts and Whole – Raised by that?


Guest Post by Willis Eschenbach

As with many of my twists and turns through the scientific landscape, this sentence begins with “I must wonder…”.

In this case, I have to wonder how the Central England Temperature (“CET”) matches the temperature of the planet.

In part, I wonder because I keep reading that the Little Ice Age, which bottomed around AD 1700, was just a European phenomenon. I often wonder if just one part of the world can cool as much as during the Little Ice Age but the rest of the world will cool too.

CET is one of the longer temperature records. It is an odd record in that it is made up of a combination of the temperature records of a range of variable stations in the general area of ​​Central England. It spans from 1659 to the present. This is the more recent portion of the CET record (seasonal calculation removed) and the Berkeley Earth’s global temperature record.

Figure 1. Monthly temperatures in Central England (CET) and Berkeley Earth’s global temperature.

Hmmm… looking at it, there seems to be very little relationship between the two. R^2 (lower left corner) is a measure of how close the relationship is, varying from R^2 = 0 (no relationship) to R^2 = 1 (total agreement). Reflecting on the question, I realized that what matters is that over a short period of time, months or years, not decades or centuries, the temperature in a small area of ​​the planet like central England varies greatly with the temperature of the earth.

So what I need to do is adjust the short-term variance of the CET to match the variance of the Berkeley profile, while keeping the long-term variations the same.

To do that, I first LOWESS smoothed the CET data. That gave me Figure 2.

Figure 2. Full Central England temperature profile, together with LOWER fineness of CET. You can see the coldest part of the Little Ice Age around 1700AD.

Then I subtract the LOWESS smoothness from the recent CET data (from 1850 to present to match the time period of the Berkeley Earth data). This leaves me with only short-term variations (months to years, not decades or centuries) in the CET data.

I did the same thing with Earth temperature data at Berkeley, to identify short-term variations in that data.

Once I had both sets of short-term variations, I adjusted the average size of the CET short-term variations to match the mean sizes of the respective Berkeley Earth short-term variations. Finally, I re-added smooth LOWESS to reconstruct the original CET data, but with much less short-term variations.

I then used a simple linear regression on the CET data to give the best overall fit to the Berkeley Earth data. Figure 3 shows that result.

Figure 3. Temperatures in Central England, adjusted for variance, compared with Berkeley Earth’s global temperature.

This was a big surprise for me, and surprises like this are what keep me doing science. I didn’t expect the temperature of a small part of England to be so compatible with global temperatures. R^2 is 0.67, much larger than the previous R^2 of 0.07 shown in Figure 1. And since the Little Ice Age is clearly visible in the previous part of the CET record shown shown in Figure 2, which increases the odds that the Little Ice Age was a global phenomenon.

Now, I have also heard the claim about US temperature record, that US covers only ~2% of global area and hence we shouldn’t expect it to be similar to global record. So I used the same technique to compare the Berkeley Earth US record with the global Berkeley Earth record. Figure 4 shows that result:

Figure 4. US temperature, adjusted variance, compared with Berkeley Earth’s global temperature.

Now, the US is much bigger than Central Britain, and so, as we might expect, the global temperature agreement is even better than the CET deal. R^2 now goes up to 0.76. Over the past 170 years, US temperatures have come very close to global temperatures. Who knows? Definitely not me.

Next, here is the correlation of the individual 1° latitude x 1° longitude grid cells, adjusted for variance as described above, with the average global temperature.

Another surprise. Land masses in general correlate well with average global temperatures, as do most oceans…with the exception of the North Atlantic, which is negatively correlated with global mean temperatures.

In the end, with all of the above, I’m going to go out there and say that the Little Ice Age was most likely a global phenomenon.

And that’s my scientific surprise for today… how is your day?

My best wishes to everyone,

w.


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