SWAG – Frustrated with that?

Guest Post by Willis Eschenbach

As more of my posts started, “I have to think about…”.

In this case, I have to think of the Berkeley Earth’s global temperature dataset. So I got their grid file”Average monthly temperatures over land + ocean with sea ice air temperatures“Include 1850 to 2021 and take a look at it. I started with data for the first month, January 1850… and my jaw hit the floor.

Figure 1. Berkeley Earth’s surface temperature, January 1850. White areas have no data.

What shocked me was the orange-red circle in the north center of New Zealand, as well as the semicircle in northern South America.

Obviously, what they’re doing is reading a temperature at a point and extrapolating it to a surrounding area. How big is the area? Well, the northern circle of Kiwiville is ~1,600 km (~1,000 mi) in diameter. It covers an area of ​​8,700,000 square kilometers (3,360,000 sq mi). It’s about the area of ​​the continental United States… estimated from one temperature reading.

And there are no islands near the center of that circle, so it would be the temperature taken from a ship…

Now, if you look closely, you will see that the southern part of the circle is more orange, it’s a bit cooler. That leads me to think that they took modern measurements of the temperature gradient around the center and adjusted them to accommodate a single surface temperature measurement. To test that, let me look at that area’s January temperatures over time… I’m writing this while analyzing the data, so I’ll be back soon.

…

OK, here’s what I found.

Figure 2. January temperatures from 1850 to 2021 of a vertical line (North/South) that cuts through the middle of the red circle north of New Zealand in Figure 1. Slices run from 16°S to 46°S. Temperature is represented by the anomaly around the temperature at the center of the circle, at 31° South latitude.

It seems my speculation is not too wild, they are using some sort of procedure like that.

But is extrapolating the temperature of an area of ​​ocean the size of the continental United States from a single temperature measurement a reasonable process?

I’ve spent a wonderful life at sea, I’ll have to wonder. I’ve seen areas where the ocean changes in temperature by a few degrees or more over a few hundred meters. Where the cold current touches the warm current, there is usually a clear dividing line and little mixing on the line.

And on land, the changes are much larger, like in northern South America in Figure 1.

So… the whole of America from just one thermometer? For example, where I live, it almost never freezes. But a kilometer (~half a mile) away, it freezes over a number of times per year. Here is the freeze warning for tomorrow. I live near the north coast of San Francisco, in a narrow green patch near the coast to the left of the “S” in “Santa Rosa”…it probably won’t freeze here. The stretch along the coast in this area to the west of the first range of hills, ranging in elevation from about 600′ to 900′ (180m to 270m), is known locally as the “Banana Belt” because it almost never freezes. We grow lemons, limes and avocados on our land.

Figure 3. Freeze warning for Wednesday, February 23, 2022

So I’ll leave it to the reader to decide if one thermometer is enough to estimate the temperature of the entire continental United States… and while you look at that, here’s a video round of the coverage. for the first twenty years (240 months) of the Berkeley Earth Global Surface Temperature Data.

Figure 4. Berkeley Earth’s first 240-month global surface temperature video loop.

I find the change in Australian coverage over time the most confusing.

At the end of the day, I was wondering… when will Berkeley Earth finally reach global coverage? This is the sad answer.

Figure 5. Coverage rate, Berkeley Earth’s surface temperature, broken down by land and ocean.

Interesting. The effect of wars on temperature reports from ocean shipping is fairly clear. And even extrapolating so that a single thermometer covered an area the size of the continental United States, land cover did not exceed 90% until after World War II… and total coverage did not. achieved until 1978.

I have no overall insights from this study, other than the striking nature of not only this Berkeley Earth dataset but most climate data has always been a thorn in the side for researchers, and it gives All climate conclusions are very exploratory.

Oh, yes… about the title of the post, “SWAG”.

“WAG” is a “Wild Ass Guess“. And no, I didn’t make it up.

And a “SWAG”, on the other hand?

It was a much more advanced being, a “Science Wild Ass Guess“ … Like different estimates of the average global temperature in the 1800s.

My best wishes to all, rain of blessings here, what’s not to like?

w.

ONEs is my custom: When you comment, I ask you quote the exact words you are discussingso we can all be in the know about who and your stuff.