Guest Post by Willis Eschenbach (@weschenbach on eX-Twitter)
I love science because of the surprises. Today I have some. My first surprise today was the evidence of a strong negative feedback in surface temperature. Let me note that I do not claim to be the first person to make these observations. I’m just saying, I’m surprised.
My method of scientific investigation is based on graphics. I take chunks of numbers, sometimes tens of thousands, and display them graphically. And sometimes the results are what I want, or even want.
But other times, the latest chart pops up on the silver screen and I say “What?” … it’s the surprise that makes it all worthwhile. And that’s where the interesting path begins. Come amble with me on one of the roads.
As a result of a series of misunderstandings and coincidences, I ended up taking a look at the month-by-month changes in the net effect of clouds on radiation. “net effect” show the fact that the clouds are both warm and cool on the surface.
cold occurs as a result of clouds blocking sunlight from hitting the ground by reflecting sunlight back into space or by absorbing sunlight. One way cools the surface.
Heating occurs from a part of the thermal radiation emitted by the cloud that hits and is absorbed by the ground.
“net effect” it is the difference between two opposite effects-including two effects, which are warming clouds or cooling the surface, and how much?
Not surprisingly, this is known as the “surface net cloud radiative effect”, or “surface net CRE”, hereafter “CRE”. When CRE is negative, it means the net radiative effect of the cloud is cooling the surface. Additionally, a positive CRE means that clouds warm the surface through radiative change. Figure 1 shows an average of 24 years of CERES satellite records of the CRE net surface.
Figure 1. The effect of clouds on the total amount of radiation (longwave and shortwave) absorbed by the earth’s surface. The horizontal dashed line near the equator marks the tropical edge (23.5° N/S). The horizontal dashed line near the pole is the two polar circles (66.5° N/S). The unit is watts per square meter (W/m2).
There are several interesting things about Figure 1.
• Overall, surface cooling clouds are about -19 watts per square meter (W/m2)
• The ocean is almost three times colder than the land.
• The region polewards of the two polar circles is heated by clouds.
• The only areas that are warmed on average by clouds are polar regions and deserts.
• The greatest cooling is in the inter-tropical convergence zone over the Equator and the Pacific Warm Pool north of Australia.
But what I have never seen is a monthly record of surface net CRE. Of course, to see that we have to look at the hemispheres separately, to avoid the effects of the opposite seasons in the two hemispheres. Figure 2 below, showing the variation of the northern hemisphere by month, was my first surprise.
Figure 2. Monthly net surface cloud radiation effect, northern hemisphere.
I do not expect the effect to vary from slight warming in winter to -40 W/m2 cooling in summer. It is a giant swing in the effect of the clouds.
It is also interesting to see the net cooling effect of -0.2 W/m2 per decade. The decadal increase in CO2 pressure is +0.27 W/m2 (95% CI: 0.22 W/m2 – 0.32 W/m2). So during the recording period, small changes in the CRE surface are of the same order of magnitude and act in opposition (cooling) to the warming effect of CO2 forcing.
Of course, I thought about how different no-day radiation effects are on summer and winter temperatures…which led me to create Figure 3.
Figure 3. The current temperature of the northern hemisphere (black), and the theoretical temperature without the effect of cloud radiation (other things being equal, which of course does not exist). Values ​​in all cases were completed in units of W / m2, and then converted to temperature using the Stefan-Bolzman equation with an emissivity of 0.95.
Thus, whereas in the northern hemisphere the average summer temperature is about 72°F (22°C), without the varying radiative effects of clouds, the daytime temperature is about 84°F (29°C ). Yes! And the winter will be a bit colder too.
(And yes, I know that without clouds, a lot of other things will change, so my chart is pure theory. I’m just trying to give people an idea of ​​how cloudiness swings from +5 W/m2 in winter to -40 W/m2 in summer correct.)
Intrigued, I decided to take another look at the whole globe as in Figure 1, but this time in the northern hemisphere midwinter (December) and midsummer (June) separately. Here are the two graphics.
Figure 4. As in Figure 1, but showing midsummer and midwinter cloud surface net radiative effect. Average December and June. The horizontal dashed line marks the edge of the tropics (23.5° N/S), and the two polar circles (66.5° N/S).
Again, the rest is interest. In the middle of NH winter (December), the clouds warm over almost all areas north of about 35°N or more. In the southern hemisphere in the middle of winter (June), they are the same. Warm clouds in the south around 35°S.
Another oddity. In most cases, the white/black contour lines represent desert regions where, according to CERES, clouds warm regardless of season. Why?
Next, I looked at scatterplots of surface temperature versus surface cloud radiative effect, using 1° latitude by 1° longitude gridcell data. For each hemisphere there are 32,400 data points. I plotted the data by season and hemisphere. And while doing so, I noticed the most curious oddity. This is the second surprise.
The graph of the relationship between midwinter temperature and midwinter cloud radiative effect is almost the same in the two hemispheres.
And the same is true of the relationship between them midsummer cloud radiative effect and midsummer temperature. Both hemispheres have the same summer relationship. Here is a comparison.
Figure 5. Gridcell scatterplots. The top panel shows the midwinters—the northern helisphere midwinter (December) and the southern hemisphere midwinter (June). The bottom panel shows the midsummers-northern hemisphere midsummer (June) and southern hemisphere midsummer (December).
There are some interesting points here. First, the correspondence between the two winters (top frame) and between the two summers (bottom frame) is surprising.
The main difference is that in the summer in the gridcells the temperature is low. The southern hemisphere has open seas almost all the way to the ice-covered Antarctic Plateau. In winter and summer, the clouds are warm in Antarctica. So in summer, the change in the effect of cloud radiation in the Antarctic coastline region is a sudden and almost vertical change to warming (left corner of the orange/black line, bottom frame). In the Arctic, because the poles are covered by water rather than the high land of the South Pole, the change to polar warming is slower and more gradual (top left blue/black line, bottom frame)
In addition, the two hemispheres are almost identical. Most importantly, in summer and winter, as temperatures are above 26°C or more, cloud cooling rapidly strengthens and increases faster with each additional level of surface warming.
The seasonal similarity of the oceans of the two hemispheres is important to me for a strange reason. I have used a gridcell-based scatterplot analysis of the type in Figure 5 above for things like below to see how temperature and CRE are related to the entire globe. See my post Observational and theoretical evidence that cloud feedback reduces global warming for a discussion of the implications of Figure 6 below.
Figure 6. Scatterplot, net surface cloud radiation effect versus surface temperature, all 1° latitude by 1° longitude surface gridcells.
The main objection that people make to using gridcell-based scatterplot analysis of the type in Figures 5 and 6 above is the claim that they are investigating. based on location relationship, and thus does not demonstrate a direct relationship between two variables.
Another way to express this view is that it is certain that certain locations have some relationship between temperature and CRE—the relationship is governed by the location-based characteristics of the gridcells in question. Maybe there are ocean currents or mountains that control temperature and CRE.
Now, that doesn’t seem logical to me, because in Figure 6, CRE values ​​are grouped by the average gridcell surface temperature. And there are many grid cells all over the planet with the same average temperature. But I haven’t figured out how to counter that argument, to show that it’s not based on location.
However, the similarity of the hemispheric ocean midwinters, and of the hemispheric ocean midsummers, shows that the relationship between temperature and cloud radiative effect is not due to some location-specific characteristics.
Can’t be location specific, because no location is common to both hemispheres. These are very different grid cells in different oceans in different hemispheres, with different currents, different depths, different landmasses… but the relationship between temperature and surface cloud radiation exactly the same.
So, with the third and biggest surprise of the day, after starting down a completely different path, I found a way to counter the main objection I had to gridcell-based scatterplot analysis.
Funny how life can be when I follow random byways without a guiding star other than endless curiosity about the glory of this world.
===
The moon rose above the red tree. It must be time for me to go look at the moon. I just need someone with a uniform and a Glock to come every few hours and say “Get off the computer sir, keep your hands off the keyboard so no one gets hurt!”
Next, my friends, and the best to you all – may your life be full of wonders, adventures, and all sorts of surprises.
w.
As usual: I politely request that when you comment, you quote the exact words you are discussing. Avoid endless misunderstandings.
related
