Welcome aboard Rickeroo.
Rickeroo said:
Greetings all. Brand new here, I came across this site Googling for the 270/385/1500ppm warming experiment under controlled conditions. So far, it's the closest I've come to an answer, which is I'll see essentially no difference in the temperature between the two containers. This makes sense to me when dealing with a trace gas, and it's what I expected.
The atmospheric greenhouse effect arises in ten kilometers of atmosphere, with a substantial temperature gradient (lapse rate). It's not just the absorption that matters; but the fact that the portions of the atmosphere for which thermal radiation can escape into space are much colder, because they are at a high altitude. Without this temperature gradient, there would be no greenhouse effect.
The 270/385/1500 ppm CO2 corresponds to about 4/6/23 kilograms of CO2 per square meter, in about 10 kilometers of atmosphere. The forcing from this is very well known, and follows from well measured properties of CO2 and radiation, along with some basic thermodynamics.
The experiments that give the physical basis for inferring CO2 "forcings" do not work by simply testing a ten kilometer gas cell with atmospheric compositions. What experiments give you are the emissivity/absorbtivity of the gas at different frequencies, along with all the basic physics of thermodynamics that gives you the way heat flows through different materials of all kinds.
You can calculate from well established thermodynamics what is called the "Planck response", which gives you a temperature required for Earth to radiate back out again the solar input, but only for
given fixed conditions. That's enough to define the "greenhouse effect" by itself, which is actually one of the most straightforward aspects of climate there is, and not in any credible scientific doubt at all.
This is a long LONG way from a full understanding of climate! The real problem is that conditions are NOT fixed. The Earth is a complex system, and all the genuine uncertainties of climate and temperature are not with the basics of the greenhouse effect itself, but with the whole sensitivity of the Earth climate system. You can't just use Planck response by itself, because as temperature changes, you also get changes in surface cover, humidity, cloud, carbon cycle, and so on. These are called "feedbacks", because they are changes driven by temperature that impact the variables that in turn establish the basic temperature response.
I've also been on other threads, pointed to "whole atmosphere" experiments and direct measurements, where there are no doubt infinite variables. Basic scientific procedure, at least to me, would be to eliminate your variables and isolate what you want to test. Without 2 controlled containers of atmosphere, there will be a difficulty in convincing some of CO2's warming ability.
Frankly, it is pretty much impossible to convince some people, and I am personally fairly relaxed about that. My main interest here is to try and help give a better general understanding of the underlying physics.
Experiments are nice, but they work best in the context of a theory to be tested by the experiment. For example, if you set up a long 10 kilometer tunnel, with a big lamp at one end to represent the sun, and used that to try and infer impact of different densities of CO2, you'd get effects quite different from the atmosphere, because you don't have a gradient of pressure with an adiabatic lapse rate driven by convection. And how would you know that this is important? Mainly, by knowing the theory of the greenhouse effect that you are supposedly testing.
The real issue for most people, I think, is not the lack of experiment. There are heaps of experiments and measurements that demonstrate the simple fact of a powerful greenhouse effect on Earth, but to see their relevance, you have to first understand the physics that they are testing. One of the clearest direct measurements of our greenhouse effect, in my opinion, is simply the direct measurement of the huge flux of atmospheric infrared backradiation coming down to the surface from the sky, with the spectrum matching our major greenhouse gases.
Atmospheric thermodynamics are quite complicated, but it is well within the capacity of a decent physics student to learn the basics of how the greenhouse effect works. The physics behind it is truly not in any credible doubt at all.
That being said, I've correlated two common data sets and I'd like your thoughts.
My first thought, on this sentence in isolation, is that correlation is a weak basis for confidence. It can be very useful as a test of predictions from theory, but in my opinion you don't really understand a physical situation until you have a theory; which means a proposed explanation of how something occurs. Finding correlations can be suggestive in looking for theories, but until you have the theory that is consistent with the observed correlations, the correlation alone can only be suggestive.
- The year to year CO2 ppm increase at Mauna Loa differed by as much as 600%, 1992 vs 1998.
- I was able to predict which years were cool, versus which years were warm, simply by looking at the ppm increase for that year. Lower ppm increases were associated with lower temperature for that year.
This isn't because of a greenhouse effect.
You are looking at a rate of increase of CO2, and comparing that with temperature. You can't explain this correlation (if it holds up) by proposing that CO2 is driving temperature. If CO2 was all that mattered, then you would expect temperature to rise all the time as CO2 is rising, but when CO2 rises more gradually, temperature would rise more gradually. But you are looking at temperature that goes up and down, which means there's something more than CO2 going on here for temperature.
And of course, there is. There's a heck of a lot going on with climate, all the time, which gives all kinds of natural variation on short terms. The major factor the big temperature increase in 1998, for example, was a very strong El Nino in that year. 1992 was cool, mainly because of the big Pinatubo volcano eruption. And so on. These are not merely correlation based arguments; there are good physical theories which indicate why you get hotter years with El Nino, and cooler ones with a big volcanic eruption.
The changes in the rate of increase of CO2 from year to year do not lead to the big temperature swings that you are looking at. We know the forcing involved, and it's a fairly strong steady increase, but not something that has huge short term forcings to make temperature swing wildly between different years.
This correlation, which is just about perfect, occurs in an atmosphere of ever-increasing CO2. What does this mean?
I don't think the correlation is all that good. I measured it for myself with a spreadsheet just now, using the annual mean grown rate for CO2 from the
Mauna Loa site, and the GISS data underlying the graph you linked, from the
Global Land-Ocean Temperature Index. The correlation I got was 0.735.
I think the most likely reason for any such correlation, if it is a real effect, is an impact of temperature on the carbon cycle. There are enormous fluxes of carbon in and out of the atmosphere from vegetation, and temperature is likely to have an impact on that, rather than the other way around.
Note that I am guessing at a theory for the correlation. This is the first step in a genuinely scientific project. The next would be to try and test the theory, with an experiment that has the potential to falsify it. I have no idea what that might turn up. The point is... merely noting a correlation is not a sufficient basis for a good scientific theory.
Cheers -- sylas