Physics explains color in terms of frequencies — or, equivalently, in terms of wave-lengths — of light. And the colors of substances are explained in terms of what frequencies these substances absorb and what frequencies they radiate or allow to pass.

An object of some color is so because it radiates or allows to pass light of frequencies participating in that color, but absorbs all others. When the object absorbs light of other frequencies, the energy of that light is absorbed. The reason that everyday objects don't then heat-up indefinitely is that they radiate the energy as light, but in the frequencies natural to their substances, rather than simply in the frequencies that were absorbed. A blue sweater converts white light to blue light. Moreover, under stable conditions, substances radiate light in the same set of frequencies. The blue sweater stays blue.

If the Earth did not radiate back into outer-space a significant amount of the light energy in which the Earth is bathed, then it would be dramatically hotter. But, as the surface of the Earth radiates light into the atmosphere, some of that light is absorbed by the atmosphere and then radiated back towards the surface; and, as some of the light radiated by lower parts of the atmosphere is radiated upward, some of it is absorbed by higher parts of the atmosphere and then radiated downward.

What are called greenhouse gasses have their effect by absorbing light energy and then returning a share of it downward, instead of allowing it to escape into outer-space. (Actual greenhouses work by a different principle.)

The theory of anthropogenic global climate change says that release of greenhouse gasses into the atmosphere by human activity causes significant changes to climate by increasing the amount of light energy radiated back downward, instead of being allowed to escape into outer-space.

Climate surely changes, and indeed has warmed and cooled, but that much was true before the first humans appeared, and well before humans released nearly so much of greenhouses gasses since the onset of the Industrial Age. So, if we seem to observe change now, or even warming now, then we want a means of determining whether the human contribution is significant or the change is about what it would be without us.

When the theory of anthropogenic global climate change first came into fashion, its models assumed a linear effect. That is to say that doubling the amount of a greenhouse gas would double the amount of light energy trapped, and so forth. Proper economists were naturally doubtful; we are used to marginal effects beyond some point diminishing. Indeed, the particles of a greenhouse gas would have to be arranged in some remarkable configuration in the sky to have linear effect. We could also imagine remarkable configurations in which marginal effects became immeasurably tiny. It should be no surprise that the linear models failed miserably.

As it happens, the effects of the greenhouse gasses are empirically measurable. Carbon dioxide, methane, and the other greenhouse gasses are like other chemicals, including the dye of that blue sweater that I mentioned. The greenhouse gasses don't simply radiate light energy back towards the surface of the Earth; they radiate it in characteristic frequencies. If you had the resources for strategically placed sensors, then for the last ten, twenty, or thirty years you could have measured the light energy in the relevant frequencies, and could have compared these measurements against the changing levels of the gasses — if you wanted to know.

Many of the various national states have the resources, and every reason to support such a study if its results conform to the theory of anthropogenic global climate change. But the results of a study effecting such measurements on a meaningful scale have not been reported. If that silence is because the results are being kept secret, then plainly they are inconvenient to whomever has kept them secret. If the silence is because such a study has not been undertaken, then plainly that is because the results are expected to be inconvenient.

If you're not autistic, then you recognize the significance for the theory that results have not been reported.

(By saying rays impacted tree growth, the Beeb goes further than the data actually warrant. Cosmic rays are positively correlated with tree growth, but their effect may be negligible. It may be something else, also correlated with the rays, that has been affecting growth rates.)

The source paper is available here:

but a subscription is required to view more than the abstract.

Very shrewd. The real result of this demand will be to make it more difficult for states to agree to limit emissions, which in turn will allow the Saudis to sell more petroleum. (Nor will they take much blame for failure to reach agreement, as that would interfere with Yank-bashing.)