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An air of denial

29 May 2019 | Science Notes

The “ground zero” of greenhouse-gas-induced warming is not as you might suppose on the ground. All the climate models say it's about 10 km straight up above the equator, in the mid-troposphere over the tropics, where we should observe the strongest response to greenhouse gas emissions. Strange, then, that the IPCC goes to great lengths to avoid talking about that region. Perhaps due to the conspicuous lack of warming there. Recently meteorologist John Christy reviewed the evidence and showed what's at stake. The only model predictions that get the troposphere right are the ones that assume greenhouse gases have virtually no warming effect, because it's what the data are showing.

Christy's presentation begins with some simple diagrams that put carbon dioxide emissions into helpful perspective. Relative to natural variations in the factors that drive warming and cooling, changes to greenhouse gas levels only affect the energy budget by about a half a percent. So we should expect greenhouse warming trends to be small.

He and his colleagues have shown for many years that that's precisely what the satellite evidence confirms. But climate models tend to predict a lot of warming. As physicist William van Wijngaarden explains in our Simple Physics video, it's not because of CO2. And in fact it’s widely accepted even among alarmists that greenhouse gases don't cause much warming directly.

What does happen, or should, or might, according to the theories that drive the models, is that the small change GHGs trigger changes in atmospheric water vapour and cloud cover in ways that cause an amplified “greenhouse effect”. But nobody really knows how water vapour and clouds behave, in response to warming or anything else. So especially given the ruckus about “evidence-based decision-making” the model predictions absolutely need to be checked against the data, and as Christy shows, when that's done, the models look ridiculous. On average they predict about three times too much warming in the tropical troposphere (which is not redundant because troposphere does not mean “tropical atmosphere”; it’s the lowest layer of the atmosphere, between about 6 and 18 km deep depending where you are, in which almost all weather happens).

Christy also describes his efforts to get the Intergovernmental Panel on Climate Change to take note of the discrepancy. As a reviewer for the IPCC, he insisted that they show the data. So they did, reluctantly slipping the charts into a supplemental appendix that was published online after the report was printed, in a place nobody would think to look. The chart compared warming predictions all through the atmosphere to predictions from two types of models: those run with greenhouse-gas-induced warming, and those run with no greenhouse gas warming. The first batch doesn't overlap with the observations at all: They predict far too much warming all the way up to the top of the troposphere. The second batch matches the observations perfectly. The atmosphere is acting as if carbon dioxide has no effect at all. The very air we breath is a “denier”.

To make the story truly fitting as a parable of modern science, Christy then shows that the next generation of climate models, rather than dialing down the warming to match the data, are showing even stronger warming than before. And he predicts, glumly, that the quaint notion that when it has become clear that global warming theories don't match the data, it's more likely that the data will be ignored rather than the theories.

One comment on “An air of denial”

  1. Excellent article that should be published on the front page of the NP and sent to every MP along with Dr Christie ‘s paper.
    When observations don’t agree with the hypothesis, the hypothesis is wrong. This is the scientific method . But sadly we are dealing with a religious cult where beliefs cannot be questioned.

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