John Christy has written a report for the Global Warming Policy Foundation called climate models have been predicting too much warming. The basic conclusion of the report is that climate models predict far more warming in the tropical troposphere than is observed; essentially it’s suggesting that there is a missing tropical tropospheric hot spot.
One thing that the report doesn’t make clear is that amplified tropical tropospheric warming is not simply a signature of greenhouse gas-driven warming; it’s expected for any kind of warming. I think it’s also worth reading this Climate Dialogue discussion, in particular that by Steve Sherwood, who pointed out that
[w]eaker upper-tropospheric warming and hence weaker water-vapour feedback actually implies, on average, slightly stronger overall positive feedback due to lapse rate and water vapour combined
However, what I wanted to highlight was the end of the report, which discusses what one might conclude from the comparison between the observations and the models and which suggests that one option is that
- [t]he models are failed hypotheses.
The report then finishes with
I predict that the ‘failed hypothesis’ option will not be chosen. Unfortunately, that’s exactly what you should do when you follow the scientific method.
The reason that it would not be chosen is because it doesn’t really make sense. Unless a model is so simple that it really only incorporates one bit of physics, it isn’t a hypothesis. Models are typically a combination of multiple bits of physics that, together, allow one to investigate a complex system. Typically, the underlying physics is so well tested that even if the model doesn’t match the observations, one wouldn’t conclude that some of the underlying physics had been falsified.
Of course, a model can be wrong, but that’s not the same as it being a falsified hypothesis. The problem, though, is that all models are wrong, so how does one decide if it’s so wrong that it has no use whatsoever? Even though it might appear that the models are predicting more tropospheric warming than is observed, there are many areas where models have been shown to be skillful.
Determining tropospheric temperature trends is also very tricky, and these are observations that have been corrected on a number of occasions. One really can’t rule out that the mismatch is a problem with the observations, rather than with the models.
As George Box said all models are wrong, but some are useful. Climate models are very useful for trying to infer what might happen if we continue to dump greenhouse gases into the atmosphere. This is especially true if we are interested in trying to understand how it will likely respond on various time, and spatial, scales. If we throw out complex climate models, we’d simply become less well informed. This is not, however, to suggest that we shouldn’t be open about their limitations.
However, our basic understanding of climate change is not really dependent on complex climate models. Our understanding of how our climate responds to radiative perturbations is based on many different lines of evidence. We have models of a variety of complexities. We have recent observations of surface warming, ocean warming, sea level rise, ice sheet mass loss, and many other indicators. We can study changes to our climate that have occured in the past to also understand how it responds to external perturbations. It’s bizarre to suggest that a potential mismatch between complex climate models and observations of one region of the climate system indicates that these models are failed hypotheses.
Even though I’ve been commenting on this kind of thing for a reasonable amount of time now, I still find myself surprised that supposedly serious people will present such simplistic arguments. It’s almost as if they’re looking for something that suits their preferred narrartive, rather than actually trying to help improve our understanding of how our climate is likely to respond to increasing atmospheric CO2 concentrations. Surely not, though?
The missing tropical hot spot – Climate Dialogue discussion about the supposedly missing tropical hot spot.
Tropospheric hot spot – a post of mine about a paper that finds amplified warming in the tropical troposphere.
One satellite data set is underestimating global warming – John Abraham article about another paper that finds amplified warming in the tropical troposphere.
Climate change is real and important – article a group of us wrote that also discusses why climate models are actually skillful.
More errors identified in contrarian climate scientists’ temperature estimates – John Abraham article highlighting the occasions on which John Christy’s satellite temperature dataset has had to be adjusted.
Climate model projections compared to observations – Realclimate post showing various model-observation comparisons.