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Do climate models predict extreme weather?

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Re: Do climate models predict extreme weather?

#51

Post by godelski »

fasteddie31003 wrote: post #7

I believe in climate change, but if you look into how the climate change computer models are written, it really makes me feel like it is contrived. Here's the problem with climate change modeling, you are modeling a complex chaotic system, you just cannot do it accurately. You have to be honest about it.

This is verifiably false.

We can look at the predictions (inference) from older models and check how accurate they were at predicting the future. No back testing required. Those models have been very accurate. Current models have only improved and reduced error.

We can test the accuracy, you have to be honest about it.

https://www.science.org/content/article/even-50-year-old-cli...

Re: Do climate models predict extreme weather?

#52

Post by brutusborn »

fasteddie31003 wrote: post #28
avianlyric wrote: post #26

Earlier quoted context omitted.

It’s complex and chaotic, sure. But as you increase time horizons, and area of simulation larger and larger, that complexity and chaos starts to average out. So you can’t take a singular datapoint from a climate model, and make any concrete statements, but you can take thousands to millions of them and start making probabilistic statements. Additionally it’s not like these models are untested. Their predictions are c…

Can you give me another example of a chaotic system that can be correctly forecasted years out?

Calculation of the future locations of astronomical bodies?

The difference is, Astronomical models can be simplified significantly, whereas climate models must be high fidelity to produce accurate results.

To me the critical question is at what fidelity are the models useful for our (humanities) purposes?

If our purpose is to predict climate and its impact we will need at least +/- 0.1C at a resolution of 100km at a timestep of 1 month. It must be possible to do mesh refinements to determine how accuracy changes with changing resolution, and then combine that with the prior resolution conditions to choose an appropriate mesh.

As far as I know most modern climate models are accurate to within a degree for at least a 30 year range. I haven't looked at the mesh sizes for a while but I'm sure someone has done something similar.

Re: Do climate models predict extreme weather?

#53

Post by yed »

fasteddie31003 wrote: post #29
WoahNoun wrote: post #19

Earlier quoted context omitted.

Examples? This is a pretty dubious claim.

Just simple extrapolating logic. Climate is chaotic. Chaotic systems cannot be forecasted years out. Therefor a computer model for climate forecasting is not going to be accurate.

Climate is not chaotic, weather is chaotic. Without any models at all we can predict that the Sahara desert will be hot and dry many many years out.

Re: Do climate models predict extreme weather?

#54

Post by foxes »

timmg wrote: post #5

One of the things about "extreme weather attribution" that makes me uncomfortable is the asymmetry of it. To be clear: I'm in no way an expert (or even educated) in the area. To give an example. Let's say there's a 1% chance every year that there will be a catastrophic wildfire in some particular area. Now let's say climate change increases a chance of drought in that area. Then we get a wildfire one year and the att…

This comment reads more like dismissive pedantry. What happens on the whole statistically matters more than hoping to get lucky with perhaps some local effects cancelling each other out.

What is your actual point?

Re: Do climate models predict extreme weather?

#55

Post by sanxiyn »

dpierce9 wrote: post #45
contravariant wrote: post #25

Earlier quoted context omitted.

That's why in these discussions it's usually better to talk about specific statistics like 'the chance of a wildfire has gone up by 20%', or perhaps more clearly 'the average time between extreme floods has gone down from once every 100 years to once every 60' (which I find communicates the point a bit more clearly). That said personally I think that should be as far as the discussion goes, talking about a specific e…

Replace ‘extreme weather’ with ‘lung cancer’ and ‘climate change’ with ‘smoking’ to see the soundness of this reasoning.

Lung cancer risk was established with control group. We don't have control group for a planet so we use climate models. The article is about remembering that we use models because of lack of alternatives, not because they are as good as control group.

Re: Do climate models predict extreme weather?

#56

Post by tasty_freeze »

Statistics are tricky to think about, even for people with technical educations.

Something that was a lightbulb moment when someone was discussing professional baseball players. I forget the exact point the blog was making, but it came down to this: many things in life, like the ability to throw or hit a baseball, falls on a distribution that is close enough to a gaussian distribution. But when talking about professional baseball players, they represent just the very right hand tip of that distribution. Whatever intuitions you might have about gaussian distributions needs to be thought about in light of that.

The same applies with extreme weather events. It is easy to look at articles and headlines describing an exponential increase in the frequency of extreme weather events. But think for a second about the equation of a gaussian distribution. When you shift the offset by a small, fixed amount, the area under that right hand tip goes up exponentially.

No, one cannot point to climate change as the cause of any individual weather event. But it is a measured certainty that the warming is happening; the number of record high temperatures are a multiple higher than the number of record low temperatures every year for the past couple of decades. It would be weird if the temperature rose and the number of extreme events went up, say, linearly.

Re: Do climate models predict extreme weather?

#57

Post by a_square_peg »

fasteddie31003 wrote: post #7

I believe in climate change, but if you look into how the climate change computer models are written, it really makes me feel like it is contrived. Here's the problem with climate change modeling, you are modeling a complex chaotic system, you just cannot do it accurately. You have to be honest about it.

Climate models have shown to be very accurate predicting the climate change that we've been able to observe so far - what aspect of climate change model are you referring to?

It makes no sense to talk about the 'chaotic' nature of a system without relating to the scale and scope of the model. Weather is a chaotic system but this doesn't mean we can't predict it at all what it'll be like an hour later or tomorrow. As we scale it out further, the accuracy decreases but we can predict with high certainty that it's not going to snow in Los Angeles six months out from today.

Re: Do climate models predict extreme weather?

#58

Post by godelski »

8note wrote: post #37
avianlyric wrote: post #26

Earlier quoted context omitted.

It’s complex and chaotic, sure. But as you increase time horizons, and area of simulation larger and larger, that complexity and chaos starts to average out. So you can’t take a singular datapoint from a climate model, and make any concrete statements, but you can take thousands to millions of them and start making probabilistic statements. Additionally it’s not like these models are untested. Their predictions are c…

Generally the defining feature of non linear mechanisms is that the long term behaviour is non-intuitive. I'd expect that to include not having a predictable mean

Non intuitive doesn't mean not predictable. Nor does chaos. Chaos just means that a small perturbation in input parameters can result in a large change in the output. So to have good predictive power you need to pick good inputs with good accuracy. But chaos is also a spectrum so not all chaotic systems are as sensitive as others.

Re: Do climate models predict extreme weather?

#59

Post by sampo »

freen wrote: post #18
pmjones wrote: post #10

Models say only what the modeler tells them to say.

I am 100% sure that the Exxon model from 1982 was not what Exxon wanted. It also has been and continues to be tremendously accurate and predictive. https://xkcd.com/2500

> https://xkcd.com/2500

I am unable to find any 1982 Exxon prediction that would meander like the line in that graph. The only plot I was able to find is this [1] from this 1982 Exxon report [2], which is just a slightly curved upward rising sketch, not nearly as detailed as in the xkcd graph.

> the Exxon model from 1982

I also failed to find any signs of there having been any "1982 Exxon model". What [2] is, is a 39-page report, a synthesis and review of publicly available climate research. The list of references is quite extensive: 10 pages.

[1] https://pbs.twimg.com/media/D6fbaqdWwAEPg5Z.png

[2] https://www.climatefiles.com/exxonmobil/1982-memo-to-exxon-m...

Re: Do climate models predict extreme weather?

#60

Post by dpierce9 »

sanxiyn wrote: post #55
dpierce9 wrote: post #45

Earlier quoted context omitted.

Replace ‘extreme weather’ with ‘lung cancer’ and ‘climate change’ with ‘smoking’ to see the soundness of this reasoning.

Lung cancer risk was established with control group. We don't have control group for a planet so we use climate models. The article is about remembering that we use models because of lack of alternatives, not because they are as good as control group.

The parent was suggesting causal inference from general statistical evidence to particulars is impossible.

You seem to be suggesting there can be no causal inference where there are no control groups.

Both positions are wrong.

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