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Comment by skrowl | Hacker News Reader

There is definitely no shortage of doomsday climate models. CREDIBLE models is a different story.

Look back at ones from 20+ years ago to see what they predicted would be happening by now. It's pretty funny actually.

The models from 20 years ago overshot by several confidence intervals because they underestimated mixing the deep ocean. "The barrel is bigger than we expected" doesn't make the rising water in the barrel any less concerning, but it's not the triumph of foresight that you seem to imply.

Grandparent didn't imply it was a triumph of foresight, but rather a failure of foresight.

I think that's what he's saying - a general point that people's understanding of climate (and thus predictions about it) are poorer than commonly believed.

Well, one day we might realize that we underestimated some critical aspect of climate change. Having overestimated it in the past is not an argument for relaxing today, and is certainly not a laughing matter.

Are there any models that predict accurately backwards?

All of them, because that's how you build models? Or do you mean something different?

Pretty sure he ment modern models that prove to be more right than others using past data.

Interesting question imo

I mean per the other response that is how you build models like this aka yes, all of them. Source: Am a Statistician

edit: that doesn't mean they are correct going forward necessarily and most of the doomsday models I've seen are simulations that run thousands of times and a very small number of the simulations predict doom and a very small number predict no effects. The average of these expiriments is often the most likely scenario but doesn't really make headlines.

I don't need models when I have the historical record. The historical record says mean sea level is going to be hundreds of _meters_ above current levels in the not-too-distant future.

This is why people don't listen to the scientists, because absurd FUD like this gets spread and it discredits the entire movement. Even the most doomsday predictions are on the order of inches, maybe over a foot in the next 50 years. Such a rise would still be incredibly devastating, don't get me wrong, but it would take about a hundred years of a completely runaway warming cycle to raise the seas a single meter, much less hundreds.

I'm quite serious about the historical record. This is not FUD, this is data. The historical record shows that the last time atmospheric CO2 concentration was at the level we are at currently, several things were true. 1) temperatures were 4-5C higher. 2) there was no permanent surface ice anywhere on the planet as far as they can tell. 3) mean eustatic sea level was anywhere from 50 to 200m above current levels.

http://onlinelibrary.wiley.com/doi/10.1029/2008PA001615/full

Keep in mind, it's not just melting you need to figure in, there's also the thermal expansion of water.

Also models do not currently project the Antarctic losing all of its ice, yet this is what the historical record suggests is likely. The models also do not account or undercount the contribution of non-anthropogenic forcing factors such as the one this article refers to -- they assume that _we_ are the main feedback loop, and yet there is evidence that we have entered a regime where we could reduce emissions to zero and the non-anthropogenic feedback would continue to add CO2 and methane to the atmosphere at a rate equal to or exceeding our current emissions.

I believe the main reason you aren't hearing things like this is because scientists are picking their most defensible claims because they know that they will be hounded by climate change deniers. They are not talking about their worst fears, for worry of being labeled FUD.

It's not just melting and thermal expansion. There's also loss of mass at the poles, which increases sea level elsewhere.

Edit: sense

You really defended your position quite effectively, thanks for the perspective.

When I read the paragraph 55 of the article, I think that it tells a different story. Basically, it's 20-30 meters higher seas; a good part of it coming from tectonic stuff. And they also say that sea level increase appeared before warming.

The volume of the ocean basin is something that I haven’t been able to find data for one way or the other. The timeline is different — there is a lot of data and of course it doesn’t all line up perfectly. The generally accepted reference timeline, which is based on a single south Atlantic core sample, is calculated using an assumption about the annual rate of sediment deposition. There is evidence that mid ocean sediment deposition dropped during PETM while coastal deposition increased. This is likely because the oceans become inhospitable due to increasing acidity and warming caused the same thing we see today — increased evaporation rate and warmer air being able to hold more moisture as water vapor leads to increased rainfall and therefore river flows increased generally. There have been attempts to try and correct for this factor using iron deposition variability which may correlate with planetary precession and other techniques, some of which change the timeline fairly drastically at the scale we’re talking about.

Long story short — yes this is an oddity but there’s not a well accepted explanation for it and there is reason to question whether we have the PETM timeline correct for the area of interest. (the onset is quite sudden, geologically speaking, although not as sudden as the data we are producing right now!) I would encourage you to do more reading and build an opinion based on the sum of evidence rather than that one paper, which I linked to simply because it has an accessible graph for sea level variability compared to today.

wow that's an answer ! I'm out of my league :-)

> I don't need models when I have the historical record. The historical record says mean sea level is going to be hundreds of _meters_ above current levels in the not-too-distant future.

What in the historical record says this?

Edit: saw your reply to my sibling after I posted this.

http://onlinelibrary.wiley.com/doi/10.1029/2008PA001615/full

Feel free to do your own research, obviously. You are looking for eustatic sea level during PETM (Paleo-Eocene Thermal Maximum).

You will likely find a lot of studies which show coral reefs and anything that lives in the ocean and has a shell is about to have an even worse time of it than we are!

(To be clear, hundreds is the most extreme value -- the variability at different sites is fairly high, but roughly 50m is the minimum.)

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