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Simulation is one way to produce a numerical forecast, but the prediction of any forecast model would never be the result of a single simulation run. Model pred

Simulation is one way to produce a numerical forecast, but the prediction of any forecast model would never be the result of a single simulation run. Model predictions are always (or should always) be reported as an expected value, or the average over many simulation runs. The expected value of a random variable (e.g. mode output) is probably the most fundamental concept in all of statistics/probability, and many mind-wrenching (read: wrong+incoherent) internet hot takes are rooted in logical fallacies about the science of prediction. The reason that there are more predictions (17) than models (14) is that several of the models (eg Hansen 1981) consider several distinct “scenarios” based on differing assumptions about future levels of GHG emissions. Secondly, the forecast models evaluated in the study are from the likes of James Hansen, William Nordhaus, and the IPCC (in other words, authoritative sources). So at the very least this adds weight to the hypothesis that the models published by the IPCC are accurate and methodologically sound. Sure, there is some probability that the models and reality corresponded by random chance, but that probability is made ever more diminishingly small as evidence accumulates. So, I don’t think any of the comments in this thread that accuse the authors of retrospective cherry-picking of climate models are anything but embarrassing examples of pseudo-intellectual contrarianism and/or confusion over basic statistics. The models considered by the study, their predictions, and the methodology used are all located here and were easily found after 30s of digging: https://github.com/hausfath/OldModels https://github.com/hausfath/OldModels

benmaraschino 7y ago
Agreed. The point of criticism that the authors didn’t include all relevant models is among the lowest of the low-hanging fruit I can imagine one picking. And while the process of peer review isn’t without its flaws, I can also imagine that fruit has long since been picked by the reviewers, who have far deeper knowledge of the published models than I or just about anyone else in this thread, save for the actual climate scientists among us.
- mturmon 7y ago
  Thirded. The posting of climate-related stories on HN brings out a lot of un-informed skepticism. The resulting back-and-forth tends to crowd out everything else. In many of these cases, it's clear that the commenters have done no background reading, and have no climate science background. Their comments thus consist of simple armchair speculation (your "lowest of the low-hanging fruit"). In these comments, I have found people with strong opinions on the lack of seriousness of climate science, who have no idea we have gravimetric measurements of ice sheet mass. This is a dataset going back almost 20 years that has revolutionized geoscience. HN commenters have expressed strong opinions about melting ice, with no knowledge of this data and what it means. I have found people who think that climate science consists of having a stable of models each with a host of knobs, and the research method is to turn the knobs or choose new models until the results look dramatic enough to publish. The gap between the firmness of these claims and the knowledge to back it up just boggles the mind. The most basic step people could take to fix this is to read the executive summary of the IPCC AR5 report, or (even better/easier) the executive summary of the NCA (https://science2017.globalchange.gov https://science2017.globalchange.gov). This report was specifically written by people who really know this stuff, for people like us.
  - mistermann 7y ago
    Serious question: based on what I've written, do you believe I am one of the people you describe?
    - mturmon 7y ago
      Your comment is an example of the "middlebrow dismissal" [1] and overdone and uninformed skepticism that is prevalent on HN climate threads. There's no indication that the authors are cherry-picking their models but the comments above are assuming this (without reading the original paper to get a sense of the care of the analysis). It's really easy to find supposed gotchas in this way - basically any analytic step can be questioned. If you live in the Bay Area, AGU is next week at Moscone Center. It's the biggest one-stop-shop in the world for geoscience research. Maybe it's worth paying a one-day admission fee to see some of this in person? [1] https://news.ycombinator.com/item?id=5072224 https://news.ycombinator.com/item?id=5072224

benmaraschino 7y ago

Agreed. The point of criticism that the authors didn’t include all relevant models is among the lowest of the low-hanging fruit I can imagine one picking. And while the process of peer review isn’t without its flaws, I can also imagine that fruit has long since been picked by the reviewers, who have far deeper knowledge of the published models than I or just about anyone else in this thread, save for the actual climate scientists among us.

mturmon 7y ago
Thirded. The posting of climate-related stories on HN brings out a lot of un-informed skepticism. The resulting back-and-forth tends to crowd out everything else. In many of these cases, it's clear that the commenters have done no background reading, and have no climate science background. Their comments thus consist of simple armchair speculation (your "lowest of the low-hanging fruit"). In these comments, I have found people with strong opinions on the lack of seriousness of climate science, who have no idea we have gravimetric measurements of ice sheet mass. This is a dataset going back almost 20 years that has revolutionized geoscience. HN commenters have expressed strong opinions about melting ice, with no knowledge of this data and what it means. I have found people who think that climate science consists of having a stable of models each with a host of knobs, and the research method is to turn the knobs or choose new models until the results look dramatic enough to publish. The gap between the firmness of these claims and the knowledge to back it up just boggles the mind. The most basic step people could take to fix this is to read the executive summary of the IPCC AR5 report, or (even better/easier) the executive summary of the NCA (https://science2017.globalchange.gov https://science2017.globalchange.gov). This report was specifically written by people who really know this stuff, for people like us.
- mistermann 7y ago
  Serious question: based on what I've written, do you believe I am one of the people you describe?
  - mturmon 7y ago
    Your comment is an example of the "middlebrow dismissal" [1] and overdone and uninformed skepticism that is prevalent on HN climate threads. There's no indication that the authors are cherry-picking their models but the comments above are assuming this (without reading the original paper to get a sense of the care of the analysis). It's really easy to find supposed gotchas in this way - basically any analytic step can be questioned. If you live in the Bay Area, AGU is next week at Moscone Center. It's the biggest one-stop-shop in the world for geoscience research. Maybe it's worth paying a one-day admission fee to see some of this in person? [1] https://news.ycombinator.com/item?id=5072224 https://news.ycombinator.com/item?id=5072224