<story><title>Even 50-year-old climate models correctly predicted global warming</title><url>https://www.sciencemag.org/news/2019/12/even-50-year-old-climate-models-correctly-predicted-global-warming</url></story><parent_chain><item><author>ekianjo</author><text>Where is the story hère though? So they looked retroactively and found some models in the past that fitted with current observations even though they had no clue that China would become such a powerful force in terms of CO2 emissions?&lt;p&gt;If you run random models and wait long enough you will always be able to find at least one model that predicted the current observations. That does NOT mean the models were right, it means that you are basically ignoring all the other models that made bad predictions. So in order to make a headline out of this you would need to make a extensive review of all the models we had back then and found out HOW MANY were actually not bad.&lt;p&gt;Would not make that much of a headline because you would find most models were bad. Anyone involved with forecasting will know what I mean.</text></item></parent_chain><comment><author>DennisP</author><text>Whether or not China emitted lots of CO2 doesn&amp;#x27;t matter here. The old studies didn&amp;#x27;t predict how much CO2 the world would emit. They predicted how much the planet would warm, for various amounts of CO2 emissions. It turned out they were correct about that.&lt;p&gt;Among the models this study looked at was Hansen&amp;#x27;s. That&amp;#x27;s the NASA scientist who testified about global warming to Congress in 1988. It&amp;#x27;d be quite a coincidence if there were lots of models with a wide variety of predictions, and the one model that was presented to Congress just happened by chance to be one of the few that got it right.&lt;p&gt;But if you can actually show that there were in fact a bunch of models by scientists of similar stature, which made really different predictions and were left out of this study, then that would be interesting.</text></comment>
<story><title>Even 50-year-old climate models correctly predicted global warming</title><url>https://www.sciencemag.org/news/2019/12/even-50-year-old-climate-models-correctly-predicted-global-warming</url></story><parent_chain><item><author>ekianjo</author><text>Where is the story hère though? So they looked retroactively and found some models in the past that fitted with current observations even though they had no clue that China would become such a powerful force in terms of CO2 emissions?&lt;p&gt;If you run random models and wait long enough you will always be able to find at least one model that predicted the current observations. That does NOT mean the models were right, it means that you are basically ignoring all the other models that made bad predictions. So in order to make a headline out of this you would need to make a extensive review of all the models we had back then and found out HOW MANY were actually not bad.&lt;p&gt;Would not make that much of a headline because you would find most models were bad. Anyone involved with forecasting will know what I mean.</text></item></parent_chain><comment><author>starpilot</author><text>Yeah, this could be survivorship bias: &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;motls.blogspot.com&amp;#x2F;2017&amp;#x2F;03&amp;#x2F;selection-of-climate-model-survivors.html&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;motls.blogspot.com&amp;#x2F;2017&amp;#x2F;03&amp;#x2F;selection-of-climate-mode...&lt;/a&gt;&lt;p&gt;As someone who&amp;#x27;s written basic fluid dynamics codes, I&amp;#x27;m blown away by the complexity of climate models. The errors I ran into in debugging my relatively straightforward codes were incredibly subtle. Like pressures, velocities still &amp;quot;looking right&amp;quot; but still being wrong, due to numerical viscosity and other artifacts of the inexact solutions to Navier-Stokes. This is for flow in a box in a steady state. For an entire planetary atmosphere at a time scale of decades, I can&amp;#x27;t even imagine how they can track down every error without duct taping &amp;quot;corrections&amp;quot; (overfitting) on everything.</text></comment>