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Politics : Formerly About Advanced Micro Devices -- Ignore unavailable to you. Want to Upgrade?

To: Brumar89 who wrote (1419262)	9/18/2023 6:14:22 PM
From: Wharf Rat	2 Recommendations Recommended By Eric Land Shark Read Replies (2) \| Respond to of 1578157

"what do those two guys models show?" They were the guys figuring out how to make the models. Pioneering Climate Modelers Earn Nobel Prize in Physics \| Quanta Magazine ...What did Manabe’s early climate models show? Manabe’s models in the 1960s “can be considered as the first realizations of the dream of Arrhenius,” according to the Nobel committee. These models considered a single, vertical column of the atmosphere stretching from the ground to the stratosphere. Treating this column as a series of grid points, Manabe and his collaborators studied how the concentration of a greenhouse gas like carbon dioxide within the column affects the flow of heat and air between grid points. He accounted for the fact that hot air is lighter than cold air, so it rises, and that hotter air also carries more water vapor, which is a powerful greenhouse gas. (Greenhouse gases such as water vapor and carbon dioxide strongly absorb and reemit the heat radiating upward from Earth’s surface, blocking much of it from escaping to space. This is the key mechanism that causes warming.) Manabe and his collaborators also considered that, high up in the column, the air is colder, and so cloud drops form, releasing latent heat stored in the water vapor. By accounting for the interplay between these variables in each column of the sky while ignoring horizontal transport of air and heat, they could extrapolate to the whole globe and approximate the overall “sensitivity” of the climate: how much the air temperature increases as a result of doubling the carbon dioxide level. Their early estimates — that the global temperature would rise by 2.3 degrees Celsius in response to doubling of the carbon dioxide concentration — remain impressively accurate even when measured against modern climate models. By 1975, Manabe and his colleague Richard Wetherald had extended their column model into a primitive global model, calculating (on a computer with half a megabyte of RAM) the global climate sensitivity to be 2.93 degrees Celsius. Current models predict a range of 2.5 to 4 degrees Celsius for the climate sensitivity. To gauge the extent of this predicted level of warming, consider that Earth during the last ice age was 6 degrees Celsius colder than it is today. How does weather interact with climate? Climate is long-term; weather is short-term. And yet the two are related. How? In the 1970s, Klaus Hasselmann developed climate modelsthat incorporated weather events, instead of averaging over them, as had been done before. He relied on the premise that the climate slowly evolves as an overall response to the fast, random fluctuations we know as weather. To do this, he developed equations that coupled a slowly varying function representing the climate with a rapidly varying function representing weather. He showed that the latter impacts the former in the same way that the random motion of air molecules on microscopic scales affects the random motion of dust particles on macroscopic scales — an effect called Brownian motion. This analogy with Brownian motion proved very powerful as a way of understanding the interplay between different physical scales in the climate system. How do climate modelers distinguish natural and human causes of climate change? For decades, researchers struggled to systematically tease apart the effects of random weather events, volcanic eruptions and other natural changes from human-caused climate change. In three papers spanning from 1979 to 1997, Hasselmann created a framework for doing this, a way of comparing climate models and observations in order to assess whether the models were faithfully capturing the effects of natural variability. In his framework, he devised “optimal detection” techniques for identifying the signals of human-caused warming. He showed that such signals are best detected, for instance, not in the parts of climate data where they are strongest, but where noise is weakest. A recent articleabout the history of climate science described one of Hasselmann’s optimal-detection papers as “the first serious effort to provide a sound statistical framework for identifying a human-caused warming signal.” The authors go on to write that “Instead of looking for a needle in a tiny corner of a large haystack (and then proceeding to search the next tiny corner), Hasselmann advocated for a more efficient strategy — searching the entire haystack simultaneously” for signals with unique characteristics, or “fingerprints,” that show they do not stem from noise. The fingerprints of human-caused warming grew more pronounced as the decades wore on, driving a growing consensus among climate researchers. Earlier this year, the Intergovernmental Panel on Climate Change concluded that “it is unequivocal that human influence has warmed the atmosphere, ocean and land.” == How good are models? 1390080 RealClimate: Climate model projections compared to observations Warming faster than Hansen's first model, tracking the B, BAU scenario from his famous '88 paper. More models at the RC link. Global mean surface temperature anomalies Hansen et al (1981) Hansen et al (1988)