[{"data":1,"prerenderedAt":93},["ShallowReactive",2],{"blog-\u002Fblog\u002Fwhat-is-abrupt-4xco2":3},{"id":4,"title":5,"author":6,"body":7,"date":74,"description":75,"experiment":16,"extension":76,"furtherReading":77,"meta":87,"navigation":88,"path":89,"seo":90,"stem":91,"__hash__":92},"content\u002Fblog\u002Fwhat-is-abrupt-4xco2.md","What is the abrupt-4xCO2 experiment?","Charles Turner, ACCESS-NRI",{"type":8,"value":9,"toc":68},"minimark",[10,22,27,30,34,37,61],[11,12,13,17,18,21],"p",{},[14,15,16],"strong",{},"abrupt-4xCO2"," is an idealised stress-test. Starting from the pre-industrial\ncontrol climate, the carbon dioxide concentration is ",[14,19,20],{},"instantly quadrupled"," and\nthen held there while the model runs on.",[23,24,26],"h2",{"id":25},"what-it-does","What it does",[11,28,29],{},"Nothing about this is meant to be realistic — no real scenario quadruples CO2\novernight. That is the point. By applying one large, clean, well-defined push, we\ncan watch the climate system respond without the clutter of volcanoes, aerosols\nand gradually changing emissions getting in the way.",[23,31,33],{"id":32},"why-we-care","Why we care",[11,35,36],{},"This experiment is how we measure some of the most important numbers in climate\nscience:",[38,39,40,47,53],"ul",{},[41,42,43,46],"li",{},[14,44,45],{},"Climate sensitivity"," — how much the planet ultimately warms for a given\nincrease in CO2.",[41,48,49,52],{},[14,50,51],{},"Feedbacks"," — how clouds, water vapour, ice and the like amplify or damp\nthat warming.",[41,54,55,56,60],{},"How quickly the ocean takes up heat, which sets the ",[57,58,59],"em",{},"pace"," of warming.",[11,62,63,64,67],{},"Because every model runs exactly the same idealised experiment, ",[65,66,16],"code",{},"\ngives us a clean way to compare one model against another.",{"title":69,"searchDepth":70,"depth":70,"links":71},"",2,[72,73],{"id":25,"depth":70,"text":26},{"id":32,"depth":70,"text":33},"2026-07-04","A deliberately extreme idealised run: quadruple the CO2 instantly and watch how the climate responds.","md",[78,81,84],{"title":79,"url":80},"WCRP CMIP — the Coupled Model Intercomparison Project","https:\u002F\u002Fwcrp-cmip.org\u002Fcmip7\u002F",{"title":82,"url":83},"Eyring et al. (2016): CMIP6 experimental design and organisation (defines the DECK, including abrupt-4xCO2)","https:\u002F\u002Fdoi.org\u002F10.5194\u002Fgmd-9-1937-2016",{"title":85,"url":86},"Carbon Brief: explainer on climate sensitivity","https:\u002F\u002Fwww.carbonbrief.org\u002Fexplainer-how-scientists-estimate-climate-sensitivity\u002F",{},true,"\u002Fblog\u002Fwhat-is-abrupt-4xco2",{"title":5,"description":75},"blog\u002Fwhat-is-abrupt-4xco2","hw0eYjW8bKPPsMycmgBmnqXOAyx1dBrxmdZYuMeF9Hw",1784888533712]