How much of a lag is there between current atmospheric CO2 levels and the resulting increase in global average temperature?
Apparently, global average temperatures have not increased nearly as rapidly as CO2 levels have over the past 100+ years.
Looks like there should be an increase in global average temperature by something like 4-6 C compared to CO2 levels according to that climate skeptist graph. Definitely more than 1C.
We're at 1.5+ C above baseline, right?
Thanks.
That is the question...of the 'test tube earth'. We have none to close to none (see 'Paleocene hyperthermals') records of such global warming events where the rise of co2 precedes warming. Not good ones, at least. Thus climate models. This question is a mess to solve. Much of climate science connects to this question, as it is the one that gives rise to the threats to mankind. The 4 to 6 degrees rise of T the atmospheric levels of ghgs seem to indicate is delayed by the ice and oceans. By how much? We might check the speeds of ocean currents their heat capacity, how long does it take the atmospheric heat to reach specific levels in oceans? Add in ice on the planet you get questions people ask here, how stable are ice sheets to warm water intrusions, how much (and if) the clouds in summer delay the yearly melt in the arctic... This is not much of an answer.
We might seek the fastest local or areal changes seen in records. These, for sure, have happened. Thus we get headlines of western (and central) American megadroughts or speedy restructurations of ocean currents in North Atlantic, there are many such events in areal records. These somewhat tie to the studies of 'stuck weather' several top scientists are nowadays pursuing. I, for one, am not surprised anymore if I hear of a heat wave of over some 2-3 degrees above previous records, that is what the atmosphere would be giving us, if the oceans (and remaining ice) would not warm up so slowly. Areal changes in climte system may change very rapidly geologically speaking, the system could enter 'permanent (or was it mega-) el nino' imho at anytime. The same goes for currents in North Atlantic giving rise to some 'alarmist' calls here in the forum of imminent 'Blue Ocean Event' after which it is assumed that most of the North Atlantic would soon warm up. This imho takes at least 10 years, but the catch 22 here is there would be no going back to ice gerönerating condition (potential searches 'hysteresis in climate system', 'irreversible climate change' ?). A large rise in T belittleling the size of medieval warming period would ensue, according some. More conservative estimates (style ipcc) are plentiful in the forum (40-50 years), some still hope the meltwater off of Greenland Ice Sheet provides a buffer against this for longer period ('stopping of the Gulf stream (and the whole north atlantic gyre)). I don't see this last one happening.
I don't remember if the Alley lecrure included an estimate of this. The simplest way to look at this question, we might take the 1,5 degrees pretty close realised (-aerosols) nowadays and look for the time when the co2 was on equivalent level... Here too we have a bit of complications due the 'early anthropocene hypothesis' and due the earliest temperature measurements ('18th to 19th century temperature records). Without going to detail, the resulting answer to the question of delay doesn't change much, but this is again speaking climatologically, so the exact answer may vary by a decade or even two.
Still not much of an answer, if one is after a specific number of years, but some might throw in an exact number in discussions if they've calculated one recently. Not much more I remember straight away wrt Big Question without going through some notes snd papers so 'PMTs crash course on Paleoclimate' stops here. And mind you, I'm not a practising scientist, though have studied some climate stuff. All the errors in the above are my owm and as before, please correct if the text is dramaticlly off the regular scientific thoughts.