Potemkin wrote:We're in an Ice Age, @Rich. It began about two and a half million years ago, and it's still ongoing. It is highly unusual in the overall history of our planet for there to be year-round ice on both poles. Highly unusual.
It is also notable that our entire evolutionary history from homo erectus on has been during the Quaternary Ice Age. And it's also no accident that agriculture, urbanisation and industrial production only got off the ground after the end of the last glacial stadial. Geography may be fate, but climate is fate too.
Well, that may be true, or maybe not.
However, I saw and posted here about a climate scientist who has shown that all but the last interstadials have had the same general temp profile. It is that--- the temp increases rapidly from the lows typical of the time when ice is 2 miles thick to melt the ice. This was forced by the Earth's orbital cyclical changes, but this triggers an increase in CO2 in the air, and this is the main cause of the temp increases
This goes on until the Earth reaches a max. temp of about 1 or 2 deg. C lower than we see now, and then the temp slowly falls for about 10K years, when the temp begins to fall much faster. This may be because somehow CO2 in the air begins to decrease.
This climate scientist says that clearly the last 10K to 12K years have not followed the pattern for the previous 15 interstadials. For the last 10K years the temp has been very flat compared to the normal swings we see in all other parts of the temp curve. He claims that this is a result of humans discovering how to grow crops and tend cattle. He says growing rice and cattle releases methane to the air. He says that other crops add more CO2 because of replacing forest trees with crop fields. We have liked forest floor soils better than farming grassland soils, at least until steel plows could be made. This is because plowing up grass is much harder and the grass keeps coming back from the roots. Also, forests indicate more rainfall, grass being more tolerant of low rainfall.
. . . Yes, there were small changes like the Medieval Optimum and the Little Ice Age.
. . . He says that he can show why we can see those specific swings. IIRC, the Medieval Optimum was caused by a general increase in population. Remember these are for the whole world, not just Europe. IIRC, the Little Ice Age was caused by the Black Death, which reduced the world's population which reduced the area of crops, which let trees grow back, which removed CO2 from the air. Then the LIA ended in about 1800 as population recovered, especially the Br./Am. in N. America, who grew exponentially. This growth being exponentially, means it gets faster and faster. Also, Europeans were beginning to be burning coal by 1770.
The grand take away form his talk is that humans have been changing the climate for 10K years.
So, as of 2021 humans have added enough CO2 and GHG to the air to have ended the Ice Age. The Ice Age will not return for at least 30K and maybe 100K years even if there are just 1M humans left in the far north and south living in mud huts. It will take at least that long for nature to remove the excess CO2 from the air. [If my sources are correct.]
. . . If it does take 100K years then the next stadial cold period will be skipped, then the next interstadial warm period, and only then another Ice Age advance.
OTOH, if we save civilization and reduce the population to 2B, then we will keep all Ice Age advances from happening by fine tuning the CO2 in the air to make our climate "just right".
.