On this blog site there are a number of posts under the category Oceans Make Climate, pointing to the oceans as climate heavyweights on human timescales. Those essays describe various cycles and circulations that cause climate system changes on scales from decades up to millennia.
When we look longer term, other heavyweights show off their punching power.
Bill Illis has done some impressive gathering of data and presenting the scope of natural climate variations over long time scales. “I have the biggest database of paleoclimate Temperature and CO2 estimates of anyone I guess. 17,000 individual temperature estimates going back 2.4 billion years and 2600 CO2 estimates going back 750 million years.”
The diagram below is his remarkable display showing the major climate changes resulting from geologic forces and shifts. (h/t to Paul Vaughn for linking to this chart, new to me)
Illis explains the implications:
Antarctica glaciates over, no change in CO2. Then CO2 finally falls below 280 ppm for perhaps the very first time in history and Antarctica promptly unglaciates. CO2 stays flat for another 13 million years while Antarctica is only half glaciated. Then 14 million years ago, the glaciers advance and CO2 does not change. etc. etc. CO2 has nothing to do with it. It is whether the Antarctic Circumpolar Current is fully operating or not. And that is determined by continental drift and whether individual continental landmasses or even small cratons between South America and Antarctica are blocking it.
To dramatize the lack of correlation between CO2 changes and temperature changes, Bill Illis presents the diagram below. The orange line represents estimated temperatures assuming 3C warming for each doubling of CO2 concentrations
During 40 million years of history, geologic, astronomic and oceanic forces have shaped the planet’s climate. We conclude that CO2 fits into the flyweight climate class, perhaps even “mini flyweight” or “atom weight.”
Footnote Nov. 4
There is a lot of fuss about limiting global warming to +2 Celsius. According to the charts above, the variations have been within + or – 2 Celsius during the last 2 million years.