First of all have approximate optimum levels of CO2 in our atmosphere ever been established? Or better yet an optimum range, this might mean some sacrifices as melted ice and loss of land, possibly even a change in ocean ph, but overall optimum range that supports life.
Second, as oil reserves start to run out or are replaced by clean energy sources will a point be reached where CO2 levels become static as the ocean and other sources that use CO2 process it as fast as it is being made avaliable?
Third, if we did pass that point that was considered optimum and serious problems started happening how long would it take to reabsorb the excess and return to normal.
To your first question, atmospheric CO2 hovered around 375 ppm for the entire history of humanity, and that seems to be (by definition) the optimum range for us to evolve and thrive. It is possible that a new optimum given our current stage of development and technology could be found. It is, I suppose, also possible that we would have evolved and thrived under different levels, but counterfactuals are hard to pin down.
Yes. There should be a point of equilibrium unless we get into some sort of runaway greenhouse effect where the carbon cycle ceases to operate. Nobody (at least that I have seen) is claiming this is a possibility.
Finally, there are a variety of estimates on the half life of CO2 in our atmosphere ranging from 30 years to 500 years (try Google scholar). I don’t know the current state of this science so I can’t gauge how accurate they are, but I highly expect that the sequestration of carbon is dependent on the biosphere and thus its ability to scrub carbon dioxide from our atmosphere will be affected by how much there is and how much damage it has done…
ETA Perhaps Gigobuster or Jshore (wouldn’t that be cool) will come by and answer more coherently.
As a truck mechanic one of our accounts sold CO2 to nurseries for greenhouses. They were using thousands of tons a year just for growers. I have no idea what saturation levels they kept the greenhouses at.
Life has existed and thrived on Earth under very different levels of CO2. For example, the Late Cretaceous was a greenhouse world with much higher levels of CO2 and temperatures. Despite this several groups of plants and animals diversified during this period.
The problem now isn’t the level of CO2, it’s the extreme rate of increase. Other increases have taken place over tens or hundreds or thousands of years. This allows species time to adapt to new conditions. The current increase is happening across a period of mere decades, so species don’t have time to adapt or migrate.
The optimal level for plant growth, all other things being equal, is a higher level of CO2 than we have today. The question is whether 1) photosynthesis may become less effective at higher temperatures caused by the buildup of CO2; and 2) whether changes in climate will cause changes in rainfall that will cause some areas to become less productive.
As a species history may one day find that the greatest contribution the extinct species of man made to the earth was to release all the locked up carbon back into the atmosphere so that evolution could continue on its way for another 50 million years or so.