The earth has had higher CO2 levels in the past.
The quote below if from this link;
A Graphical History of Atmospheric CO2 Levels Over Time | Earth.Org
The most distant period in time for which we have estimated CO2 levels is around the Ordovician period, 500 million years ago. At the time, atmospheric CO2 concentration was at a whopping 3000 to 9000 ppm! The average temperature wasn’t much more than 10 degrees C above today’s, and those of you who have heard of the runaway hothouse Earth scenario may wonder why it didn’t happen then. Major factors were that the Sun was cooler, and the planet’s orbital cycles were different.
I can see how they can measure CO2 from rocks from 500 million years ago, but I am not sure how you can know the sun was cooler except by simulations. The main point is CO2 is the not the only variable. There appears to be other variables that can counter the expected greenhouse affect from CO2. Today we are at a whopping 420 PPM while the earth has been somewhere between 3000-9000 ppm. Why wasn't the earth 150 degrees?
The graph in graph supplied by Subduction Zone is interesting in that it shows the seasonal variable of CO2. The CO2 drops in the warm weather; Northern Hemisphere, and rises in the cold weather. The latter is due to fewer active plants and more snow than rain. In the warm weather, rain can scrub the CO2 and allow it to react with silicates in the soil; carbon fixation. While active plants in the warm weather also fix CO2. Snow is not reactive the same way as liquid water, and inactive plants do have much photosynthesis.
Seasonal variation and the importance of active plants tells me that the expansion of civilization and defoliation is reducing the total carbon fixation by plant life. This will cause CO2 to rise.
In 1800 there were 1 billion people on earth and now there are 7 billion people. That is a lot of new houses, farms and commercial real estate. Wood and trees have played a major role in this human progress, for more and more people. The CO2 increase is also due to less natural CO2 fixation as we take down old world forest. If we have to give up fossil fuels maybe we need also give up wood products and chopping down wood environments. We also need to prevent forest fires since these are a double loss; add CO2 and lower carbon fixation.
If we were to stop manmade CO2 production, while still using chopping down trees for wood, the loss of plant CO2 fixation will cause the CO2 to keep rising from natural sources.
Here is an interesting graph from NOAA;
Global Monitoring Laboratory - Carbon Cycle Greenhouse Gases
It shows that fire is second leading cause of CO2 and carbon emissions. What it does not show is how the loss of plant life in forest fires makes the green part of the graph get smaller. If the amount below zero gets smaller the CO2 rises even if we do nothing different.
If you look from 2014 to 2016 the green part of the plot got smaller by a large amount. For some reason the earth's land was not absorbing carbon via its soils and trees by a large amount. The oceans were flat.