No, it is you who obviously don't understand. That Summer dip is not CO2 being sequestered in any meaningful way - just temporarily being converted into biomass which decomposes and returns it to the atmosphere every Winter. To actually sequester carbon, you have to take it permanently out of circulation - as sea floor and lake bed sediments, formation of carbonates from weathering of volcanic rock. That's a very, very slow process. Those fluctuations that you make so much of are just that - fluctuations that have very little effect on the long-term trend value.
