We only move a small portion of the 40 billion tons. Most of the mass of CO2 is oxygen, which was already present in the atmosphere before we combined it with carbon.

Even assuming you can do some kind of reaction in-place, CO2 is over 25% carbon by mass. 10 billion tons is still a massive challenge.

But don't we only need to "first" remove just enough of that 10 billion tons to maintain where we are now, so that we can then remove more to "go back to levels earlier in modern time"?

Yeah, we need to go extremely carbon-negative, not merely carbon-neutral. It's so easy to forget this.

Why?

Why do we need to go carbon-negative? Because the atmosphere already has too much CO2, and reducing net emissions to 0 means that CO2 will stay there. We've emitted that CO2 in the course of (say) 300 years but need to pull it down in (say) < 50 years, hence we need to pull it down much faster than we emitted it.

Not sure if that answered your question or if you meant something else.

Yes, but what I wanted to know is if we kept the current concentrations would temeperature keep rising or would it stay basically the same as it is today.

It would stay the same. And nature would reduce current concentrations back to normal over the next few centuries.

Thanks - that did help me.