The Goldilocks zone for a reasonably stable climate for us humans is having CO2 (Carbon Dioxide) in the atmosphere of around 320 ppm (parts per million).  We are currently sitting above 415 ppm; to return we need to remove around 700 gigatonnes (billion tonnes). Exacerbating the problem is, we humans are adding over 36 gigatonnes of CO2 annually, overloading the Carbon Cycle and increasing  CO2 in the atmosphere year on year by 2 ppm.

If we can remove at least 40 gigatonnes of CO2 annually, we may have a chance of getting the  atmosphere back into the Goldilocks zone, back into balance in a time frame that is not unreasonable. The problem is scale, just to remove 1 gigatonne of CO2 from the atmosphere annually, we would need to scrub approx 1,320,000 cubic kilometers at 100% efficiency.  To put this in some kind of perspective, you would need a flow rate of approx 42,000,000  cubic metres per second,  about the same as completely changing the air in approx 84,000 average homes every second.