On the order of 0.

From what I read, we can expect a 1 degree increase if we release somewhere in the ballpark of 100 billion tons of CO2. Using those figures, 3.93 megatons is 0.0000393 degrees.

As a point of comparison, humans release roughly 40 gigatons of CO2 per year; 3.93 megatons is 0.0098% of that.

As another point of comparison, around 550 gigatons of CO2 is released (and absorbed) by the planet "naturally". 3.93 megatons is 0.0007% of that.

> As another point of comparison, around 550 gigatons of CO2 is released (and absorbed) by the planet "naturally".

So we are currently within 20% of what the planet does naturally, which seems not that bad actually.

Unfortunately it's not that simple, because the planet absorbs that CO2 too.

So in reality, the important thing is we're going from a delta of 0 gigatons of CO2 per year, to a delta of +40 gigatons of CO2 per year.

40 / 550 is less than 10%. That's actually a huge number considering that the planet has an "equilibrium". Your actions can affect that balance and the whole planet goes into disarray. Not saying that's what will happen, though. The planet could also just absorb our extra CO2 (which is why it's becoming greener).