Sure.
Without any green house effect whatsoever, the Earth would be roughly ~33ºC cooler.
The actual scientific papers on this require a subscription, so this is the EPAs web site which cites that information. Keep that number in mind for later.
Of the total green house effect, 95% of it is water.
Very widely known in the scientific community, but not often mentioned elsewhere.
The remaining 5% of the greenhouse effect is actually divided up by many trace gasses throughout our atmosphere. This includes Ozone, Methane, nitrous oxide, other trace gases, and of course Carbon Dioxide. For the sake of simplification, we will assume the entire 5% is due to CO2 exclusively.
Of the total CO2 created annually, humans only account for a tiny fraction of the created CO2. Unfortunately, like most Earth sciences, there is varying number depending on what methodology you use.
3.2% or
3.4%
and I've seen 4%, which I assume is the same numbers rounded up. Again, to make things simple, let's round up to 4% and roll with that.
So humans are responsible for 4% of CO2 which is responsible for only 5% of the green house effect. 4% of 5% is 0.2% We are responsible for 0.2% of the greenhouse effect.
Now, what does that translate into temperature wise? Remember we said that naturally the green house effect rises the temperature by 33ºC. 0.2% of 33ºC is 0.066ºC
Therefore, 0.066ºC is the total effect of the cumulative CO2 of the entire human race to this point.
In order for human CO2 to cause an increase in temperature of just 1ºC, we would have to collectively increase our total CO2 emissions by 16 fold, which would be difficult even if we made it a goal. Yet even then it wouldn't be enough.
The reason for that is, the greenhouse effect does not increase linearly with CO2 concentrations. It is "logarithmic", or in simple speak, follows the rule of diminishing returns. This is because simply having more CO2 in the atmosphere, does not mean that there is more long-wave light energy to absorb.
Another way in which eco-screamers twist numbers is by looking at CO2 concentration in the atmosphere, and claiming we are responsible for all increases. This however relies heavily on the assumption that the natural carbon cycle is in constant balance, and that any change must be due to human activities.
This tends to ignore the fact that CO2 levels in history have both been much lower, and much higher, without any human effects.
Yet even in these calculations the results are similar. If we assume that all increases in CO2 our directly due to human activity, we account for only 25% of CO2, which again is only 5% of the greenhouse effect. 25% * 5% = 1.25%
1.25% of the 33ºC equals roughly 0.4ºC. Which again means that using broad assumptions, you still get a temperature increase far too small for human skin to even notice, let alone apocalyptic dire predictions of future destruction.
Far more likely, changes in Earth temperature are due to change in the suns energy output.
