If so called global warming is true, then how does one know that it is caused by human activity and not natural occurrence?

So there is this figure saying the temperature has risen 1.8 degrees since 1880? How could you possibly break down the cause over 140 years? Let's say someone theorizes that half is caused by human activity and the other half is caused naturally. That means .9 degrees is responsible for each. So what is... show more So there is this figure saying the temperature has risen 1.8 degrees since 1880? How could you possibly break down the cause over 140 years?

Let's say someone theorizes that half is caused by human activity and the other half is caused naturally.

That means .9 degrees is responsible for each.

So what is the margin of error on that .9 degree figure? What is the margin of error on the 1.8 figure?

It seems a little hokey to say you can possibly know a relatively minuscule change over 140 years by measuring retrospectively and with models that have margins of error.
Update: How could possibly keep a straight face by saying your less than 2 degree figure should not be questioned?
Update 2: How could you possibly keep a straight face by saying your figure is accurate to 1/10th of a degree?
0