"It's Us"

Uploaded by Etheoperatorsmanual on 07.11.2011

So physics and chemistry tell us that adding
carbon dioxide to the atmosphere warms things up.
And Earth's climate history shows us
there will be impacts, from melting ice sheets,
to rising sea level.
But how do we know, with equal certainty,
that it's not just more natural variation,
that humans are the source of the increasing CO2?
When we look at a landscape like this one
we know immediately that volcanoes
put out all sorts of interesting things.
And that includes CO2.
So how do we know that the rise of CO2
in the atmosphere that we see,
comes from our burning of fossil fuels,
and not from something that the volcanoes have done?
Well, the first step in the problem is just bookkeeping.
We measure how much CO2 comes out of the volcanoes.
We measure how much CO2 comes out of our smokestacks
and tail-pipes.
The natural source is small.
Humans are putting out 50 to a 100 times more CO2
than the natural volcanic source.
We can then ask the air whether our bookkeeping is right,
and the air says that it is.
Volcanoes make CO2 by melting rocks
to release the CO2.
They don't burn and they don't use oxygen.
But burning fossil fuels
does use oxygen when it makes CO2.
We see that the rise in CO2 goes with a fall of oxygen,
which says that the rising CO2
comes from burning something.
We can then ask the carbon in the rising CO2
where it came from.
Carbon comes in 3 flavors:
the lightweight carbon 12,
which is especially common in plants.
The medium-weight carbon 13,
which is a little more common
in the gases coming out of volcanoes.
And the heavyweight carbon 14.
It's radioactive and decays almost entirely
after about 50,000 years,
which is why you won't find it
in very old things like dinosaur bones or fossil fuels.
We see a rise in carbon 12, which comes from plants.
We don't see a rise of carbon 13,
so the CO2 isn't coming from the volcanoes.
And we don't see a rise in carbon 14,
so the CO2 can't be coming from recently-living plants.
And so the atmosphere says that the rising CO2
comes from burning of plants
that have been dead a long time...
That is fossil fuels.
The CO2 is coming from our fossil fuels.
It's us.