I dont question the fact that co2 is a greenhouse gas
Im questioning whether or not the very small amount by comparison man made co2 is the cause of global warming
But the problem is that you keep harping on this "4%" thing. And BTW I think you're actually misinterpreting this entirely by saying man-made CO2 is only 4% of the CO2
in the atmosphere, when the reality is that man-made CO2 is actually about 4 (potentially 5%) of
annual emissions.
But it's actually WAY more complicated than that, due to the carbon cycle. Because there are natural emissions and natural sinks of carbon, these things go in a cycle. However, we DO have the ability to determine somewhat the source of carbon based on the ratio between C12, C13, and C14 isotopes of carbon in the atmosphere as the ratio. And this is what we see.
https://skepticalscience.com/print.php?r=384Isotopic Signature Shows Increased Fossil Fuels Emissions in Atmosphere
Isotopic evidence points to fossil fuels as the source of CO2 emissions. Carbon is composed of three different isotopes: carbon-12, 13, and 14. Carbon-12 is by far the most common, while carbon-13 is about 1% of the total, and carbon-14 accounts for only about 1 in 1 trillion carbon atoms in the atmosphere.
CO2 produced from burning fossil fuels or burning forests has a different isotopic composition than CO2 in the atmosphere. This is because plants have a preference for the lighter isotope (carbon-12); thus they have lower carbon-13 to 12 ratios. Since fossil fuels are ultimately derived from ancient plants, plants and fossil fuels all have roughly the same carbon-13 to 12 ratio – about 2% lower than that of the atmosphere. As CO2 from these materials is released into, and mixes with, the atmosphere, the average carbon-13 to 12 ratio of the atmosphere decreases.
Reconstructions of atmospheric carbon isotope ratios from various proxies, such as tree rings and ice cores, have determined that the carbon-13 to 12 ratios in the atmosphere are the lowest today than they’ve been in the last 10,000 years. Furthermore, the carbon-13 to 12 ratios begin to decline dramatically just as the CO2 starts to increase — around 1850 AD. This is exactly what we expect if the increased CO2 is in fact due to fossil fuel burning beginning in the Industrial Revolution. These isotopic observations confirm that the increase in atmospheric CO2 comes from plant-based carbon, not from the oceans or volcanoes.
How can this be, if human activity is only 4-5% of annual emissions?
I tried to explain via diet. If you weigh a certain amount, and your body is in equilibrium, with 2500 calories consumed each day and 2500 calories burned, you'll remain at a steady weight. But if each day you add ONE light beer--a Mich Ultra at 96 calories--without changing anything else and assuming no metabolic changes, you'll gain 100 lbs over 10 years. In actuality, this won't be true--metabolism does adjust and the energy spent digesting that beer will be somewhere between 0 and 96 calories. And as you start gaining weight your metabolism will increase from daily energy expenditure of being bigger. So you'll actually end up putting on weight, but probably not as much as predicted by the math.
We see the same thing in climate. The Earth was in equilibrium between the amount of natural CO2 emitted and the amount that it was able to sink every year. Predictably (based on the fact that long term climate stability) there was an additional amount of CO2 that the earth could sink. This was covered in an earlier post. Natural emissions are about 120 gigatons of CO2, and based on what we've seen over the last 100+ years of burning carbon, about 122 gigatons can be taken up by the earth. Unfortunately, we're burning an additional 7 gigatons (for 127 GT total), and thus the actual atmospheric carbon is rising because the earth can't absorb it. It's only 4-5% of the annual total, but because it exceeds the earth's capability to sink, it has nowhere to go but stay in the atmosphere.
It can be explained via picture:
The pipe at the bottom is only so big. We'll call it having a maximum capability flow rate of 122 gallons per minute. At 120 gpm emissions, the water pressure stays low enough that only 120 gpm flows out. At 122 gpm, the water pressure increases but can remain in equilibrium so the water level stays constant (at a slightly higher level).
But if you increase the inflow to 127 gpm, then the water level just keeps rising, and rising, and rising. Now, if you do that ONE time, for ONE minute, and then it drops back to 120 gpm, the tub will eventually return to equilibrium. But if you just keep the inflow at 127 gpm in perpetuity, eventually the tub overflows.
A 4% increase in
annual emissions is enough to overwhelm the system.
