A Few Things Ill Considered

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

Objection:

It's clear from the ice cores and other geological history that CO2 fluctuates naturally. It is a bogus assumption that the rise happening today has to be from humans.

Answer:

Surely it is not so hard to believe that since we emit billions of tons of CO2 into the air and, lo and behold, there is more CO2 in the air, therefore the CO2 rise is our fault. But if this simple common sense is not enough there is more to the case than that and that case has been well made. (It is worth noting that the investigation of this very issue by the climate science community is a pretty good indication that they are not taking things for granted or just making assumptions, not even the reasonable ones!)

It is true that CO2 has gone up on its own in the past, most notably during the glacial interglacial cycles. During this time CO2 rose and fell by over 100 ppm, ranging between around 180 to 300ppm. But these rises, though they look steep over a 400Kyr timeframe, took 5 to 20Kyrs depending on which glacial cycle you are looking at. By contrast, we have seen an equivalent rise of 100ppm in just 150 years! Check this plot for a very dramatic juxtaposition of the slow glacial termination versus the industrial revolution.

But there is still more to the case than the initial common sense argument and the circumstantial evidence above. By analysing the isotopes of the carbon and oxygen atoms making up the atmospheric CO2, in a process similar to carbon dating, scientists can, and have, detected a human "fingerprint" of what is now accumulating in the atmosphere. What they have found, via the isotope signatures can be thought of as "old" carbon, which could only come from fossil fuel deposits, combined with "young" oxygen, as is found in the air all around us. So, present day combustion of fossilized hydrocarbon deposits (natural gas, coal and oil) are most definitely the source of the CO2 that we see accumulating, just as common sense tells us.

For more of the nitty gritty technicalities straight from the climate scientists, including links to the actual research that has established this, please visit RealClimate's article on how we know the CO2 is ours.

Of all the pillars holding up the theory of Anthropogenic Global Warming, this really is one of the most unassailable.

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

"The CO2 Rise Is Natural" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.