The Carbon Cycle Behind Net Zero

What happens to carbon dioxide after we emit it? Half is absorbed within a year or two by plants and the oceans, the rest, in effect, stays in the atmosphere. So, does that mean we have to halve emissions to stop concentrations rising? Unfortunately, no.

Despite the vast reserves of carbon dissolved in the oceans, carbon dioxide released by burning fossil fuels does not get diluted away, but makes an indelible mark on climate for hundreds of thousands of years.

A lecture by Myles Allen recorded on 7 March 2023 at Barnard's Inn Hall, London.

The transcript and downloadable versions of the lecture are available from the Gresham College website:

[MrAytch]

Thank you to all involved in this presentation. The attention required was well rewarded!

[TheMrCougarful]

This was well done. I'm a biologist, the constant narrative about how the biosphere will solve the problem for us is simply 100 percent incorrect. On the timescales of global system dynamics, carbon capture by plants is essentially zero. Plants are part of the carbon cycle. CYCLE. This is not the solution you suppose it to be.

[dhruvtripathi]

Thank you for all the energy you put into such a detailed and wonderful presentation. Especially appreciate how you give credit to all the scientists whose work you cited. It's multiple lifetimes of research which has given us the knowledge and insight into the crisis we have today. Thank you once again for bringing it all together so comprehensively.

[Kangaroo_Caught]

Of course, one factor which I have Never heard discussed in relation to climate change is human responses to increased CO2.
Our respiration rate is driven by blood CO2 levels. I understand that we really struggle when the local atmospheric CO2 concentration reaches about 1000 ppm. In my lifetime, over the last 55 years, atmospheric CO2 has risen from about 320 ppm to over 420 ppm. Do we know at what level of atmospheric CO2 those with compromised respiratory systems will start to be seriously affected?

[DrEnvironmentscientist]

Amazing understanding and explanation of concepts

[whatabouttheearth]

2:50 that blinking you see in South America is the fluctuation between day and night, so between photosynthesis and respiration. So in that one video, at the same time you can see the daily fluctuation of CO2 from plants (due to the fluctuation of day photosynthesis and night respiration), and the yearly fluctuation of CO2 from plants (due to the seasons). Really cool! 😎

[xenocampanoli]

One thing that seems to always be left out is that when the higher carbon waters in the deep ocean re-emerge some hundreds of years in the future when there is presumably more warming, suddenly the surface warming will accelerate exhausting carbon.

[whatabouttheearth]

"Radioactive Carbon 13"? What?

C12 and C13 are stable, C14 is the radioactive isotope. And we are seeing an increase in the C12/C13 ratio found in plants (more "lighter" C12 than "heavier" C13) but not a relative increase of radioactive C14. This is because it is ancient plants that are majority of fossil fuel CO2 (coal) so it no longer has the radioactive C14, neither does petroleum (fossil plankton/algae).

[xenocampanoli]

I'm afraid the pipes example, which is helpful to those who think logically, is useless for helping those who are deniers to understand the problem, because they are unable to think logically with adequacy to getting the message. They will just ridicule the example out of ignorance.

[philclancaster]

Really well presented and clear, thanks

[xenocampanoli]

Given the deep oceans hold massive amounts, but get circulated every so often, it seems that overturning period, presumably something between 100 and 1000 years, runs one time after recapture is turned off, we will then be doomed to all that repository's worth, which I suspect is a whole lot.

[no-one-knows]

Like to know what the ideal earth temperature is?