An Estimate of Climate Sensitivity
Charles Rotter / August 31, 2020
Reposted from edmhdotme
Assuming the logarithmic diminution premise to be appropriate, this diagram indicates:
there is no direct, straight-line relationship between atmospheric CO2 concentration and its influence on temperature
the “Greenhouse” warming effectiveness of CO2 diminishes logarithmically with increasing concentrations, which, as a result, implies:
· at 20 ppmv, ~42% of CO2 warming effectiveness is already taken up
· at 100 ppmv, ~67% of CO2 warming effectiveness is taken up
· at 150 ppmv, the CO2 level of plant / planet viability, ~72% of CO2 warming effectiveness is taken up
· at 280 ppmv, the approximate pre-industrial CO2 level, ~82% of CO2 warming effectiveness is taken up
· at the current level of atmospheric CO2, 410 ppmv, ~88% of CO2 warming effectiveness is taken up
Equilibrium Climate Sensitivity, (ECS), is assessed as the further temperature increase that arises from a doubling of CO2 in the atmosphere
the logarithmic diminution graph shows that a doubling of CO2 from 410 ppmv to 820 ppmv should result in a temperature increase of about +0.35°C, because the warming capability of CO2 is now so close to saturation: this calculation takes no account of feedbacks, which are undeterminable
a rise of +0.35°C would be so marginal as to be undetectable within the noise of Global temperature measurements
such a further doubling of atmospheric CO2 to ~820 ppmv would take more than 150 years at the present rate of CO2 emissions
cooling of the Oceans, again re-absorbing CO2 from the atmosphere — is the only way that atmospheric CO2 levels will decrease; that will only happen in the next coming ~100,000-year glaciation period
life on Earth is dependent on its atmospheric CO2 used by plants via photosynthesis to release oxygen and generate organic compounds
as the present Holocene interglacial epoch advanced the planet warmed, so have warmer Oceans out-gassed CO2 to reach a pre-industrial level of about 280 ppmv
that slow CO2 out-gassing process from warmer Oceans is continuing, and has been supplemented largely by human-caused CO2 emissions since the 1850s from the burning of fossil fuels; thus, the measured CO2 level has now reached about 410 ppmv
Water vapour and clouds in the atmosphere are responsible for the greatest part of the Greenhouse effect
CO2 is a significant “Greenhouse Gas”, even though it is only present in trace amounts, (now ~410 parts per million by volume)
CO2 is considered to be responsible for roughly 10% of the total +~33°C “Greenhouse” effect, or about +3.3°C
plant productivity improves radically with increasing atmospheric CO2, and NASA has reported about +15% more green growth worldwide over the last 50 years — which has enhanced agricultural productivity and enabled greater food supply for a growing global population
plant productivity is hampered by colder weather, and any cooling will lead to agricultural losses.
photosynthesis stops, and plants and therefore life on Earth, can no longer survive — if atmospheric CO2 levels fall below 150 ppmv
When plants first flourished (~400,000 years ago), atmospheric CO2 levels were ~10- to 20-times higher than at present, and no runaway global warming occurred; “20 times higher” would have been 8,200 ppmv.
those high levels of CO2 atmosphere have progressively diminished, with CO2 both being absorbed by the oceans to be sequestered as limestone by ocean life, or converted into fossil fuels
about 20,000 years ago, in the depths of the Last Ice Age, Life on Earth came very close to total annihilation when atmospheric CO2 concentration fell to 180 ppmv, which was only ~15% above its terminal value:
this process is driven by colder oceans being able to absorb more atmospheric CO2 and thatby carbonate being progressively sequestered by marine life as limestone.
This is the way that all life on Earth might be extinguished — during some future ice age — due to atmospheric CO2 starvation.
Therefore, all extra CO2 in the atmosphere today — extends the viability of Life on Earth.
This arithmetic shows that human-made additions of CO2 to the atmosphere can only have very marginal further temperature effect into the next century and beyond.
Climate modellers assert that there is substantial positive temperature feedback from the warming induced by added CO2 which could increase the level of water vapour in the atmosphere. In order to reach the much feared +2°C temperature increase, that feedback from water vapour and clouds would have to be at least 5-fold, or even more, to achieve their higher predictions. There is no evidence of such positive feedbacks and observations show feedback is likely to be marginally negative.
This simple math, and the fact that the warming effect of CO2 is already close to being saturated, shows that any level of future atmospheric CO2 — increased by humankind’s burning of fossil fuels — can never cause Catastrophic Anthropogenic Global Warming.
Hmm… I thought plant life (as in algae in the sea) happened about a billion years ago??
Good point. I think the better terminology would be — “When plants first flourished ~400,000 years ago, …”