From Dr. Roy Spencer’s Global Warming Blog
by Roy W. Spencer, Ph. D.
The goal of achieving global man-made carbon dioxide emissions sounds extremely difficult. While humanity continues to produce CO2 at an ever-increasing rate (temporarily paused during the COVID pandemic), how can we reach a point where these emissions begin to decline, rather let alone reaching net zero by 2050 or 2060?
What is not discussed (as far as I can tell) is the fact that atmospheric CO2 levels (which we will assume for the purposes of discussion are the cause of global warming) will begin to decrease even when humanity is emitting a lot of CO2.
Let me repeat that, in case you’re missing the point:
Atmospheric CO2 levels will begin to decline even as human-made CO2 emissions decline modestly.
Why so? The reason is something called the CO2 “sink rate.” It has been observed that the more CO2 there is in the atmosphere, the faster nature removes the excess. Last year I published one paper The record for atmospheric CO2 at Mauna Loa, HI shows that each year nature removes an average of 2% of the excess in the atmosphere above 295 ppm (parts per million). The purpose of the paper is not only to show how well a simple CO2 budget model fits CO2 measurements at Mauna Loa, but also to demonstrate that the common assumption that nature is increasingly less able to remove CO2 “Excess” from the atmosphere seems wrong. a phenomenon of El Nino and La Nina activity since monitoring began in 1959. As a result, that 2% sink rate has remained remarkably constant over the past 60 years. (By the way, the popular “air CO2 ratio” used to have big problems as a meaningful statistic and I wish it had never been invented. If you doubt this, just assume CO2 emissions are reduced by half and see what the proportion in the air is calculated to be.)
Here’s my latest model that fits the Mauna Loa record through 2023, to which I’ve added the term stratospheric aerosol to account for the fact that large volcanic eruptions actually *reduce * CO2 in the atmosphere due to photosynthesis increases as sunlight diffuses deeper into plant canopies:
What effect would reducing global CO2 emissions by a “modest” 1% per year have?
The United Nations claims that CO2 emissions will need to fall rapidly to achieve Net Zero by mid-century. Specifically, they said a 45% reduction below 2010 levels would have to be achieved by 2030, and Net Zero would need to be achieved by 2050, to limit future global warming to the target (quite arbitrary) is 1.5 degrees. C.
But let’s see how a much more modest reduction in CO2 emissions (1% per year) will affect future atmospheric CO2 concentrations. Here’s a diagram of the history of global CO2 emissions and how that trajectory will change with a 1% reduction each year from 2023 onwards. (Even this may seem optimistic, but we can all agree that the UN’s goal is an illusion),
When we run the CO2 model with these hypothetical emissions, this is the response of atmospheric CO2 concentrations:
Although CO2 emissions continue, atmospheric CO2 concentrations begin to decline around 2060. There are also four CMIP5 scenarios of future CO2 emissions given for reference, of which RCP8.5 is often the one used to scare people about future climate change, although the possibility is very unlikely.
The message here is that CO2 emissions do not need to be cut much for atmospheric CO2 levels to reverse their increases and begin to decline. The reason is that nature removes CO2 in proportion to the excess CO2 that exists in the atmosphere, and that removal rate can actually exceed our CO2 emissions with modest emissions reductions.
I don’t understand why this issue is not discussed. All the Net Zero rhetoric I see seems to imply that warming will continue if we don’t cut CO2 emissions essentially to zero. But that’s not true, because it’s not the way nature works.
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