Guest Post by Willis Eschenbach
I’ve read comments from several folks claiming that despite the COVID lockdowns reducing emissions, there’s been no corresponding decrease in the airborne CO2. Here’s a typical claim, complete with graphic, saying that this proves that human emissions aren’t the reason for the gradual increase in airborne CO2.
The COVID shutdown reduced man’s emissions of CO2 by about 20%. Yet the growth of CO2 in the atmosphere then was almost EXACTLY what it was during preceding years.
What didn’t change was natural emissions. So much for Willis’s [saying] “it’s man made”, and settled science.
Hmmm … y’all who know me know that I’m a data guy. So I thought I’d take a look at the situation. I reasoned that a “year-over-year” comparison would be much more valuable than the more general graph above. A year-over-year comparison is a graph showing, for each month in the record, how much the CO2 level increased over the same month in the previous year. If we want to understand changes in CO2, we need to look at changes in CO2, not the absolute values the commenter used above. Airborne CO2 has been growing at about 2.5 ppmv per year or so. Figure 1 shows recent data detailing the year-over-year growth in airborne CO2.
Figure 1. “Year-over-year” analysis of airborne CO2. Each data point shows how much the airborne CO2 increased over the same month a year previous. Units are parts per million by volume (ppmv). Photo is of Mauna Loa in Hawaii, location of the CO2 measuring station.
Hmmm … didn’t really expect that the variation would be quite that large. The big peak in the middle is from the El Nino/La Nina of 2015-2016. The peak and drop at the start if from the Nino/Nina of 2009-2010. What causes the other variations is far from clear. What is clear is that the values vary from smallest to largest by no less than four hundred percent, from an annual increase of less than one part per million by volume (ppmv) to an increase of over four ppmv … a large natural variation.
Next, we have to ask the question the commenter who I quoted above didn’t ask—just how much would we expect the CO2 to change due to the lockdowns?
Now, the author of the comment above says there’s been a 20% decrease in 2020 emissions … but that makes my Bad Number Detector start ringing. In general, carbon emissions for the globe, as well as the resulting changes in global atmospheric CO2 levels, are a linear function of global Gross Domestic Product (GDP). The GDP is the sum of all of the goods and services produced during the year.
And as you’d expect, if we increase the amount of stuff we make, we increase the CO2 emissions correspondingly. (For the math inclined, global annual carbon emissions ≈ 6.3 Gtonnes + .4 * global GDP (trillions of constant 2010 $).
Looking around the web, I see estimates for the lockdown-caused drop in 2020 GDP of from 4.5% up to 5.3%. And since emissions and the resulting atmospheric levels are a linear function of GDP, that would mean that the year-over-year CO2 increase should be smaller by something on the order of five percent.
This lets us calculate what the increase in CO2 would have been if there were no lockdowns. Over 2020 you’d expect CO2 emissions, and thus the resulting annual airborne CO2 increase, to have been 5% greater if there had been no lockdowns.
So to be very conservative in our estimate, let’s say the lockdowns actually decreased emissions by twice that, or 10%. If we use ten percent as our figure, our results will be solid.
So … what would the Figure 1 graph above look like without that 10% drop in 2020 emissions? Figure 2 shows that result. Just for interest’s sake, I’ve also added what a 20% difference in emissions would look like. That’s four times the actual ~ 5% change expected from the drop in GDP.
Of course, up to 2020 there is no change …
Figure 2. As in Figure 1, but with lines added showing a 10% (yellow) and a 20% (orange) increase in CO2 no-lockdown emissions would look like.
Again … hmmm. Gotta say, in a system that variable, a 10% or even a 20% difference is not distinguishable from the background. I mean, any one of those three lines is totally believable.
My main conclusion is that despite the huge, almost incalculable human cost of the lockdowns, the change in the rate of increase of CO2 is lost in the noise … which certainly doesn’t prove anything either way about whether the increase is human-caused.
My other conclusion is that this should give great pause to those who are blithely recommending totally restructuring the global economy to replace fossil fuels … look at the real-world costs of the lockdowns all around you, and look at the meaningless CO2 benefits in the graph above. Not worth doing on any planet.
My best wishes to all in this most curious year of 2020, can’t be over soon enough for me,
via Watts Up With That?
November 16, 2020 at 04:47PM