By Willis Eschenbach – Re-Blogged From WUWT
I keep reading about all kinds of crazy schemes to reduce US CO2 emissions. Now, I don’t think that CO2 is the secret knob that controls the climate. I think that the earth has a host of emergent thermoregulatory mechanisms that act to keep the temperature within narrow limits (e.g. 0.6°C temperature change over the entire 20th Century). I don’t believe the claims that the modern changes in CO2 will affect the temperature.
But solely for the purposes of this post, let’s assume that the alarmists are correct. And for purposes of discussion only, let’s assume that the Earth’s temperature is free to go up and down any amount. Let’s assume that CO2 is, in fact, the secret control knob that controls the temperature of the earth. And let’s further assume that the pundits are right that the “climate sensitivity” is three degrees of warming for every doubling of CO2.
And finally, let’s assume that in 2018 the US magically stopped emitting any CO2 at all.
With all of those assumptions as prologue, here’s the question of interest.
Other things being equal, if the US stopped emitting CO2 entirely in 2018, and stayed at zero CO2 emissions indefinitely, how much cooler would that make the planet in the year 2050?
Five degrees cooler? Two degrees? One degree?
With the (probably untrue but very widely held) assumptions we’ve made above, we can actually calculate the temperature savings if the US could stop emitting CO2.
To start with, we need to look at the actual history of CO2 emissions. Figure 1 shows the emission records, divided into the US emissions and the emissions from the rest of the world.
Figure 1. Historical CO2 emissions. Data from CDIAC and BP Statistical Review of World Energy.
Now, this is interesting in itself. First, the current US emissions are about the same as they were back around 1978 (dashed black line). So over the last forty years, our emissions haven’t increased at all. Makes no difference to me, but if you think CO2 is important that’s not a bad record, I’d say.
In addition, US emissions peaked in 2007 and have decreased since that time. On the other hand, as Figure 1 shows, since 1959 the emissions of the rest of the world have steadily been … well … heading for the sky.
Next, we need to calculate what would happen to the amount of CO2 in the atmosphere if US emissions went to zero. We can calculate that by noting that it takes 13.3 gigatonnes of CO2 emissions to increase the atmospheric CO2 by one part per million by volume (ppmv).
So to calculate future atmospheric CO2 levels, I assumed that CO2 would continue rising as it has in the past. This is called a “business as usual” (BAU) scenario. And for the purposes of this calculation, I assumed that the US emissions went to zero in the year 2018. Figure 2 shows the amount of difference that would make in the atmospheric CO2.
Figure 2. Historical and projected increases in atmospheric CO2. “Business as Usual” assumes that emissions continue to increase as they have in the past, so it is a smooth extension of historical changes in atmospheric CO2. The lower red line is done in the same way, but assuming that the US emissions went to zero in 2018. The yellow shaded area shows future projections.
Why so little difference? US emissions are no longer a major player. In 1959, US emissions were about half those of the rest of the world. But by 2017, US emissions had fallen to only 20% of emissions of the rest of the world. And the emissions of the rest of the world are continuing to rise. As a result, US emissions going to zero doesn’t have a very large effect. It only decreases emissions by 11 ppmv by 2050, which is only about a 2% decrease in atmospheric CO2.
Next, we need to convert CO2 levels to temperature. According to the prevailing theory, a doubling of CO2 will increase the temperature by about 3° Celcius. Using that relationship gives us Figure 3, the temperature change theoretically due to the change in CO2.
Figure 3. Theoretical historical and projected temperature increases due to increasing CO2. The yellow shaded area shows future projections. These are temperature anomalies with respect to 1959.
So we’ve arrived at the answer to the question we started out with, and the answer is:
If we magically stopped emitting CO2 at the end of 2017, and stayed at zero CO2 emissions indefinitely, by 2050 the world would be cooler by a measly tenth of one degree …
How small is a tenth of a degree C? To start with, it is far too small for us to detect with our senses. It is also too small to detect with a normal thermometer. It’s the cooling you’d experience from going up three flights of stairs. Or in terms of weather and the ambient temperature, it’s a cooling equivalent to moving five miles (eight km) poleward from wherever you live …
However, the magnified scale of Figure 3 gives an exaggerated idea of the real-world difference that stopping US emissions would make. To get an accurate idea of just how trivial the temperature change would be, Figure 4 shows it on a normal outdoor thermometer scale:
Figure 4. Exactly the same data as in Figure 3, but to the scale of a regular thermometer. The yellow shaded area shows future projections. (As a side note, the blue line shows a warming of 1.6°C from 1959 to 2050 … greater than the dreaded 1.5°C warming target that everyone is hyperventilating about. Scary looking change, huh? But I digress …)
Just as in Figure 3, in Figure 4 there are actually two lines showing the temperature—a red line for the US going to zero and a blue line for the business as usual scenario. But you can’t see the red line, because it only differs from the business as usual blue line by a tenth of a degree C …
And that means that regarding the question of how much cooling we’d get by 2050 if the US stopped emitting CO2 entirely, the real-world answer is … no perceptible difference at all. None. Far too small for anyone to sense directly. Far too small to register on your outdoor thermometer. The US could go to zero emissions and in 2050 we’d never notice the temperature difference.
So the next time someone tries to get you to sign on to yet another brilliant plan that the US is supposed to sign on to in order to “reduce our carbon footprint”, like the plans for everyone in the US to stop eating meat or to stop flying in airplanes or to buy electric cars or to cover half the US landscape with solar panels or to tax energy until the poor people put on yellow vests and throw rocks … well, the next time one of those charming folks proposes one of those plans, all of which come with a multi-billion dollar price tag, feel free to point them to this analysis and tell them “Even cutting US emissions to zero will make no perceptible difference by 2050! None!”.
[UPDATE] An alert commenter pointed out that Pat Michaels wrote about this issue in Forbes magazine, in which he pointed out an online calculator to show temperature savings from various reductions. Good stuff.