Do the math: climate policies cannot change century-end temperature more than 0.5ºC

Guest essay by Alberto Zaragoza Comendador

Read any article on the Paris agreement and you’ll find lots of degrees. If we follow this pathway we can still keep under two degrees, if we follow the Paris agreement the warming by the end of the century will be three degrees, if we do nothing it will rise ‘by 4-6ºC or more’.

It’s nonsense. Warming depends on emissions, which depend on:

• GDP
• The CO2 efficiency of GDP

So how much we warm depends greatly (or mostly) on how much GDP grows. Which nobody knows, of course; world GDP might grow by only 1% a year or jump 4% every year.

The thing is, whatever the GDP growth rate happens to be, it is not controlled by climate policies*

It is therefore a fallacy to assume that climate policies can let us choose between high-warming and low-warming scenarios. If the climate policies don’t aim to make emissions smaller by making GDP smaller, then they can only work by making GDP more CO2-efficient.

Thus the questions are:

a) Have climate policies had any success so far in decarbonizing the global economy?

b) If they have some success in the future, how much influence can this have on temperatures?

Before addressing the first question, may I link to my recent article showing that a rising carbon efficiency is the rule, not the exception. Most countries, most of the time, increase their GDP faster than their CO2 emissions. This increase is what I call the decarbonization rate. Have the 22 COP meetings had any success in increasing it?

Epic fail of climate policies – in one chart

We get GDP data from the World Bank and emissions data from BP; I put it all together here. And, surprise surprise:

The climate-crazy period after Kyoto is by far the worst in terms of decarbonization. Whereas the global economy had been decarbonizing at a rate of 1.4% over 1966-1999, in 2000-2015 this slumped to 0.6%. #fail

Now, I don’t believe the decline in the decarbonization rate was a result of these policies; the period just happened to coincide with the construction of a lot of new coal plants, mostly in China. Still, global agreements have to be judged by global results. What we can say is that there is no evidence policies have had any effect raising the decarbonization rate, which is what matters.

How big an effect can climate policies have on global temperatures?

This is admittedly a clunky, simplistic calculation – but it’s still 1,000 times better than the junk pushed by climate bureaucrats and ‘policy experts’.

The rate of growth of global GDP since 2010 has been 2.7% a year. It has been declining, in large part because population growth is also slowing down (and some believe a population peak will happen later this century). Nevertheless, to be ‘pessimistic’ (emissions-wise) I assume this growth rate will continue indefinitely.

We take the average decarbonization rate over 1966-2015, which is 1.1%. We assume this is the ‘normal’ rate, so emissions should grow 1.6% a year from 2015 on. (That year, emissions from fossil fuel combustion were 33.5 gigatons, i.e. 33.5 billion tonnes)

If this 1.6% growth rate in emissions continued until the end of the century, then we would release 6,073 gigatonnes. Applying a division by 7.81, that’s 778 parts per million of CO2. With a 45% airborne fraction, the amount added to the atmosphere would be 350 ppm. On top of 2015’s 404 ppm, that gives us an end-of-the-century concentration of 754 ppm.

What if climate policies manage to increase the decarbonization rate by 1%? This would essentially double the decarbonization rate. It’s not clear if such a thing is even possible, but still, what if? Well in that case we would emit 3,723 gigatonnes. That’s 477 ppm, or 215 airborne ppm, which brings us to a 619 ppm concentration by the end of the century. So we have 754 / 619 = 1.22

In other words: if we do nothing, CO2 levels might be 22% higher than if we follow a successful decarbonization program.

How many degrees is that?

Since the warming effect of CO2 is logarithmic, a 22% increase is actually more than a ‘proportional’ or linear increase; it’s equivalent to 28.5% of a doubling, because 1.22^3.5 = 2 and 1 / 3.5 = 1.285

As it happens the transient climate response seems to be about 1.35ºC, so an additional 28.5% of warming effect will mean the world is 0.38ºC warmer by the end of the century than if we had forgotten about the whole climate thing.

PS: so why does the headline say 0.5ºC, instead of 0.38ºC? Well, there are non-CO2 GHGs and climate policy might have an effect on those. But it must be mentioned: CO2 makes up about 80% of the warming effect seen in recent years, and the other gases are far less actionable, as their emissions cannot be tied to something as easy to count as fossil fuel burning.

*Unless your notion of climate policy is a planned recession.