In Part One I created a simple model to illustrate how easily the world could reach or exceed the emissions projected by RCP8.5: (Long-term GDP growth) x (smaller annual improvements in emissions intensity) = way too much CO2.
In Part Two, as promised, I'm going to look at some of the "ground truth" of global development that makes those rising emissions in my very simple model plausible.
First, the goal posts: RCP8.5 projects 88Gt/year of CO2 emissions in 2100. Without fussing too much about the area under the curve, if a scenario gives us >88Gt/year of CO2 emissions in 2100, we can conclude that RCP8.5 is realistic, presuming said scenario is realistic. Make sense? So our first data points:
RCP8.5, Co2 emissions in 2100: 88Gt
RCP8.5, CO2e: 120Gt
Current CO2 emissions (2019): 37Gt
We're going to ignore CO2-equivalents for now, because the non-CO2 forcings are largely short-lived, more easily reversible problems, such as methane, which are less relevant on the century scale.
If I were asked to sum up in a single phrase the reason RCP8.5 cannot be ruled out, and is, in fact, highly plausible, it would be "economic growth."
Leaving aside the bright spot of the Great Depression -- sarcasm very much intended -- and the hangover from WWI and the 1918 influenza pandemic, the world has not seen less than 3% growth over any five-year period for the past hundred years.
It is hoped that population growth will continue to slow in the coming decades, but that is unlikely slow economic growth overall -- if anything, the relationship between economic growth and population growth tends to be the inverse of that.
Even 3% growth, sustained over the next 80 years, leads to a world where the average person is richer -- far richer -- than the average American is today: ($170k/year at purchasing power parity.)
What might such a world look like in terms of greenhouse gas emissions?
We had better hope they don't emit like Americans, because that would be the ball game:
US carbon emissions per capita: 16.5 tons/year
If the world in 2100 emits like the US: 181.5Gt/year
So to put the question in a deliberately stringent way, for RCP8.5 or something worse to NOT unfold over the next 80 years, either long-term GDP growth needs to fall precipitously, which would be a vast crisis of human suffering in its own right, and which virtually no one thinks is just or even sane, OR the population must fall dramatically, OR we are positing a world in which 11 billion people are 2-3 richer than present-day Americans, but produce nothing remotely resembling an American's average greenhouse gas emissions.
Note that this is just another, hopefully slightly more concrete and accessible, way of talking about carbon intensity and the "decoupling" of economic growth: finding a way for 5-10 billion people to be richer than Americans without producing anything remotely like the GHG emissions we do.
I wish "not remotely" were a rhetorical flourish, but it isn't. Doing 20%, 30%, 50% better than we do in terms of CO2 per unit of production is not enough.
Germany, for example, has invested a vast amount in renewable energy, grid improvements, and conservation. The exact figure is debated, but the total investment to date is generally agreed to be on the order of hundreds of billions of dollars. So let's imagine a wealthy world that invests heavily in renewables and makes the progress Germany has made.
German CO2 emissions: 11 tons/year per capita
If the world in 2100 emits like Germany: 121Gt/year
Again, our simple thought experiment blows past the RCP8.5 scenario and into uncharted territory. The same thing happens in a world that emits like China (although with 3% growth, said world would be an order of magnitude richer than China, $170k/year per capita vs $17k):
China: 8.5 tons
If the world in 2100 emits like China today: 93.5Gt
Just to be clear, this thought experiment imagines a world where carbon intensity is vastly improved, producing ten times as much per unit of CO2 emitted compared to China today. It's not enough. RCP8.5 is still on the table.
These thought experiments illustrate why (Long-term GDP growth) x (smaller annual improvements in emissions intensity) is such a menacing equation. Since the advent of modern capitalism and the Industrial Revolution, two of the most predictable things about human history is that people will make more people and those people will strive to get rich. And eventually, in more or less time depending on things like the level of governmental dysfunction, frequency of wars and revolutions, and availability of capital, people do get rich (compared to where they or their parents started.)
So when assessing the likelihood of RCP8.5 or worse, we can break it down to several simple wagers:
- The population in 2100 will be dramatically lower than today: bad bet.
- Economic growth, averaged over decades, will halt or reverse itself, in contradistinction to the entirety of human history since the beginning of the Industrial Revolution: bad bet.
- Vastly richer and more numerous human societies will, without significant exception, produce vastly more goods and services per unit of emissions: Unknown (policy dependent.)
In Part Three, I'll discuss the four main lines of reasoning offered to justify playing down or ruling out RCP8.5, and why I think these rhetorical mountains are practical molehills.