The Truth of Global Warming: Part 6 - The impact of population growth on global warming

Published: Feb. 26, 2024, 1:58 p.m. (UTC) / Updated: Nov. 22, 2024, 12:04 a.m. (UTC) 🔖 0 Bookmarks

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The relationship between population and $CO_2$ emissions

If the increase in $CO_2$ emissions is a consequence of human activities, it prompts curiosity about how $CO_2$ concentrations have changed in accordance with population growth, or how much $CO_2$ concentration increases with each additional person. One might expect a wealth of related information on the correlation between global population trends and $CO_2$ emissions. However, upon searching the internet in the later half of 2023, there is surprisingly little information available on this topic! Perhaps because it's considered such basic knowledge, few seem concerned. Nonetheless, the absence of documented verification of such fundamental facts by various sources is a troubling trend. Hence, ultimately, we have created this ourselves.

Is the increase in CO2 emissions caused by the growth of the world's population?

World population statistics were obtained from worldmeter, while emission data utilized The Global Carbon Budget 2022. The following figure shows the annual correlation between world population and $CO_2$ emissions from 1959 to 2021.

Let's make the following argument from here.

There is a clear correlation between world population and $CO_2$ emissions.
The natural interpretation of this fact is that the increase in $CO_2$ emissions is caused by the growth of the world's population.

In other words, using the regression equation above, if we have future projections for world population, we can estimate the $CO_2$ emissions at that time.

Is the increase in CO2 emissions not caused by the growth of the world's population?

The interpretation of the above figure actually requires some explanation. Simply because there is a strong correlation, people may mistakenly infer causation. The point is, if we look at the period from 1959 to 2021, it could be purely coincidental that the world population increased while $CO_2$ emissions also increased. There may not be a clear causal relationship between the two. Engaging in discussions based on false assumptions could lead to significant errors in decision-making for humanity. Therefore, it is essential to discuss this matter more carefully.

Indeed, when examining emissions by country, interpretation can be confusing due to contradictory cases, such as developed nations having higher emissions than regions experiencing population explosions (this will be discussed in detail in later chapters). Looking at various literature sources, the pathways of population growth can be essentially condensed into two routes:

First Pathway: Technological innovation occurs => More work can be done with higher energy efficiency => Country develops and can sustain larger population => Medical care improves leading to lower death rates, education also improves leading to further technological innovation (cycle repeats)
Second Pathway: Poverty exists => Must have children to secure labor force => Oversupply of labor prevents escape from low wages (cycle repeats)

Looking at just these pathways, we can interpret the situation as follows: Significant CO₂ emissions primarily occur through the first pathway, corresponding to industrialized nations, where population growth is not dramatic. Meanwhile, serious population explosions are mainly occurring through the second pathway in developing countries, where CO₂ emissions are not significant. Since these are independent phenomena, the earlier graph may have shown what appears to be a causal relationship but is actually unrelated.

How Should We Really Interpret This? The Key Lies in Understanding the "Human Activity" System

Most discussions end up circling around the above points, making it unclear whether that single graph truly represents the essence of the matter. As mentioned at the beginning of this paper, there is little information online explaining the connection between population growth and CO₂ emissions, likely due to these complexities.

We are humans with intelligence. With this intelligence, we can sometimes use philosophical insight to consider the essence of things. At the beginning, I mentioned that if "human activity" causes increased CO₂ emissions... And "world population" was simply the most straightforward variable indicating the scale of this "human activity". Let's examine the content of "human activity" more closely.

First, let's review the history of "human activity". After the last ice age, our ancestors, having acquired intelligence, began agriculture. This was the acquisition of a more efficient means of life maintenance and self-preservation. The advent of agriculture necessitated more organized behavior and led to the concentration of wealth and power. Settlement also began land ownership. Currency was developed to preserve and transfer wealth. Organized warfare became more frequent. Large numbers of slaves were needed to support more powerful and wealthy nations. Those with power created laws to establish foundations for maintaining their class and interests in governing nations.

Naturally, in trade with other nations, being beyond domestic jurisdiction, they could pursue conditions favorable to themselves without limit. With power, they could subjugate others. They learned that exploitation was more profitable than direct territorial expansion and state management. This created a structure where wealthy nations could continuously exploit poorer nations. This became an implicit premise upon which social institutions, traditions, discrimination, and prejudices accumulated to form human activity.

This can be considered a universal aspect of "human activity" that has remained unchanged from ancient times to the present. Such a "human activity" system actually tends to stabilize society as a whole, making it harder for people to die and easier for population to increase, while the wealthy need more people to exploit to become wealthier, thus also driving population growth. In other words, the two pathways of population growth mentioned above may appear independent but should be interpreted as two wheels of the same vehicle that keeps the "human activity" system running.

With this understanding in mind, let me assert again:

Looking at history from a broader perspective, the picture where CO₂ emissions can be largely explained by world population is actually correct
However, the world population variable includes both aspects of human development and prosperity, and aspects of human exploitation of humans

This fact might be an "inconvenient truth" for some politicians and interest groups. However, based on this immutable simple fact, this paper will proceed with the following discussion. Therefore, if humanity can improve the "human activity" system in the near future, the premises will change, and the following discussion will need to be revised.

Future CO₂ Emissions as Seen from Long-term World Population Projections

The red dotted line in the figure below shows estimated future CO₂ emissions using the regression equation from the above graph, based on the UN's future world population projections (medium variant).

Naturally, while both population and CO₂ emissions are determined by various factors and cannot be simply estimated for the future using a basic regression equation, the strong correlation between population and carbon dioxide emissions is unlikely to change easily, as explained in the "human activity" system. If this holds true, the following assertions can be made from this analysis.

The world population will peak at approximately 10.43 billion people in 2086, at which point CO₂ emissions will be about 14 billion tons, representing the maximum annual emission rate.

This leads to the next question: "Is 14 billion tons annually a lot or a little?" The issue becomes how we can estimate the impact of these emission levels.

Accumulation of Emitted CO₂ in the Atmosphere

We are interested in how much temperature rise will occur as a result of the above maximum CO₂ emissions. To understand this, we first need to know how much emitted CO₂ accumulates in the atmosphere. The following figure is quoted from The Global Carbon Budget 2022.

Against CO₂ emissions from fossil fuels (fossil carbon) and incremental emissions from land-use changes including deforestation (land-use change), oceans (ocean sink) and forests (land sink) absorb some, and the remainder accumulates in the atmosphere (atmosphere). From this, we can understand the following:

Forests do not absorb enough CO₂ to justify saying "it's okay to burn fossil fuels because forests will absorb the CO₂"
Because oceans absorb CO₂, separate problems are arising due to increased CO₂ concentrations in the oceans
Through the burning of fossil fuels, CO₂ steadily accumulates in the atmosphere

By the way, do these figures for CO₂ absorbed into the atmosphere match the actual observed CO₂ concentrations in the atmosphere? If these numbers don't match, we would have to suspect major deception in the global warming debate. Let's calculate the total mass of CO₂ from the concentrations observed in Earth's atmosphere.

Earth's atmospheric mass is $M_e = 5.28\times10^{18}kg$
CO₂ concentration in 1959: $\rho_{1959} = 316.9ppm$
Current CO₂ concentration: $\rho_{2021} = 414.71ppm$
Average molecular weight of 1 mol of dry air is $m_{air}28.96$, CO₂ is $m_{CO_2}=44$
(1 mol refers to a collection of $6.02\times10^{23}$ molecules. The "molecular weight" is this mass expressed in grams.)

Therefore:

Mass of CO₂ in Earth's atmosphere in 1959: $M_{CO_2 1959}= M_e*\rho_{1959}*\frac{m_{CO_2}}{m_{air}} =2,542\times10^{12}kg$
Mass of CO₂ in Earth's atmosphere in 2021: $M_{CO_2 2021}= M_e*\rho_{2021}*\frac{m_{CO_2}}{m_{air}} =3,327\times10^{12}kg$

Thus, the mass equivalent of CO₂ concentration increase from 1959 to 2021 is $M_{CO_2 2021} - M_{CO_2 1959} =785\times 10^{12}kg$.

Meanwhile, according to The Global Carbon Budget 2022, the atmospheric accumulation of CO₂ from 1959 to 2021 is $783\times 10^{12}kg$.

In other words, we found that the cumulative CO₂ emissions almost exactly match the results of long-term observations of increases in actual atmospheric concentrations. Therefore, the argument that CO₂ emissions caused atmospheric CO₂ concentrations to rise is correct. (Incidentally, the average global temperature rise during the same period was approximately $+0.74{}^\circ C$.)

However, isn't this comparison result quite surprising? This is because it shows that results obtained from completely different information sources and collection processes match over a long period, whereas typically there would be larger observational errors or items that couldn't be counted by one method or the other, leading to discrepancies. These numbers reflect scientists' strong commitment to the principle that 'a single phenomenon must yield the same results regardless of how it is observed.'

Impact of Future CO₂ Emissions

When considering future population growth, how much CO₂ will actually accumulate? What will be its impact on temperature?

Estimating Ocean Absorption Capacity: Oceans Absorb 25% of CO₂ Emissions from Fossil Fuels

Assuming oceans remain sufficiently large and vast, we'll consider that the proportion of CO₂ absorption by oceans from the past to present will remain constant in the future. Comparing the amount of CO₂ emitted from 1959 to 2021 with the amount absorbed by oceans according to The Global Carbon Budget 2022 data yields the following graph (dotted line shows regression).

Calculation for 2100: Average Temperature at 17.3°C

Let's assume that land-use changes and forest absorption remain constant at 2022 levels for projected CO₂ emissions from 2022 to 2100. This isn't an unrealistic assumption as emissions from land-use changes have historically remained at a constant level. Regarding forests, which we'll discuss in detail later, forest resources are declining yearly, so assuming constant CO₂ absorption by forests actually underestimates atmospheric accumulation. The following discussion should be interpreted as "this is the minimum estimate, and the actual inconvenient reality might be worse." Considering the relationship above, assuming oceans absorb 25.53% of additional emissions, the additional CO₂ accumulating in the atmosphere from 2022 is estimated to be 1,553×10¹²kg by 2100, as shown in the graph below.

Using this result and the T_co2() function created in the previous chapter, we can conclude: Due to fossil fuel use, additional CO₂ accumulating in the atmosphere from 2022 to 2100 will increase CO₂ concentration to 608ppm, resulting in an average atmospheric temperature of 17.3°C. Assuming pre-industrial temperature was around 13.76°C, this represents a 3.54°C increase. This is comparable to the high-emission scenario (SSP1-7.0) in the IPCC's Sixth Assessment Report. Summarizing our discussion so far:

IPCC prediction results can be roughly reproduced using just observational data and simple mathematical modeling
While IPCC's "high-emission scenario" is depicted as a pessimistic scenario, it should be viewed as an "optimistic scenario" based on median population projections (reasonable level) and optimistic estimates of Earth's CO₂ absorption capacity; reality might be worse
Additionally, as repeatedly mentioned, these calculations ignore amplification effects from water vapor, etc., suggesting reality might follow an even "worse scenario"

While this is already quite pessimistic, there's something even more concerning.

Issue Raised: The IPCC only forecasts until 2100, but considering the above cumulative effects, shouldn't we estimate until 2200-2500 to meaningfully assess future impacts, since accumulation will steadily continue beyond 2100? Particularly, since CO₂ accumulated in the atmosphere and oceans won't easily return to natural levels, isn't it irresponsible of humanity not to simulate that far ahead? At minimum, using 2100 as the discussion endpoint seems inappropriate. The author believes that the real risk of extinction for natural flora and fauna might actually peak after 2100 (this will be discussed in later installments).

Calculation Script for the Above

# Script for above calculations
M2100 = 1553 # Additional CO₂ mass accumulating in atmosphere from 2022 to 2100 [10^{12}kg]
Mco2 = 3327  # Mass of CO₂ in Earth's atmosphere in 2021 [10^{12}kg]
rho_present = 414.71  # Current CO₂ concentration ppm
T_industrial_revolution = 13.764 # Atmospheric temperature during industrial revolution [C]
rho = rho_present * (M2100 + Mco2)/Mco2 # CO₂ concentration in 2100
T = T_co2(rho, T_0=3.77)
print("CO₂ concentration: ", rho, "\nTemperature: ", T, \
     "C\nincrease from Industrial revolution:", T-T_industrial_revolution)

Climate Response to Cumulative CO₂ Accumulation

According to the IPCC's Sixth Assessment Report, as shown in the figure below, there is an "almost linear" relationship between global temperature rise since the industrial revolution and cumulative CO₂ emissions during the same period. This figure was likely created to clearly communicate to people that while some CO₂ emissions are absorbed by oceans and forests, temperature rise ultimately correlates with humanity's cumulative emissions.

In ①Do You Really Understand "Global Warming"? of this series, we introduced scientists' claims that "While the IPCC states that 'global warming increases in proportion to humanity's total emissions,' it actually increases logarithmically. In other words, warming progresses much more slowly than the IPCC suggests. Perhaps the crisis is being unduly exaggerated by groups dissatisfied with insufficient global warming countermeasures." Indeed, looking carefully at the above figure, the slope of the line appears to decrease towards the right. The IPCC might be adjusting from a linear to a logarithmic display, considering the scientists' claims about logarithmic relationships. However, the logarithmic proportion claim is probably also incorrect, and it should likely take an exponentially asymptotic form like equation (7) in the integrated model introduced in The Truth About Global Warming: ⑤Verification Through Mathematical Models of Global Warming.