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Human emissions do not accumulate

The present level in the atmosphere is a natural level and fully in line with the present greenness of the Earth, and the increase can be fully explained by the higher temperature. There is therefore no need to presume a special (ad hoc) behavior for human CO₂ in the atmosphere to account for the current CO₂ levels. The residence time of human CO₂ is not different from that of any other CO₂ in the well-mixed atmosphere, and human CO₂ does not accumulate. The impact of human emissions is therefore relatively small.

Blaming humans for the CO₂ rise is only possible if you assume a special behavior for human emissions. While all other CO₂ remains in the atmosphere for around 4 years, it is believed that half of the emissions accumulate in the atmosphere and stay there for an extremely long time. Annual human emissions of CO₂ are currently approximately 5% of natural emissions from land and sea to the atmosphere. Nature therefore emits 20 times more CO₂ than humans every year. Yet the generally accepted idea is that this relatively small contribution is responsible for the entire annual CO₂ increase.

Here we will show that a single 5% increase in emissions doesn't lead to an endless increase in concentration and that accumulation is not possible. The human impact on the CO₂ rise is therefore small.

No endless rise

To make it clear in a simple way how illogical the current paradigm is, we make the comparison with the heating of a house. Suppose we increase the heat inflow by 5%, for example by consuming 5% more natural gas. This will make it a little warmer in the house. Due to the slightly higher temperature, the outflow of heat also increases a little (via the walls, roof, etc.). Shortly, a new equilibrium is established between the interior and exterior, where the energy outflow equals the inflow. The temperature will not continue to rise indefinitely.

No accumulation of CO₂ in the atmosphere
Figure 1: The idea that atmospheric CO₂ levels will rise indefinitely if the inflow increases by 5% is as illogical as believing that a house's temperature will keep rising without limit under a 5% increase in energy input.

This is very similar to the CO₂ flows to and from the atmosphere. Human emissions increase the annual flow to the atmosphere by 5%. This slightly larger inflow causes the concentration in the atmosphere to rise slightly. Due to this higher concentration, the outflow also increases slightly. Here as well, a new equilibrium will establish itself shortly, where the outflow matches the inflow, preventing any further increase in concentration.

In a home the heat loss is proportional to the temperature difference from inside and outside. In the atmosphere the outflow (down flux) is proportional to the actual concentration. The environment is much larger than the house. A slightly larger energy outflow from the house (in the form of heat loss) is unnoticeable in the environment. This is also very similar. The amount of carbon in the oceans and sink are much larger than in the atmosphere.

This behavior of a first order system can be found in many more examples in nature: the water level in a reservoir, the electric current to a capacitor connected through a resistor, the behavior of other atmospheric gases like for example water vapor, etcetera.

It is important in the example that day and night differences or seasonal changes are not an issue. The large daily CO₂ 'breathing' due to photosynthesis and respiration of vegetation is often used as an argument to justify a different residence time for human CO₂. But in the case of the house this is no different. Even if there are large fluctuations between day and night or summer and winter, a small additional heat flow will not lead to an endless increase in temperature. This is also true for an energy-neutral house, which lacks its own heating system, where the house may warm up during the day from sunlight and then gradually cool down during the night. The large inflow and outflow being tied to diurnal and seasonal variations does not significantly impact the behavior of the atmosphere.

Accumulation of human CO₂ in the atmosphere is not possible

The large natural flows to and from the atmosphere ensure that almost a quarter of all CO₂ is exchanged with land and oceans every year. The average residence time of CO₂ molecules in the atmosphere is therefore slightly more than 4 years. In order to argue that human CO₂ is the cause of the increase in the atmosphere, the IPCC assumes that human CO₂ accumulates and remains in the atmosphere for an extremely long time (up to more than 100,000 years).

This assumption could only be correct if part of the CO₂ in the atmosphere has a very different residence time than the rest. But the atmosphere is not divided in compartments and is well mixed due to the high air turbulence. All CO₂ molecules therefore have the same average residence time. This immediately shows how illogical the IPCC's assumption is. We will delve deeper into the discussion that a prolonged residence time for a portion of the atmosphere is not feasible, and thus, human emissions cannot be the cause of the increasing CO₂ concentrations.

The simplest method to show that human CO₂ does not accumulate in the atmosphere, contrary to IPCC assertions, is to consider the oceans' regulatory impact. The oceans, which cover more than 2/3 of the Earth's surface, contain the vast majority of all carbon on Earth. Much more than in the atmosphere, but also much more than on the land and in the soil.

Schematic representation of the CO₂ exchange between the atmosphere and oceans
Figure 2: Schematic representation of the CO₂ exchange between atmosphere and oceans. 1 PgC = 1 Petagram of carbon = 1 Gigaton of carbon (1 billion tons).

All CO₂ exchanged between a well-mixed atmosphere and the oceans (and other waters, and water in organisms) is the result of differences in the concentration above and below the surface. This is a direct result of Henry's Law. This gas law states that the amount of dissolved gas in a liquid is directly proportional to the partial pressure and therefore to the concentration of the gas. Thus, when the CO₂ concentration in the air is elevated, water absorbs more CO₂, whereas at a lower concentration, the absorption decreases, or the water releases CO₂ into the air. The extent to which this happens depends on the temperature.

The majority of CO₂ in water undergoes transformation into various carbon compounds, such as carbohydrates, carbonate ions, and bicarbonates, via complex biological and chemical processes. These processes significantly affect the levels of CO₂ in the water, which in turn impacts the exchange of CO₂ with the atmosphere. However, these processes do not change the fact that the oceans will absorb CO₂ when the atmospheric concentration is high compared to that in surface waters.

The only condition is that the surface layer of the oceans is not saturated with CO₂, but that is certainly not the case. Due to the equilibrium reactions of dissolved CO₂ with (bi)carbonates, the share of dissolved CO₂ in the surface water remains small (see below). In addition, there are various processes that ensure that dissolved carbon compounds find their way to deeper layers. Most important is the large upwelling and downwelling to and from the deeper ocean, which is about 100 times greater than the net exchange between air and water.

Something similar happens on land. Plants will absorb more CO₂ as the concentration increases. Under the influence of the higher concentration in the atmosphere, the greening of the earth has increased significantly. According to NASA greening has resulted in an increase in plants and trees over an area equivalent to two times the area of ​​the United States.

So if the concentration in the atmosphere increases slightly, land and oceans will absorb more. The small surplus of human CO₂ (5%) will therefore not remain in the atmosphere longer than any other CO₂ (4.1 years according to IPCC). Hence, there is no justification for treating CO₂ very differently from all other gases. In the well-mixed atmosphere each gas has its own single average residence time, which may depend on various factors (such as temperature), but certainly not on the origin of the gas.

Nuclear bomb tests

A very clear proof that human CO₂ does not accumulate in the atmosphere comes from an unintended real experiment as a result of nuclear bomb tests in the 1950s and 1960s. These tests were responsible for a dramatic increase of the amount of the carbon isotope 14C in the atmosphere. 14C is naturally produced in the upper atmosphere, but only in trace amounts (of the order of 1 × 10−12). The tests produced large fluxes of thermal neutrons, which reacted with atmospheric nitrogen-14 to form carbon-14. After the ending of the tests around 1965, the concentration of 14C in atmosphere has been declining steadily. Considering that the half-life of 14C is approximately 5700 years, decrease was not caused by radioactive decay but by the absorption of CO₂ by other reservoirs.

In the chart of Figure 3 we can see the changes of the Δ14CO₂ concentration: a sharp increase in the late 50s, followed by an exponential decrease. Δ14C is the relative 14C concentration compared to the most common 12C concentration. See Wikipedia.

14C decline
Figure 3: The increase and decline of the Δ14CO₂ concentration in the atmosphere. The rapid decline demonstrates that excess CO₂ does not accumulate in the atmosphere as the IPCC claims. Source: Hua, Q. et al., 2022

If the accumulation theory was correct, a major part of this 14CO₂ would have remained extremely long in the atmosphere, but we can clearly see that this is not the case. The rapid decline shows that the residence time of excess 14CO₂ is much shorter than the IPCC assumes, in the order of 17 years. It refutes the idea that human CO₂ accumulates in the atmosphere. The observed behavior of 14CO₂ provides an upper bound on the anthropogenic perturbation of atmospheric CO₂. The longer residence time of 14C compared to 'normal' 12C can be very well explained.

There are good reasons for this longer time.
1. The average decline of 14CO₂ is slowed by periodic inflow of 14C-rich stratospheric air downward into the troposphere (enrichment).
2. The decline is slowed by re-emission of absorbed 14CO₂ from the Earth’s surface, which likewise offsets direct absorption.
3. Plants preferentially consume the lighter carbon isotope (12C) over the heavier isotope (14C) during photosynthetic CO₂ fixation. As a result, 14C remains in the atmosphere for longer periods.
4. Additional 14C inflows due to anomalous neutron flux (corresponding to a systematic increase of 5–10% over the last 30 years, according to Salby, M. and Harde, H., 2021.

Small impact

Assuming the same behavior for excess CO₂ as for natural CO₂, the contribution of human activities to the increase in CO₂ can be estimated based on its contribution to the down flux. A stable level of 10 PgC per year for fossil CO₂ leads to an almost equal down flux. With a residence time of 4.1 year, it results in an increase of around 40 PgC in the atmosphere, or 19 ppm, which is less than 15% of the total increase. This finding is consistent with the more accurate estimate of 4.3% of the concentration (i.e., 38 PgC or 18 ppmv in 2022) based on actual historical emissions (Harde, H. (2019).




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