7.3: Long Term Carbon Cycle

The Long-Term Carbon Cycle

Has anyone ever told you “a good way to reduce your Carbon Footprint would be to breathe less?” If so, it’s okay to laugh out loud at the suggestion. The fact is that there are trillions of organisms right now, all performing respiration, including humans. But in general, these respirations don’t add CO₂ appreciably to the atmosphere because they are quickly counteracted by photosynthesis. In short, human respiration is a component of the short-term carbon cycle and doesn’t really cause any appreciable change. In fact, the short-term carbon cycle remains fairly stable because short-term processes, such as respiration, are well balanced by others, such as photosynthesis.

The real harm to the Earth System is occurring in the Long-Term Carbon Cycle. Unlike the short-term cycle (which consists of processes that operate on a seconds-minutes-days-months timescale), the long-term carbon cycle operates over millions of years! And yet, we can still see them in plain sight every day. Imagine a raindrop falling onto a hillside; you may not know this, but that raindrop consists of a very small amount of Carbonic Acid dissolved in the water. This carbonic acid chemically weathers that hillside, producing a small amount of sediment. Over many months/years, this sediment travels downhill into streams, which eventually enter the oceans, sink, and deposit on the ocean floor. This entire process already takes significantly longer than any short-term process. However, once the sediment is deposited on the ocean floor, it takes millions of years for it to subduct (sink) into the crust, melt into magma, and then erupt back to the surface of the Earth via a volcanic eruption. The Carbon Dioxide released by such volcanic eruptions then gets absorbed by rainfall and falls back to the ground as Carbonic Acid, restarting the cycle. This entire cycle is called the Geologic Leg of the Long-Term Carbon Cycle. Figure \(\PageIndex{1}\) is a diagram of the Geologic Leg of the Long-Term Carbon Cycle.

Figure \(\PageIndex{1}\): The Geologic Leg of the Long-Term Carbon Cycle and associated Feedback Loops. (CC-BY-SA 4.0; Gretashum via Wikipedia). Alternative Description of Image

There’s some good news that this cycle conveys. A warmer world is going to be a wetter world. Increased rainfall would result in more Carbon Dioxide being absorbed from the atmosphere, enhancing this cycle. This would remove additional Carbon Dioxide from the atmosphere and could potentially slow down warming. This is called the Chemical Weathering Feedback Loop, and is considered a negative feedback loop because, while the trigger is warming (which leads to more precipitation), the ultimate result is cooling.
The Geologic leg is not where human activity has disrupted the Long-Term Carbon Cycle.

The Biological Leg of the Carbon Cycle

Humans have disturbed the Biological Leg, which encompasses life, death, burial, and the long-term oxidation of living organisms.

15. One key contribution to Climate Change has been the use of _____________ by humans:
    1. Wind Power
    2. Fossil Fuels
    3. Solar Power

Humans have increased the concentration of carbon dioxide in the atmosphere by digging up and burning dead organic matter. Basically, living things died, were buried, compressed into either Coal or Oil, or decomposed by bacteria into Natural Gas, and then dug up by humans. If left alone, these “Fossil Fuels” would remain buried below ground for millions of years, eventually rise back up to the surface of the Earth via crustal upwelling, and oxidize over millions of additional years. To see how this process works, take a lump of coal and set it outside. It doesn’t burn on its own; instead, it slowly oxidizes and emits CO₂.

Indeed, it’s the digging up and burning of fossil fuels that has most disrupted the Carbon Cycle. If left untouched, it would take the same fossil fuels millions of years to rise to Earth's surface and oxidize back into the atmosphere as Carbon Dioxide. However, human activity has made that process significantly faster, and natural processes simply can’t keep up.

How humans have impacted the Carbon Cycle

The remainder of this investigation will cover a few charts regarding human fossil fuel use. Figure \(\PageIndex{2}\) shows the total global fossil fuel usage since the beginning of the Industrial Revolution (approximately 1800). The graph is split up into three color shadings for Coal, Oil, and Natural Gas.

Figure \(\PageIndex{2}\): Global Fossil Fuel Consumption by Type. (CC-BY 4.0; Global Fossil Fuel Consumption via Our World In Data). Alternative Description of Image.

16. Prior to 1950, the vast majority of fossil fuel usage was in the form of:
    1. Oil
    2. Gas
    3. Coal
17. In the past few decades, Coal usage has leveled off. However _____________ has seen noticeable increases in usage (hint, look at how “thick” the color wedge is rather than how high on the chart).
    1. Oil
    2. Natural Gas
    3. Both

If you notice, at the very top of the graph, there was a slight dip in fossil fuel usage several years before the graph ends. This was 2020, and the dip was largely due to decreased travel caused by the COVID-19 Pandemic. However, as the pandemic-related restrictions eased, fossil fuel consumption has continued to increase. So who’s to blame for all of this? Figure \(\PageIndex{3}\) shows the Fossil Fuel usage (total) by country in 2024, and Figure \(\PageIndex{4}\) shows the same data but as a line graph for the period ending in 2024.

Figure \(\PageIndex{3}\): Map of Fossil Fuel Consumption by Country in 2024. (CC-BY 4.0; Fossil Fuel Consumption via Our World In Data). Alternative Description of Image.

Figure \(\PageIndex{4}\): Line graph of Fossil Fuel Consumption by Country since 1965. (CC-BY 4.0; Fossil Fuel Consumption via Our World In Data). Alternative Description of Image.

18. The country that consumed the most fossil fuel in 2024 was:
    1. The United States
    2. The European Union
    3. China
19. The country that consumed the second most fossil fuel in 2024 was:
    1. The United States
    2. India `
    3. China

This may seem somewhat different from the common understanding. We tend to think that the United States is the largest consumer of fossil fuels, but in fact, the tide has turned over the past few decades. But before we begin to shift blame away from the US, it’s important to investigate why such a change may be occurring and why the United States is not innocent in the change. Rapidly developing countries, such as China and India, are seeing larger increases in their fossil fuel consumption. Figure \(\PageIndex{4}\) shows that since 2000, China has more than tripled its consumption of fossil fuels, and India has more than doubled, while much of the developed world, such as the US, Japan, and the European Union, has leveled off or even decreased its consumption levels. Here are a few key reasons why:

• Massive populations: Both India (1.408 billion) and China (1.412 billion) have populations almost four times that of the United States. In fact, almost one in three humans on Earth is either Chinese or Indian.
• Massive economic growth: Both India and China have seen massive economic growth, with India seeing an over five-fold increase (from $500 billion to $2.9 trillion) in GDP and China seeing an over ten-fold increase (from $1.47 trillion to $14.8 trillion) from 2000 to 2021.
• Outsourcing: As developed countries move into a post-industrial world, they have shifted most of their manufacturing jobs and factories to developing countries, such as China and India. In essence, countries like the United States and members of the European Union are still at fault for much of the world’s fossil fuel consumption… but since they have outsourced many of their factories to other countries, they have, in essence, given other countries their problem.

This leads to an ethical question that is beyond the scope of this class... As we begin to reduce the consumption of fossil fuels in order to fight Climate Change, who should be leading the effort? Post-industrial countries like the United States, which had the luxury of using fossil fuels without any hesitation to grow economically, or developing countries like China and India, which are currently experiencing massive economic growth, but ultimately cannot continue on the same consumption path that the United States did, if we want to prevent the worst of Global Warming? Who should be cutting back… us or them?

Before we wrap up this investigation, one piece of information that may help answer that question is each nation's per capita fossil fuel consumption. Figure \(\PageIndex{5}\) is a graph showing per-capita (per-person) fossil fuel consumption in 2021 for the same nations/regions as in Figure \(\PageIndex{4}\).

Figure \(\PageIndex{5}\): Fossil Fuel consumption per capita in 2024. (CC-BY 4.0; Fossil Fuel Consumption via Our World In Data). Alternative Description of Image.

20. Although China is currently the largest consumer, on a per-capita basis, the average citizen of the United States consumes ___________________ as much:
    1. Significantly less
    2. More than twice
    3. More than five times
21. In fact, on a per-capita basis, the United States is:
    1. The largest consumer of fossil fuels
    2. Still significantly lower than other developed nations
    3. About the same as China and India in fossil fuel consumption
22. This shows that, while large developing nations are becoming large Fossil Fuel consumers, the United States ____________ if we want to seriously reduce global fossil fuel usage:
    1. Still needs to reduce its consumption of fossil fuel
    2. No one needs to worry about its consumption of fossil fuel

One quick note: There are a few small, mostly oil-producing countries (Kuwait, Qatar, Trinidad and Tobago, etc.) with very tiny populations but oversized oil industries that contribute to outrageously high per-capita fossil-fuel consumption levels. These countries were intentionally left off this chart because their overall fossil-fuel consumption is very small compared to developed/developing countries, and their higher per-capita usage is driven not by the average citizen but by their fossil-fuel industry.